363 - Segmental Internal Pudendal Artery Dose-Volume Parameters as a Novel Predictor of Long-Term Sexual Function after Prostate Radiation Therapy with and without a Hydrogel Spacer

09:35am - 09:45am ET

Room 253

Presenter(s)

Omar Awad, MD, MS - Baylor College of Medicine, Houston, TX

O. Awad^1,2, A. S. Mohamed^1,3, Z. A. Siddiqui¹, C. G. Candano¹, Z. A. Seymour⁴, T. J. Quinn⁴, C. Knill⁵, H. Mekdash¹, and D. A. Hamstra¹; ¹Department of Radiation Oncology, Dan L. Duncan Comprehensive Cancer Center, Baylor College of Medicine, Houston, TX, ²Clinical Oncology Department, Faculty of Medicine, Alexandria University, Alexandria, Egypt, ³Department of Radiation Oncology, The University of Texas M.D. Anderson Cancer Center, Houston, TX, ⁴Department of Radiation Oncology, Corewell Health William Beaumont University Hospital, Royal Oak, MI, ⁵Univ of Michigan, Ann Arbor, MI

Purpose/Objective(s): The internal pudendal artery (IPA) has emerged as a potential organ-at-risk for sexual function preservation during prostate radiation therapy. However, the IPA traverses regions of varying dose exposure. We hypothesized that segmental IPA analysis would identify the dosimetrically relevant portion driving sexual quality of life (QOL) decline and clarify the mechanism of hydrogel spacer-mediated sexual function preservation.

Materials/Methods: In a single-blind phase III trial, 222 men receiving 79.2 Gy prostate IG-IMRT were randomized 2:1 to SpaceOAR hydrogel or control. Bilateral IPAs were auto-segmented and divided at the prostate apex into a caudal and a cranial segments. Sexual QOL was assessed using EPIC; minimally important difference (MID) was defined as =11-point deterioration from baseline. Analysis included patients with baseline sexual scores =60 and available segmental IPA dosimetry (n=71). DVH parameters were compared between MID groups using Mann-Whitney U tests. Recursive partitioning analysis (RPA) identified optimal thresholds. Paired Wilcoxon tests compared pre- versus post-hydrogel dosimetry. Penile bulb DVH was analyzed as a comparator.

Results: Seventy-one patients had sexual QOL data at 12 months or beyond (SpaceOAR: 51, Control: 20). Sexual MID=11 was observed in 65% of control vs 61% of SpaceOAR patients; at 36 months, rates were 80% versus 52%. Prostate to IPA distance was not significantly different between control and spaceOAR arm. DVH analysis of the segmented IPA revealed that the caudal IPA had the strongest association with sexual outcomes, demonstrating significant DVH parameters in the low-dose range (V7-V22, p < 0.05), with patients reaching sexual MID = 11 receiving higher doses across this range. The complete bilateral IPA showed significant parameters (V0-V15), while the cranial IPA and penile bulb each showed no significant DVH correlates. RPA identified caudal IPA V22 = 93% as the strongest predictor of sexual MID = 11 (p = 0.0007), patients above this threshold had 81% sexual MID =11 vs 41% below. Paired analysis showed SpaceOAR significantly reduced caudal IPA dose across 47 DVH parameters with mean V22 decreasing from 89% to 82% (p=0.001), while the cranial IPA showed no significant reduction. Friedman testing confirmed the caudal segment had significantly greater dose reduction than the cranial segment (p=0.0005). Penile bulb dose in this sub-set of patients did not correlate with sexual function.

Conclusion: The caudal IPA nearest the prostate is the critical segment predicting long-term sexual dysfunction after prostate IMRT, while the cranial IPA and penile bulb have no predictive value. Caudal IPA V22 = 93% identifies high-risk patients with 81% probability of sexual deterioration (p=0.0007), representing a potential planning dose constraint. SpaceOAR selectively reduces caudal IPA dose while not altering cranial IPA dose, supporting segment-specific dose optimization for sexual function preservation.