Radiation Therapy Advances for Prostate Cancer

Data from three studies presented during the American Society for Radiation Oncology's annual meeting in Boston, MA, September 25–28, should better guide physicians in making decisions about treating low- or intermediate-risk prostate cancer with radiotherapy. One study examined the impact of an accelerated treatment schedule on side effects and quality of life; another found that stereotactic body radiotherapy (SBRT) compares well to the current standard, intensity-modulated radiotherapy (IMRT). A third concluded that prostate brachytherapy on its own may be sufficient.

Deborah Bruner, RN, PhD, of Emory University in Atlanta, GA, and her colleagues assessed whether hypofractionated IMRT—delivered in higher doses over 28 days, versus the conventional schedule of 41 days—led to an increase in side effects affecting quality of life. Their phase III trial enrolled 962 men with low-risk prostate cancer, randomly assigned to receive either conventional or hypofractionated IMRT. The patients then completed questionnaires evaluating bowel, urinary, and sexual functions. Data from these questionnaires showed no statistically significant differences between the study arms at baseline or at 6 and 12 months post-treatment, Bruner reported. As such, although hypofractionated IMRT is still widely considered investigational, “we think we aren't going out on a limb to suggest that it should be a standard option,” she said.

“Remember that men with low-risk prostate cancer have many options, including watchful waiting,” Bruner added. “Therefore, if a treatment is chosen, it should be the shortest possible, with the least amount of side effects.”

According to data on 309 men whose newly diagnosed low- or intermediate-risk prostate cancer was treated with SBRT, this form of radiotherapy offers a high rate of disease control with low toxicity, in fewer treatments. SBRT is technologically more advanced than IMRT: The beams converge from a spherical orientation, or multiple angles, instead of a single plane. As such, higher doses of radiation can be delivered precisely to the target tissue, and an entire course of treatment takes just five visits, which is potentially more cost-effective, said Robert Meier, MD, of the Swedish Cancer Institute in Seattle, WA. Five years after SBRT, 97% of patients were recurrence-free, which he noted was superior to the historical rate of 93% with IMRT. Fewer than 2% of patients experienced serious genitourinary or gastrointestinal side effects during treatment.

“SBRT is an example of how advanced technology has radically improved our ability to treat prostate cancer,” Meier added. “To date, we've only had single-institution reports on its overall utility. Ours is the first study to contribute multicenter data supporting SBRT as first-line therapy for this disease.”

Even so, external radiation may not even be necessary for some patients with intermediate-risk prostate cancer. Bradley Prestidge, MD, of DePaul Medical Center in Norfolk, VA, reported findings from a phase III trial in which 579 patients received brachytherapy—the direct implantation of radioactive seeds into the prostate—alone, or combined with a form of external beam radiation, such as IMRT. Five years after treatment, the groups had similar progression-free survival rates: 86% and 85%, respectively. However, those in the combination therapy group were significantly more likely to experience side effects requiring medical intervention—for instance, a urinary catheter, Prestidge noted.

“We started our study thinking that the more aggressive combination would result in a superior cancer control rate,” he said. “However, it looks like external beam radiation, with its increased cost and toxicity, is not a required addition in managing intermediate-risk prostate cancer. Brachytherapy alone may well be sufficient.” –Alissa Poh