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In this report, investigators from Mount Sinai evaluated factors associated with erectile dysfunction following permanent prostate seed implants with or without external beam radiation therapy. They concluded that the use of external beam radiation therapy increased the risk of erectile dysfunction. Based on a review of the data and the associated conclusions concerning the dose/volume/clinical outcome data for penile bulb for patients treated with external beam radiation therapy, this finding should come as no surprise [1]. Most, but not all, studies find an association between impotence and dosimetric parameters (e.g. threshold doses) and clinical factors (e.g. age). It appears that it is prudent to keep the mean dose for 95% of the penile bulb volume to < 50 Gy. The penile bulb itself is not the critical component of the erectile apparatus, but it appears to be a surrogate for yet to be determined structure(s) critical for erectile function. Patients who are treated with brachytherapy combined with external beam radiation therapy may be at greater risk for exceeding the tolerance suggested, but using image guided intensity modulated radiotherapy it should be possible to cure many of these patients without substantially increasing the risk of erectile dysfunction. Clearly awareness and more research are warranted.

In the meantime standard methods to define the penile bulb and associated critical structures should become more widely used and a standard method to score erectile dysfunction should be more widely adopted. We recommend that patients undergo pre- and post-radiotherapy assessment of erectile dysfunction using the International Index of Erectile Function Scale. Patients can be grouped into five groups based on their scores, e.g. none (25–22), mild (21–17), mild to moderate (16–12), moderate (11–8), severe (7–5). In addition, dosimetric/imaging studies including the accumulated ‘true total dose distribution’ should be well characterized. These investigators have taken a first step.

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