A method for implementing the American Association of Physicists in Medicine Task Group-43 dosimetry recommendations for 125I transperineal prostate seed implants on commercial treatment planning systems

Abstract

Purpose : To present our experience implementing the American Association of Physicists in Medicine (AAPM) Task Group #43 (TG-43) recommendations for 125I dosimetry parameteres utilizing two commercially available treatment planning systems. Methods and Materials : Single seed point 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 each system, and (c) hand calculations. Additional calculations and intercomparisons were perfoemd for a typical 35 cm 3 prostate volume implant with a prescribed dose of 160 Gy. Results : Intercomparisons of calculations for single seed point source approximations with previously published data and TG-43 data indicated good agreement between the two systems at a disance of 1 cm. Point source comparisons between previously published data and TG-43 recommendations show a difference in dose of 11% to the 1 cm point. Calculations for a 35 cm 3 permanent interstitial prostate implant showed the 160 Gy isodose line pulled centrally toward the seeds 1–2 mm as a result of the 11% change. Conclusions : It is advisable for physicians, physicists, and dosimetrists to exercise caution when incorporating the TG-43 recommendations for 125I into treatment planning systems. The effects caused by differences in dosimetry parameters need to be understood and accounted for when matching prescribed doses in order to ensure continuity of treatment and clinical results as reported in the current literature.