The latest results from the Radiation Therapy Oncology Group (RTOG) 0126 clinical trial studying the effect of radiation therapy (RT) dosage in the treatment of localized prostate cancer in the United States, were presented at the American Society for Radiation Oncology (ASTRO) 56th Annual Meeting.

The study was conducted at 104 U.S. centers and compared high-dose radiation therapy (79.2 Gy), considered to be the standard of care for this group of patients, with standard-dose RT (70.2 Gy) in the treatment of more than 1,500 men with intermediate-risk prostate cancer, (T1b to T2b disease), with Gleason scores ranging from 2 to 7 and prostate-specific antigen (PSA) levels between 10 ng/mL and 20 ng/mL. All patients had negative lymph nodes and no metastases and none had received previous hormone therapy.

One-third of men in the trial received intensity-modulated radiation therapy (IMRT) and two-thirds received 3-dimensional conformal radiation therapy (3D-CRT).

At a follow up of 10 years, no significant difference in overall survival was observed between the two groups, with 66.7% vs 65.6% in high-dose RT vs standard-dose RT, respectively.

Moreover, no increase in toxic side effects was observed between the two groups.

“The conundrum we face now is that high-dose radiation has already become standard of care in this country. I think it is safe to say that high-dose treatment should not be considered mandatory in patients with intermediate-risk prostate cancer, and may be overutilized,” Danny Song, MD, from Johns Hopkins University in Baltimore said in a Medscape interview.

The trial results were divulgated since the study crossed a predetermined futility boundary that indicated the hoped-for 23% reduction in the risk for death would not be reached. This is partly because death due to prostate cancer was very uncommon, occurring in only 3% of all patients and accounting for 13% of all deaths during the trial. However, dose escalation improved local control and distant metastases-free and biochemical disease-free survivals.

There are different factors that can be used to understand if a patient will be a good candidate for lower-dose radiotherapy, such as advanced age (older than 70 years), patients with favorable-risk disease (1 or 2 intermediate-risk factors), less than 50% of cores positive, a PSA velocity below 2 ng/mL per year, and comorbidities.

“Other patients may benefit from dose escalation, but there is no level 1 evidence of survival improvement,” Dr. song concluded.