No Need to Raise Salvage Radiation Dose After Prostatectomy

By Marilynn Larkin

June 25, 2021

NEW YORK (Reuters Health) - Conventional-dose salvage radiation is sufficient for patients with early biochemical progression after prostatectomy, researchers say.

For the phase 3 SAKK 09/10 trial, Dr. Pirus Ghadjar of Bern University Hospital and colleagues recruited 350 men with biochemical progression after radical prostatectomy (RP) and randomly assigned them to treatment with 64 Gy or 70 Gy to the prostate bed without hormonal therapy.

The primary endpoint was freedom from biochemical progression (FFBP).

The median age at randomization was 67, and the median prostate-specific antigen level was 0.3 ng/ml.

As reported in European Urology, after a median follow-up of 6.2 years, the median FFBP was 8.2 years in the 64 Gy arm and 7.6 in the 70 Gy arm (hazard ratio, 1.14). Six-year FFBP rates were 62% and 61%, respectively.

No significant between-group differences were observed in progression-free survival, time to hormonal treatment, or overall survival.

However, late grade 2 and 3 genitourinary toxicity occurred in 21% and 7.9% of patients in the 64 Gy arm, and 26% and 4% in the 70 Gy arm.

Further, late grade 2 and 3 gastrointestinal toxicity was seen in 7.3% and 4.2% of those in the 64 Gy arm, and 20% and 2.3% in the 70 Gy arm.

The authors conclude, "Conventional-dose SRT to the prostate bed is sufficient in patients with early biochemical progression of prostate cancer after RP."

Dr. Madhur Garg, Clinical Director, Radiation Oncology at Montefiore Health System and a professor at Albert Einstein College of Medicine in New York City commented on the study in an email to Reuters Health. "This is the first-of-its-kind study looking at two different dose levels in a specific patient population, and it confirms that higher doses are not necessary if the disease is microscopic."

"It is our standard practice to use lower (standard) dose in patients who only have microscopic disease," he said. "Patients who have gross disease on MRI are treated with higher dose of radiation."

"The study did not include higher risk patients with gross recurrence or positive margins after surgery, both which are risk factors after surgery where patients have been found to benefit from higher doses of radiation," he noted.

"Research done at Montefiore has shown that prostate cancer patients who recur after surgery do better if radiation therapy is started early, when their PSA is less than 0.5 ng/ml," he said. "In addition, patients who have a declining PSA during radiation therapy are more likely to have long term remission."

Dr. Brent Rose, Assistant Professor, Radiation Oncology at the University of California San Diego also commented by email. Although the trial was well designed, he said, "There are still important caveats to consider."

"First," he noted, "the trial began accruing patients over 10 years ago and all patients completed their treatment before 2014. Since then, radiation techniques such as IMRT and image-guidance have markedly improved. These techniques substantially reduce the side effects of treatment for both the moderate and high dose radiation treatments."

"Second," he said, "the trial was relatively small, which would limit the ability to detect small improvements from higher dose radiotherapy."

"Third, the majority of patients had very low and slowly rising PSA at the time of treatment, indicating that they had a very small amount of cancer," he said. "Many patients will have disease that is more aggressive at the time of treatment, and could require higher radiation doses."

"Incorporation of advanced imaging and identifying which men would benefit from radiation to the pelvic lymph nodes may improve outcomes for men with prostate recurrence after surgery," he added.

Dr. Ghadjar did not respond to requests for a comment.

SOURCE: https://bit.ly/3d7OpLx European Urology, online June 14, 2021.

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