Institutional patient accrual volume and the treatment quality of I‑125 prostate seed implantation in aJapanese nationwide prospective cohort study.

Abstract

It is unclear whether experience at high-volume institute improves the treatment quality of prostate seed implantation. The aim of this study was to evaluate the effect of institutional experience on postimplant dosimetric parameters in anationwide prospective cohort study. From July 2005 to June 2007, 2354 patients were registered in the Japanese Prostate Cancer Outcome Study of Permanent I‑125 Seed Implantation (J-POPS), and 1126 patients treated with seed implantation alone were evaluated. As asurrogate for institutional experience, we classified the J‑POPS institutions as high-volume (patient accrual volume was ≥120 patients per institution) or low-volume institutions (patient accrual volume was <120 patients per institution). To compare treatment quality between institutions, we evaluated the postimplant dosimetric parameters including D90, V100/150 (prostatic dose parameters), UD5/90, U200 (urethral dose parameters), and rectum R100/150 (rectal dose parameters). In the 5high-volume institutions (n = 601 patients), most of the patients were treated with >144 Gy of D90, whereas in the 20low-volume institutions (n = 525) some of the patients were treated with <144 Gy. The V100 of most of the high-volume institution patients were >90%, whereas in the low-volume institutions aconsiderable percentage of patients showed lower V100. Although there was no correlation between D90 and rectal dose parameters, UD90 had amoderate positive correlation with D90 in both the high- and low-volume institutions. U200 varied more widely in the low-volume institutions. Our findings indicate that the institutional patient accrual volume is associated with the treatment quality of I‑125 prostate seed implantation.