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

3.2 HDR brachytherapy treatment room Since HDR (and, as stated, PDR) brachytherapy procedures normally deliver a large dose to patient target volumes within a relatively short period of time, many safety features and meas- ures have to be taken into consideration in the design of a HDR treatment room. Treatment rooms have to be properly shielded in construction (see next section). The shielding design should follow the rec- ommendations of international/national organizations that are recognized for providing scientific basis for radiation protection and safety. A radiation exposure survey needs to be performed by qualified physicists after the construction is completed, to en- sure that the radiation exposure levels do not exceed the limits laid down by government agencies. Safety interlocks, such as a door interlock, power interlock and backup system, and procedure interruption systems, should be installed. The procedure interruption systems should be placed where they can be easily reached by the medical staff members during a treatment. Almost all commercially available HDR systems (see e.g. Fig. 3.1, with the cover removed) are equipped with interruption systems and these should be periodically checked and evaluated. Radiation monitoring systems, which are independent of the HDR unit, should be installed inside an HDR treatment room and at the door of the room to monitor the ra- diation levels. It is preferable that monitoring systems inside the room are muted, giving out clearly visible signals (e.g., a flash- ing light) when the radiation exposure exceeds a certain level. On the other hand, it is preferable that the monitoring systems installed at the door should give out both visible and audible sig- nals to ensure awareness in case of potential loss of a radioactive source from the HDR unit. A warning sign should be installed at the room entrance to show clearly that a HDR procedure is in progress. This type of system can be placed right above or beside the room door and should be automatically turned on when a HDR treatment starts. It is important to include a video monitoring system and an in- tercom audio system in the design of a HDR treatment room

lead bricks, leaded glass, and other accessories. It is desirable to install a radiation area monitor in the hot lab to constantly mon- itor the radiation level. Radiation survey meters with different levels of sensitivity should be included in the facility design and budget. These sur- vey meters are important to ensure the integrity and accuracy of radiation safety and documentation. Depending on the type of brachytherapy procedure, consideration should be given to sur- vey meters that can also be used for particles other than photons. Emergency radiation safety kits, such as a lead container, should be also available for a brachytherapy program (12). Aspects of brachytherapy facility design are reviewed in the lit- erature (5, 9,11,12,26,36). Some important features are given be- low for LDR and HDR treatment rooms. In general all aspects of radiation safety with HDR equipment are equally valid for use of PDR equipment and here when HDR is used in this text one may substitute HDR/PDR. 3.1 LDR brachytherapy treatment room LDR brachytherapy procedures can be performed in one of two ways: 1) placement of applicators first in an operating room, then loading radioactive sources into the applicators after the com- pletion of dosimetry calculations and treatment planning; 2) loading the radioactive sources directly into or around the target volumes with or without applicators in the operating room. Most temporary brachytherapy procedures follow the first of these to minimize unnecessary radiation exposures to the members of medical staff. On the other hand, many permanent brachyther- apy procedures, such as prostate implants, are performed by di- rectly implanting radioactive sources into the target volume in the operating room. As discussed previously, for temporary LDR brachytherapy procedures, the radioactive sources are most likely to be loaded into the afterloaders in a patient treatment room. The treatment room should be suited for patient procedures that will usually last for hours to days. This treatment room does not have to be dedicated to brachytherapy procedures alone. It can be used as a regular in-patient room when there are no brachytherapy procedures. However, the room should be carefully selected in terms of its location to minimize radiation exposures to other patients, the general public, and medical staff, especially for the brachytherapy procedures that involve high energy photon emit- ting sources (the most commonly applied source types in LDR, 137 Cs and 192 Ir, are high energy photon emitting sources!). It is ideal to select a room that is located in a corner or a room that is remote from populated areas. In many cases, the brachyther- apy treatment room will need thicker walls than a normal room to reduce the radiation levels in the surrounding areas or other patient rooms. In some cases, solutions can be found by using mobile (lead) shields which are positioned close to the bed of the patient, depending on the lay-out of the room and its surround- ings. These mobile shields can be stored in a near-by room when not needed, but they can be very heavy due to the lead thickness required for high energy photon emitting sources. An intercom audio system, and sometimes a video monitoring system, is useful to avoid unnecessary time spent near the im- planted patient, hence reducing staff exposure.

Fig. 3.1 The tungsten container for the safe position of the high dose rate iridium-192 source in a high dose rate afterloader is clearly visible when the covers are removed. (Courtesy: Elekta AB, Sweden)