In an analysis from the phase III PACE-B trial reported in The Lancet Oncology, Brand et al found that shortened treatment courses with stereotactic body radiotherapy did not increase gastrointestinal or genitourinary acute toxicity vs intensity-modulated fractionated radiotherapy in low-risk to intermediate-risk localized prostate cancer.

Study Details

In the open-label trial, 874 men with low-risk or intermediate-risk prostate adenocarcinoma (Gleason score 3 and 4 excluded) from 37 centers in the United Kingdom, Ireland, and Canada were randomly assigned between August 2012 and January 2018 to receive conventionally fractionated or moderately hypofractionated radiotherapy (n = 441) or stereotactic body radiotherapy (n = 433); of these, 432 (98%) patients and 415 (96%) patients received at least one fraction of allocated treatment (per-protocol population).

Conventionally fractionated or moderately hypofractionated radiotherapy consisted of 78 Gy in 39 fractions over 7.8 weeks or 62 Gy in 20 fractions over 4 weeks, respectively. Stereotactic body radiotherapy consisted of 36.25 Gy in five fractions over 1 to 2 weeks. Androgen-deprivation therapy was not permitted.

Data are not yet mature for the primary endpoint—freedom from biochemical or clinical failure. The co-primary outcomes for the acute toxicity substudy were worst grade ≥ 2 Radiation Therapy Oncology Group (RTOG) gastrointestinal or genitourinary toxic effects up to 12 weeks after radiotherapy in the per-protocol population.

Acute Toxicity

Worst acute RTOG gastrointestinal toxicity of grade ≥ 2 occurred in 53 (12%) patients in the conventionally fractionated or moderately hypofractionated radiotherapy group vs 43 patients (10%) in the stereotactic body radiotherapy group (difference = −1.9 percentage points, 95% confidence interval [CI] = −6.2 to 2.4, P = .38). Worst acute RTOG genitourinary toxicity of grade ≥ 2 occurred in 118 patients (27%) vs 96 patients (23%; difference = −4.2 percentage points, 95% CI = −10.0 to 1.7, P = .16). Worst gastrointestinal toxic effects of grade ≥ 3 occurred in four patients (1%) vs one patient (< 1%; difference = −0.7, P = .37). Worst genitourinary toxicity of grade ≥ 3 occurred in 7 patients (2%) vs 10 patients (2%; difference = 0.8 percentage points, P = .47). No treatment-related deaths were reported.

The investigators concluded, “Previous evidence (from the HYPO-RT-PC trial) suggested higher patient-reported toxicity with ultrahypofractionation. By contrast, our results suggest that substantially shortening treatment courses with stereotactic body radiotherapy does not increase either gastrointestinal or genitourinary acute toxicity.”

Nicholas van As, MD, of the Department of Uro-oncology, The Royal Marsden NHS Foundation Trust, London, is the corresponding author for The Lancet Oncology article.

Disclosure: The study was funded by Accuray and the UK National Institute of Health Research. For full disclosures of the study authors, visit thelancet.com.