Article

Evaluating the relationship between erectile dysfunction and dose received by the penile bulb: Using data from a randomised controlled trial of conformal radiotherapy in prostate cancer (MRC RT01, ISRCTN47772397)

Academic Department of Radiotherapy and Oncology, The Royal Marsden NHS Foundation Trust and the Institute of Cancer Research, Sutton, Surrey, UK.
Radiotherapy and Oncology (Impact Factor: 4.86). 09/2006; 80(3):355-62. DOI: 10.1016/j.radonc.2006.07.037
Source: PubMed

ABSTRACT To evaluate the relationship between erectile function and the radiation dose to the penile bulb and other proximal penile structures in men receiving conformal radiotherapy (CFRT) for prostate cancer (PCa).
The Medical Research Council (MRC) RT01 trial randomised 843 men who had localised PCa to receive either 64 or 74 Gy after 3 - 6 months neoadjuvant hormonal treatment. Fifty-one men were selected who were potent prior to hormonal treatment, having completed both pre-hormone and 2-year post-CFRT Quality of Life assessments, and on whom dose volume data were available for analysis. The men were divided into three groups according to 2-year follow-up: potent, reduced potency, and impotent. The bulb of the penis together with the crura, were outlined on restored treatment plans. Dose - volume histograms were generated and compared between the three groups. An ordered logistic regression model was used to calculate the odds ratio of a range of dose - volume parameters to the penile bulb and effect on erectile dysfunction. The dose to the penile bulb was correlated to the dose received by the crura.
Of the 51 patients, 12 remained potent, 22 had reduced potency, and 17 were impotent at 2 years. No differences were seen in mean dose to the penile bulb by allocated treatment (t test = 1.61, p = 0.11). The mean doses to the penile bulb received by the potent, reduced potency, and impotent groups were 45.5 Gy (SD 17.1), 48 Gy (SD 16.1), and 59.2 Gy (SD 13.8), respectively. There was a strong correlation between the mean dose received by the penile bulb and dose to the crura (r = 0.82, p < 0.0001). 83.3% of impotent patients received a D90 > or = 50 Gy to the penile bulb compared with 29.4% of patients who maintained potency at 2 years (p = 0.006).
There is evidence from this study to suggest a dose volume effect on the penile bulb and erectile dysfunction. A D90 > or = 50 Gy is associated with a significant risk of erectile dysfunction and this should form a basis for selecting dose constraints in future dose escalation studies.

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    • "Van der Wielen et al. studied the correlation between ED and dose to penile bulb in patients treated with doses of 68–78 Gy: but there was no relation found [149]. Mangar et al. demonstrated that a dose received by 90% of the penile bulb (D90) >50 Gy was significantly associated with ED (P = 0.006) [150], results comparable to the outcomes of the study of Wernicke et al. [151]. "
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    • "The study by van der Wielen et al18 found no correlation between ED at 2 years and dose to either the crura or the penile bulb in a study of 96 patients treated with doses of 68 to 78 Gy. However, Mangar et al19 reported a significant correlation at 2 years between the penile bulb dose-volume histogram (DVH) and ED in 51 men with baseline potency who had received 3 to 6 months of hormonal treatment and 64 or 74 Gy of radiotherapy. Dose received by 90% of the penile bulb (D90) > 50 Gy was significantly associated with ED (P = 0.006). "
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    • "In order to facilitate inter-patient comparisons, the maps were normalized in the longitudinal direction by interpolation to maps of 21×21 pixels. This was implemented using in-house software Guiness (Mangar et al. 2006). Each DSM was next described as a set of binary images. "
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