Intensity-Modulated Radiotherapy Has Less Harmful Rectal Side Effects

Men with localized prostate cancer treated with a newer technology, intensity-modulated radiation therapy (IMRT), have more than one-quarter (26%) fewer late bowel and rectal side effects and a statistically improved lower dose of radiation to the bladder and rectum, compared to those who undergo three-dimensional conformal radiotherapy (3D-CRT), according to a randomized study.

The study’s findings were presented at the plenary session October 3, 2011, at the 53rd annual meeting of the American Society for Radiation Oncology (ASTRO), held in Miami Beach, FL, USA. Findings also show there is a significant increase (15%) in rectal side effects associated with white men, compared to other races, regardless of the radiation treatment. “The racial differences were definitely surprising and we are still unsure as to why this exists,” stated Jeff Michalski, MD, a radiation oncologist at Washington University Medical Center in St. Louis, (MO, USA). “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.”

3D-CRT is a type of external beam radiation therapy that uses computers and special imaging techniques to tailor precisely the radiation beams so that neighboring normal tissue receives less radiation and is able to heal more rapidly. IMRT is a newer, specialized form of 3D-CRT that allows radiation to be more precisely shaped to fit the tumor and further limits the amount of radiation received by healthy tissue near the tumor. This may also safely allow a higher dose of radiation to be delivered to the tumor, potentially increasing the chance of a cure. This study 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’ goal was to compare the toxicity rates of high dose radiation therapy to standard dose radiation treatment, using IMRT and 3D-CRT. The toxicities were scored from the grade of zero (no toxicity) to four (severe toxicity).

The study also examined what patient characteristics might be associated with toxicity. 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. Findings revealed 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% reduction in grade 2+ late rectal and bowel side effects.

“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,”Dr. Michalski concluded.

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Washington University Medical Center in St. Louis