Intensity-modulated moderately hypofractionated radiotherapy versus stereotactic body radiotherapy for prostate cancer (PACE-C): early toxicity results from a randomised, open-label, phase 3, non-inferiority trial.

BACKGROUND

Moderately hypofractionated radiotherapy (MHRT) is a standard treatment for prostate cancer. Stereotactic body radiotherapy (SBRT) is also effective, and has been shown to be non-inferior to MHRT in a lower-risk group of patients who did not require hormone therapy (PACE-B), but randomised data on toxicity for higher-risk patients are lacking. We aimed to compare the early toxicity of MHRT and SBRT.

METHODS

The randomised, open-label, phase 3, non-inferiority PACE-C trial, conducted at 53 hospitals across the UK, Republic of Ireland, and New Zealand, recruited men aged at least 18 years with intermediate-risk or high-risk histologically confirmed prostate adenocarcinoma (T1-T3a, Gleason 7-8, and prostate specific antigen 10-30 ng/mL) and with WHO performance status of 0-2. Participants were centrally randomly assigned (1:1; non-masked; permuted block size of four and six; stratified by centre and risk group) to MHRT (60 Gy; 20 daily fractions over 4 weeks) or SBRT (36·25 Gy; five daily or alternate day fractions; over 1-2 weeks) with an additional mandatory clinical target volume dose target of 40 Gy (no margin) to the prostate, and proximal 1 cm of seminal vesicles. 6 months of androgen deprivation therapy was planned and was started before commencement of radiotherapy. The primary outcome of PACE-C is freedom from biochemical or clinical failure, the data for which are not yet mature. The co-primary endpoints for this preplanned safety analysis were the percentages of Radiation Therapy Oncology Group (RTOG) grade 2 or worse gastrointestinal and genitourinary toxicities at any point during or within 12 weeks of completion of radiotherapy (the early or acute period). Analyses are by treatment received, with participants included if they had one or more fractions of MHRT or SBRT, regardless of their allocated treatment. Late toxicity and efficacy data are awaited as the trial remains in follow-up. The study was prospectively registered with ClinicalTrials.gov, NCT01584258.

FINDINGS

Between Nov 13, 2019, and June 24, 2022, 1208 participants were randomly assigned (601 to MHRT and 607 to SBRT). 608 patients received MHRT and 584 received SBRT, and thus were included in the study analysis. 1136 (95%) of 1192 patients were White, 20 (2%) were Black or Black British, 17 (1%) were Asian or Asian British, and seven (1%) were Chinese or other. During the early period (within 12 weeks of treatment), the co-primary endpoint of RTOG grade 2 or worse genitourinary toxicity was observed in 166 (27%) of 608 patients (95% CI 23·8 to 31·1) receiving MHRT and 162 (28%) of 582 patients (24·3 to 31·7) after SBRT (absolute difference 0·5%, 95% CI -4·7 to 5·7; p=0·89). For grade 2 or worse genitourinary Common Terminology Criteria for Adverse Events (CTCAE), 170 (28%) of 604 patients had events after MHRT and 195 (34%) of 581 patients had events after SBRT (p=0·050). Grade 3 CTCAE genitourinary toxicity was observed in three (<1%) patients receiving MHRT and three (1%) patients receiving SBRT. For grade 2 or worse gastrointestinal CTCAE, 60 (10%) of 604 patients had an event after MHRT and 96 (17%) of 581 patients had an event after SBRT (p=0·0011). Grade 3 CTCAE gastrointestinal toxicity was observed in three (<1%) patients receiving MHRT and four (1%) patients receiving SBRT. During the early period, the co-primary endpoint of RTOG grade 2 or worse gastrointestinal toxicity was observed in 69 (11%) of 608 patients (95% CI 9·0 to 14·2) receiving MHRT and 74 (13%) of 584 patients (10·2 to 15·8) receiving SBRT (absolute difference 1·4%, 95% CI -2·5 to 5·2; p=0·53). There were no treatment-related deaths.

INTERPRETATION

Despite an accelerated treatment schedule and a larger treated volume than PACE-B, SBRT and MHRT had similar rates of early RTOG toxicity.

FUNDING

The Royal Marsden Cancer Charity.