1. High Dose Rate Brachytherapy Boost for Prostate Cancer: Comparison of Two Different Fractionation Schemes Tania Kaprealian 1, Vivian Weinberg 3, Joycelyn Speight 1,2, Alexander Gottschalk 1, Mack Roach III 1,2, Katsuto Shinohara 2, I-Chow Hsu 1 1 Department of Radiation Oncology at the University of California, San Francisco 2 Department of Urological Surgery at the University of California, San Francisco 3 Department of Biostatistics Core UCSF Comprehensive Cancer Center A retrospective review of our experience and outcomes using high-dose-rate (HDR) brachytherapy boost for prostate cancer comparing two different fractionation schemes: 600 cGy x 3 (Group 1) compared with 950 cGy x 2 (Group 2).. Results are excellent for both groups. We did not observe differences in biochemical DFS between the2 groups; however, there are a greater number of high-risk patients in Group 2. There were no observed differences in toxicities, using CTCAE version 3, between the 2 groups. There were few events in each group. There were no differences in biochemical DFS between the groups based on the number of risk features. The two fraction regimen allows for additional patient convenience and minimizes hospital stay. PURPOSE METHODS 165 patients treated for prostate cancer using external beam radiation therapy (RT) to 45 Gy followed by an HDR brachytherapy prostate boost. Whole pelvic RT given to patients whose risk of positive nodes exceeded 15%. 64 patients were treated between 7/97 and 11/99 with an HDR boost of 600 cGy x 3. 101 patients were treated between 6/00 and 11/05 with an HDR boost of 950 cGy x 2. All but 9 patients had at least one of the following risk features: pre-treatment prostate specific antigen >10, Gleason Score (GS) > 7, and/or clinical T3 disease. HDR administered with a single implant, and all fractions were given within 24 hours.. RESULTS RESULTS (cont.) HT was most commonly 2 months of neoadjuvant HT followed by 2 months of concurrent HT with RT. Biochemical failure using the Phoenix definition, and/or local or distant disease recurrence, seen in 22 patients. Group 1, 9 failed (4 within 5 yrs. of HDR) and Group 2, 13 failed (12 during 5 yrs. after HDR). To avoid bias due to difference in follow-up between the two groups, a comparison of disease failure was limited to 5 years for both groups. There were minimal toxicities Grade 3+. Group 1, 1 patient had late and 1 patient had early Grade 3 GU toxicity and Group 2, 1 patient had early and late Grade 3 GU toxicity. Toxicities were classified using CTCAE version 3. Toxicities within 9 months from treatment were classified as acute.. RESULTS (cont.) CITATIONS CONCLUSIONS. Results are similar for High-Risk patients. Hsu I-C, et al. Combined modality treatment with high-dose-rate brachytherapy boost for locally advanced prostate cancer. Brachytherapy 2005; 4: 202-206. Vargas C, et al. High-dose irradiation for prostate cancer via a high-dose-rate brachytherapy boost: results of a phase I to II study. International Journal of Radiation Oncology, Biology, Physics 2006; 66(2): 416-423. Vargas C, et al. High-dose radiation employing external beam radiotherapy and high-dose rate brachytherapy with and without neoadjuvant androgen deprivation for prostate cancer patients with intermediate- and high-risk features. Prostate Cancer and Prostatic Diseases 2006; 9:245-253..