PURPOSE: To define the optimal dose for 125I prostate implants by correlating post implantation dosimetry findings with biochemical failure and toxicity.
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METHODS AND MATERIALS: Between 2003 and 2009, 683 patients with prostate cancer were treated with (125)I prostate brachytherapy without supplemental external beam radiation therapy and were followed up for a median time of 80 months. Implant dose was defined as the D90 (the minimal dose received by 90% of the prostate) on postoperative day 1 and 1 month after implantation. Therefore, 2 dosimetric variables (day 1 D90 and day 30 D90) were analyzed for each patient. We investigated the dose effects on biochemical control and toxicity.
RESULTS: The 7-year biochemical failure-free survival (BFFS) rate for the group overall was 96.4% according to the Phoenix definition. A multivariate analysis found day 1 D90 and day 30 D90 to be the most significant factors affecting BFFS. The cutoff points for day 1 D90 and day 30 D90, calculated from ROC curves, were 163 Gy and 175 Gy, respectively. By use of univariate analysis, various dosimetric cutoff points for day 30 D90 were tested. We found that day 30 D90 cutoff points from 130 to 180 Gy appeared to be good for the entire cohort. Greater D90s were associated with an increase in late genitourinary or gastrointestinal toxicity ≥ grade 2, but the increase was not statistically significant.
CONCLUSIONS: Improvements in BFFS rates were seen with increasing D90 levels. Day 30 D90 doses of 130 to 180 Gy were found to serve as cutoff levels. For low-risk and low-tier intermediate-risk prostate cancer patients, high prostate D90s, even with doses exceeding 180 Gy, achieve better treatment results and are feasible.
Shiraishi Y, Yorozu A, Ohashi T, Toya K, Saito S, Nishiyama T, Yagi Y, Shigematsu N. Are you the author?
Department of Radiology, Keio University School of Medicine, Tokyo, Japan; Department of Radiology, National Hospital Organization Tokyo Medical Center, Tokyo, Japan; Department of Radiology, National Hospital Organization Tokyo Medical Center, Tokyo, Japan; Department of Urology, National Hospital Organization Tokyo Medical Center, Tokyo, Japan.
Reference: Int J Radiat Oncol Biol Phys. 2014 Dec 1;90(5):1069-75.