Localized prostate cancer is typically treated with moderately hypofractionated external beam radiotherapy, allowing patients to complete treatment within 6 weeks with outcomes comparable to those associated with conventionally fractionated radiotherapy, which requires up to 9 weeks to complete. Ultrahypofractionated radiotherapy can cut total treatment course times even further, to 4 to 5 total treatments (1-2 weeks).

But concern about acute radiotoxicities has slowed wider adoption of prostate cancer radiotherapy ultrahypofractionation. The HYPO-RT-PC trial had suggested ultrahypofractionation delivered via 3-dimensional conformal radiotherapy (3dCRT) increased acute toxicities compared to conventionally fractionated radiotherapy.1

The results from the international, randomized, phase 3, open-label PACE-B noninferiority study (ClinicalTrials.gov Identifier: NCT01584258), which delivered ultrahypofractionated treatment using stereotactic body radiotherapy (SBRT), indicated that prostate cancer radiotherapy can be safety shortened without increasing acute gastrointestinal or genitourinary radiotoxicities.2

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Between 2012 and 2018, PACE-B enrolled 874 adult men with low-risk or intermediate-risk prostate adenocarcinoma and WHO performance status scores of 0 to 2, and who were not undergoing androgen deprivation, at 37 cancer centers in the United Kingdom, Ireland, and Canada.2 Patients were randomly assigned 1:1 to receive conventionally fractionated or moderately hypofractionated radiotherapy (78 Gy in 39 fractions over 8 weeks or 62 Gy in 20 fractions over 4 weeks; 441 individuals), or ultrahypofractionated SBRT (36.25 Gy delivered in 5 fractions over 1 to 2 weeks; 433 individuals).2

Grade 2 or higher severe adverse gastrointestinal events were recorded in 53 (12%) of the patients in the conventionally fractionated or moderately hypofractionated radiotherapy study control group vs 43 (10%) of 415 patients in the SBRT ultrahypofractionation group.2 Grade 2 or worse genitourinary radiotoxicities occurred in 118 (27%) of the control group versus 96 (23%) of the SBRT ultrahypofractionation group.2 No treatment-related deaths were reported.

PACE-B is a “very important study,” commented radiation oncologist Thomas Zilli, MD, of Geneva University Hospital in Switzerland. It is the first randomized trial comparing a SBRT ultrahypofractionation schedule and standard-of-care moderate hypofractionation radiotherapy, he noted.

PACE-B’s low overall acute toxicity data “show no difference” with standard moderate hypofractionation, Dr Zilli said.