3 Radiation Protection in Brachytherapy

Radiation Protection in Brachytherapy

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THE GEC ESTRO HANDBOOK OF BRACHYTHERAPY | Part I: The basics of Brachytherapy Version 1 - 01/12/2014

emphasized that planned exposure situations include both nor- mal exposures that are reasonably expected to occur (i.e., medical exposures of patients, medical exposures of comforters or public exposures in permanent low dose rate (LDR) implants, occupa- tional exposures in applications involving source handling), and potential exposures that may result from deviation from normal operating procedures (i.e., accidents). Although the focus of this chapter is on brachytherapy planned exposures, during their operation emergency exposure situations might occur due to the operation itself or malevolent action (i.e. breach of source secu- rity). Emergency exposure situations cannot be predicted; they may require urgent protective actions, and they could even lead to existing exposure situations in the form of prolonged exposure situations following emergencies. In terms of biological dose response to radiation, determinis- tic effects are characterized by dose thresholds so that there is absence of risk for harmful tissue reactions at low doses (lower than about 100 mSv; updated information on dose thresholds in the form of dose resulting in about 1% incidence are provided in ICRP 2007 (24)). Although the introduction of a practical dose threshold has been proposed for stochastic effects, it is deemed that current data support that at low doses (e.g., below 100 mSv) the incidence of cancer and heritable effects rises proportionally to the increase of radiation dose over the background. The adop- tion of this so-called Linear No Threshold model (LNT) implies that a finite risk is associated with any exposure to radiation, however small, and protection must include considerations of what level of risk is deemed acceptable. Hence, any system of radiological protection is based on the following three funda- mental principles: justification, optimization, and application of dose limits. 2.1 Justification ICRP 2007 points out that any decision that alters the radiation exposure situation should do more good than harm (24). This principle is source related and applies to all exposure situations. With regard to occupational and public exposures, planned ex- posures such as those from a brachytherapy program should not be introduced if a net benefit to individuals or the society is not warranted, and any decision to reduce further exposures from emergency and existing exposure situations should be justified in the sense that more good than harm will come from it. Justi- fication in the above situations is a broad process wherein radi- ation detriment serves as one of the many necessary inputs. For medical exposures, brachytherapy planned situations are justi- fied at a first level since the medical use of radiation is widely accepted as doing more good than harm. At a second level, the potential of new brachytherapy techniques to improve treatment should be justified by competent national and international professional bodies and authorities. At the third level, referral criteria and patient groups must be established to facilitate the justification of medical exposure to any particular individual by physicians, who should be well aware of the risks and benefits of particular brachytherapy procedures as well as potential treat- ment alternatives. 2.2 Optimization of protection According to ICRP 2007, the likelihood of incurring exposure, the number of people exposed, and the magnitude of their in- dividual doses should all be kept as low as reasonably achiev-

able, taking into account economic and societal factors (the ALARA principle) (24). This is also a source related and uni- versal principle, i.e. it applies to all exposure situations that have been justified. It is the cornerstone of any system for radiological protection and its application involves a process of prospective and iterative character with the aim of preventing or reducing future exposures. This process includes the review of an expo- sure situation, the restriction of doses likely to be delivered to a named individual, the listing of options available for protection, the selection of the best option(s) under the circumstances using quantitative methods and cost-effect analysis, the implementa- tion of the optimization option decided and its dynamic evalu- ation. Dose restriction is applied in the form of dose constraints for planned exposure situations (except for medical exposure of patients), and reference levels for emergency and existing expo- sure situations which represent upper bounds of dose predicted in optimising protection from a particular source. These must be defined in the planning stage of optimization. Exceeding these constraints and reference levels in such an analysis should trig- ger an investigation and optimisation of protection should aim at establishing acceptable dose levels below them. For medical exposures of patients, optimisation assumes the form of a set of measures to ensure that dose is in accordance with the medical purpose. For diagnosis, reference dose levels are set that are not individual patient dose constraints but levels of dose indicating that patient dose is neither too high nor too low for a particular procedure. Patient dose management informa- tion for equipment and imaging techniques used in conjunction with brachytherapy, such as fluoroscopically guided interven- tional procedures, computed tomography and digital radiology, are provided in the literature (18, 19,20). Reference dose levels do not apply to radiation therapy itself, where optimization in- volves the delivery of the prescribed dose to the target while also planning the protection of healthy tissues (16). This is related to quality assurance procedures and accident prevention that are dealt with in other publications; see also (12, 22, 41) and several AAPM reports. 2.3 Application of dose limits Again quoting from ICRP 2007 “…the total dose to any individ- ual from regulated sources in planned exposure situations other than medical exposure of patients should not exceed the appro- priate limits specified by the Commission…” (24). In contrast to the previous two principles, this one is individual related and applies to planned exposure situations only (except for medical exposures of patients). ICRP recommendations for dose limi- tation are summarized in Table 3.1. Regulatory dose limits are set by national competent authorities taking into account these recommendations, and variations from country to country may occur (32). Members of the public involved in patient comforting and care giving are not subject to the dose limit for public exposure (but a prospectively defined, reference level should apply). For female workers who declare pregnancy, additional controls must be im- plemented to ensure protection for the embryo similar to that for the public. Dose limitation is a means of regulatory control to prevent the occurrence of deterministic effects and confine the risk of sto- chastic effects to levels currently deemed acceptable. The im-