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

lations appropriate to their individual countries. Information in this chapter should therefore be considered for information only and carefully checked against local regulations prior to adoption.

Table 3.1: Dose limits recommended by the ICRP (24)

PUBLIC EXPOSURE

OCCUPATIONAL EXPO- SURE 20 mSv per year averaged over 5 years and less than 50 mSv in any single year

Effective dose limit:

1 mSv per year

3. DESIGN CONSIDERATIONS OF BRACHYTHERAPY FACILITIES

Eye lens equivalent dose limit: Skin equivalent dose limit: Hands and feet equiv- alent dose limit:

15 mSv

150 mSv*

A brachytherapy program normally requires the availability of physical plant facilities that include an operating room, ra- diograph imaging room, patient treatment room, and/or a hot lab, as described in the IAEA TecDoc 1040 (12). Each of these facilities has its own functionality and plays a unique role in a brachytherapy program. For radiation protection purposes, they may need to be designated controlled or supervised areas (24). Controlled areas are those where specific protection measures are required to control normal exposures and prevent/limit po- tential exposures. These measures include a clear delineation of the area, appropriate labelling, access restriction, radiological surveillance and the establishment of written procedures and working instructions. Supervised areas, often surrounding con- trolled areas, are those where protection measures are not nor- mally needed but occupational exposures are kept under review. Areas may be designated according to the magnitude of expected exposure, i.e. in the UK and several other countries. Areas where annual dose could be greater than 6 mSv and 1 mSv are designat- ed controlled and supervised areas, respectively (11). Brachytherapy treatment rooms and source preparation/storage rooms (“hot labs”), as well as imaging rooms, are controlled ar- eas. Operating rooms could fall into a designated area category depending on application and source loading procedure, and high dose rate (HDR) and pulsed-dose rate (PDR) treatment consoles are supervised areas. The operating room is used for catheter/applicator placement and sometimes for radioactive source “hot loading”. Depending on the type of brachytherapy procedure, the operating room may require sterilization condi- tions. The availability of an imaging room/equipment is critical to the success of a brachytherapy program. The radiograph imag- ing room/equipment is typically used to acquire patient 2D/3D images on which the target volumes, critical organs, and/or cath- eters/applicators can be localized for accurate dosimetry calcu- lations and treatment planning. A CT/MR scanner room can be used for this purpose although it is important to bear in mind that catheters/applicators compatible with the imaging modality are desirable to avoid image artifacts. A conventional 2D simu- lator is a reasonable option although it is difficult or impossible to identify soft tissue target volumes from the images. In some cases, a C-arm type fluoroscopy machine is used in the operating room to ensure precise placement of brachytherapy instruments. The images acquired with the C-arm machine can be directly used for dosimetry calculations and treatment planning. Patient treatment rooms must be designed and prepared appro- priately for a brachytherapy program. The requirements for the treatment room are different for LDR and HDR/PDR programs. A hot lab should be designed and made available for long-term or temporary storage of radioactive sources. In addition, many physics related procedures, such as seed assay and preparation, wipe test, etc., should be conducted in the hot lab. The hot lab should be equipped with a well shielded source storage cabinet,

50 mSv

500 mSv

-

500 mSv

*After review of epidemiological evidence suggesting threshold doses might be lower than previously considered, irrespective of rate of dose delivery, ICRP issued a statement on tissue reactions (25) and an equivalent dose limit for the lens of the eye of 20 mSv in a year, averaged over defined periods of 5 years, was recommended for occupational exposure in planned exposure situations. This recommendation, which is significantly lower than corre- sponding ICRP 103 (24) recommendations, was adopted in the IAEA Basic Safety Standards (15) and will very likely be implemented in national dose limits in the coming years.

portance of optimization cannot be overstressed. Source specific dose constraints and reference levels for planned exposures of workers and members of the public cannot be greater than dose limits and are an aid to ensuring that the latter will not be ex- ceeded due to exposure from different sources. 2.4 General comments on the recommendations The introduction of remote afterloading devices has brought a radical change in brachytherapy practice as a whole, as well as in radiation protection in particular. Occupational doses have been drastically reduced by technical advances (7) to levels com- parable to those in external beam therapy. Still, brachytherapy reserves its special niche due to the storage of sealed sources emitting radiation constantly, permanent implants, and the need for source manipulation in permanent implant applications (i.e. for prostate treatment) or, less frequently, applications involv- ing manual source loading (i.e. eye plaque applicators for ocu- lar melanoma treatment, or use of pin and wire sources). For example, the use of sealed radionuclides for brachytherapy and unsealed radionuclides for radiopharmaceutical therapy are col- lectively identified as radionuclide therapy in the NCRP 155 re- port which offers guidance for the management of radionuclide therapy patients (36). Neither the above summary of the internationally adopted ra- diological protection system and its recommendations, nor the remainder of this chapter seeks to replace the need for a thor- ough review of the literature, in the form of published articles as well as reports from the cited international bodies and national or international professional societies, and their implementa- tion in brachytherapy. This chapter merely aims to summarize selected technical and procedural information to aid the process of optimisation of protection in brachytherapy, and to highlight some key elements of this process by elaborating on aspects of radiation protection in practice. A word of caution is in order. This chapter does not attempt to summarize regulatory or licens- ing requirements. This would be impractical since international bodies leave it to national protection bodies to formulate regu-