ASTRO: IMRT has fewer side effects than 3D-CRT for prostate cancer

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Men with localized prostate cancer who receive intensity modulated radiation therapy (IMRT) have fewer side effects and receive a lower dose of radiation to the bladder and rectum compared with those who undergo basic 3D conformal radiation therapy (3D-CRT), according to a study to be presented at the 53 rd Annual Meeting of the American Society for Radiation Oncology (ASTRO) in Miami, Oct. 2-6.

The randomized study, conducted by Jeff Michalski, MD, of Washington University Medical Center in St. Louis, and colleagues, was a preliminary analysis of acute and late toxicity in men receiving high dose radiation therapy on a phase III Radiation Therapy Oncology Group (RTOG) dose-escalation trial. The researchers sought to compare the toxicity rates of high dose radiation therapy to standard dose radiation treatment, using IMRT and 3D-CRT. The study also examined what patient characteristics might be associated with toxicity.

Results showed men treated with IMRT had 26 percent fewer late bowel and rectal side effects compared with those who underwent 3D-CRT. There was also a significant increase of 15 percent in rectal side effects associated with white men, regardless of the type of radiation treatment, compared with other races.

"The racial differences were definitely surprising and we are still unsure as to why this exists," Michalski said in a statement. "While it could be a real difference in the tolerance to treatment, it could also represent cultural differences in reporting side effects and physician interpretation of patient descriptions. This will be the topic of further investigation."

The study involved 748 men who were randomized to the high dose arm of the trial. Of this group, 491 were treated with 3D-CRT and 257 with IMRT. Toxicities were scored from the grade of zero (no toxicity) to four (severe toxicity), and findings show that IMRT is associated with a statistically significant decrease in acute Grade 2+ rectal/bowel and urinary toxicity. There was also a trend for a 26 percent reduction in Grade 2+ late rectal and bowel side effects in patients undergoing IMRT compared with patients undergoing 3D-CRT.

"This study supports the continued use of IMRT in the management of prostate cancer. It is a safe and very well-tolerated therapy with fewer complications than 3D-CRT," Michalski said.