In this study, we evaluated in a serial manner whether radiation dose to the bulb
of the penis is predictive of erectile dysfunction, ejaculatory difficulty (EJ), and
overall satisfaction with sex life (quality of life) by using serial validated self-administered
questionnaires.
Twenty-nine potent men with AJCC Stage II prostate cancer treated with three-dimensional
conformal radiation therapy alone to a median dose 72.0 Gy (range: 66.6-79.2 Gy) were
evaluated by determining the doses received by the penile bulb. The penile bulb was
delineated volumetrically, and the dose-volume histogram was obtained on each patient.
The median follow-up time was 35 months (range, 16-43 months). We found that for D(30),
D(45), D(60), and D(75) (doses to a percent volume of PB: 30%, 45%, 60%, and 75%),
higher than the corresponding median dose (defined as high-dose group) correlated
with an increased risk of impotence (erectile dysfunction firmness score = 0) (odds
ratio [OR] = 7.5, p = 0.02; OR = 7.5, p = 0.02; OR = 8.6, p = 0.008; and OR = 6.9,
p = 0.015, respectively). Similarly, for EJD D(30), D(45), D(60), and D(75), doses
higher than the corresponding median ones correlated with worsening ejaculatory function
score (EJ = 0 or 1) (OR = 8, p = 0.013; OR = 8, p = 0.013; OR = 9.2, p = 0.015; and
OR = 8, p = 0.026, respectively). For quality of life, low (< or =median dose) dose
groups of patients improve over time, whereas high-dose groups of patients worsen.
This study supports the existence of a penile bulb dose-volume relationship underlying
the development of radiation-induced erectile dysfunction. Our data may guide the
use of inverse treatment planning to maximize the probability of maintaining sexual
potency after radiation therapy.