No abstract

To study the relationships between absorbed dose to penile base structures and erectile dysfunction (ED) in patients treated with ultrahypofractionated (UHF) radiotherapy (RT) or conventionally fractionated (CF) RT for prostate cancer. Specifically, we investigated if any dose-volume objectives can be recommended to prevent ED. Materials/Methods: One thousand two hundred patients with intermediate to high risk prostate cancer were included in the HYPO-RT-PC trial 1 (median follow up 5 y) where patients were randomized to CF (39x2.0 Gy, 8 weeks) or UHF (7x6.1Gy, 2.5 weeks). The treatment schedules were designed to be equi-effective for late normal tissue complications (a/bZ3 Gy). No androgen deprivation therapy was allowed. Erectile dysfunction was reported by patients (ED PROM) on an ordinal scale (0-10; severe ED 8). Erectile function was assessed by physicians as: enough for intercourse, not enough for intercourse or severe erectile dysfunction (ED S). Only patients with erectile function enough for intercourse at baseline where included in this study (CF: nZ338, U-HF: nZ349, median age 68 y), 59% of trial patients. The penile bulb (PB) and crus were retrospectively delineated on the treatment planning CT scans. Dose-volume descriptors were derived, both relative and converted to 2 Gy with a/bZ3 Gy (EQD2 3). Uni-and multivariable Cox and logistic regressions were used to find predictors of ED S occurring 6 months or later after start of RT. ED PROM was analyzed with ordinal regression. Results: Severe ED PROM was reported in 9%, 18%, 24% and 30% at baseline, 6, 12 and 24 months, respectively. There was a strong correlation between ED S and ED PROM. ED S was present in 6%, 12% and 18% at 6, 12 and 24 months, respectively. Cox regression revealed that age was significantly associated with ED S (p<0.001). There was a trend (pZ0.08) for D 2% (PB) (the dose-volume descriptor with the strongest association to ED). No significant differences in ED S were found between CF and UHF. The medians (IQRs) for D 2% (PB) and D 2% (crus) were 59 (22-75) Gy 3 and 44 (14-66) Gy 3. In univariable analyses age was significant for ED S and ED PROM at 6, 12, and 24 months, whereas D 2% (PB) and D 2% (crus) were significant for ED S at 12 and 24 months and for ED PROM at 12 months. In multivariable analyses age together with D 2% (PB) or D 2% (crus) were all significant at 12 and 24 months for ED S and at 12 months for ED PROM. The best cutoff doses for predicting ED S were for D 2% (PB) at 55 Gy 3 and D 2% (crus) at 30 Gy 3 which was supported by the analyses of ED PROM. Conclusion: There was no statistically significant difference in ED between CF and UHF. The strongest predictor for ED was age followed by the dose to the penile bulb and crus. We propose D 2% (PB) < 55 Gy 3 and D 2% (crus) < 30 Gy 3 as suitable objectives to be applied in the treatment planning process. 1 A.