The prognosis of patients with prostate cancer receiving permanent seed implantation stratified by prostate volume: Should we be reluctant to treat with brachytherapy because of a very small prostate (<15 cc)?

We evaluated the treatment outcomes of different prostate volumes (PVs), <15 cc, 15-20 cc, and > 20 cc, in patients with prostate cancer who underwent permanent seed implantation (PI) ± external beam radiation therapy ± hormone therapy in a national Japanese prospective cohort study (J-POPS).Of the 6721 patients in J-POPS from 2005 to 2011, 6652 were included in the analysis population. We categorized the patients into the following three PV groups: <15 cc, 15-20 cc, and > 20 cc. We evaluated the effect of PV on biochemical freedom from failure (bFFF), prostate cancer-specific mortality (PCSM), and all-cause mortality (ACM) using the Phoenix definition and Cox proportional hazard models.The median follow-up period was 60.0 months. Patients in each PV group was 491 (7.4%), 1118 (16.8%), and 5043 (75.8%), respectively. No difference was observed in bFFF (94.7%, 96.2%, and 95.7%, p = 0.407), PCSM (99.8%, 99.7%, and 99.8%, p = 0.682), and ACM (98.2%, 96.7%, and 97.2%, p = 0.119) at 5 years for each PV group. In univariate and multivariate analyses, PV was not associated with bFFF, PCSM, ACM, or grade 2 toxicity. The percentage of positive biopsies was the single most significant predictor for all treatment outcomes.Our results obtained by analyzing a very large Japanese prospective database showed no difference in treatment outcomes according to PV (<15 cc, 15-20 cc, and ˃20 cc). Our study confirmed that PI in small prostates (even < 15 cc) remains an effective treatment option.