SU-F-T-653: Radiation Exposure from Cs-131 Permanent Seed Implants.

PURPOSE: Permanent seed implants have traditionally been used to treat prostate, lung and head or neck cancers using I-125 and Pd-103. Cs-131, which has higher dose rate is being used to treat brain, head and/or neck cancers in our clinic, therefore, we chose to monitor the dose received by surgeons during the extensive procedure. The aims of this work are to assess the level of radiation exposure to surgeons and the instantaneous exposure at bedside and 1 m from patients.

METHODS: Ten patients received Cs-131 implants for recurrent brain,head and/or neck cancer; the median implanted activity, number of implanted seeds and prescription dose at 0.5 cm from the perpendicular plane of the implant were: 54.3 mCi (14.52 - 77); 19 (4 - 24) and 60 Gy (range 42 - 60) respectively. Radiation exposure was recorded at bedside and 1 m from the patient using Victoreen ion chamber (Fluke Biomedical, Cleveland, OH). Exposure to surgeons was measured using TLD (Mirion Technologies (GDS), Inc., USA).

RESULTS: The median equivalent dose rate at 1 m and bedside immediately following implantation were 1.49×10-2 mSv/h (8.77×10-3-2.63×10-2) and 7.76×10-2 mSv/h (3.1×10-2- 1.53×10-1) respectively. Median equivalent dose to surgeons' hands was 0.60 mSv (0.33 - 1.48) and no doses were detected for whole-body. Surgical reconstruction for one patient was performed 71 days post-implant and resulted in zero exposure to surgeons.

CONCLUSION: The recorded exposure rates were low when compared with the literature. Post procedure surveys at bed site and 1 m indicated that all patients were within safe limits for discharge (< 0.05 mSv/h at 1 m). However, as a precautionary measure, patients were advised to avoid direct contact with children and pregnant women within four weeks of the implant and stay at least at 3 ft from other people. Surgeons doses were well within occupational dose limits.