113 Background: Conventional dosimetric standards for implant quality do not adequately predict patient reported QoL measures following prostate brachytherapy. We used a dynamic learning knowledgebase (Oncospace) to explore relationships between dose and patient-reported outcomes. Methods: Patient reported quality of life outcomes were prospectively collected for 366 patients with stage cT1-T2 PCa over a 10 year interval. Patients received Pd-103 seed implantation under real-time ultrasound guidance, and completed a QoL instrument (IIEF-5) prior to treatment and at follow-up. Multivariate risk models were used to evaluate dose/toxicity relationships and the Oncospace learning environment generated prediction models using granular dose volume relationships. Results: Median follow-up was 36 months (SD 28.5). In the cohort, 23.7% (n = 87) received combined brachytherapy and EBRT; 14.7% (n = 54) had received prior androgen suppression therapy. Sexual QoL data at minimum of 2 years was available in 141 men. The mean decrement in sexual function per the IIEF-5 instrument was 3.76 points (SD 10.3), with 17.0% of men reporting a decrement of 10 points or greater. There was no significant association with prior androgen suppression (p = 0.20) or combined EBRT use (p = 0.69). DVH curves were queried and dichotomized according to stable sexual function vs significant decline ( > 10) at 2 years post-implant. A logistic regression model was used to generate probability surface maps of volumetric dose effects on outcomes. Logistic regression revealed a correlation between dose to the cavernosal nerves and total SHIM score throughout the high dose region of the DVH curve (p < 0.05). No similar dose/volume correlation with sexual function emerged for structures. Conclusions: Granular dose/volume and toxicity correlation using the Oncospace learning environment exposed a statistically significant relationship between volumetric dose to the cavernosal nerves and sexual function decline in patients undergoing LDR brachytheramarpy. Minimization of dose to the cavernosal nerves may preserve sexual function after permanent prostate seed brachytherapy.