SU‐E‐T‐653: Dosimetric Evaluation of Prostate Brachytherapy Using Single Isotope and Hybrid Seeds

Abstract

Purpose: Clinically, single isotope, such as I‐125 or Pd‐103, is commonly used in the seeds in brachytherapy for prostate cancer. A mixture of two isotopes in the seeds has been proposed for prostate cancer treatment. This study investigates the differences in biological effective dose (BED) between the treatment plans of such hybrid sources and plans of single isotope. Methods: Five prostate cancer cases previously treated using single isotope seeds were selected for this study. Hybrid seed plans of a 50/50 mixture of I‐125 and Pd‐103 and a single isotope Pd‐103 were generated based on the original I‐125 plans. Number and location of seeds were the same between the plans. A numerical approach was implemented in the BED calculation. Dose and BED homogeneity in PTV, mean BED in organs at risk (OAR) and hot BED to OAR were compared between the plans. Results: To achieve the same BED (110 Gy) to cover 90% of PTV, the corresponding dose is 145, 120 and 136 Gy for I‐125, Pd‐103 and 50/50 hybrid seeds respectively. The hybrid plans demonstrated the most homogeneous dose and BED in PTV. The mean highest BED delivered to a 1.0 cc volume of rectal tissue by the I‐125, Pd‐103, and 50/50 hybrid modality was 49.85±30.24, 93.73±38.33, and 82.52±34.08 Gy respectively, delivered to a 1.0 cc volume of bladder was 41.6±19.5, 66.8±27.9 and 61.6±25.2 Gy respectively, and to other normal tissue was 303.41±63.84, 363.95±197.29, and 319.14±146.72 Gy respectively Conclusions: The prescription dose to cover 90% PTV by a BED of 110 Gy is 145, 120 and 136 Gy for I‐125, Pd‐103 and 50/50 hybrid seeds respectively. Based on the BED data, the best OAR sparing occurs with I‐125 treatment plans, followed by the 50/50 hybrid plans, and finally the Pd‐103 plans.