A METHOD FOR IMPLEMENTING THE AMERICAN-ASSOCIATION-OF-PHYSICISTS-IN-MEDICINE TASK GROUP-43 DOSIMETRY RECOMMENDATIONS FOR I-125 TRANSPERINEAL PROSTATE SEED IMPLANTS ON COMMERCIAL TREATMENT PLANNING SYSTEMS

Purpose: To present our experience implementing the American Associati on of Physicists in Medicine (AAPM) Task Group #43 (TG-43) recommendat ions for I-125 dosimetry parameters utilizing two commercially availab le treatment planning systems. Methods and Materials: Single seed pain t source calculations were performed on two treatment planning systems and intercomparisons were conducted between known points of interest for (a) previously published data on each system, (b) TG-43 data on ea ch system, and (c) hand calculations, Additional calculations and inte rcomparisons were performed for a typical 35 cm(3) prostate volume imp lant with a prescribed dose of 160 Gy. Results: Intercomparisons of ca lculations for single seed point source approximations with previously published data and TG-43 data indicated good agreement between the tw o systems at a distance of 1 cm, Point source comparisons between prev iously published data and TG-43 recommendations show a difference in d ose of 11% to the 1 cm point, Calculations for a 35 cm(3) permanent in terstitial prostate implant showed the 160 Gy isodose line pulled cent rally toward the seeds 1-2 mm as a result of the 11% change. Conclusio ns: It is advisable for physicians, physicists, and dosimetrists to ex ercise caution when incorporating the TG-43 recommendations for I-125 into treatment planning systems, The effects caused by differences in dosimetry parameters need to be understood and accounted for when matc hing prescribed doses in order to ensure continuity of treatment and c linical results as reported in the current literature. (C) 1997 Elsevi er Science Inc.