Radiation dose-volume effects and the penile bulb

Abstract

The dose, volume, and clinical outcome data for penile bulb are reviewed for patients treated with external-beam radiotherapy. Most, but not all, studies find an association between impotence and dosimetric parameters (e.g., threshold doses) and clinical factors (e.g., age, comorbid diseases). According to the data available, it is prudent to keep the mean dose to 95% of the penile bulb volume to <50 Gy. It may also be prudent to limit the D70 and D90 to 70 Gy and 50 Gy, respectively, but coverage of the planning target volume should not be compromised. It is acknowledged that the penile bulb may not be the critical component of the erectile apparatus, but it seems to be a surrogate for yet to be determined structure(s) critical for erectile function for at least some techniques.

Fig. 1

Penile and erectile tissue anatomy with CT (A) and MR (B–D) images of the penile bulb (*). Adapted from Wallner et al. (16).

Fig. 2

Incidence of erectile dysfunction according to the radiation dose to the penile bulb. The x axis values are estimated according to the range of doses reported. The data for Fisch et al. (7) at 20, 55, and 80 Gy represent the reported rates of erectile dysfunction at <40, 40–70, and >70 Gy, respectively. Similarly, for Wernicke et al. (14) and Roach et al. (10), each symbol represents the rates of erectile dysfunction at ≤42 vs. >42 and <52.5 vs. ≥52.5 Gy, respectively. The dashed horizontal lines reflect the dose ranges ascribed to each data point. The upper x-axis range of the highest data point for Fisch et al. (7) and Roach et al. (10) are unknown. The mean doses of van der Wielen et al. (13) and Mangar et al. (8) are estimated from the subgroup data. The x-axis values for Wernicke et al. (14) are D60 and for Fisch et al. (7) are D70 (i.e., minimum dose received by 60% or 70% volume of the penile bulb). A thick solid line represents the fitted model with sample size correction, with 95% confidence intervals (dotted curves).