Sildenafil (Viagra) and Erectile Dysfunction following Conformal Radiotherapy for Prostate Cancer: A Randomized, Double-Blind, Placebo-Controlled, Cross-Over Study

Ryan Smith, MD
University of Pennsylvania Cancer Center
Last Modified: November 7, 2001

Presenter: L. Incrocci
Presenter's Affiliation: University Hospital Rotterdam-Daniel
Type of Session: Scientific


  • The incidence of Erectile Dysfunction (ED) following external beam radiation therapy is commonly reported as 35-45%.
  • With the author's form of conformal therapy, the first 1/3 of the penis lies within the radiation field, thus putting the patient at high risk for the development of ED
  • Retrospective data indicates a response to sildenafil in 75-90% of patients.
  • This is a study investigating the use of sildenafil to treat ED in patients following external beam radiation therapy.

    Materials and Methods

  • This is a prospective, randomized, double blind, placebo-controlled trial of 60 patients who comlained of erectile dysfunction following external beam radiation therapy.
  • Randomization was to either sildenafil (50 mg/d) or placebo taken, as needed, one hour prior to sexual activity. Dose could be increased to 100 mg at week 2. At week six, patients crossed over to the other arm.
  • Mean age of patients was 68 years
  • Mean radiation dose was 66 Gy, with a mean energy of 23 MV, using a 3-field technique.
  • Patients were required to be involved in a stable relationship where there was the opportunity to engage in sexual activity at least once per week.
  • The International Index of Erectile Dysfunction scale was used to score ED profiles.


  • Mean time after radiation therpay was 39 months (15-55 month range).
  • Increase in the dose to 100 mg was required for effect in 90% of patients.
  • Overall, there was a significant increase in mean scores for patients on sildenafil compared to placebo.
  • There was an increase in scores pertaining to improvement of erections in 45% of patients (vs. 8% in placebo)
  • There was an increase in scores pertaining to improvement in successful intercourse in 55% of patients (vs. 18% of placebo patients).
  • Side effects of headache (42%), flushing (13%), and dyspepsia were higher in the sildenafil groups.

    Author's Conclusions

  • Sildenafil is effective in the treatment of ED after conformal radiation therapy.
  • Sildenafil is well tolerated while being used in this setting.
  • The dose required is 100 mg in most patients.

    Clinical/Scientific Implications
    As stated previously, ED is a major side effect of external beam radiation therapy for the treatment of prostate cancer. Though there has been retrospective data indicating the usefulness of sildenafil in this aspect, this prospective, randomized trial makes a strong argument for its efficacy. However, though the scores increased, it is not known if they increased over the threshold for clinical usefulness (i.e.-improvement in erections is often useful in men only if it allows for sexual penetration). The improvements in sexual intercourse supports the fact that this threshold is crossed. Also, as in many radiation toxicities, as the time after treatment increases, the toxicity worsens. Therefore, even though sildenafil appears to be efficacious for the treatment of early impotence, it will be interesting to note its effect 2-3 years further out of treatment.

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