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The following position statement was developed by a special committee of the Costa Rican Academy of Oral and Maxillofacial Radiology (ACROM). The document summarizes evidence-based recommendations regarding radiation protection in oral and maxillofacial radiology, and it is intended to guide national practitioners on the responsible use of ionizing radiation in the local setting.
Introduction
Using ionizing radiation, such as X-rays, is of significant diagnostic value in dentistry since dentoalveolar tissues can be represented with great precision due to their calcified nature. However, ionizing radiation can cause adverse health effects, which can be classified into deterministic or tissue effects and stochastic effects. Deterministic effects occur at high doses, so they usually do not occur in dentistry (1, 2). On the contrary, stochastic effects occur at low doses, such as those used in dentistry, and do not have a dose threshold; at any radiation dose, occurrence is probable (1, 2). In dentistry, therefore, the main effect associated with using X-rays is the probability of cancer development (1), which is proportional to the increase in dose (1,2,3,4,5,6). These effects manifest late; that is, there is a period between the exposure to ionizing radiation and the clinical diagnosis of neoplasia, which might take several years (6).
Due to the risk posed by ionizing radiation in dentistry, the implementation of radiation protection measures is required, both for the operator and the patient (1, 4). One of these radiation protection measures is the application of the optimization principle, the basic principle for acquiring radiographic images with the lowest radiation dose. This principle states that the desired clinical benefit should be achieved with radiation doses that are as low as reasonably achievable (ALARA) and as low as diagnostically acceptable (ALADA) (7). Furthermore, in pediatric patients, in whom the radiosensitivity of the tissues is greater because the mitotic processes are increased (8, 9), the use of ionizing radiation should be carried out with greater caution; that is, the use should be oriented by the indication and specific according to the physiological and morphological characteristics of each patient (ALADAIP, As Low as Diagnostically Acceptable Being Indication-oriented and Patient- specific) (10). To apply this principle, the use of all available resources to protect minors and adults is established: using patient protection barriers, such as the lead apron, thyroid protector, and rectangular collimation (11).
Following this reasoning of radiation protection, in 2007, several academic groups formed the Alliance on Radiation Safety in Pediatric Imaging - Image Gently. This campaign aimed to improve the safety and effectiveness of diagnostic images in children worldwide. In 2014, dentomaxillofacial radiology was included, with a 6-step plan to minimize exposure to ionizing radiation in children, including rectangular collimation and thyroid protectors. The use of these protective barriers is recommended because rectangular collimation reduces the dose by 40% (12), and thyroid protectors reduce the dose to the thyroid by approximately 50%. Many other academic and professional associations, including the American Dental Association (ADA), have supported the Image Gently alliance (13).
Recently, the ADA published the article Optimizing Radiation Safety in Dentistry, Clinical Recommendations and Regulatory Considerations (14). Based on the available evidence, this study aimed to update the recommendations on the safe use of ionizing radiation in dentistry in the American context. Thus, the most controversial modification regarding the 2012 ADA recommendations was the suspension of the use of thyroid protectors and lead apron during intraoral, panoramic, cephalometric, and cone-beam computed tomography (CBCT) (15, 16). However, the evidence shown to justify such a change does not adapt to the Costa Rican context. Therefore, this statement aims to discuss why the authors recommend that these radiation protection measures should be maintained, from a national perspective.
Reasons for upholding radioprotection measures
Since using available resources to protect people is established to comply with the optimization principle, using protective barriers that reduce the radiation dose in tissues outside the region of interest is an optimization strategy. Therefore, using lead vests and thyroid protectors, when the technique allows it, should not be considered an excess of care but rather a technical and ethical obligation to benefit patients, as previous studies confirmed a decrease in dose due to these radio- protection devices (11,12,13, 18,19,20,21,22). Currently, the ADA, in the article in question, seeks to justify that thyroid protectors and abdominal (gonadal) protectors can introduce artifacts by blocking the primary beam (14). However, the references for such justification do not mention this recommendation (23, 24). Although thyroid protectors can produce artifacts in some radiographic images, which could lead to the repetition of the study, there are approaches that experts in image acquisition can apply, to avoid them. In this sense, these protective barriers are only dispensed in selected cases when the risk of producing artifacts is greater (21).
The ADA also justifies that patient radiation doses can be minimized more effectively using rectangular collimation and optimal patient positioning during imaging procedures (14). However, in the Latin American scenario, particularly in Costa Rica, intraoral radiographic equipment mainly uses circular collimation, which implies a larger irradiated area and, consequently, a higher radiation dose. Access to equipment with rectangular collimation in the local market is limited, as is access to adaptable or universal rectangular collimators. Even in developed countries, such as the United States, rectangular collimation is not the norm since it is used in 0.6% of dental clinics, and only 22% of pediatric dentists reported the use of rectangular collimation, according to data from the years 2015 and 2020, respectively (25).
On the other hand, optimal patient positioning is not always achieved in the clinical setting, either by acquiring radiographic images during the intraoperative period, with the patient in a supine position, or by circumstances inherent to each patient (e.g., reduced mobility, anatomical variations). In these circumstances, areas far from the region of interest, such as the thyroid gland, end up being irradiated.
Another factor to consider, included in the Image Gently campaign recommendations, is the type of image receptor to be used since more sensitive image receptors require a lower amount of radiation to generate a diagnostic-quality radiographic image. The most recommended for intraoral radiology are F-speed analog films and digital receptors. For extraoral radiology, high-speed films and rare earth intensifying screens are recommended if analog equipment is used (13). However, using more sensitive sensors or films is not enough; it is also necessary to calibrate the acquisition parameters of the X-ray equipment, so it produces a lower radiation dose. Given that, in Costa Rica, only some dental clinics have adopted the use of digital image receptors, it is impossible to assume that this optimization recommendation is generally used to reduce patient exposure. Therefore, it is reasonable to maintain other radiation protection means, such as the use of the thyroid protector.
A recent study estimated the rate of possible cancer cases associated with dental radiographic examinations in the United States, estimating 967 cases associated with dental radiographic images in 2019. Of these cases, 827 were associated with intraoral x-ray examinations and 84 with the acquisition of cone beam computed tomography. Using rectangular collimation and appropriate indication criteria would reduce the number of possible cancer cases to only 237 per year (25). From this perspective, the dentist's responsibility in an adequate prescription and application of radiographic examinations should not be underestimated.
Conclusion
If the goal of an imaging examination that uses ionizing radiation is to improve the health of our patients, any protective measure against the possible harmful effects derived from its use will never be excessive. Thus, until longitudinal clinical studies demonstrate that the radiation doses used in dentistry are incapable of producing stochastic effects, dental professionals must implement all available radioprotection measures, which include, undoubtedly, the use of the thyroid protector and the lead apron.
Author contribution statement
Conceptualization and design: D.C.S., L.B.R. and A.C.R.I.
Literature review: D.C.S., L.B.R. and A.C.R.I.
Writing-original draft preparation: D.C.S., L.B.R. and A.C.R.I.
Writing-review & editing: D.C.S., L.B.R. and A.C.R.I.
