Patient Protection in Dentistry. Safe Use of Radiation Sources


Academic Paper, 2013
41 Pages, Grade: 4.0

Free online reading

CONTENTS

ABSTRACT

2.0 INTRODUCTION
2.1 BACKGROUND
2.1.1 Discovery of X-rays
2.1.2 BENEFICIAL USES OF X-RAYS
2.1.3 EARLY DITRIMENT FROM X-RAYS
2.1.4 Genesis of radiation protection and safety
2.2 RELEVANCE AND JUSTIFICATIONS
2.3 SCOPE OF PROJECT WORK

3.0 LITERATURE REVIEW
3.1 RADIATION DOSE, DAMAGE AND RISK
3.1.1 radiation dose in dental radiology
3.1.2 radiation damage
3.1.3 risks from radiation exposure
3.2 JUSTIFICATION
3.3 OPTIMIZATION
3.3.1 IMAGE RECEPTOR SELECTION
3.3.2 IMAGE RECEPTOR holders
3.3.3 collimation
3.3.4 beam filtration
3.3.5 OPERATING POTENTIAL AND EXPOSURE TIME
3.3.6 PATIENT PROTECTIVE EQUIPMENT
3.3.7 FILM EXPOSURE AND PROCESSING
3.3.8 FILM STORAGE
3.3.9 IMAGE VIEWING
3.3.10 QUALITY ASSURANCE
3.3.11 diagnostic reference levels
3.3.12 TECHNIQUE CHARTS/PROTOCOLS
3.3.13 TRAINING AND EDUCATION

4.0 Discussions
4.1 RADIATION DOSE, DAMAGE AND RISK
4.1.1 RADIATION DOSE IN DENTAL RADIOLOGY
4.1.2 RADIATION DAMAGE
4.1.3 RISKS FROM RADIATION EXPOSURE
4.2 JUSTIFICATION
4.3 OPTIMIZATION
4.3.1 IMAGE RECEPTOR SELECTION
4.3.2 IMAGE RECEPTOR HOLDERS
4.3.3 COLLIMATION
4.3.4 BEAM FILTRATION
4.3.5 OPERATING POTENTIAL AND EXPOSURE TIME

5.0 CONCLUSION AND RECOMENDATIONS
5.1 conclusion
5.2 recommendations

6.0 REFERENCES

ACKNOWLEDGEMENT

The support of the International Atomic Energy Agency and the Government of Ghana through the University of Ghana; School of Nuclear and Allied Sciences in organizing and providing material support for the PostGraduate Educational Course (PGEC) in radiation protection and safe use of radiation sources is greatly acknowledged. I also wish to express my profound appreciation to Dr. J. Yeboah and Dr. Mary Boadu for their contribution to the successful completion of this project by supervising it.

ABSTRACT

Current literature on dental radiology was reviewed in order to seek justification for radiological protection of patients in dental radiography, to explore the different factors affecting patient dose and to derive practical guidance on how to achieve radiological protection of patients in dentistry. Individual doses incurred in dental radiology are in general relatively low, however it is generally accepted that there is no safe level of radiation dose and that no matter how low the doses received are, there is a mathematical probability of an effect. Hence appropriate patient protection measures must be instituted to keep the exposures as low as reasonably achievable (ALARA). The literature review demonstrated that there is considerable scope for significant dose reductions in dental radiology using the techniques of optimisation of protection. The techniques of optimization of protection that can be used to ensure patient dose is as low as reasonably achievable whilst achieving clinically adequate image quality include the following: image receptor selection, image receptor holders, collimation, beam filtration, operating potential and exposure time, patient protective equipment, film exposure and processing, film storage, image viewing, quality assurance, diagnostic reference levels, technique charts and training and education

CHAPTER ONE

1.0 INTRODUCTION

1.1 BACKGROUND

1.1.1 Discovery of X-rays

X-rays were discovered by Wilhelm Roentgen in November 1895 [1], while experimenting with a highly evacuated cathode ray tube called a Crooke’s tube [2]. After Roentgen saw the bones of his hand clearly displayed in an outline of flesh when he held the hand between the cathode ray tube and a barium-coated screen, he took a radiograph of his wife’s hand (Figure 1) which he later included in the report of his discovery [3]. Roentgen announced his discovery on January 1, 1896, in a paper that he prepared to the Physical Medical Society of Würzburg. The benefits of this discovery were immediately recognized by healthcare professionals as X-rays started being used in medicine for diagnosis and therapy within a year. Fourteen days after Roentgen published his discovery, Dr. Walkhoff, a dentist in Braunschweig, Germany, produced radiographic images of teeth. These intraoral radiographs were produced with small glass photographic plates wrapped in sheets of black paper and rubber. About twelve dentists in the United States of America were using X-rays in their practices by 1900. After a period of debate and skepticism over the benefits of radiographs compared to transillumination, dentists came to rely greatly on x-ray machines for the diagnosis of disease and for the identification of anatomical structures for treatment planning.

Abbildung in dieser Leseprobe nicht enthalten

Figure 1: Radiograph of Mrs. Roentgen’s hand

Source: The Genesis and Development of CBCT for Dentistry [3]

1.1.2 BENEFICIAL USES OF X-RAYS

As stated previously, almost immediately after X-rays were discovered their benefit in medicine was recognised. Besides the genesis of dental radiography fourteen days after Roentgen published his discovery, general medical diagnostic radiography and radiotherapy started within a year of Roentgen’s discovery. One of the first treatments with X-rays was done in 1896 [7] while the first successful use of X-rays to cure cancer was in the year 1899 [1]. The curative radiotherapy was performed on a woman who had a cancer called basal-cell carcinoma on the face. The use of x-rays in medical diagnosis evolved over time from the initial plain radiography to Computed Tomography (CT) which was introduced in 1973 [5]. Other modalities of X-ray technology used in diagnostic radiology include the following: fluoroscopy, Interventional radiology and Mammography. Non-medical uses of X-ray technology include X-ray spectrometers and diffractometers in analytical chemistry and crystallography, and in inspection and control devices [1]. Another non-medical use of x-rays is in Industrial radiography where x-rays are used to examine welds, detect cracks and help prevent failure of engineering structures [6].

1.1.3 EARLY DITRIMENT FROM X-RAYS

Almost immediately after ionizing radiation was discovered, its deleterious effects became apparent [1]. At about the same time that X-rays were discovered, Emile Grubbe , an American physicist who was experimenting with Crooke’s tube, similar to the one used by Roentgen, suffered severe burns on his hands as a result of holding the energized tube in his hands. Then, in May of that same year, a man who had a diagnostic radiograph made of his head suffered skin burns and loss of hair on the side of his face that had been exposed to the X-rays. Therefore, from the initial use of X-rays for beneficial purposes, harmful effects were observed.

1.1.4 Genesis of radiation protection and safety

Reports of harmful radiation effects continued as the usefulness of radiation in medicine and science was being discovered. This caused various practitioners to suggest a variety of radiation safety rules. In 1915, the British Roentgen Society took the first organized action in radiation safety. A committee of the British Roentgen Society called the X-ray and Radium Protection Committee published further recommendations in 1921 and in 1927.

In 1925, the radiological societies of several countries convened the First International Congress of Radiology in London. Radiation protection and the need for a committee to deal with questions of radiation safety were among the main topics discussed at the meeting. At the second International Congress of Radiology, held in 1928, a committee called the International X-ray and Radium Protection Committee was established to provide guidance in these matters. At the time of formation of this committee and for many years afterward, its main concern was the safety aspects of medical radiology. The committee’s interests in radiation protection expanded with the widespread use of radiation outside the sphere of medicine, and, in 1950, its name was changed to the International Commission on Radiological Protection (ICRP) in order to describe its area of concern more accurately. Since its formation, the ICRP has been recognized as the leading agency for providing guidance in all matters of radiation safety.

For the purposes of radiation protection, ICRP 103 categorizes all ionizing radiation exposures into three types: occupational exposure, public exposure, and medical exposure. It defines medical exposure as follows:

Exposure incurred by patients as part of their own medical or dental diagnosis or treatment; by persons, other than those occupationally exposed, knowingly, while voluntarily helping in the support and comfort of patients; and by volunteers in a program of biomedical research involving their exposure.

This paper specifically deals with the protection of patients during exposures incurred as part of their own dental diagnosis. ICRP 103 gives three fundamental principles of radiological protection, namely justification, optimization and the application of dose limits and clarifies how they apply to radiation sources delivering exposure and to individuals receiving exposure. However ICRP 103 states that dose limits are not recommended for medical exposure of patients because they may reduce the effectiveness of the patient’s diagnosis or treatment, thereby doing more harm than good. Diagnostic reference levels are instead recommended for use in medical exposure of patients. This paper will therefore explore how justification of medical procedures, optimization of protection and the use of diagnostic reference levels can be used for radiological protection of patients in dentistry.

OBJECTIVES

The objective of this project work is to review the current literature on Dental radiology in order to achieve the following: to give justification for the need for radiological protection of patients in dental radiography, to explore the different factors affecting patient dose in dental radiography and to derive practical guidance on how to achieve radiological protection of patients in dentistry.

1.2 RELEVANCE AND JUSTIFICATIONS

Most dental professionals are not convinced of the need for regulatory control of the use of ionizing radiation for patient diagnosis in dentistry. They believe that the doses used in the dental practice are too low to warrant regulatory control and consequently patient protective measures. This project seeks to give justification for the need of patient protection measures in dentistry in the hope that dental professionals will understand the rational for patient protection. It seeks to give practical guidance that can be followed by health professionals to achieve radiological protection of patients in dentistry.

1.3 SCOPE OF PROJECT WORK

This project work seeks to justify the need for patient protection in dental radiology. It provides practical guidance on how to achieve radiological protection of patients from exposures resulting from their own dental diagnosis. The project work demonstrates how to apply the three fundamental principles of radiological protection to dental radiology for patient protection. This includes guidance on how equipment factors can be used to reduce radiation doses to patients. The project work deals only with standard dental imaging techniques of intraoral and common extraoral examinations, excluding cone-beam computed tomography (CBCT).

CHAPTER TWO

2.0 LITERATURE REVIEW

2.1 RADIATION DOSE, DAMAGE AND RISK

2.1.1 radiation dose in dental radiology

According to UNSCEAR reports [8, 9], medical applications are the largest man-made source of radiation exposure for the world’s population and they continue to grow at a substantial rate. Table 1 from UNSCEAR 2008 [9] shows that the global annual per caput effective dose from Diagnostic medical radiology is 0.62 mSv while that from Diagnostic dental radiology is 0.0018 mSv. As shown on the table, the per caput effective dose from Diagnostic medical radiology accounts for 20% of global annual per caput effective dose to the global population due to all sources of ionizing radiation while the contribution from diagnostic dental radiology accounts for less than 0.1%. A graphical illustration of the results in Table 1 is shown in Figure 2. The UNSCEAR report [9] states that the Global annual total collective effective dose attributable to diagnostic exposures including dental is approximately 4.2 million man Sv. However only 11 000 man Sv of this is attributable to Diagnostic dental radiology as shown in Table 2. As shown in Table 3 adapted from the report, the average effective dose per dental radiological examination is 0.024mSv. This is very low in comparison to the average effective dose per medical radiological examination which is stated as 1.28 mSv.

UNSCEAR 2008 states that dental radiological examinations are among the most common medical exposures. Approximately 3.14 billion diagnostic medical radiological examinations are done annually whereas for diagnostic dental radiology the number of examinations done annually is 0.48 billion. This means that just over 87% of radiological examinations worldwide are diagnostic medical while 13% are diagnostic dental. A comparison of the contribution to frequency from diagnostic dental radiology examinations with that from CT scanning which accounts for 6% of all diagnostic examinations shows how common radiological dental examinations are. The per caput effective dose and the collective effective dose from diagnostic dental radiology are relatively low as compared to diagnostic medical radiology, however according to UNSCEAR 2008, the number of dental examinations may be under-reported in many countries [9].

Abbildung in dieser Leseprobe nicht enthalten

Table 1: Global per caput effective dose

Abbildung in dieser Leseprobe nicht enthalten

Source: UNSCEAR 2008 [9]

Table 2: Global annual collective effective dose

Abbildung in dieser Leseprobe nicht enthalten

Source: UNSCEAR 2008 [9]

Figure 2: Annual per caput effective dose (mSv) 1997-20007

Abbildung in dieser Leseprobe nicht enthalten

Source: UNSCEAR 2008 [9]

Table 3: Population-weighted average effective doses assumed in the global model for diagnostic practice with medical and dental examinations (1997-2007)

Abbildung in dieser Leseprobe nicht enthalten

Source: UNSCEAR 2008 [9]

2.1.2 radiation damage

During an X-ray examination, millions of x-ray photons pass through a patient’s body. The X-ray photons can damage any molecule by ionisation, but according to the European guidelines on radiation protection in dental radiology [11], damage to the DNA in the chromosomes is of particular importance. Most DNA damage is repaired immediately, but on rare occasion, a mutation may occur in a portion of a chromosome leading ultimately to the formation of a tumor. According to the UNSCEAR 2010 report [10] it is the simultaneous damage of both strands of DNA double helix that is difficult to repair correctly. The report states that this damage often results in breakage of the DNA molecule with associated complex chemical changes. The report further states that even at low doses of radiation it is likely that there is a very small but non-zero chance of the production of DNA mutations that increase the risk of cancer developing. The European guidelines on radiation protection in dental radiology state that the latent period between exposure to X-rays and the clinical diagnosis of a tumor may be many years. It further states that the risk of tumor being produced by a particular X-ray dose can be estimated given that the doses received by radiological techniques are known.

UNSCEAR 2010 [10] defines low doses as those of 200 milligrays (mGy) or less and low dose rates as 0.1 mGy per minute (averaged over one hour or less) for radiations such as external X-rays and gamma rays. Although the doses in dental radiology are low, as per the above definition, European guidelines on radiation protection in dental radiology [11] site a number of epidemiological studies that have provided evidence of an increased risk of brain , salivary gland and thyroid tumors for dental radiography. This is in contrast to Canadian Safety Code 30 [13], published four years earlier, which assets that there is no known occurrence of cancer or genetic damage that has been observed from doses delivered in modern dentistry. These radiation effects are classified as stochastic. ICRP 103 [4] defines stochastic effects of radiation as follows:

Malignant disease and heritable effects for which the probability of an effect occurring, but not its severity, is regarded as a function of dose without threshold

The European guidelines on radiation protection in dental radiology [11] states that the effects of radiation described above are believed to have no threshold radiation dose below which they will not occur. The guidelines consider them as stochastic effects, where the magnitude of the risk is proportional to the radiation dose.

UNSCEAR 2010 [10] states that there is increasing evidence of low dose radiation exposure leading to increased incidence of cataracts; however according to the European guidelines on radiation protection in dental radiology [11] deterministic effects such as cataract formation, skin erythema and effects on fertility occur at threshold doses of a magnitude far greater than those given in dental radiography. ICRP 103 [4] defines deterministic effects as follows:

Injury in population of cells, characterised by a threshold dose and an increase in the severity of the reaction as the dose is increased further.

2.1.3 risks from radiation exposure

The European guidelines on radiation protection in dental radiology [11] state that radiation detriment can be considered as the total harm experienced by an irradiated individual. They further state that in terms of stochastic effects, this includes the lifetime risk of fatal cancer, non-fatal cancer and hereditary effects. ICRP 103 [4] defines Detriment as follows:

The total harm to health experienced by an exposed group and its descendants as a result of the group’s exposure to a radiation source. Detriment is a multi-dimensional concept. Its principal components are the stochastic quantities: probability of attributable fatal cancer, weighted probability of attributable non-fatal cancer, weighted probability of severe heritable effects, and length of life lost if the harm occurs.

Research indicates that the detriment-adjusted risk factor for the whole population is 5.7 x 10-2 Sv-1 [4, 11]. For cancer, the radiation detriment considers cancer incidence weighted for lethality and life impairment. Table 4 shows the breakdown of this summed figure into its constituent elements. The figures in Table 4 have been derived from ICRP 103 [4].

Studies have shown that there is no direct evidence of radiation risks of heritable diseases to humans [4, 10, 13]. According to UNSCEAR 2010 report [10] the clearest demonstration of heritable effects of radiation exposure come from extensive experimental studies on animals at high doses, particularly laboratory mice. Nevertheless ICRP 103 [4] sates that experimental observations argue convincingly that risks of heritable diseases for future generations should be included in the system of protection. With specific reference to the low doses used in dental radiology, the European guidelines on radiation protection in dental radiology [11] state that hereditary effects are believed to be negligible in dental radiology. This is in contrast to the Canadian Safety Code 30 [13], which states that although the radiation dose may be small and appear to cause no observable damage, the probability of chromosomal damage, with consequences of mutations giving rise to genetic defects can make such doses significant, when considered for a large population. Safety Code 30 further states that it is generally accepted that there is no safe level of radiation dose and that no matter how low the doses received are, there is a mathematical probability of an effect.

Abbildung in dieser Leseprobe nicht enthalten

Table 4: Nominal lifetime probability coefficients for stochastic effects

*The lifetime probability co-efficient for non-fatal cancer represents detriment rather than true incidence, which would be significantly greater

Source: ICRP 103 [4]

According to studies [11,12,14] radiation risk is age dependent, being highest for the young and least for the elderly. Research [11,14] indicates that risks given in Table 4 are for an adult patient at 30 years of age. The research further states that the risks can be modified using the multiplication factors given in Table 5 to calculate the risks for different ages. According to the research, values used represent averages for the two sexes. Furthermore, risks for females are slightly higher and those for males are slightly lower at all ages.

Table 5: Risk in relation to age

Abbildung in dieser Leseprobe nicht enthalten

Source: European guidelines on radiation protection in dental radiology [11]

According to the research [11,14], the data in Table 5 represents relative attributable lifetime risk based upon a relative risk of 1 at age 30. It assumes the multiplicative risk projection model, averaged for both males and females. The research states that beyond 80 years of age, the risk becomes negligible because the latent period between X-ray exposure and the clinical presentation of a tumor will probably exceed the life span of a patient. It further states that the tissues of younger people are, in contrast, more radiosensitive and their prospective life span is likely to exceed the latent period.

In addition to the fact that radiation risk is highest for young and least for elderly people, data from the UNSCEAR 2008 global survey of medical radiation usage and exposures shows that dental radiology tends to be performed more on younger individuals aged between 16 and 40 years [9]. This is in contrast to medical radiology which is performed more frequently on elderly individuals. The UNSCEAR report shows that there is an almost equal split of examinations between the two sexes.

2.2 JUSTIFICATION

Since any X-ray exposure entails a risk to the patient, all medical exposures to ionizing radiation must be justified [4,11,12,14-19]. Justification is one of the three fundamental principles for the system of protection described in ICRP publications [4,12,15]. According to the reviewed literature [4,11,12,14-19], medical exposures should be justified by weighing the expected diagnostic benefits that they yield against the radiation detriment that they might cause, taking into account the benefits and risks of available alternative techniques that do not involve medical exposure. Although most of the benefits and detriment accrue to the individuals undergoing diagnosis or treatment, all the resulting exposures, including the occupational and public exposures, and any potential exposures, should be taken into account [4,12,14]. ICRP 105 [15] states that most of the assessments needed for the justification of a radiological practice in medicine are made on the basis of experience, professional judgment, and common sense. According to the latest International publications [4,15,16] the principle of justification applies at three levels in the use of radiation in medicine.

At the first and most general level, the use of radiation in medicine should do more good than harm to the patient. The ICRP publications [4,15] state that the proper use of radiation in medicine is accepted as doing more good than harm to society therefore this level of justification can now be taken for granted. However, the International Basic Safety Standards [16] state that the regulatory body must ensure that provision is made for the justification of any type of practice and for review of the justification, as necessary, and ensure that only justified practices are authorized.

At the second level, also called generic justification, a specified procedure with a specified objective is defined and justified (e.g. chest radiographs for patients showing relevant symptoms, or a group of individuals at risk to a condition that can be detected and treated). The aim at this level is to judge whether the radiological procedure will usually improve the diagnosis or treatment, or will provide necessary information about the exposed individuals. This justification of the radiological procedure should be done by national and international professional bodies, in conjunction with international organisations. The justification of specific radiological procedures should be reviewed from time to time, as more information becomes available about the risks and effectiveness of the existing procedure and about new procedures.

At the third level, the application of the procedure to an individual patient should be justified (i.e., the particular application should be judged to do more good than harm to the individual patient). Therefore all individual medical exposures should be justified in advance, taking into account the specific objectives of the exposure and the characteristics of the individual involved. The justification of individual exposures should include checking patient records to ascertain whether the required information is not already available. It should also include checking whether the proposed examination is the most suitable method of providing the clinical information required. No additional justification is usually needed for the application of a simple diagnostic procedure to an individual patient with the symptoms or indications for which the procedure has already been justified in general [15]. Relevant national or international guidelines must be taken into account for the justification of the medical exposure of an individual patient in a radiological procedure [4,15,16]. To that effect, such guidelines called referral criteria or selection criteria have been established by a number of national and international bodies for dental radiology [11,14,20].

Earlier publications [12,19] do not separate justification into three distinct levels. They however recognize the need for justification of any practice including a practice leading to medical exposure. This is referred to as the first and most general level of justification by the latest international publications [4,15,16]. These earlier publications also recognize the need for a case by case justification of each procedure. This may be interpreted to be the same as individual justification. The publications do not distinctly describe second level justification.

Reviewed publications specifically addressing radiation protection in dental radiology [11,14,17,18] also do not describe three distinct levels of justification. However they all demonstrate the need for third level justification by stating that all examination must be justified on an individual patient basis by demonstrating that the benefits to the patient outweigh the potential detriment. Whereas some publications [11,18] are silent on the first level of justification, other publications [14,17] demonstrate the need for the first level justification as well. According to some publications [11,14,18] the anticipated benefits are that the X-ray examination would add new information to aid the patient’s management. These publications further state that when referring a patient for a radiographic examination, the dentist should supply sufficient clinical information (based upon a history and clinical examination) to allow the practitioner taking clinical responsibility for the X-ray exposure to perform the justification process.

2.3 OPTIMIZATION

According to ICRP publications there is considerable scope for dose reductions in diagnostic radiology using the techniques of optimisation of protection [12,15]. ICRP 105 [15] defines optimization as follows:

The optimisation of radiological protection means keeping the doses ‘as low as reasonably achievable, economic and societal factors being taken into account’, and is best described as management of the radiation dose to the patient to be commensurate with the medical purpose.

Optimisation is one of the three fundamental principles for the system of protection described in ICRP publications [4,12,15]. Some publications also call this principle the ALARA (As Low As Reasonably Achievable) principle [14]. According to the International Basic Safety Standards [16] the application of the optimization principle to the medical exposure of patients requires a special approach because too low a radiation dose could be as bad as too high a radiation dose, in that the consequence could be that the images taken are not of suitable diagnostic quality. It is of paramount importance that the medical exposure leads to the required outcome. Reviewed literature [12,15,17] states that doses can be reduced without loss of diagnostic information by using low-cost measures. Processes that should be considered in optimisation of radiation exposures include the design, selection and maintenance of appropriate equipment as well as the adoption of systematic procedures and standardization of criteria in order to obtain the necessary diagnostic information using the lowest radiation dose that can be reasonably achieved [14]. ICRP publications [12,15] state that the extent to which these measures are used varies widely. The following section is a review of literature that discusses how equipment factors can be optimized for patient protection in dentistry.

2.3.1 IMAGE RECEPTOR SELECTION

According to literature [20,21] the American National Standards Institute and the International Organization for Standardization have established standards for film speed. The available film speeds for dental radiography are the following: D-speed, E-speed and F-speed, with D-speed being the slowest and F-speed the fastest. A FDA publication [20] indicates that switching from D to E speed can produce a 30 to 40 percent reduction in radiation exposure. However, other publications [8,11] show slightly more percent reduction of up to 50 percent in radiation exposure on switching from D to E speed film. Table 6 obtained from UNSCEAR 2000 [8] shows a 50 percent reduction in effective dose.

Table 6: Variation of technique of the typical effective dose from dental radiography

Abbildung in dieser Leseprobe nicht enthalten

a applied potential.

b focus to skin distance.

Source: UNSCEAR 2000 [8]

Literature shows that the use of F-speed film can reduce exposure 20 to 50 percent compared to use of E-speed film, without compromising diagnostic quality [11,20]. Hence some publications [18,21] recommend that film of a speed slower than E-speed should not be used for dental radiographs. The fastest film consistent with the requirements of the examination should be used for exposures in intraoral radiography [11,13,17,18]. Films that have passed the manufacturer’s recommended expiry date must not be used [17].

Intensifying screens are required to minimize radiation exposure to patients extraoral films have to be exposed such as in panoramic and Cephalometric radiography [11,20,21]. Previous generations of intensifying screens were made up of phosphors such as calcium tungstate. Reviewed publications [8,11,20,21] recommend rare-earth intensifying screens because they reduce a patient’s radiation exposure by 50 percent compared with calcium tungstate-intensifying screens. According to literature [11,20,21] rare-earth film systems, combined with a high-speed film of 400 or greater, can be used for panoramic radiographs and Cephalometric radiology. Some publications [20,21] state that older panoramic equipment can be modified to accommodate the use of rare-earth, high-speed systems in order to reduce radiation exposure. Also of crucial importance is that the light sensitivity of the film should be correctly matched with the intensifying screens [11,18]. Radiographic film must not be used without intensifying screens for dental radiological purposes except for intraoral dental radiography [17].

According to the FDA publication [20] patient doses can be further reduced by 40-60 percent if Digital imaging is used. There are three types of receptors that take the place of conventional film in digital radiography. These are: charge-coupled device (CCD), complementary-metal-oxide-semiconductor (CMOS), and photo-stimulable phosphor (PSP) plates. When CCD and CMOS based solid state detectors receive energy from the x-ray beam, the CCD or CMOS chip sends a signal to the computer and an image appears on the monitor within seconds. These solid state detector systems are called direct digital radiography. On the other hand when PSP plates are irradiated, a latent image is stored on them until the plate is scanned and the scanner transmits the image to the computer. These systems are called “indirect.” UNSCEAR 2000 report [8] puts the doses associated with CCDs and PSP to up to approximately 50% and 80% lower, respectively, than those associated with conventional techniques. Another publication [11] states that a CCD system provided reduction in average skin entrance dose of 51-60%. Although digital radiography offers a significant dose reduction, the number of retakes due to bad positioning and the need for multiple exposures to compensate for the smaller sensor sizes my result in increased dose for the patient [11,21]. The European guidelines on radiation protection in dental radiology [11] state that dose reduction is most effective with intraoral systems. They further state that it is unlikely that digital panoramic and Cephalometric radiography can routinely offer dose reduction compared with conventional screen/film combinations.

2.3.2 IMAGE RECEPTOR holders

Reviewed literature [11,17,18,20,21] recommends the use of holders that align the receptor precisely with the collimated beam in periapical and bitewing radiography. It is said that this facilitates standardising the technique thus reducing the necessity for retakes [17]. When a dental film or digital detector cannot otherwise be kept in position, it should only be held by the patient [18]. Under extraordinary circumstances in which members of the patient’s family or other caregiver must provide restraint or hold a receptor holder in place during exposure, such a person should wear appropriate shielding and use a pair of forceps or other appropriate holder to avoid direct irradiation of the fingers [18,20,21]. Dental professionals should not be the ones holding the receptor holder during exposure [17,20,21].

2.3.3 collimation

Research shows that collimation limits the amount of both primary and scattered radiation to which a patient is exposed [20,21]. Besides limiting the dose to patients by reducing the size of the X-ray beam to the minimum size needed to image the object of interest, collimation also limits the volume of the patient that is irradiated by limiting the beam area on the skin surface [11]. Rectangular collimation has an added benefit of improving contrast as a result of a reduction in fogging caused by secondary and scattered radiation. Literature [18,20,21] states that the x-ray beam should not exceed the minimum coverage necessary. According to some publications [20,21] each dimension of the beam should be collimated so that the beam does not exceed the receptor by more than 2 percent of the source-to-image receptor distance. Guidelines from the UK National Radiological Protection Board [18] state that Rectangular collimators should be designed so that the beam size at the end of the collimator does not exceed 40 by 50 mm (ie does not overlap the dimensions of the standard ISO film size 2 by more than 5 mm at any edge). They further sate that it would be preferable for this to be further reduced such that it does not exceed 35 by 45 mm (i.e. no more than a 2.5 mm overlap at any edge).

Some literature [20,21] state that a rectangular collimator decreases the radiation dose by up to fivefold as compared with a circular one. The UNSCEAR 2000 report [8] shows a different decrease in the radiation dose. As shown in Table 6, the UNSCEAR 2000 report shows that the use of a rectangular collimator decreases the effective dose by 50% when compared with a circular one. The European guidelines on radiation protection in dental radiology [11] report that various investigators have estimated that rectangular collimation can achieve dose reductions exceeding 60% in dental radiography. The same guidelines also cite a study that reported that both long and short rectangular collimation resulted in the lowest effective doses, with values 3.5 to 5 times less than round collimation. It is for this reason that it is recommended for radiographic equipment to provide rectangular collimation for exposure of periapical and bitewing radiographs [8,11,18,20,21].

According to literature [11,18,20] use of a receptor-holding device minimizes the risk of cone-cutting (non exposure of part of the image receptor due to misalignment of the x-ray beam). It is recommended that the position-indicating device should be open ended and have a metallic lining to restrict the primary beam and reduce the tissue volume exposed to radiation [20,21]. Because of the divergence of the X-ray beam, the X-ray source to skin distance plays a role in limiting doses. Increasing this distance reduces the divergence within the patient and therefore reduces the volume irradiated [11]. The Canadian Safety code 30 [13] recommends a focal spot to skin distance of not less than18 cm. Other publications [11,18] recommend that collimators be open ended and provide a minimum focal spot to skin distance of 20 cm. However, the UK National Radiological Protection Board guidelines [18] recommend a minimum of 20 cm focal spot to skin distance only for equipment operating at 60 kV or greater. They recommend a focal spot to skin distance of at least100 mm for equipment operating at below 60 kV. According to some guidelines [20,21], it has been found that the use of long source-to-skin distances of 40 cm, rather than short distances of 20 cm, decreases exposure by 10 to 25 percent. Source-to-skin distances of between 20 cm and 40 cm are appropriate, but the longer distances are optimal and therefore are recommended [20,21]. According to European guidelines on radiation protection in dental radiology [11,18] existing equipment can easily be adapted to allow rectangular collimation.

2.3.4 beam filtration

According to the European guidelines on radiation protection in dental radiology [11] filtration is invaluable as a means of reducing skin doses to patients. It reduces skin doses to patients by preferentially removing lower energy X-ray photons from the beam. Hence Filtration using aluminium is an established part of dental X-ray equipment. The Canadian Safety Code 30 [13] gives a table of minimum first half-value layers of aluminium for corresponding X-ray tube voltages that must be complied with. The values are displayed in Table 7.

Table 7: Half-Value Layer

Abbildung in dieser Leseprobe nicht enthalten

Source: Canadian Safety Code 30 [13]

The European guidelines on radiation protection in dental radiology [11] state that such filtration is a factor that is not readily under the control of the dentist. This is because it is fitted at manufacture. A number of researchers have investigated additional filtration using materials (K-edge filters) other than aluminium, such as rare-earth materials, as means of dose reduction in intraoral dental radiography [11]. The primary reason for their use is that they ‘shape’ the X-ray spectrum and more closely match the spectral sensitivity of dental film. The evidence appears to be that all offer reductions in dose, but that the benefit must be balanced against effects on image quality, cost, and the likely increase in exposure times associated with their use. Dose reduction due to the use of K-edge filters has also been demonstrated for panoramic radiography. The use of rare-earth filtration in intraoral radiography offers some dose reduction, however it should only be adopted after advice from a medical physics expert on setting new exposure factors.

2.3.5 OPERATING POTENTIAL AND EXPOSURE TIME

The radiation dose and backscatter radiation are affected by the operating potential of dental units [20,21]. Lower voltages result in higher-contrast images and higher entrance skin doses, and lower deep-tissue doses and levels of backscatter radiation. On the other hand, higher voltages result in lower contrast images that enable better separation of objects with differing densities. Therefore, the diagnostic purposes of the radiograph should be used to select the appropriate kilovolt setting. According to the FDA guidelines [20] a setting above 90 kV(p) will increase the patient dose and should not be used. The guidelines state that the optimal operating potential of dental x-ray units is between 60 and 70 kVp. An earlier publication by the American Dental Association [21] states that the operating potential of dental X-ray machines should range between 60 and 80 kVp. They also state that it is required of Manufacturers of low-kVp (less than 60) dental radiographic equipment to install internal aluminum beam filters so that the mean beam energy will approach 60 kVp.

The FDA guidelines [20] state that filmless technology is much more forgiving to overexposure often resulting in unnecessary radiation exposure. They recommend that facilities strive to set the x-ray unit exposure timer to the lowest setting providing an image of diagnostic quality. They further recommend that the operator always confirm that the dose delivered falls within the manufacturer’s exposure index, if available. Furthermore the imaging plates should be evaluated at least monthly and cleaned as necessary.

2.3.6 PATIENT PROTECTIVE EQUIPMENT

According to literature [20] the amount of scattered radiation striking the patient’s abdomen during a properly conducted dental radiographic examination is negligible. The thyroid gland is more susceptible to radiation exposure during dental radiographic exams due to its anatomic position, particularly in children. Protective thyroid collars and collimation significantly reduce radiation exposure to the thyroid gland during dental radiographic procedures [20]. The American Dental Association Council [21] strongly recommends thyroid shielding with a leaded thyroid shield or collar for children and pregnant women, because these patients may be especially susceptible to radiation effects. According to ARPANSA Code of Practice & Safety Guide [17] the need for radiography in children should be carefully assessed and appropriate protective measures such as leaded aprons and thyroid shields considered, particularly during occlusal views of the maxilla where the X-ray beam is directed vertically downwards towards the patient’s trunk. Some publications [20,21] state that because every precaution should be taken to minimize radiation exposure to all patients, protective thyroid collars should be used whenever possible. However other publications say that protection of the thyroid may be relevant only for some examinations such as those involving children [17].

Literature states that if the recommendations for limiting radiation exposure to a patient are rigorously put into practice, the gonadal radiation dose will not be significantly affected by use of abdominal shielding [20,21]. Consequently, the use of abdominal shielding may not be necessary [20,21]. However, if any of the recommendations is not implemented, then a leaded apron should be used [21] to protect the patient. According to ARPANSA Code of Practice & Safety Guide [17] routine use of abdominal shielding is unnecessary because of the very low effective doses involved in properly conducted dental radiography. However the safety guide recommends provision of a leaded drape when the X-ray beam is directed downwards towards the trunk of women patients of reproductive capacity, for instance when taking occlusal views of the maxilla. The safety guide further states that there is no need to defer dental radiography during pregnancy on radiation protection grounds. Contrary to other publications the Canadian Safety Code 30 [13] says that all patients must be provided with a shielded apron, for gonad protection, and a thyroid shield, especially during occusal radiographic examination of the maxilla. However, like other publications, Safety Code 30 recommends the use of thyroid shield especially for children.

Protective aprons and thyroid shields should be hung or laid flat and never folded to prevent cracks from occurring in the leaded shield [20,21]. The FDA guidelines [20] recommend that all protective shields be evaluated for damage (e.g. tears, folds, and cracks) monthly using visual and manual inspection.

2.3.7 FILM EXPOSURE AND PROCESSING

According to literature [11,13,18,21] film processing procedures and exposure settings can affect the quality of the radiographic image. Hence, all film should be processed in accordance with the recommendations from the film and processer manufacturer [11,13,17,18,20,21]. These manufacturer recommendations include processing time, temperature and chemistry [11,13,17,18,21]. In addition to satisfying the manufacturer’s recommendations, manual processing of films must satisfy the following requirements [13,17]:

- the temperature of developing solutions must be measured;

- an appropriate time-temperature chart must be used to calculate the processing time;

- the temperature of the developing solutions must be maintained during processing; and

- the time of processing must be measured.

The concentrations of developing solutions must also be in accordance with the manufacture’s specifications. Furthermore, replenishment or replacement of the developer and fixer must be done at appropriate intervals to maintain adequate image quality at acceptable patient doses [11,13,17]. If oxidized or depleted film developer is used, the blackening of the film will not be optimum and the tendency of the X-ray operator will be to increase radiation dose to achieve proper image density [13].

The use of automatic film processors for conventional dental X-ray film will produce films of more uniform density with, on average, lower patient dose than when processing is done manually [13]. Hence, manual processing of conventional dental X-ray films is not recommended especially for high workload facilities. Manual film processing is acceptable for facilities where the workload is very low, only a few films per day.

Cleanliness of processing equipment is extremely important for reducing film artifacts in both manual and automatic film processing [13]. When manual processing is used proper stainless steel processing tanks complete with water bath and lids must be used. For automatic processors, cleaning of the film transport mechanisms must be done frequently [11,13].

According to the Canadian Safety Code 30 [13] regular monitoring of developing solutions must be done as even unused developer deteriorates with time. It further states that the developer must not be used when film processing times become significantly longer than what is recommended by the manufacturers or the radiation dose necessary to obtain an acceptable film density has increased also significantly.

Once optimum processing is achieved, the x-ray operator can establish a technique that will provide consistent dental radiographs of diagnostic quality by adjusting the tube current and time [21]. Dental films should not be processed by sight [17,21]. This is a poor processing technique which most often results in underdeveloped films, forcing the X-ray operator to increase the dose to compensate, resulting in patient and personnel being exposed to unnecessary radiation [20]. Exposure techniques must not be adjusted to compensate for poor film processing [17]. Images of poor diagnostic quality can also result from radiographs that are over-exposed and then underdeveloped. This practice results in greater exposure to the patient and dental health care worker [21].

A safelight does not provide completely safe exposure for an indefinite period of time, therefore the length of time for which a film can be exposed to the safelight should be determined for the specific safelight/film combination in use [20,21]. It has been determined that extraoral film is much more sensitive to fogging [20]. According to the European guidelines on radiation protection in dental radiology [11] routine checks should be made to ensure that safelights do not produce fogging of films and darkrooms remain light tight [11]. This can be done by a simple ‘coin’ test.

2.3.8 FILM STORAGE

According to the European guidelines on radiation protection in dental radiology [11] the quality of radiographs can be reduced by inadequate film storage conditions. The guidelines say that poor storage conditions such as excessive temperature, close proximity to X-ray equipment or poor handling can all lead to artifacts. In order to ensure that excessive irradiation of film by X-rays does not occur, the film storage container must be adequately shielded [13,17]. According to the Australian Radiation Protection and Nuclear Safety Agency code of practice [17] an alternative to a shielded film storage is to store the films in an area remote from any X-ray unit. The Canadian Safety Code 30 [13] states that the film storage should be such that no film receives more than 1.75 Gy (0.2 mR) of radiation before use. The amount of shielding required to satisfy the given absorbed dose limit will depend on the storage time and on the workload of the facility. The Canadian Safety Code 30 [13] further states that a shielding of 1.5 mm of lead will be more than adequate for the majority of facilities. The other optimal film storage conditions are a cool and dry area [13,17]. It is also recommended that films be stored away from chemical contamination such as that from film processing chemicals [17]. According to the European guidelines on radiation protection in dental radiology [11] film should not be used after its expiry date. The guidelines further state that the film quality assurance programme should include stock control measures to ensure that expired film is not used. The film quality assurance programme and storage must be in accordance with the manufacturer’s recommendations [11,17].

2.3.9 IMAGE VIEWING

According to the European guidelines on radiation protection in dental radiology [11] ideal viewing conditions are crucial in order to obtain maximum diagnostic information output from a radiograph. Literature [11,21] states that this requires the use of a dental light box positioned well away from strong ambient light to reduce reflections and the peripheral masking of films to prevent glare and loss of visual acuity. The dental light box should preferably have variable intensity in order to allow for optimization of high- and low-density areas [21]. Whereas the American Dental association recommendations [21] just state that magnification should be used as needed, the European guidelines on radiation protection in dental radiology [11] are more prescriptive as they recommend a method of magnifying the image by a factor of two. Film viewers which combine peripheral masking and magnification are commercially available [11]. According to the European guidelines on radiation protection in dental radiology [11] research has shown that considerable improvement in diagnostic interpretation and yield can be achieved by the use of dedicated viewing conditions. The guidelines also recommend routine cleaning of the viewing surface as part of routine quality procedures.

2.3.10 QUALITY ASSURANCE

Quality assurance protocols for the x-ray machine, imaging receptor, film processing, dark room, and lead aprons and thyroid shields should be developed and implemented for each dental health care setting [20,21]. All quality assurance procedures, including the following should be logged for documentation purposes: date, procedure, results, and corrective action. All X-ray units should be surveyed by a qualified expert on their placement and should be resurvey every four years or after any changes that may affect the radiation exposure of the operator and others.

The film processor should be assessed at its first installation and on a monthly basis thereafter. The processing chemistry should be assessed every day, and each type of film should be evaluated every month or when a new box or batch of film is opened.

Lead aprons and thyroid shields should be visually inspected every month for creases or clumping that may indicate voids in their integrity. The lead protective equipment should be examined fluoroscopically on an annual basis [21]. Damaged lead aprons and thyroid shields should be replaced [20]. Specific methods of quality assurance procedures from reviewed literature [20,21] are listed in Table 8. The listed quality assurance methods include the following: inspection of the x-ray unit, the film processor, the image receptor devices, the darkroom and lead aprons and thyroid shields [20,21]. It is vital that the operator’s manual for all imaging acquisition machines is readily available to the user. It is also imperative that the equipment is operated and maintained following the manufacturer’s instructions, including any appropriate adjustments for optimizing dose and image quality [20].

Table 8: Quality Assurance Procedures for Assessment of Radiographic Equipment

Abbildung in dieser Leseprobe nicht enthalten

Source: U.S. FDA Recommendations for Patient Selection and Limiting Radiation Exposure [20]

2.3.11 diagnostic reference levels

In order to ensure that patient doses are kept as low as reasonably achievable, it is necessary to ensure that patient doses are monitored on a regular basis [11,16]. This optimization is achieved through the use of Diagnostic Reference Levels (DRLs). The UK National Radiological Protection Board guidelines [18] define Diagnostic Reference Levels as dose levels in Radio-diagnostic practices for typical examinations for groups of standard-sized patients or standard phantoms for broadly defined types of equipment. The guidelines further state that DRLs would not normally be expected to be exceeded without good reason. Therefore DRLs can be used as investigation levels [11,15,16].

In essence, the purpose of DRLs is to provide reference levels of easily measurable patient dose quantities against which facilities can compare their average doses [11,15]. DRLs are not intended to be applied to individual exposures of individual patients [11,15]. They are rather intended to indicate an upper level of acceptability for current normal radiological practice [11]. Literature [11,15,16] states that the use of DRL’s is a simple way of identifying situations well away from the optimum where corrective action is most urgently needed.

Attainment of average dose below a relevant DRL does not necessarily indicate that dose is optimised [11,18]. It just gives some confirmation that patient doses in a particular facility are reasonably in line with other facilities [11]. Further dose reduction may still be practical; therefore facilities are encouraged to periodically review local patient dose data to determine whether their procedures and equipment would support the adoption of a DRL value lower than the current national DRL [18].

On the other hand, doses consistently above a DRL would definitely indicate that patient dose is not in line with the principle of ALARA and that a thorough review of radiographic practice must be made and action should be taken to reduce dose [11,15,18]. If the doses are not reduced to below the DRL then justification must be made for the continued use of the high doses [18].

According to literature [11], the most usual method of setting a DRL is by basing it on the third quartile of field measurements performed in a large number of facilities. As a result, DRLs are based on current practice across a wide range of different facilities, not on results from a select group of facilities with a high level of equipment and expertise [11,16].

The European guidelines on radiation protection in dental radiology [11] state that although some European countries have established national dental DRLs, European wide DRLs have not, so far, been promulgated for dental radiography. Nevertheless the guidelines recommend a DRL of 4 mGy absorbed dose in air measured at the end of the spacer cone for a standard maxillary molar projection. The guidelines also give a summary of dose surveys and current national DRLs for European and North American countries.

It is not expected that dental practices will have the facilities to be able to assess how their average doses compare with national DRLs themselves therefore they will require the services of a medical physics expert [11]. It is recommended that these dose assessments be carried out on a regular basis, at least every 3 years or as required by national legislation [11].

The UK National Radiological Protection Board Guidance Notes [18] draw attention to a new concept known as ‘Achievable Dose’. The Achievable Dose will be based on operational and technological factors and is likely to be gradually introduced to support DRLs so as to encourage practices already below current DRLs to optimize patient protection.

2.3.12 TECHNIQUE CHARTS/PROTOCOLS

According to the FDA guidelines [20] technique charts are tables that indicate appropriate settings on the x-ray machine for a specific anatomical area. The guidelines further state that in order to ensure that radiation exposure is optimized for all patients, size-based technique charts/protocols with suggested parameter settings are essential. Literature [13,17,20] states that technique charts must be displayed near the X-ray unit control panel whenever exposure factors for specific examinations are not marked on the unit. The purpose of using the charts is to ensure the use of exposure factors that will result in the least amount of radiation exposure to the patient and produce a consistently good-quality radiograph [13,20]. According to the Canadian Safety Code 30 [13] technique charts must be established after optimizing the film processing procedure.

The FDA guidelines [20] state that technique charts for intraoral and extraoral radiography should list the following: type of exam, the patient size (small, medium, large) for adults and a pediatric setting, the speed of film used, or use of a digital receptor. The guidelines also state that a technique chart should be developed for each x-ray unit and that the chart should be regularly updated. Furthermore the charts should be updated whenever a different film or sensor, new unit, or new screens are used [20].

2.3.13 TRAINING AND EDUCATION

Literature [20,21] states that personnel certified to take dental radiographs should receive appropriate education. Furthermore, it is recommended that dental health practitioners remain informed about safety updates and the availability of new equipment, supplies and techniques that could further improve the diagnostic quality of radiographs and decrease radiation exposure. Other publications [11,14] are more explicit about the training and education requirements for dental practioners. The publications state that dental practitioners must have not only adequate theoretical and practical training for the purpose of radiological practices but they must have relevant competence in radiation protection appropriate to dental radiography as well. The UK Guidance Notes for Dental Practioners on the Safe Use of X-Ray Equipment [18] is even more elaborate about the education and training requirements for dental practioners. It states that adequately trained dental practioners must have an undergraduate degree conforming to the requirements for the undergraduate dental curriculum in dental radiology and imaging and the core curriculum in dental radiography and radiology for undergraduate dental students.

Dental practioners are also required to undertake continuing education and training after qualification [11,14,18]. The publications further state that when new techniques are adopted, such as when a dentist buys a new type of equipment or changes to using digital radiography, specific training should be undertaken. According to the UK Guidance Notes for Dental Practioners on the Safe Use of X-Ray Equipment [18], continuing education for dental practioners is expected to cover the following:

(a) the principles of radiation physics;

(b) risks of ionising radiation;

(c) radiation doses in dental radiography;

(d) factors affecting doses in dental radiography;

(e) the principles of radiation protection;

(f) statutory requirements;

(g) selection criteria;

(h) quality assurance;

Besides the equipment operator, all other staff in a dental practice must be aware of the risks associated with the use of X-ray equipment, the precautions required to keep their dose ALARA and the importance of complying with these arrangements [11]. Free training materials for reducing patient exposure to X-rays in dental radiography can be accessed through the International Atomic Energy Agency website [22]. The American Dental Association’s website also provides access to a continuing education course list in topics such as dental radiographs and radiation Safety (“www.ada.org/prof/ed/ce/index.asp”).

CHAPTER THREE

3.0 Discussions

3.1 RADIATION DOSE, DAMAGE AND RISK

3.1.1 RADIATION DOSE IN DENTAL RADIOLOGY

The reviewed literature shows that individual doses involved in diagnostic dental radiology are comparatively low when compared to those in diagnostic medical radiology. The global annual per caput effective dose and the average effective dose per examination for both diagnostic medical radiology and diagnostic dental radiology are 0.62 mSv, 1.28 mSv and 0.0018 mSv, 0.024 mSv respectively [9]. However the high frequency of examination in dental radiology justifies the need for radiation protection in dentistry. The literature review reveals that 0.48 billion diagnostic dental radiology examinations are done annually representing 13% of radiological examinations worldwide. The frequency of dental examinations is very high when compared to other diagnostic examinations such as CT scanning which accounts for 6% of all diagnostic examinations. The likely hood that the number of dental examinations may be under-reported in many countries and the fact that the use of X-rays in dentistry continues to grow at a substantial rate make a compelling case for radiation protection measures in dental radiology now and in the future.

3.1.2 RADIATION DAMAGE

It is clear that the deleterious effect of radiation that is of most concern in dental radiology is that arising from damage to the DNA in the chromosomes. The simultaneous damage of both strands of DNA double helix is of particular importance due to the difficulty in correct repair of such damage. It is reported that such damage often results in breakage of the DNA molecule with associated complex chemical changes which, on rare occasion, may result in a mutation in a portion of a chromosome leading ultimately to the formation of a tumor. Early publications such as the Canadian Safety Code 30 [13] claim that there is no known occurrence of cancer or genetic damage that has been observed from doses delivered in modern dentistry. However the European guidelines on radiation protection in dental radiology [11], published four years later, site a number of epidemiological studies that have provided evidence of an increased risk of brain , salivary gland and thyroid tumors for dental radiography. It may be the case that no known evidence of increased risk of cancer to organs at risk in dentistry was available at the time of publication of the Canadian Safety Code 30 [13] but later such evidence became available.

UNSCEAR 2010 [10] states that there is increasing evidence of low dose radiation exposure leading to increased incidence of cataracts. On the other hand the European guidelines on radiation protection in dental radiology [11] report that deterministic effects such as cataract formation, skin erythema and effects on fertility occur at threshold doses of a magnitude far greater than those given in dental radiography. None of the other publications reviewed indicate any occurrence of deterministic effects at doses encountered in diagnostic dental radiology. One may therefore conclude that the reported increasing incidence of cataracts at low dose radiation exposures is due to doses below 200 milliSieverts (mSv) but higher than the doses encountered in diagnostic dental radiology.

3.1.3 RISKS FROM RADIATION EXPOSURE

None of the literature reviewed has reported direct evidence of radiation risks of heritable diseases to humans. The European guidelines on radiation protection in dental radiology [11] report that hereditary effects are believed to be negligible in dental radiology. Although it is accepted that there is no direct evidence of radiation risks of heritable diseases to humans [4, 10, 13], other literature does not take this risk as negligible. The Canadian Safety Code 30 [13] considers the risk of hereditary effects significant when considered for a large population. It is generally accepted that there is no safe level of radiation dose and that no matter how low the doses received are, there is a mathematical probability of an effect. The detriment-adjusted risk factor for hereditable effects for the whole population is 0.2 x 10-2 Sv-1[4,11]. As stated in ICRP 103 [4] experimental observations argue convincingly that risks of heritable diseases for future generations should be included in the system of protection.

Studies show that even at low doses of radiation it is likely that there is a very small but non-zero chance of the production of DNA mutations that increase the risk of cancer developing. The detriment-adjusted risk factor for the cancer incidence weighted for lethality and life impairment for whole population is 5.5x10-2 Sv-1[4,11].

A sum of the above two risk factors gives the detriment-adjusted risk factor for the whole population as 5.7 x 10-2 Sv-1 [4, 11]. The hereditable and cancer effects of radiation described above are believed to have no threshold radiation dose below which they will not occur. They are known as stochastic effects, where the magnitude of the risk is proportional to the radiation dose

It has also been shown that radiation risk is age dependent, being highest for the young and least for the elderly [11,12,14]. This is because tissues of younger people are more radiosensitive and their prospective life span is likely to exceed the latent period between X-ray exposure and the clinical presentation of a tumor. In addition the radiation risk for younger people is comparatively increased in dental radiology due to the fact that dental radiology tends to be performed more on younger individuals aged between 16 and 40 years [9].Risks for females are slightly higher and those for males are slightly lower at all ages while there is an almost equal split of examinations between the two sexes.

3.2 JUSTIFICATION

The requirement for justification of all medical exposures to ionizing radiation is echoed by reviewed literature [4,11,12,14-19] . According to the literature, medical exposures should be justified by weighing the expected diagnostic benefits that they yield against the radiation detriment that they might cause, taking into account the benefits and risks of available alternative techniques that do not involve medical exposure. Whereas the latest International publications [4,15,16] describe the principle of justification as applying at three distinct levels in the use of radiation in medicine, other earlier publication describe only two levels of justification while some do not make any distinction of justification levels at all. What is common through all the reviewed literature dealing with medical exposure justification is that they express the need for all examination to be justified on an individual patient basis by demonstrating that the benefits to the patient outweigh the potential detriment.

Radiation protection would be enhanced if all medical exposures were justified at the three levels described in the literature review. At the first and most general level, the use of radiation in medicine should do more good than harm to the patient. The proper use of radiation in medicine is accepted as doing more good than harm to society therefore this level of justification can now be taken for granted[4,15]. National regulatory authorities ensure that only practices justified at this level are authorized in accordance with the International Basic Safety Standards [16]. At the second level, a specified procedure with a specified objective is defined and justified. The aim at this level is to judge whether the radiological procedure will usually improve the diagnosis or treatment, or will provide necessary information about the exposed individuals. At the third level, the application of the procedure to an individual patient should be justified (i.e., the particular application should be judged to do more good than harm to the individual patient). Therefore all individual medical exposures should be justified in advance, taking into account the specific objectives of the exposure and the characteristics of the individual involved

3.3 OPTIMIZATION

There is considerable scope for dose reductions in diagnostic radiology using the techniques of optimisation of protection [12,15]. The aim of optimization is to keep the doses ‘as low as reasonably achievable, economic and societal factors being taken into account’, and is best described as management of the radiation dose to the patient to be commensurate with the medical purpose.

Optimisation, also called the ALARA principle, is one of the three fundamental principles for the system of protection described in ICRP publications [4,12,15]. Review of literature [16] shows that the application of the optimization principle to the medical exposure of patients requires a special approach because too low a radiation dose could be as bad as too high a radiation dose, in that the consequence could be that the images taken are not of suitable diagnostic quality. Doses can be reduced without loss of diagnostic information by using low-cost measures [12,15,17]. Processes that should be considered in optimisation of radiation exposures include the design, selection and maintenance of appropriate equipment as well as the adoption of systematic procedures and standardization of criteria in order to obtain the necessary diagnostic information using the lowest radiation dose that can be reasonably achieved [14]. The extent to which these measures are used varies widely [12,15].

3.3.1 IMAGE RECEPTOR SELECTION

Dental radiography films have different speeds which require different amounts of radiation exposure to produce a radiograph of acceptable diagnostic quality.

The different films are as follows: D-speed, E-speed and F-speed, with D-speed being the slowest and F-speed the fastest. Various studies have established that switching from D to E speed results in a reduction in radiation exposure [8,11,20]. The percent reduction in reviewed literature ranges from 30 to 50 percent. Although there is a variation in the percent reduction in radiation exposure, what is most important is that switching from D to E speed leads to a substantial reduction in patient dose.

Studies [11,20] show that switching from E-speed film to F-speed film can reduce radiation exposure by 20 to 50 percent without compromising diagnostic quality. This explains why some publications [18,21] recommend that film of a speed slower than E-speed should not be used for dental radiographs. As new and faster films are designed as time goes on it is better to recommend the use of the fastest film consistent with the requirements of the examination for exposures in intraoral radiography.

Where extraoral films are used such as in panoramic and Cephalometric radiography, intensifying screens are required to minimize radiation exposure to patients [11,20,21]. Hence radiographic film must not be used without intensifying screens for dental radiological purposes except for intraoral dental radiography [17]. Review of literature [8,11,20,21] demonstrates that switching from previous generations of intensifying screens made up of calcium tungstate to rare-earth intensifying screens reduces a patient’s radiation exposure by 50 percent. Consequently a combination of rare-earth film systems and high-speed film of 400 or greater is recommended for both panoramic and Cephalometric radiology. Facilities which have older panoramic equipment do not necessarily have to purchase new equipment in order to achieve optimization using this technique. This is because older equipment can be modified to accommodate the use of rare-earth, high-speed systems [20,21]. The light sensitivity of the film should also be correctly matched with the intensifying screens in order to achieve optimization of patient doses [11,18].

The literature review in section 2.3.1 shows that patient doses can be further reduced by the use of digital imaging instead of conventional techniques. Studies reviewed give varying percentage reduction of doses on switching from conventional to digital imaging. The percentage reduction ranges from 40-80 percent [8,11,20]. Although digital radiography offers a significant dose reduction, retakes due to bad positioning and the need for multiple exposures to compensate for the smaller sensor sizes in digital radiography may result in increased dose for the patient [11,21]. Dose reduction is most effective with intraoral systems. On the contrary, it is unlikely that digital panoramic and Cephalometric radiography can routinely offer dose reduction compared with conventional screen/film combinations [11].

3.3.2 IMAGE RECEPTOR HOLDERS

Reviewed literature [11,17,18,20,21] recommends the use of holders that align the receptor precisely with the collimated beam in periapical and bitewing radiography. It is said that this reducing the necessity for retakes [17]. When a dental film or digital detector cannot otherwise be kept in position, it should only be held by the patient [18] except under extraordinary circumstances in which case members of the patient’s family or other caregiver must provide restraint or hold a receptor holder in place. The caregiver should wear appropriate shielding and use a pair of forceps or other appropriate holder to avoid direct irradiation of the fingers [18,20,21]. Dental professionals should not be the ones holding the receptor holder during any exposure [17,20,21].

3.3.3 COLLIMATION

Literature [18,20,21] states that the x-ray beam should not exceed the minimum coverage necessary to image the object of interest. Two ways of quantifying the allowable excess X-ray field size were encountered in review of literature. Some publications [20,21] state that each dimension of the beam should be collimated so that the beam does not exceed the receptor by more than 2 percent of the source-to-image receptor distance. Other publications [18] state that Rectangular collimators should be designed so that the beam size at the end of the collimator does not exceed 40 by 50 mm (i.e. does not overlap the dimensions of the standard ISO film size 2 by more than 5 mm at any edge). They further sate that it would be preferable for this to be further reduced such that it does not exceed 35 by 45 mm (i.e. no more than a 2.5 mm overlap at any edge). If a choice has to be made between the two methods then the more restrictive method that results in the smallest allowable excess radiation beam size should be adopted.

The publications [8,20,21] reviewed demonstrate that the use of rectangular collimation can achieve significant dose reductions when compared with round collimation. However the publications give various percentages of dose reduction on switching from round collimation to rectangular collimation. The various percentage reductions range from 50 to 80%. Due to the demonstrated advantage of rectangular collimation, it is recommended that radiographic equipment provide rectangular collimation for exposure of periapical and bitewing radiographs [8,11,18,20,21].

It is especially recommended that receptor holding devices be used with rectangular collimators. According to literature [11,18,20] use of a receptor-holding device minimizes the risk of cone-cutting (non exposure of part of the image receptor due to misalignment of the x-ray beam).

Increasing the X-ray source to skin distance reduces the divergence of the X-ray beam within the patient and therefore reduces the volume of tissue irradiated [11]. Some of the reviewed publications [11,13,18] recommend different minimum focal spot to skin distances ranging from 18 to 20 cm. One publication [18] recommends a minimum of 20 cm focal spot to skin distance only for equipment operating at 60 kV or greater and atleast100 mm for equipment operating at below 60 kV. It has been found that the use of long source-to-skin distances of 40 cm, rather than short distances of 20 cm, decreases exposure by 10 to 25 percent. Source-to-skin distances of between 20 cm and 40 cm are appropriate, but the longer distances are optimal and therefore are recommended [20,21].

3.3.4 BEAM FILTRATION

Filtration reduces skin doses to patients by preferentially removing lower energy X-ray photons from the beam. It is therefore an invaluable means of reducing skin doses to patients [11]. Filtration using aluminium is an established part of dental X-ray but additional filtration using materials other than aluminium such as rare-earth materials is also possible. It is reported that the rare-earth materials additional filters ‘shape’ the X-ray spectrum and more closely match the spectral sensitivity of dental film thereby reducing the dose required for diagnostic images of acceptable quality. The benefits of using additional filters must be balanced against effects on image quality, cost, and the likely increase in exposure times associated with their use. Although the use of rare-earth filtration in intraoral radiography offers some dose reduction, it should only be adopted after advice from a medical physics expert on setting new exposure factors

3.3.5 OPERATING POTENTIAL AND EXPOSURE TIME

Two different ranges of optimal operating potential for dental X-ray units were identified in a review of the literature. One publication [20] gives the operating potential as ranging between 60 and 70 kVp while another publication [21] produced six years earlier gives a range of 60 and 80 kVp. It is reasonable to adopt the optimal operating potential given by the latest publication. Manufacturers of low-kVp (less than 60) dental radiographic equipment are required to install internal aluminum beam filters so that the mean beam energy will approach 60 kVp [21] as lower energy X-ray photons are preferentially removed from the beam. On the other hand a setting above 90 kV(p) will increase the patient dose and should not be used [20].

Digital imaging makes it easy to work with overexposed images due to post exposure processing. This often results in unnecessary radiation exposure [20]. Facilities should therefore strive to set the x-ray unit exposure timer to the lowest setting providing an image of diagnostic quality. The operator should always confirm that the dose delivered falls within the manufacturer’s exposure index so that overexposures can be detected and prevented in future.

CHAPTER FOUR

4.0 CONCLUSION AND RECOMENDATIONS

4.1 conclusion

The global annual per caput effective dose and the average effective dose per examination of 0.0018 mSv and 0.024 mSv respectively demonstrate that doses incurred in dental radiology are in general relatively low, however 0.48 billion diagnostic dental radiology examinations are done annually representing 13% of radiological examinations worldwide and therefore merit specific attention with regard to radiation protection.

It is generally accepted that there is no safe level of radiation dose and that no matter how low the doses received are, there is a mathematical probability of an effect, so appropriate patient protection measures must be instituted to keep the exposures as low as reasonably achievable. Radiation risk is highest for younger age groups due to the fact that they are more radiosensitive and their prospective life span is likely to exceed the latent period between X-ray exposure and the clinical presentation of a tumor. The risk for this age group is also heightened because dental radiography is most frequently performed in this age group. For these reasons more conscious effort has to be put in reducing the doses incurred by younger people during dental radiological examinations.

In order to ensure that patients are not subjected to unnecessary dental radiography all medical exposures must be justified at three levels. The proper use of radiation in medicine is accepted as doing more good than harm to society therefore justification at the first level can now be taken for granted. At the second level, a specified procedure with a specified objective is defined and justified. At the third level justification must be done on an individual patient basis by demonstrating that the benefits to the patient outweigh the potential detriment. The anticipated benefits are that the X-ray examination would add new information to aid the patient’s management.

This project work has demonstrated that there is considerable scope for significant dose reductions in dental radiology using the techniques of optimisation of protection. The principle of ALARA can be applied to dental radiology in order to decrease patient exposure to radiation without loss of critical diagnostic information and without too much expense or inconvenience. The techniques of optimization of protection include the following: image receptor selection, image receptor holders, collimation, beam filtration, operating potential and exposure time, patient protective equipment, film exposure and processing, film storage, image viewing, quality assurance, diagnostic reference levels, technique charts and training and education.

4.2 recommendations

The following section gives recommendations that can be followed by healthcare professionals in order to achieve radiological protection of patients in dentistry.

- All X-ray examinations must be justified at three levels. At the first level, the use of radiation in medicine should do more good than harm to the patient. At the second level, a specified procedure with a specified objective is defined and justified. At the third level justification must be done on an individual patient basis by demonstrating that the benefits to the patient outweigh the potential detriment. The anticipated benefits are that the X-ray examination would add new information to aid the patient’s management.

- The fastest film consistent with the requirements of the examination should be used for exposures in intraoral radiography.

- A combination of rare-earth film systems and high-speed film of 400 or greater is recommended for both panoramic and Cephalometric radiology.

- For equipment using extraoral films, the light sensitivity of the film should be correctly matched with the intensifying screens in order to achieve optimization of patient doses.

- When purchasing new equipment for intraoral radiography, facilities should choose digital imaging instead of conventional radiography equipment.

- Image receptor holders that align the receptor precisely with the collimated beam should be used in periapical and bitewing radiography.

- Rectangular collimation should be used for optimisation of exposures in periapical and bitewing radiography.

- Rectangular collimators should be chosen such that the x-ray beam does not exceed the minimum coverage necessary. The beam size at the end of the collimator should give no more than a 2.5 mm overlap at any edge of the image receptor.

- The use of source-to-skin distances of between 20 cm and 40 cm is appropriate, but longer distances are optimal and are therefore recommended.

- Use of additional filters made of rare-earth materials to reduce patient doses should only be adopted after advice from a medical physics expert on setting new exposure factors.

- The optimal operating potential of between 60 and 70 kVp should be used for dental X-ray units and a setting above 90 kVp should not be used as it increase patient dose.

- Facilities should strive to set the x-ray unit exposure timer to the lowest setting providing an image of diagnostic quality.

- Protective leaded thyroid collars should be used whenever possible. However they are strongly recommended for children and pregnant women, because these patients may be especially susceptible to radiation effects.

- If any of the recommendations for limiting radiation exposure to a patient is not implemented, then a leaded apron should be used to protect the patient.

- Dental films should not be processed by sight.

- All films should be processed in accordance with the recommendations from the film and processer manufacture.

- For manual processing of films the following requirements must be satisfied: the temperature of developing solutions must be measured; an appropriate time-temperature chart must be used to calculate the processing time; the temperature of the developing solutions must be maintained during processing; and the time of processing must be measured.

- Replenishment or replacement of the developer and fixer must be done at appropriate intervals to maintain adequate image quality at acceptable patient doses.

- Use of automatic film processors is recommended especially for high workload facilities.

- Films must be stored in a cool and dry area away from chemical contamination. The storage should be such that no film receives more than 1.75 Gy (0.2 mR) of radiation before use.

- Films should not be used after their expiry date.

- Radiographs should be viewed using a dental light box positioned well away from strong ambient light to reduce reflections and peripheral masking of films should be done to prevent glare and loss of visual acuity.

- Quality assurance protocols for the x-ray machine, imaging receptor, film processing, dark room, and lead aprons and thyroid shields should be developed and implemented for each dental health care setting. All quality assurance procedures, including the following should be logged for documentation purposes: date, procedure, results, and corrective action.

- Patient doses should be assessed on a regular basis and compared with diagnostic reference levels in order to check whether patient doses are optimized. The assessment should be done at least every 3 years or as required by national legislation.

- Size-based technique charts/protocols with suggested parameter settings must be displayed near the X-ray unit control panel whenever exposure factors for specific examinations are not marked on the unit.

- All dental health practioners involved in radiography should have received adequate theoretical and practical training for the purpose of radiological practices and relevant competence in radiation protection appropriate to dental radiography. Continuing education and training after qualification is also required, especially when new techniques or equipment are adopted.

CHAPTER FIVE

5.0 REFERENCES

[1] Cember, H., Johnson, T. E., (2009) Introduction to Health Physics, 4th Edition, McGraw-Hill, New York

[2] Martin, J. E., (2006) Physics for Radiation Protection: A handbook, 2nd Edition, Wiley-VCH, Weinheim

[3] Mah, J., (2010) The Genesis and Development of CBCT for Dentistry, The Academy of Dental Therapeutics and Stomatology

[4] INTERNATIONAL COMMISION ON RADIOLOGICAL PROTECTION (ICRP), (2007) The 2007 Recommendations of the International Commission on Radiological Protection, ICRP Publication 103, Pergamon Press, Oxford and New York

[5] Furlow, B., (2010) Radiation Dose in Computed Tomography, Vol. 81/No. 5, Radiologic Technology

[6] Podgorsak, E. B., (2005) Radiation Oncology Physics: A handbook for teachers and students, International Atomic Energy Agency, Vienna

[7] International Atomic Energy Agency, (2013) Module 14: Protection Against Occupational Exposure in Radiation Therapy, PowerPoint slides, School of Nuclear and Allied Health Sciences, Accra

[8] United Nations Scientific Committee on the Effects of Atomic Radiation, (2000) Sources and Effects of Ionizing Radiation: UNSCEAR 2000 Report to the General Assembly, with Scientific Annexes, Vol. 1, United Nations, New York

[9] United Nations Scientific Committee on the Effects of Atomic Radiation, (2010) Sources and Effects of Ionizing Radiation: UNSCEAR 2008 Report to the General Assembly, with Scientific Annexes, Vol. 1, United Nations, New York

[10] United Nations Scientific Committee on the Effects of Atomic Radiation, (2011) Report of the United Nations Scientific Committee on the Effects of Atomic Radiation 2010, Fifty-seventh session, includes Scientific Report: summary of low-dose radiation effects on health, United Nations, New York

[11] EUROPEAN COMMISSION, (2004) European guidelines on radiation protection in dental radiology. The safe use of radiographs in dental practice, Radiation Protection 136, European Communities, Luxembourg, viewed 02 March 2013, <http://ec.europa.eu/energy/nuclear/radioprotection/publication/doc/136_en.pdf>

[12] INTERNATIONAL COMMISION ON RADIOLOGICAL PROTECTION (ICRP), (1990) 1990 Recommendations of the International Commission on Radiological Protection, ICRP Publication 60, Pergamon Press, Oxford and New York

[13] Environmental Health Directorate, (2000) Radiation Protection in Dentistry: Recommended Safety Procedures for the Use of Dental X-ray Equipment, Safety Code 30, Minister of Public Works and Government Services, Canada

[14] SEDENTEXCT, (2012) Radiation Protection No 172: Cone Beam CT for Dental and Maxillofacial Radiology, European Commission, Luxembourg

[15] INTERNATIONAL COMMISION ON RADIOLOGICAL PROTECTION (ICRP), (2008) Radiological Protection in Medicine, ICRP Publication 105, Elsevier, Oxford

[16] International Atomic Energy Agency, (2011) Radiation Protection and Safety of Radiation Sources: International Basic Safety Standards, Safety standards Series No. GSR Part 3,Interim Edition, IAEA, Vienna

[17] Australian Radiation Protection and Nuclear Safety Agency(ARPANSA), (2005) Code of Practice & Safety Guide: Radiation Protection in Dentistry, Radiation Protection Series No. 10, Commonwealth of Australia, Canberra

[18] Guidance Notes for Dental Practioners on the Safe Use of X-Ray Equipment, (2001) National Radiological Protection Board, UK, viewed 28 February 2013, <http://www.hpa.org.uk/web/HPAwebFile/HPAweb_C/1194947310610>

[19] International Atomic Energy Agency, (2002) Radiological Protection for Medical Exposure to Ionizing Radiation, Safety Standards Series No. RS-G-1.5, IAEA, Vienna

[20] U.S. Food and Drug Administration, (2012) Dental Radiographic Examinations: Recommendations for Patient Selection and Limiting Radiation Exposure, viewed 02 March 2013, <http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/MedicalImaging/Medical-Rays/ucm116504.htm>

[21] American Dental Association Council on Scientific Affairs, (2006) The use of dental radiographs: Update and recommendations, American Dental Association, Chicago, viewed 05 March 2013, <http://jada.ada.org/content/137/9/1304.full?sid=c87667cc-de45-4d5b-bf0d-c968d596020d >

[22] International Atomic Energy Agency, (2013) Diagnostic and Interventional Radiology, IAEA, Vienna, viewed 06 March 2013, <https://rpop.iaea.org/RPOP/RPoP/Content/AdditionalResources/Training/1_TrainingMaterial/Radiology.htm>

[...]

41 of 41 pages

Details

Title
Patient Protection in Dentistry. Safe Use of Radiation Sources
College
University of Ghana, Legon  (School of Nuclear and Allied Sciences)
Grade
4.0
Author
Year
2013
Pages
41
Catalog Number
V415759
ISBN (Book)
9783668666764
File size
947 KB
Language
English
Tags
dental radiography, dental radiology, Radiation Protection, radiological Protection, Dentistry, Dental X-ray, Patient Protection
Quote paper
Peter Selato (Author), 2013, Patient Protection in Dentistry. Safe Use of Radiation Sources, Munich, GRIN Verlag, https://www.grin.com/document/415759

Comments

  • No comments yet.
Read the ebook
Title: Patient Protection in Dentistry. Safe Use of Radiation Sources


Upload papers

Your term paper / thesis:

- Publication as eBook and book
- High royalties for the sales
- Completely free - with ISBN
- It only takes five minutes
- Every paper finds readers

Publish now - it's free