Medscape Medical News 2009. © 2009 Medscape
 

February 27, 2009 — A 5-week course of high-dose radiotherapy was as effective and well-tolerated as the standard 7.5-week course in reducing the risk for prostate cancer recurrence.

These results are from an interim analysis of a new phase 3 study of men with intermediate- and high-risk disease, which is comparing treatment with standard intensity-modulated radiotherapy (SIMRT) and hypofractionated intensity-modulated radiotherapy (HIMRT).

"We were able to show similar results using a regimen that is 2 and a half weeks less than the standard," commented lead author Alan Pollack, MD, PhD, professor and chair of the Sylvester Comprehensive Cancer Center at the University of Miami Miller School of Medicine, in Florida.

Five weeks is more convenient and less taxing for patients.

"Five weeks is more convenient and less taxing for patients," said Howard Sandler, MD, chair of radiation oncology at the Samuel Oschin Cancer Institute, Cedars-Sinai Medical Center, in Los Angeles, California. Dr. Sandler is not involved in the study, but moderated a press conference at which the study was discussed during the 2009 Genitourinary Cancers Symposium.

The symposium is cosponsored by the American Society for Clinical Oncology, the American Society for Radiation Oncology, and the Society of Urologic Oncology.

The study also indicates that prostate cancer has a higher α/β ratio, a parameter used to determine the optimal dose for treating a particular type of cancer, than previously thought.

"This should cause a rethinking about very short radiotherapy regimens," said Dr. Sandler, explaining that regimens shorter than 5 weeks are dependent on prostate cancer having a low ratio. "The ratio is related to how fast cancers grow. The low ratio allows us to treat with less radiation," he added.

A "small but vocal minority" of radiologists uses very short regimens, said Dr. Sandler. They might need to assess the feasibility of delivering enough radiation in a very short period if there is a new higher ratio, he suggested.

Biochemical Failure Rates Comparable

In the study, Dr. Pollack and his colleagues from the University of Miami and Fox Chase Cancer Center, in Philadelphia, Pennsylvania, compared biochemical failure rates in 152 men with prostate cancer randomly assigned to 38 SIMRT treatments over 7.5 weeks (2.0 Gy per treatment; 76 Gy total dose) and 151 men randomly assigned to 26 HIMRT treatments over 5.1 weeks (2.7 Gy per treatment; 70.2 Gy total dose, but biologically equivalent to 84.4 Gy).

The study design also involved 34 intermediate-risk patients in the SIMRT group who received short-term androgen deprivation (STAD) therapy for a median of 4 months and 102 high-risk patients in the HIMRT group who received long-term androgen deprivation (LTAD) therapy for a median of 24.5 months.

After a median follow-up time of 39 months, 17% of the HIMRT group and 21% of the SIMRT group experienced a biochemical recurrence. The difference was not significant.

There was also no significant difference between treatment groups in the distribution of patients by T-category, Gleason score, pretreatment initial prostate-specific antigen level, or use of STAD or LTAD.

"The goal of the study is to determine if the high-dose shorter course of treatment is better than standard radiotherapy. However, it seems to be about the same," Dr. Sandler told Medscape Oncology.

There was also no significant difference in adverse effects of grade 2 or higher toxicity between the 2 groups. The adverse effects observed most commonly were rectal bleeding and increased frequency and urgency of urination, the researchers said in a statement. However, Dr. Pollack noted that there was the possibility of trends indicating slightly higher biochemical failure in the SIMRT group and slightly higher toxicity in the HIMRT group.

There is a planned end point analysis for biochemical failure in 2 years, he added. If, at the end of the study, there is no difference between the groups, then the α/β ratio could be 6.5, which would have implications in the design of future trials, said Dr. Pollack.

The researchers have disclosed no relevant financial relationships.

2009 Genitourinary Cancers Symposium: Abstract 4. Presented February 26, 2009.