In an analysis from a phase III trial (PACE-C) reported in The Lancet Oncology, Tree et al compared early toxicity rates with intensity-modulated moderately hypofractionated radiotherapy (MHRT) vs stereotactic body radiotherapy (SBRT) in patients with intermediate- and high-risk prostate adenocarcinoma.
The previously reported PACE-B trial showed similar outcomes with MHRT and SBRT in patients with lower-risk disease.
Study Details
In the open-label trial, 1,192 evaluable patients (T1–T3a, Gleason 7–8, prostate-specific antigen = 10–30 ng/mL) from sites in the United Kingdom, the Republic of Ireland, and New Zealand were randomly assigned between November 2019 and June 2022 to receive MHRT at 60 Gy in 20 daily fractions over 4 weeks (n = 608) or SBRT at 36.25 Gy in 5 daily or alternate-day fractions over 1 to 2 weeks (n = 584); patients received an additional mandatory clinical target volume dose of 40 Gy (no margin) to the prostate and proximal 1 cm of seminal vesicles. Patients were planned to receive 6 months of androgen-deprivation therapy started before radiotherapy. The primary outcome of PACE-C is freedom from biochemical or clinical failure (data are immature). The co-primary outcome measures in this preplanned safety analysis were Radiation Therapy Oncology Group (RTOG) grade 2 or worse gastrointestinal and genitourinary toxicities at any point during or within the early period of treatment (ie, 12 weeks of completion of radiotherapy).
Key Findings
During the early period, RTOG grade 2 or worse genitourinary toxicity was observed in 166 patients (27%, 95% confidence interval [CI] = 23.8%–31.1%) receiving MHRT and 162 patients (28%, 95% CI = 24.3%–31.7%) receiving SBRT (absolute difference = 0.5%, 95% CI = –4.7% to 5.7%, P = .89). During the early period, RTOG grade 2 or worse gastrointestinal toxicity was observed in 69 patients (11%, 95% CI = 9.0%–14.2%) receiving MHRT and 74 patients (13%, 95% CI = 10.2%–15.8%) receiving SBRT (absolute difference = 1.4%, 95% CI = –2.5% to 5.2%, P = .53).
No treatment-related deaths were observed.
The investigators concluded: “Despite an accelerated treatment schedule and a larger treated volume than PACE-B, SBRT and MHRT had similar rates of early RTOG toxicity.”
Alison Tree, MD, of Royal Marsden NHS Foundation Trust, London, is the corresponding author of The Lancet Oncology article.
Disclosure: The study was funded by The Royal Marsden Cancer Charity. For full disclosures of all study authors, visit The Lancet Oncology.
