Assessment of radiation safety instructions to patients based on measured dose rates following prostate brachytherapy

Purpose To validate radiation safety instructions to patients and to evaluate the potential radiation doses to members of the public after 125I or 103Pd prostate implantation. Methods and materials Radiation dose rate measurements were made in the immediate postoperative period on 636 consecutive patients with stage T1-T2 prostate cancer who underwent transperineal 125I or 103Pd implantation at Memorial Sloan-Kettering Cancer Center during the period from August 1995 through January 2003. Results The mean radiation dose rate at the anterior skin surface following a prostate implant was 37 μSv/hr for 125I and 8 μSv/hr for 103Pd. At 30 cm from the anterior skin surface, these dose rates were reduced to 6 μSv/hr for 125I and 3 μSv/hr for 103Pd. At 1 m from the anterior skin surface the dose rates from both types of implants were reduced to less than 1 μSv/hr. The effect of body weight on dose rates from 125I sources was examined for a select sub-group of patients and the measured dose rate was found to decrease with increasing body weight. In another group of patients, dose rate measurements were made on both lateral skin surfaces and were less than 16.8 μSv/hr in all cases. Assuming a 33% occupancy factor and utilizing the mean measured dose rate for 125I, the time required to reach an effective dose equivalent limit of 5 mSv for caregivers was estimated to be 19 days on contact with the skin surface. Using a similar calculation, the lifetime doses for 125I at a distance of 30 cm from the anterior skin surface, as well as the lifetime doses for 103Pd on contact with the skin surface and at 30 cm from the anterior skin surface can be shown to be less than 5 mSv. Conclusions The large number of cases available for this study permits a validation of radiation safety recommendations and provides concrete information from which the permitted exposure times following implantation can be estimated. The data support the conclusion that patients treated with these implants do not represent a radiation risk to members of the public.