Hypofractionated Radiotherapy a Viable Option for Intermediate- to High-Risk Prostate Cancer

Delivering higher daily doses of radiation in fewer days (hypofractionation) is as effective as conventional radiotherapy in preventing recurrence of intermediate- or high-risk prostate cancer (PCa) at five years after treatment, according to study findings presented at the American Society for Radiation Oncology annual meeting.
“Hypofractionation is rapidly gaining momentum for many types of cancers. The results presented here bring us much closer to effectively treating prostate cancer in a shorter period of time, with acceptable side effects,” said lead investigator Alan Pollack, MD, Chairman of Radiation Oncology at the University of Miami Miller School of Medicine.

The strategy to compress treatment schedules using hypofractionation is based on years of studies indicating that there could be a radiobiologic advantage to this approach. Prior research has indicated that tumor cells would be killed to a greater degree with hypofractionation than the potentially damaging effects of other treatments on the surrounding normal tissues, namely the rectum, penile structures affecting erections, and bladder. Another newer approach to hypofractionation incorporated into this trial is the use of intensity modulated radiotherapy (IMRT), which further limits dose to the normal tissues. IMRT has proven value in limiting adverse effects in the treatment of PCa with external beam radiotherapy.

The new study involved 303 men with intermediate- or high-risk PCa randomized to receive either hypofractionated IMRT (HIMRT) or conventionally fractionated IMRT (CIMRT). High-risk patients also received androgen deprivation therapy for two years. The patients were followed for up to five years.

Although investigators hypothesized that HIMRT would be superior, they observed similar tumor control rates. Twenty-one biochemical failures occurred in the HIMRT group and 20 occurred in the CIMRT group. The five-year cumulative incidence rates of biochemical failure were 13.9% and 14.4%, respectively. Thus, the hypofractionated approach achieved comparable results with two and a half fewer weeks of treatment.

"This long-term study confirms that hypofractionated radiation … is a practical approach to effectively controlling prostate cancer, as compared to the more standard treatment for men with intermediate to high-risk prostate cancer," Dr. Pollack said.

He noted, however, that a follow-up period longer than five years is needed to have a better idea about the effects of treatment on urinary function. These effects take much longer to appear compared with GI problems, he added.
The two treatment arms had similar adverse effect rates. Grade 2 or higher GU toxicities occurred in 8.9% and 13.8% of the conventional and hypofractionated IMRT groups, respectively. Grade 2 or higher GI toxicities were 4.1% and 5.9%, respectively. The difference between treatment arms was not statistically significant.