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
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
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