A form of radiation therapy that uses higher doses of radiation but fewer rounds of treatment is as effective as conventional radiation therapy in treating intermediate or high-risk prostate cancer patients, according to a new study.

But even though the technique, called hypofractionated radiation therapy, shaves about two and a half weeks off patient treatment times, it's linked with a slightly higher risk of urinary problems, according to the researchers, sharing the long-term follow-up results of an earlier trial.

The study, the abstract of which was released Monday, is going to be presented next week at the American Society for Radiation Oncology's 2011 annual conference in Miami.

The trial was based on a dosing regimen derived from earlier experiments at Cleveland Clinic, and the idea that fewer, but stronger, doses of radiation would hurt the tumor more than it would injure the surrounding healthy tissue.

"I don't think it has yet been adopted broadly because of the need to acquire longer-term follow-up and determine the risks more completely," Dr. Alan Pollack, lead researcher and chair of radiation oncology at the University of Miami's medical school, told reporters on a call Monday.

The current study, which ran from 2002 to 2006, involved 303 men with intermediate to high-risk prostate cancer. They were randomly assigned to a hypofractionated, or conventional treatment group.

The hypofractionated regimen involved delivering 2.7 Gy per treatment over 5 weeks (total dose, 70.2 Gy), compared with a conventional regimen, which delivered 2 Gy over 7.5 weeks (total dose, 76 Gy).

Both sets of patients were treated with intensity modulated radiation therapy, which allows doctors to sculpt the beam to better target the cancer. The highest risk patients in each group also received two years of hormone therapy.

Both kinds of radiotherapy appeared to be equally effective in controlling the biochemical failure rate. This occurs when prostate-specific antigen levels rise after treatment, often indicating cancer's return. There were 41 cases of biochemical failure in the study, divided about evenly between each group.

After correcting for competing risks, for follow-up more than five years out, less than 10 percent of patients in the hypofractionated group had persistent urine control problems, compared with less than 5 percent of patients in the conventional radiation therapy group.

"We didn't see any statistically significant difference until follow-up was over five years," Pollack said. "It's still lower compared to multiple other reports of urinary side effects after radiation."

There were no significant differences in risks to the bowel, rectum or ability to obtain an erection, Pollack said.

The researchers didn't do a cost-effectiveness analysis, but they said cutting two and a half weeks off treatment time could result in savings to patients, not just in upfront costs, but in time lost from work. "It's hard to put into dollars," though, Pollack said.

The abstract, "Five Year Results of a Randomized External Beam Radiotherapy Hypofractionation Trial for Prostate Cancer," will be presented at 2:15 p.m. on Oct. 3 at ASTRO's 2011 conference in Miami.