Sexual function and dosimetric relationships to neighboring neurovascular substructures among patients treated definitively with Pd-103 LDR prostate brachytherapy.

Purpose: To report sexual health outcomes related to Pd-103 prostate brachytherapy and evaluate dosimetric patterns to the nearby neurovascular structures. To assess potential relationships between dose to neurovascular substructures and erectile function outcomes in an institutional cohort treated definitively with Pd-103 LDR brachytherapy.

Materials And Methods: The study utilized an IRB-approved database of men receiving low dose rate (LDR) prostate brachytherapy from 2014 to 2019 at our institution for definitive prostate cancer treatment. Patients routinely completed quality of life questionnaires at consultation and at subsequent follow up visits. Outcomes data related to sexual toxicity were evaluated based on the Sexual Health Inventory (SHIM) Questionnaire. Patients with pre-existing erectile dysfunction (SHIM <17 or SHIM confidence score <3) were excluded. The pudendal arteries, neurovascular bundles, subapical region, and penile bulb, were contoured on postimplant imaging and dosimetric data was analyzed. For all statistical comparisons, a student's t-test was used with alpha of 0.05 indicating significance.

Results: About 62 patients met criteria and were included in the analysis. All patients had either very low, low, favorable intermediate or unfavorable intermediate disease at diagnosis. Median follow-up was 5.5 years with total 380 individual questionnaires completed; 58 (93.5%) patients had follow-up greater than 2 years, and 28 (45.2%) patients had follow-up longer than 5 years. Mean baseline SHIM confidence score was 4.0 (SD 0.9). At most recent follow up, 34 patients (53%) had a SHIM confidence score greater than or equal to 3. Mean confidence SHIM for the cohort decreased from 4 to 3 after treatment and did not return to baseline over time. At the 6-month, 2-year, 4-year, and 5-year time points, the high dose NVB cohort demonstrated worse SHIM scores. At 5-year follow up, mean SHIM confidence was 2.2 ± 1.3 for the high dose group versus 3.6 ± 1.3 in the low dose group.

Conclusions: Erectile function appears to decrease following prostate brachytherapy with LDR Pd-103 seeds, demonstrated by a reduction in post procedural SHIM scores from baseline without recovery to preprocedure scores. The dose to adjacent neurovascular substructures other than NVBs is exceedingly low following Pd-103 LDR prostate brachytherapy and is unlikely to be the primary contributor to decreased sexual function related to this treatment modality. Out of the individual substructures, NVB dose may be the most critical.