Erectile dysfunction and radiation dose to penile base structures: a lack of correlation.

PURPOSE: To evaluate the relationship between the dose and volume of radiation to proximal penile structures and the development of erectile dysfunction after external beam radiotherapy (RT) for localized prostate adenocarcinoma. METHODS AND MATERIALS: The study cohort comprised 28 patients who were enrolled our in-house three-dimensional conformal RT dose escalation protocol. The patients were treated to 78 Gy between 1995 and 1998. This protocol included a planned quality-of-life questionnaire to assess sexual function 2 years after completing RT. All the study patients were potent before RT. The median follow-up was 66 months (range 39-95). Penile base contents were outlined retrospectively in restored treatment plans. The dose-volume histograms (DVHs) for the corpus spongiosum (penile bulb), corpora cavernosum and crura, and total penile structure (corpus spongiosum plus corpora cavernosum and crura) were calculated. Statistical significance was defined as p < 0.05. The Bonferroni correction was used to adjust for multiple comparisons. Power calculations showed that our study sample would detect radiation- induced impotence with a very high power. We also estimated that a relatively small difference of 10-15% in the DVHs between the potent and impotent patients could be detected.
RESULTS: At 2 years after RT, 10 patients (35.7%) reported new-onset erectile dysfunction and were unable to attain firm enough erections to have intercourse. Only hypertension was observed to affect erectile dysfunction after external beam RT. We found no statistically significant correlation among age, diabetes, or heavy alcohol consumption and post-RT potency. The mean radiation dose +/- standard deviation delivered to the corpus spongiosum, corpora cavernosa and crura, and total penile structure was, respectively, 42.2 +/- 8.4 Gy, 36.3 +/- 8.0 Gy, and 38.2 +/- 7.5 Gy. t test comparisons were performed between DVHs of post-RT potent and impotent patients on multiple cutpoints. No dose-volume effect was found. Analysis of the DVHs when the patients were subdivided into normotensive and hypertensive groups also showed no dose-volume response.
CONCLUSION: Our analysis did not show statistically significant correlations between potency preservation and radiation dose to the proximal penis. The entire etiology of radiation- induced erectile dysfunction remains unclear and further research is needed.