Intensity-modulated radiation therapy (IMRT) causes fewer bowel and rectal toxicities than 3D conformal radiation therapy, according to study findings to be presented October 3 at the plenary session of the American Society for Radiation Oncology (ASTRO) annual meeting in Miami Beach, FL.
A preliminary analysis of acute and late toxicity in men receiving high-dose radiation therapy revealed that patients in the IMRT arm of the clinical trial experienced 26% fewer late bowel and rectal side effects. In addition, there was a statistically improved lower dose of radiation to the bladder and rectum, according to Dr. Jeff Michalski, a radiation oncologist at Washington University Medical Center in St. Louis.
A surprising finding of the phase III, randomized, dose-escalation trial -- Radiation Therapy Oncology Group (RTOG) 0126 -- was that Caucasian men had 15% more rectal side effects than men of other races. Michalski said that the research team was unsure why this occurred, and the subject will be a topic of further investigation. The phenomenon could represent a real difference in tolerance to treatment, or it could reflect cultural differences in the patients' reporting of their side effects and the physicians' interpretation of these descriptions, he said.
A total of 748 men were randomized to the high-dose arm of the RTOG 0126 trial, which sought to compare the toxicity rates of high-dose radiotherapy and standard-dose treatment. Of the 748 men, 491 were treated with 3D conformal radiation therapy, a type of external-beam radiation that uses special imaging techniques to tailor radiation beams so that normal tissue receives less radiation. Two hundred fifty-seven men received IMRT.
Toxicities were scored from grade 0 (no toxicity) to 4 (severe toxicity), and the researchers examined which patient characteristics might be associated with toxicities. IMRT was associated with a statistically significant decrease in acute grade 2+ rectal/bowel and urinary toxicity. There was also a trend for a 26% reduction in grade 2+ late rectal and bowel side effects, Michalski said.
