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

facility designs with a maze. This study also includes illustrative Monte Carlo results of air-kerma rate distributions in the five facilities studied, for both 192 Ir and 60 Co sources. See Fig. 3.5. The responsibility for shielding design goes beyond the calcu- lation of required thickness of a given material and includes the supervision of construction (i.e. the materialization of the shielding as planned needs to be verified in general, and particu- larly: ducts for cable, plumbing and ventilation, concrete com-

position and density that varies with local aggregate, etc) and post-construction survey. More information can be found in (5, 11,26,36).

5. RADIATION PROTECTION ISSUES ASSOCIATEDWITH SPECIFIC TECHNIQUES

Although both LDR and HDR brachytherapy procedures are treatments of patients with radioactive sources, LDR procedures differ from HDR (and PDR, with sources usually 1/10 of the strength of an HDR source) procedures in several aspects: 1) Dose rates at prescription points are significantly different. These dose rates in LDR brachytherapy procedures range from 4 cGy/hr to 200 cGy/hr while the dose rates in HDR procedures are higher than 1200 cGy/hr. 2) LDR brachytherapy can be permanent or temporary while HDR treatments are always temporary. 3) Temporary LDR brachtherapy may require continuous treat- ment for hours or days while HDR treatments usually take several minutes and will only rarely last more than 1 hour (PDR treatments usually mimic the overall treatment time of LDR, with multiple pulses). 4) Patients treated with LDR brachytherapy may be released with implanted radioactive sources while HDR patients should never be released with the radioactive source(s). These differences should be taken into account in radiation pro- tection and should be addressed specifically. 5.1 LDR brachytherapy In many LDR brachtherapy treatments, radioactive sources need to be ordered specifically for the treatments in terms of source strength and source quantity. Wipe test should be first performed after source delivery to check the source integrity. The sources should also be carefully assayed independently from manufacturers before the start of treatment to ensure the accu- racy of source strength and quantity. For radioactive sources of long half-life in storage (e.g., 137 Cs, possibly used only for con- stancy checks of measurement equipment) a periodical wipe test and assay should be conducted. Patients should be surveyed before LDR treatment to establish a radiation baseline. During the treatment procedures, the sourc- es –if not in an afterloader- need to be visually checked so that they are all accounted for. After a procedure, radiation surveys should be performed in the treatment rooms to prevent source loss. The survey should cover the entire room, while trash bins, equipment, and outfits of medical staff members should not be removed from the room without a check with the survey moni- tor. Since the source strength or the energy levels of emitted par- ticles from the sources can be relatively low, a highly sensitive radiation detector may be needed for this purpose. A radiation survey should also be conducted to evaluate whether it is safe to release the patient. If the patient is to stay in a room, such as a treatment room, recovery room or designated inpatient room, for a period of time, a radiation survey should be performed af- ter the patient moves into the room and radiation signs and safe- ty instructions for visitors, patient and medical staff should be posted on the room door. During the patient’s stay, it should be clearly documented in the patient chart that the patient is under-

a.

b.

Fig. 3.4 Radiation transmission factor T for a lead (a) and a concrete (b) shielding barrier in broad beam geometry conditions for selected radionuclides employed in brachytherapy. Presented lines correspond to a fit of the three parameter model introduced by Archer et al . (1) to the Monte Carlo simulation calculated data. Data and fitting results are available online at http://www.estro.org/about/governance-organisation/committees-activities/radiation-protec- tion for various radionuclide-shielding material combinations. (Courtesy: P. Papagiannis)