San Antonio, October 19, 2015—Hypofractionated radiation therapy (RT), which is delivered in larger doses over a shorter time period than conventional RT, results in similar rates of cure and side effects compared to a longer treatment schedule for some men with low-risk prostate cancer, according to research presented today at the American Society for Radiation Oncology's (ASTRO's) 57th Annual Meeting.

RTOG 0415 was a phase III study conducted from April 2006 to December 2009 across the U.S. and Canada that compared the five-year disease-free survival (DFS) rate of 1,115 men with low-risk prostate cancer. DFS refers to the length of time after the primary treatment for cancer ends that a patient survives without any signs or symptoms of the cancer. Patients in the trial were randomly assigned to receive either hypofractionated RT or a conventional RT schedule. Baseline characteristics were similar between the two groups, including the patients' age (median age 65) and pretreatment prostate specific antigen (PSA) scores (median PSA = 5.4 ng/mL).

The primary purpose of the study was to determine if hypofractionated RT results in five-year DFS that is not lower than conventional RT by more than seven percent. The study also looked at overall survival (OS) rates and patients' biochemical recurrence (which is a rise in PSA levels following treatment).
A total of 1,105 men qualified for the study protocol and were randomized to two groups: conventional RT, consisting of 73.8 Gy in 41 fractions delivered over 8.2 weeks was administered to 547 of the men, while 554 men received hypofractionated RT, consisting of 70 Gy in 28 fractions delivered over 5.6 weeks. At a median follow-up of 5.9 years, the results demonstrated that hypofractionated RT results in similar disease-free survival, as compared to conventional RT for men with low-risk prostate cancer, It is estimated that seven-year disease-free survival rates is 76 percent for patients assigned to conventional RT, and 82 percent for patients assigned to hypofractionated RT.

Comparison of biochemical recurrence and overall survival also met protocol non-inferiority criteria. Additionally, both groups reported a similar rate of Grade 3 late side effects. Of the patients who received conventional RT, 3 percent had gastrointestinal side effects and 5 percent had genitourinary (relating to the genital and urinary organ) side effects, compared to 5 percent of the patients in the hypofractionated RT group who had gastrointestinal side effects and 6 percent who reported genitourinary side effects.

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