The etiology of the improved long-term sexual function seen following MRI-guided stereotactic body radiotherapy (SBRT) with aggressive margin reduction for prostate cancer remains unknown.
To investigate potential explanatory mechanisms for this finding, we conducted a secondary analysis of data collected for the prospective, randomized phase III MIRAGE trial. Dosimetric data for the structures hypothesized to drive sexual function decline (neurovascular bundles (NVB) and internal pudendal arteries (IPA)) were retrospectively collected and analyzed for correlations with treatment arm or clinically significant sexual function decline as measured by patient reported outcome (PRO) surveys focused on sexual function, namely the EPIC26-SF and SHIM scores.
One-hundred-and-seventeen participants from the MIRAGE trial (CT-arm: 58, MRI-arm: 59), corresponding to 75 % of the overall cohort, had complete sexual function PRO survey responses at 24 months. Baseline SHIM score was slightly higher in the MRI arm although EPIC26-SF was the same. No significant differences were noted in treatment characteristics (such as hydrogel spacer, GTV boost, or ADT use) between the study arms. Patients in the MRI group were noted to have significantly lower V36Gy and V20Gy for the NVBs and IPAs. Maximum dose to the right NVB was associated with increased likelihood of sexual function decline (p < 0.05).
Although this analysis is limited in its exploratory nature, the data suggest that the unintentional sparing effect of aggressive margin reduction may be associated with a reduction in volume of the NVBs and IPAs receiving intermediate- or low-dose radiation. This, in turn, could explain the reduced rates of sexual function decline experienced by patients receiving MRgSBRT.
Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology. 2026 Jul 11 [Epub ahead of print]
Jonathan Massachi, Tommy Jiang, Beth K Neilsen, Holly Wilhalme, Dan Ruan, Maria Casado, Natalie Chong, Lily Zello, James M Lamb, Ting Martin Ma, Luca F Valle, Minsong Cao, Michael L Steinberg, Amar U Kishan
UCLA Dept of Radiation Oncology, United States., UCLA Dept of Radiation Oncology, United States. Electronic address: ., UCLA Dept of Radiation Oncology, United States. Electronic address: .