Dosimetric Predictors of Problematic Receptive Anal Intercourse After Prostate Radiation Therapy

While the effects of prostate radiation therapy on erectile function are well documented, data on receptive anal intercourse (RAI) remain sparse, despite its prevalence among gay and bisexual men. This study investigated associations between radiation dose to RAI functional anatomy and problematic RAI to identify preliminary, clinically meaningful dosimetric parameters.

Fourteen prostate cancer survivors who engaged in RAI and completed Patient-Reported Outcomes Measurement Information System questionnaires were retrospectively evaluated. RAI functional anatomy (anal canal, levator ani, erectile tissues, neurovascular bundles, and internal pudendal arteries [IPAs]) was delineated, and dosimetric parameters were extracted. Dose-outcome relationships were assessed using Spearman's correlation (ρ) and logistic regression.

Anal canal maximum dose (Dmax; minimum dose to the hottest 0.03 cm3) and minimum dose tot he hottest 2 cm3 (D2cm3) were strongly associated with orgasm ability (ρ = -0.63), while mean dose (Dmean) showed a moderate association (ρ = -0.57); all anal canal parameters were moderately associated with orgasm pleasure (ρ range, -0.50 to -0.56). Levator ani Dmean and D2cm3 were moderately associated with orgasm ability and pleasure (ρ range, -0.48 to -0.58). Erectile tissue high-dose parameters were strongly associated with orgasm ability (ρ range, -0.61 to -0.68) but not with orgasm pleasure (ρ range, -0.39 to -0.46). IPA Dmax was moderately associated with orgasm ability (ρ = -0.52) and pleasure (ρ = -0.55). Neurovascular bundle dosimetry and anal pain showed no evidence of association. Exploratory dose thresholds corresponding to a 10% probability of dysfunction, in equivalent doses in 2 Gy fractions with an α/β ratio of 3 (EQD2[3]), were identified for the anal canal (Dmax, 40; Dmean, 9; D2cm3, 4), levator ani (Dmean, 31), erectile tissues (Dmax, 20; Dmean, 5), and IPA (Dmax, 35).

This study provides the first evidence on the association between radiation dose to RAI functional anatomy and problematic RAI. While exploratory, these results may help guide future studies and inform counseling.