A phase 3 trial reports that stereotactic body radiotherapy (SBRT), which takes significantly less time than standard-of-care intensity-modulated fractionated radiotherapy (IMRT), is equally safe for patients with prostate cancer.
The international, open-label PACE-B trial (NCT01584258) randomized 874 men with low- or intermediate-risk prostate adenocarcinoma in a 1:1 ratio to receive either SBRT (36.25 Gy) in five fractions over one to two weeks, or conventionally fractionated or moderately hypofractionated radiotherapy, consisting respectively of 78 Gy in 39 fractions over 7.8 weeks or 62 Gy in 20 fractions over four weeks. Patients were required to have a World Health Organization (WHO) performance status of 0 to 2, and those with a Gleason score of 4 + 3 were excluded. Androgen deprivation was not permitted. The PACE-B trial, which is ongoing, has a primary end point of freedom from biochemical or clinical failure. For this substudy of acute toxicity, which has now been published in The Lancet Oncology, the coprimary outcomes were the worst grade 2 or higher severe Radiation Therapy Oncology Group (RTOG) gastrointestinal and genitourinary toxic effects scores in the 12 weeks following radiotherapy.
Grade 2 or higher severe gastrointestinal toxic events occurred in 10% of 415 patients receiving SBRT compared with 12% of 432 patients receiving IMRT, with a P value of 0.38. Grade 2 or higher genitourinary toxic events also occurred less frequently in the SBRT group (23% vs 27%, P=0.16). There were no treatment-related deaths.
"To our knowledge, we present the first published prospective phase 3 acute toxicity results for random assignment of patients between five-fraction stereotactic body radiotherapy and either conventional or moderately hypofractionated radiotherapy," write the researchers, led by first author Douglas H. Brand, MD, PhD, MRes, Clinical Research Fellow in Oncology at The Institute of Cancer Research, London, and Specialist Registrar in Clinical Oncology at The Royal Marsden NHS Foundation Trust. "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."
"If the data on longer-term side effects and efficacy are also positive, we expect our trial could be practice-changing," commented Dr. Brand. "This would enable us to deliver curative treatment over fewer days, meaning that men would get the same benefit from their radiotherapy while having to spend less time in hospital."
For More Information
Brand DH, Tree AC, Ostler P, et al (2019). Intensity-modulated fractionated radiotherapy versus stereotactic body radiotherapy for prostate cancer (PACE-B): acute toxicity findings from an international, randomised, open-label, phase 3, non-inferiority trial. Lancet Oncol. [Epub ahead of print] DOI:10.1016/S1470-2045(19)30569-8
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