A single session of stereotactic body radiotherapy (SBRT) versus multiple sessions appears safe and effective for controlling disease in men with localized prostate cancer, according to a study published June 18 in JAMA Oncology.
The finding is from a prospective phase I/II trial in 43 patients at low or intermediate risk recruited at five academic centers in Europe and the United States, reported lead author Thomas Zilli, MD, of the Oncology Institute of Southern Switzerland in Bellinzona, and colleagues.
“Single-fraction SBRT is a feasible and well-tolerated treatment strategy that warrants further investigation as a potential option for carefully selected patients with localized prostate cancer,” the group wrote.
SBRT is a form of external-beam radiation therapy that delivers high doses of precisely targeted radiation to tumors. It is an established treatment option for patients with localized prostate cancer and is most commonly delivered in five fractions, the authors explained. However, studies have demonstrated that regimens delivered in four, three, or even two fractions are comparable in terms of outcomes and safety, and in this study the researchers aimed to determine whether a single session can further improve treatment efficiency and resource use.
To that end, the researchers launched the ONE-SHOT trial and recruited 45 men (median age, 72 years old) with low- or intermediate-risk localized prostate adenocarcinoma. Between 2017 and 2022, all patients were treated with a single 19-Gy fraction using volumetric modulated arc therapy (TrueBeam, Varian) with urethra-sparing and intrafraction motion control.
The primary end point was biochemical relapse-free survival (bRFS) at three years, while secondary end points included occurrence of genitourinary, gastrointestinal, and sexual adverse events and quality of life assessment. The median follow-up was 55.3 months.
According to the results, the estimated three-year bRFS was 92.9%. Four patients with intermediate-risk disease experienced biochemical recurrence, including three local relapses. Toxicity at three years was low, with grade 2 genitourinary and gastrointestinal adverse events seen in 10% and 5% of patients, which is consistent with rates reported for five-fraction SBRT, the researchers reported.
One patient experienced grade 3 rectal bleeding at month 12, which resolved by month 18, while grade 2 or higher erectile dysfunction increased from 21% at baseline to 38% at three years.
“The ONE-SHOT trial demonstrated that single-fraction 19-Gy SBRT for localized prostate cancer provides encouraging three-year biochemical control and an acceptable safety profile,” the researchers wrote.
Ultimately, the group noted that the limited statistical power of the trial constrains the interpretability of the findings, with five-fraction SBRT regimens remaining the reference standard. Trials with larger cohorts with longer follow-up are required to confirm a definitive role for single-fraction SBRT, they wrote.
“Nevertheless, the present results deserve serious consideration in regard to the role of single-fraction radiotherapy treatments,” the group concluded.
The full study is available here.