Hypofractionated RT Non-Inferior to Conventional RT in Prostate Cancer

A hypofractionated shorter course of radiotherapy (RT) was not inferior to conventional RT in men with localized prostate cancer, according to results of a study presented at the 2016 American Society of Clinical Oncology (ASCO) Annual Meeting, held June 3–7 in Chicago (abstract 5003).

Localized prostate cancer patients are often treated with high-dose RT over 8 to 9 weeks. “The α-β ratio which describes the dose-response of tumors and normal tissues to fractionated RT is low for prostate cancer,” wrote study authors led by Charles N. Catton, MD, of Princess Margaret Cancer Centre in Toronto, in an abstract. “Hence, hypofractionation RT may be more efficacious in prostate cancer.”

The new study included 1,206 men with intermediate-risk disease, randomized to either conventional RT or hypofractionated RT. The conventional regimen included 78 Gy in 39 fractions over 8 weeks (598 patients), and the hypofractionated regimen shortened the course to 4 weeks, with 60 Gy delivered in 20 fractions (608 patients).

The median age of patients was 72 years in the hypofractionated group and 71 years in the standard group, and patients were enrolled across 27 sites in Canada, Australia, and France. Most patients (63% and 64% in the two groups) presented with a Gleason score of 3+4, and about half the patients had a prostate-specific antigen (PSA) in the 5 to 10 ng/mL range.

After a median follow-up of 6 years, there were 166 biochemical-clinical failure (BCF) events in the hypofractionated group and 170 in the conventional group. BCF was defined as any of the following: any semi-annual PSA rise of at least 2 ng/mL above the nadir; local or distant recurrence, including starting androgen deprivation therapy; or death from any cause. The most common BCF event in both groups was PSA failure, followed by death from any cause.

The BCF event rate at 5 years was 21% in both study groups. The hazard ratio (HR) for BCF was 0.99 (90% CI, 0.83–1.19), which met the criteria for non-inferiority (P = .0044). Catton noted that there was no divergence of the survival curves beyond 5 years. Overall survival was also similar between the groups, with an HR of 0.97 (95% CI, 0.71–1.34); there were 76 deaths in the hypofractionated group and 78 in the standard group.

In the acute period, genitourinary/gastrointestinal toxicity grade > 3 was similar between the groups. Though it did not reach statistical significance, late toxicity favored the hypofractionated patients (3.6% vs 5.4% with conventional RT; P = .14). There was also no difference between the treatment arms on various measures of quality of life.

“The shorter radiation regimen is non-inferior to the standard regimen for disease control,” Catton concluded. “Based on patient convenience and cost, the shorter radiation regimen should be considered as a new standard for intermediate-risk prostate cancer.”

W. Robert Lee, MD, of Duke University School of Medicine, was the discussant for the session, and he said that moderate hypofractionation has now been tested and is a proven option. Other trials of “extreme” hypofractionation that would further reduce the course of RT are now ongoing, but such regimens have yet to be proven in this disease setting.