Pam Harrison

September 29, 2016

Men with favorable intermediate-risk prostate cancer can be safely and effectively treated with radioactive-seed brachytherapy alone without needing additional external-beam radiation, a phase 3 Radiation Therapy Oncology Group (RTOG) study indicates. The finding represents a paradigm shift, say the researchers, and an outside expert agrees.

"Brachytherapy alone has been used from its inception for many years in patients with low-risk (Gleason 6) prostate cancer, but the dogma has been, if a man has Gleason 7 or higher disease, you shouldn't use brachytherapy alone because it would be inadequate to treat the disease," Bradley Prestidge, MD, medical director, Bon Secours Cancer Institute at DePaul Medical Center, Norfolk, Virginia, told Medscape Medical News.

"But based on our study results, I think we can now say that people should feel fairly comfortable using brachytherapy alone if they have a favorable intermediate-risk patient."

The study was presented during the American Society for Radiation Oncology (ASTRO) 2016 Annual Meeting.

The NRG Oncology/RTOG 0232 study was a phase 3, multi-institutional trial carried out in the United States and Canada between 2003 and 2012.

Its main objective was to evaluate whether external-beam radiotherapy added to transperineal interstitial permanent brachytherapy was associated with better progression-free survival (PFS) and cancer control at 5 years than brachytherapy alone.

"For this study, patients had to have Gleason 7 cancer and the prostate-specific antigen (PSA) had to be below 10 so it was a more favorable type of intermediate-risk prostate cancer," Dr Prestidge said at a press briefing.

Alternatively, the patient's PSA could be as high as 20 but the Gleason score had to be under 7 if the PSA was high, he added.

A total of 588 men were accrued to the study and randomly assigned to the combination group or to the brachytherapy-alone group.

"It was up to the investigator to choose what radioactive seed they wanted to use," Dr Prestidge noted, the choice being radioactive iodine-125 (I-125) or palladium-103 (Pd-103).

Brachytherapy was prescribed to 110 Gy with I-125 or 100 Gy with Pd-103 as a boost dose in the combination group and to doses of 145 Gy or 125 Gy, respectively, in the brachytherapy group.

Men in the combination group received 45 Gy of partial pelvis external-beam therapy, followed by brachytherapy 2 to 4 weeks later.

Median follow-up for all patients was 6.7 years, and a total of 579 patients were evaluable for the primary endpoint.

"Both arms had the same freedom from progression in terms of first failure, either biochemical or other causes, but most of which were biochemical in nature as would be expected," Dr Prestidge noted.

At 5 years, the PFS rate was 85% for the combination group and 86% for the brachytherapy-alone group.

Acute toxicity rates of grade 2 and higher were also nearly identical for the two groups: 28% for the combination group and 27% for the brachytherapy-alone group.

However, late toxicities of grade 2 and greater were more prevalent in the combination group, at 53% compared with 37% for the brachytherapy-alone group (P = .0001).

Severe toxicities were very minimal and the same in both groups, Dr Prestidge added.

"What this means clinically is that men with intermediate-risk prostate cancer may be quite well managed with brachytherapy alone, and this represents a bit of a paradigm shift compared to when the study was originated," Dr Prestidge concluded.

Commenting on the study, press briefing moderator Colleen Lawton, MD, Medical College of Wisconsin, Milwaukee, felt that Dr Prestidge was "underselling" his results.

"When this study opened up, there were people who believed that you could not treat intermediate-risk prostate cancer with anything but the combination of external-beam radiation and brachytherapy, but this study shows that's not true, that patients only need the implants, at least those in the subset as defined by investigators in this trial, " she said.

"So the vast majority of these men don't need the toxicity of external-beam radiation and they don't need the cost of it either," she said.

"I think this is very exciting data and I also think this represents a paradigm shift for us," Dr Lawton added.

Dr Prestidge reports serving on an advisory panel for Varian and IsoRay. Dr Lawton has disclosed no relevant financial relationships.

American Society for Radiation Oncology (ASTRO) 2016 Annual Meeting. Abstract 7. Presented September 26, 2016.

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