RTOG 0126: IMRT reduced late bowel, rectal toxicity by 26%

Men treated with intensity-modulated radiation therapy for localized prostate cancer had significantly lower rates of late bowel and rectal adverse effects, and received less radiation to the bladder and rectum vs. patients who underwent 3-D conformal radiation therapy.

Researchers conducted this phase 3 dose-escalation trial to compare the toxicity rates for high dose IMRT vs. 3-D conformal radiation therapy (3-D CRT). IMRT showed a trend for a 26% reduction in grade-2 or higher late gastrointestinal toxicity (P=.099).

Additionally, univariate analysis indicated a statistically significant reduction in late grade-2 or higher gastrointestinal toxicity associated with IMRT (P=.039), despite a small number of events.

"IMRT is associated with significantly less grade-2 rectal and bowel toxicity," Jeff Michalski, MD, said. "We've seen a 26% reduction in the rate of late grade-2 late rectal and bowel side effects, from 22% to 15%, with the use of IMRT. This study shows that IMRT is not only safe and well-tolerated, it is associated with much fewer complications than 3D-CRT, both acute and late, and I believe the study supports the continued use of IMRT in the management of localized prostate cancer."

Michalski, a radiation oncologist at Washington University Medical Center in St. Louis, discussed results from a preliminary analysis Monday during a press conference in advance of the 53rd ASTRO Annual Meeting.

Patients in the 3-D CRT group (n=491) were randomly assigned to 55.8 Gy to the prostate and proximal seminal vesicles followed by 23.4 Gy to the prostate only. Men in the IMRT group (n=257) were treated with 79.2 Gy to the prostate and proximal seminal vesicles.

Median follow-up was 4.6 years in the 3-D CRT group and 3.5 years in the IMRT group.

The rate of grade-2 acute toxicity was 16.9% in the 3-D CRT group, and the rate of grade-3 toxicity was 2.5% compared with 13.9% grade-2 toxicity and 2.4% grade-3 toxicity in the IMRT group. There was no incidence of grade-4 toxicity for 3-D CRT vs. 0.4% for IMRT. There were no cases of grade-5 toxicity in either group.

For late toxicity, 23.6% of patients experienced grade-2 or higher adverse events in the 3-D CRT group compared with 19.9% in the IMRT group. Roughly 9% of patients in the 3-D CRT group experienced grade-3 toxicity compared with 4.7% in the IMRT group. Rate of grade-4 late toxicity was 0.4% in both groups.

There was a statistically significant decrease in grade-2 or higher acute collective gastrointestinal/genitourinary for IMRT on both univariate and multivariate analysis. Researchers did not observe any significant differences between the treatment groups for acute or late grade-2 or higher or grade-3 or higher genitourinary toxicities.

"Across the board, IMRT was always better with the respect to the dose the bladder and rectum were receiving compared to 3-D CRT," Michalski said. "Radiation going to the bladder and rectum only contributes to side effects and toxicity, and the use of IMRT was significantly associated with lower doses to those organs than the older modality."

White men were 15% more likely to experience rectal adverse effects. Michalski called the racial differences "surprising" and said the topic required further study.

For more information:

Michalski J. #2. To be presented at: the 53rd ASTRO Annual Meeting; Oct. 2-6, 2011; Miami Beach.

This shows us that the improved and more costly technology of intensity-modulated radiation therapy does appear to yield real benefit in terms of a significant decrease in toxicity in comparison with 3-D conformal radiation therapy. It's important as we go forward that we prove that the technology advances that we make, particularly when they're associated with increased cost, show benefit or value to the patient.

- Michael L. Steinberg, MD
ASTRO President-elect

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