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Stereotactic body radiotherapy (SBRT) for prostate cancer appears to have the same impact on sexual function as other forms of radiotherapy.
Changes in erectile dysfunction and sexual quality of life following SBRT for prostate cancer are being investigated in a prospective phase II clinical trial that enrolled 32 consecutive patients (mean age, 68 years) with newly diagnosed, low-risk prostate cancer. None of the participants received androgen deprivation therapy.
The rate of erectile dysfunction, defined as having erections not adequate for intercourse, increased progressively during a median follow-up of almost 3 years (range, 12 to 62 months). Whereas only 12 men (38%) reported ED at baseline, the ED rate rose to 71% at 50 months after treatment. Of the 20 men who were fully potent at baseline, as many as 12 patients (60%) still remained potent at last follow-up, reported principal investigator Christopher King, MD, PhD, formerly of Stanford University School of Medicine, Stanford, CA, and now associate professor of radiation oncology at UCLA School of Medicine.
However, when outcomes were analyzed with men stratified by age, the data showed that about 4 years after treatment, 60% of men who were younger than 65 years old at the time of radiotherapy maintained good sexual function compared with only 12% of their counterparts aged 70 years or older.
"With these initial results, we are beginning to understand the effect of SBRT on sexual function. However, longer follow-up in a larger population is needed to better characterize the effect, including possible underlying risk factors."
To put the study results in perspective, Dr. King and colleagues conducted a comprehensive search of the radiotherapy literature and extracted data from studies that shared certain similarities to the SBRT trial. Studies were selected as comparators only if their patients had radiation without androgen deprivation, potency information available pre- and post-treatment collected with validated questionnaires, and at least 12 months of follow-up.
Among patient populations that were 100% potent at baseline, the potency rate decreased to 46% to 65% after external beam radiotherapy (EBRT), to 70% after low-dose rate brachytherapy, and to 53% to 60% after EBRT with high-dose rate brachytherapy boost. Within studies where not all men were potent at baseline, the percentage drop in potency rates ranged widely from 15% to 70%.
In addition to determining changes in potency rate, the impact of SBRT on sexual function was assessed by monitoring ED medication use and patient self-assessed responses for sexual domain items on the Expanded Prostate Cancer Index Composite (EPIC), a validated quality of life questionnaire that was completed by patients at baseline and every 3 to 6 months thereafter. Corresponding with the data on ED rates, the EPIC sexual summary score showed progressive worsening with a clinically relevant decrease noted at 20 months.
The change was driven primarily by the sexual "function" subdomain score, which followed a similar temporal pattern, whereas there was relatively less worsening in the sexual "bother" subdomain score and the decline plateaued at 20 months.
"The EPIC score for patients in our study at baseline was similar to that reported for similarly aged men without prostate cancer, whereas the mean score at 50 months after treatment is within the range reported in recent studies of men undergoing standard fractionated EBRT," Dr. King said.
"Importantly, despite the high rate of loss of sexual function among men in our study, only 25% of them considered sexual function a 'moderate' or 'big' problem. Perhaps this is a reflection of their older age."
The rate of ED medication use increased eightfold, from 3% at baseline to 25% at last follow-up.
"On a positive note, most men using ED medication achieved success," according to Dr. King.