Presenter(s)
D. Song1, M. Dabkowski2, I. Shpunt3, E. Sapir4, B. Vanneste5, E. V. Limbergen6, O. Boychack7, P. Costa8, E. M. Soffen9, R. Hudes10, M. Kos11, and S. H. Zimberg12; 1Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, 2Brachytherapy Department, Center of Oncology, M. Sklodowska-Curie Memorial Institute, Warsaw, Poland, 3Rabin Medical Center, PetahTikva, Israel, 4Radiation Oncology Institute, Samson Assuta Ashdod University Hospital, Ashdod, Israel, 5Department of Radiation Oncology, Ghent University Hospital, Ghent, Belgium, 6MAASTRO Clinic Dr. Tanslaan, Maastricht, Netherlands, 7St Luke’s Hospital,, Dublin, Ireland, 8CUF Porto Instituto Rua Fontedas Sete Bicas, Senhora da Hora Matosinhos, Portugal, 9Princeton Radiation Oncology, Astera Cancer Care, Jamesburg, NJ, 10Chesapeake Urology Research, Owings Mills, MD, 11Urology Nevada, Reno, NV, 12Advanced Radiation Centers of New York, Lake Success, NY
Purpose/Objective(s):
Post-radiation erectile outcomes are strongly influenced by the delivered dose to radiosensitive pelvic erectile anatomy and may be modifiable through dose shaping. The penile bulb (PB) -a defined erectile structure routinely contoured as an organ-at-risk -has been linked to sexual dysfunction after prostate RT and is a practical planning constraint. We correlated long-term patient-reported sexual QOL outcomes through 48 months with PB mean dose in a randomized pivotal trial of definitive prostate RT with or without a biodegradable balloon rectal spacer.Materials/Methods:
Patients received definitive prostate RT to 81 Gy (or equivalent hypofractionation) in a randomized pivotal trial with a biodegradable balloon rectal spacer vs control (no spacer). PB was contoured as an organ-at-risk; PB mean dose was stratified by the cohort median. Patient-reported sexual outcomes were assessed from baseline through 48 months using EPIC-26. Minimal Clinically Important Difference (MCID) was defined as an 11-point sexual domain score decline; changes from baseline were categorized as: none (=5 points), small (6-10), moderate (11-20), or large (> 20). Fisher’s exact and Cochran-Armitage trend tests evaluated QOL shift between groups and treatment arms.Results:
The cohort was stratified by the median PB mean dose (9.94 Gy). At 48 months, EPIC-26 sexual domain change from baseline was more favorable with PB mean dose =9.94 Gy vs >9.94 Gy in the Balloon arm (+4.4 ±19.6 vs -2.5 ±26.1, p<0.001); in the Control arm, mean change was -0.4 ±11.1 vs -25.6 ±28.9 (p=0.049). Deterioration of function was dose-dependent: in the Balloon arm, 0.0% of the =9.94 Gy group met the 11-point MCID decline vs 52.9% in the >9.94 Gy group (p<0.001); in Controls, 33.3% vs 71.4% met MCID. Item-level EPIC responses at 48 months were directionally consistent across erection ability and overall sexual function.Conclusion:
Long-term sexual QOL after prostate RT correlated with PB mean dose, supporting radiosensitive erectile anatomy exposure as a key driver of outcome and a modifiable planning target. In this randomized pivotal trial, achieving PB mean dose below ~10 Gy was associated with fewer clinically meaningful 48-month declines and occurred more frequently in the balloon arm. Future studies should confirm dosimetric–outcome correlations across additional pelvic regions of interest implicated in erectile function (e.g., neurovascular and vascular structures) to better define actionable dose constraints and further mitigate sexual toxicity while maintaining target coverage.| EPIC-26 Sexual Function Item (Negative Response Category) | Arm | = 9.94 Gy | > 9.94 Gy | p-value |
| Erection Ability (Poor/Very Poor) | Balloon | 24.0% | 45.7% | 0.108 |
| Control | 71.4% | 76.2% | 0.290 | |
| Erection Quality (Not for Intercourse) | Balloon | 64.0% | 77.1% | 0.384 |
| Control | 71.4% | 90.5% | >0.999 | |
| Erection Frequency (<Half Desired) | Balloon | 32.0% | 40.0% | 0.594 |
| Control | 71.4% | 81.0% | 0.545 | |
| Sexual Function (Poor/Very Poor) | Balloon | 20.0% | 40.0% | 0.159 |
| Control | 71.4% | 71.4% | 0.288 |