5-Year Data: Hypofractionated Radiation for Prostate Cancer

Bladder Toxicity a Problem

Nick Mulcahy

September 26, 2011

September 26, 2011 — Hypofractionated radiation reduces the treatment time of prostate cancer by 2.5 weeks, compared with conventional radiation, but does not sacrifice efficacy, according to new 5-year data that will be presented at the upcoming annual meeting of the American Society for Radiation Oncology (ASTRO).

However, persistent grade 2 or greater urinary adverse effects were significantly more common in patients treated with hypofractionated therapy at 5 years, according to the lead author Alan Pollack, MD, chair of radiation oncology at the University of Miami Miller School of Medicine in Florida. He spoke at press briefing held in advance of the meeting.

When asked by Medscape Medical News if saving 2.5 weeks of treatment time was worth the potential risk of years of urinary problems for some men, Dr. Pollack replied that "there may be a trade-off with this particular regimen."

The rate of persistent urinary problems seen at 5 years in hypofractionation patients was "less than 10%," compared with "less than 5%" for those treated with conventional radiation in the study, he said.

The rate of late urinary problems was "still rather low" and "extremely favorable" in both study groups, compared with results from other radiotherapy studies, Dr. Pollack emphasized.

The multicenter phase 3 trial of 303 men with intermediate- and high-risk prostate cancer compared a 5-week course of hypofractionated intensity-modulated radiotherapy (HIMRT) with a 7.5-week course of conventional intensity-modulated radiotherapy (CIMRT).

The study hypothesis was that HIMRT would improve efficacy — the rate of prostate cancer biochemical failure — and not increase toxicities, compared with CIMRT. On both counts, the trial was not a success.

The 5-year cumulative incidence rates of biochemical failure were similar — 14.4% for CIMRT (95% confidence interval [CI], 8.8% to 21.5%) and 13.9% for HIMRT (95% CI, 8.4% to 20.9%).

Biochemical failure was defined as an increase in prostate-specific antigen (PSA) score using the nadir + 2 ng/mL definition.

On the bright side, Dr. Pollock said that the long-term rates of bowel/rectal adverse effects and erectile dysfunction were identical for the 2 radiation approaches.

HIMRT is a work in progress, said Michael Steinberg, MD, ASTRO president elect, who moderated the press briefing. "We are learning more about how to do this and who this is best for," explained Dr. Steinberg, who is from the University of California at Los Angeles Health System.

HIMRT is likely to make its way into the treatment of prostate cancer. "We will see more places do this," he said about hypofractionation, especially as these study results "get out there."

HIMRT represents a "change in how we were classically taught," added Dr. Steinberg.

The 5-year data are an update of results previously reported by Medscape Medical News, when the median follow-up was 39 months.

Notably, there was no statistically significant difference in persistent urinary problems early in the study, said Dr. Pollack; the difference emerged only at the planned 5-year analysis.

More Data

The trial compared 76 Gy in conventional 2.0 Gy fractions (CIMRT) with 70.2 Gy in 2.7 Gy fractions (HIMRT), which was estimated to be equivalent to 84.4 Gy in 2.0 Gy fractions, said Dr. Pollack. The men received treatment from 2002 to 2006.

No significant differences were seen between the treatment groups in terms of the distribution of patients by T-category, Gleason score, pretreatment initial PSA, use of androgen-deprivation therapy (ADT), or length of ADT, report Dr. Pollack and colleagues.

There were 41 biochemical failures at 5 years — 20 in the CIMRT group and 21 in the HIMRT group. Six biochemical failures occurred within 6.5 months of either local-regional failure or distant metastasis.

Rates for local-regional failure or distant metastasis were 1.0% for CIMRT and 1.3% for HIMRT at 5 years.

The 5-year cumulative incidence rates for any failure, including 4 deaths, were 15.4% for CIMRT (95% CI, 9.5% to 22.7%) and 15.3% for HIMRT (95% CI, 9.5% to 22.4%).

"The anticipated failure rate of 15% in the HIMRT arm was accurate, but fewer failures were seen in the CIMRT arm at the time of this planned analysis," write Dr. Pollack and colleagues in the study abstract.

Overall, there were no statistically significant differences in late toxicity between the groups, note the authors in the abstract. The grade 2 or higher toxicities for the CIMRT and HIMRT groups were 8.9% and 13.8% (P = .2), respectively, for the genitourinary tract, and 4.1% and 5.9% (P = .5), respectively, for the gastrointestinal tract. However, the genitourinary rates were for any event, including 1-time occurrences, said Dr. Pollack. The rates of persistent urinary problems were, as noted above, appreciably different for the 2 groups.

American Society for Radiation Oncology (ASTRO) 53rd Annual Meeting: Abstract 1. To be presented October 3, 2011.

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