title: Baseline status and dose to the penile bulb predict impotence 1 year after radiotherapy for prostate cancer.
abstract: OBJECTIVE
  To assess the predictors of the onset of impotence 1 year after radiotherapy for prostate cancer.
  
  
  METHODS
  In a multi-centric prospective study, the International Index of Erectile Function (IIEF) questionnaire-based potency of 91 hormone-naïve and potent patients (IIEF1-5 > 11 before radiotherapy) was assessed. At the time of this analysis, information on potency 1 year after treatment was available for 62 of 91 patients (42 treated with hypofractionation: 2.35-2.65 Gy/fr, 70-74.2 Gy; 20 with conventional fractionation: 74-78 Gy). Prospectively collected individual information and Dmax/Dmean to the penile bulb were available; the corresponding 2 Gy-equivalent values (EQD2_max/EQD2_mean) were also considered. Predictors of 1‑year impotency were assessed through uni- and multi-variable backward logistic regression: The best cut-off values discriminating between potent and impotent patients were assessed by ROC analyses. The discriminative power of the models and goodness-of-fit were measured by AUC analysis and the Hosmer-Lemeshow (H&L) test.
  
  
  RESULTS
  At 1‑year follow-up, 26 of 62 patients (42 %) became impotent. The only predictive variables were baseline IIEF1-5 values (best cut-off baseline IIEF1-5 ≥ 19), Dmax ≥ 68.5 Gy and EQD2_max ≥ 74.2 Gy. The risk of 1‑year impotence may be predicted by a two-variable model including baseline IIEF1-5 (OR: 0.80, p = 0.003) and EQD2_max ≥ 74.2 Gy (OR: 4.1, p = 0.022). The AUC of the model was 0.77 (95% CI: 0.64-0.87, p = 0.0007, H&L: p = 0.62). The 1‑year risk of impotency after high-dose radiotherapy in potent men depends on the EQD2_max to the penile bulb and on baseline IIEF1-5 values.
  
  
  CONCLUSIONS
  A significant reduction in the risk may be expected mainly when sparing the bulb in patients with no/mild baseline impotency (IIEF1-5 > 17).
authors.affiliation: Radiotherapy, San Raffaele Scientific Institute, Milano, Italy.
authors.forename: Cesare
authors.initials: C
authors.lastname: Cozzarini
authors.affiliation: Prostate Cancer Program, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: Tiziana
authors.initials: T
authors.lastname: Rancati
authors.affiliation: Radiotherapy, San Raffaele Scientific Institute, Milano, Italy.
authors.forename: Fabio
authors.initials: F
authors.lastname: Badenchini
authors.affiliation: Medical Physics, San Raffaele Scientific Institute, Milan, Italy.
authors.forename: Federica
authors.initials: F
authors.lastname: Palorini
authors.affiliation: Radiation Oncology 1, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: Barbara
authors.initials: B
authors.lastname: Avuzzi
authors.affiliation: Radiotherapy, Ospedale Bellaria, Bologna, Italy.
authors.forename: Claudio
authors.initials: C
authors.lastname: Degli Esposti
authors.affiliation: Radiotherapy, Ospedale ASL9, Ivrea, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Girelli
authors.affiliation: Medical Physics, San Raffaele Scientific Institute, Milan, Italy.
authors.forename: Ilaria
authors.initials: I
authors.lastname: Improta
authors.affiliation: Radiotherapy, Cliniche Gavazzeni-Humanitas, Bergamo, Italy.
authors.forename: Vittorio
authors.initials: V
authors.lastname: Vavassori
authors.affiliation: Prostate Cancer Program, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.|Radiation Oncology 1, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: Riccardo
authors.initials: R
authors.lastname: Valdagni
authors.affiliation: Medical Physics, San Raffaele Scientific Institute, Milan, Italy. fiorino.claudio@hsr.it.
authors.forename: Claudio
authors.initials: C
authors.lastname: Fiorino
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015897:Comorbidity; D007172:Erectile Dysfunction / Q000175:diagnosis / Q000453:epidemiology*; D005500:Follow-Up Studies; D006801:Humans; D007558:Italy / Q000453:epidemiology; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care / Q000379:methods*; D010413:Penis / Q000528:radiation effects; D015995:Prevalence; D011379:Prognosis; D011471:Prostatic Neoplasms / Q000453:epidemiology* / Q000532:radiotherapy*; D000069079:Radiation Exposure / Q000032:analysis*; D011832:Radiation Injuries / Q000175:diagnosis / Q000453:epidemiology*; D011879:Radiotherapy Dosage; D012044:Regression Analysis; D015203:Reproducibility of Results; D018570:Risk Assessment / Q000379:methods; D012680:Sensitivity and Specificity; D016896:Treatment Outcome
keywords: Dose-response; Erectile dysfunction; Predictive models; Prostate cancer; Radiotherapy