Radiation analysis bolsters intensity-modulated radiation therapy as current standard

May 1, 2012

A comparative effectiveness analysis of three techniques for delivering radiation therapy for the treatment of localized prostate cancer supports intensity-modulated radiation therapy (IMRT) as the current standard.

Men treated with IMRT were less likely to experience cancer recurrence or significant side effects than those who received conventional conformal radiation therapy (CRT), reported first author Nathan Sheets, MD, at the 2012 Genitourinary Cancers Symposium in San Francisco.

The analysis also revealed no advantage to the newest and costliest radiation technique, proton radiation, over IMRT.

The study validates the dramatic rise in the use of IMRT over the past decade, Dr. Chen said. In the past 10 years, IMRT has largely replaced CRT as the main radiation technique for prostate cancer, although data were lacking to support the switch.

"We observed a rapid and near-complete adoption of IMRT as the radiation technique of choice for localized prostate cancer between the year 2000 and 2008," said Dr. Sheets, a radiation oncology resident at the University of North Carolina School of Medicine.

The authors analyzed data from the Surveillance, Epidemiology, and End Results Medicare database of more than 12,000 patients with localized prostate cancer who were treated with one of the three forms of radiation therapy as their initial primary treatment from 2002 to 2007.

The number of patients in each group who required additional cancer treatments after radiation was used as a surrogate for disease control. Propensity score methods were used to balance patient characteristics among the different treatment groups and to minimize biases and confounding factors.

Fewer bowel side effects with IMRT

In comparing 6,666 IMRT-treated and 6,310 CRT-treated patients, IMRT was associated with fewer bowel side effects. The rates of adverse bowel events were 14.7 per 100 patient-years for CRT versus 13.4 per 100 person-years for IMRT, corresponding to a 9% relative reduction in bowel side effects from IMRT.

The IMRT patients also had fewer hip fractures (a 22% relative reduction), although hip fractures were a very uncommon event after radiation (0.8 per 100 patient-years in the IMRT group vs. 1.0 per 100 patient-years in the CRT group). IMRT patients experienced a relative 12% higher rate of erectile dysfunction than those treated with CRT (5.9 vs. 5.3 per 100 patient-years).

Fewer additional cancer treatments were needed after radiation in IMRT patients versus CRT patients (2.5 vs. 3.1 per 100 patient-years), a 19% relative reduction, which suggests better cancer control with IMRT.

"One potential explanation for this is dose escalation with IMRT," said Dr. Sheets.

The comparison between IMRT and proton therapy involved 684 patients treated with proton radiation matched to 684 patients treated with IMRT.

The number of proton radiation centers built in the U.S. has increased rapidly, which suggests that an increase in the use of proton radiation for prostate cancer may be coming in the near future, said Dr. Chen. Proton beam therapy in this study, however, was associated with a higher rate of bowel side effects (17.8 per 100 patient-years vs. 12.2 per 100 patient-years in the IMRT group). There was no significant difference between IMRT and proton therapy in other side effects and additional cancer treatments.

"Currently, there is no clear evidence that proton therapy is better than IMRT," Dr. Chen said.

Two additional comparative effectiveness studies of radiation technique in patients with prostate cancer are planned or are ongoing.

The current study was funded by the Agency for Healthcare Research and Quality.