Urethra-Sparing Prostate Cancer Stereotactic Body Radiation Therapy: Sexual Function and Radiation Dose to the Penile Bulb, the Crura, and the Internal Pudendal Arteries From a Randomized Phase 2 Trial

Purpose: Erectile dysfunction (ED) is a common side effect after prostate cancer stereotactic body radiation therapy (SBRT). We aimed to assess the correlation between the dose to the penile bulb (PB), internal pudendal arteries (IPA), and crura with the development of ED after ultrahypofractionation as part of a phase 2 clinical trial of urethra-sparing prostate SBRT. Methods and Materials: Among the 170 patients with localized prostate cancer from 9 centers included in the trial, 90 men with Common Terminology Criteria for Adverse Events version 4.03 grade 0 to 1 ED (ED–) at baseline treated with 36.25 Gy in 5 fractions were selected for the present analysis. Doses delivered to the PB, crura, and IPA were analyzed and correlated with grade 2 to 3 ED (ED+) development. The effect on quality of life, assessed by the European Organisation for Research and Treatment of Cancer (EORTC QLQ-PR25) questionnaire, was reported. Results: After a median follow-up of 6.5 years, 43% (n = 39) of the patients developed ED+, and 57% (n = 51) remained ED–. The dose delivered to the crura was significantly higher in ED+ patients than in ED– patients (7.7 vs 3.6 Gy [P = .014] for the D _mean and 18.5 vs 7.2 Gy [P = .015] for the D _2%, respectively). No statistically significant difference between ED+ and ED– patients was observed for the dose delivered to the PB and IPA. The median ED+-free survival was worse in patients receiving a crura D _mean ≥ 4.7 versus < 4.7 Gy (51.5% vs 71.7%, P = .005) and a crura D _2% > 12 versus ≤ 12 Gy (54.9% vs 68.9%, P = .015). No ED+-free survival differences were observed for doses delivered to the PB and IPA. Decline in EORTC QLQ-PR25 sexual functioning was significantly more pronounced in patients with higher doses to the crura. Conclusions: By keeping a D _mean and D _2% to crura below 4.7 and 12 Gy, respectively, the risk of developing ED+ after prostate SBRT may be significantly reduced.