Dosimetric Predictors of Problematic Receptive Anal Intercourse After Prostate Radiation Therapy

Purpose: While the effects of prostate radiotherapy 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.Methods: Fourteen prostate cancer survivors who engaged in RAI and completed PROMIS questionnaires were retrospectively evaluated.RAI functional anatomy (anal canal, levator ani, erectile tissues, neurovascular bundles [NVB], internal pudendal arteries [IPA]) was delineated, and dosimetric parameters were extracted.Dose-outcome relationships were assessed using Spearman's correlation () and logistic regression.Results: Anal canal Dmax and D2cc were strongly associated with orgasm ability (=-0.63),while Dmean showed a moderate association (=-0.57);all anal canal parameters were moderately associated with orgasm pleasure ( range, -0.50 to -0.56).Levator ani Dmean and D2cc were moderately associated with orgasm ability and pleasure ( range, -0.48 to -0.58).Erectile tissue high-dose parameters were strongly associated with orgasm ability ( range, -0.61 to -0.68) but not with orgasm pleasure ( range, -0.39 to -0.46).IPA Dmax was moderately associated with orgasm ability (=-0.52)and pleasure (=-0.55).NVB dosimetry and anal pain showed no evidence of association.Exploratory dose thresholds (Gy EQD2(3)) corresponding to 10% probability of dysfunction were identified-anal canal (Dmax: 40, Dmean: 9, D2cc: 4), levator ani (Dmean: 31), erectile tissues (Dmax: 20, Dmean: 5), and IPA (Dmax: 35). Conclusion: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.