ESTRO 2024 - Abstract Book

S2646

Clinical - Urology

ESTRO 2024

NHS Trust, University Hospitals Coventry & Warwickshire, Warwickshire, United Kingdom. 5 The Clatterbridge Cancer Centre NHS Foundation Trust, The Clatterbridge Cancer Centre, Liverpool, United Kingdom. 6 The Hillingdon Hospitals NHS Foundation Trust, Mount Vernon Cancer Centre, Northwood, United Kingdom. 7 South Tees NHS Foundation Trust, The James Cook University Hospital, Middlesbrough, United Kingdom. 8 University Hospitals of Leicester NHS Trust, University Hospitals of Leicester, Leicester, United Kingdom. 9 Sunnybrook Health Sciences Centre, Odette Cancer Centre, Toronto, Canada. 10 The Royal Marsden Hospitals NHS Foundation Trust, Radiotherapy Trial Quality Assurance, London, United Kingdom. 11 Belfast Health and Social Care Trust, Queen's University Belfast, Belfast, United Kingdom. 12 Cambridge University Hospitals NHS Foundation Trust, Addenbrooke's Hospital, Cambridge, United Kingdom. 13 Patient and Public Involvement (PPI) representative, Independent, London, United Kingdom. 14 Cancer Trials Ireland, St. Luke's Radiation Oncology Centre, Dublin, Ireland. 15 Beatson West Of Scotland Cancer Centre, Beatson West of Scotland Cancer Centre, Glasgow, United Kingdom. 16 Cardiff University, School of Medicine, Cardiff, United Kingdom

Purpose/Objective:

The PACE-B trial has established SBRT as a standard of care in low/favourable intermediate risk localised prostate cancer (LPCa). This is the first report of PACE-C which aims to demonstrate non-inferiority of SBRT compared to MHRT for biochemical/clinical failure for intermediate or high-risk LPCa, in combination with androgen deprivation therapy (ADT). Compared to PACE-B, a larger volume of seminal vesicles were permitted to be irradiated in PACE-C hence acute toxicity is of interest; MHRT was 60Gy in 20 fractions (f) rather than the 62Gy/20f used in PACE-B.

Material/Methods:

PACE (NCT01584258) is a phase 3 open-label multiple-cohort RCT. Men with LPCa, stage T1c –T3a, ≤ Gleason 4+4, PSA≤30ng/mL were eligible for PACE -C. Between 11/2019 and 06/2022, 1208 pts (51 centres) were randomised (1:1) to SBRT or MHRT; all were planned to receive 6-12 months ADT. SBRT dose was 36.25Gy/5f in 1-2 weeks (wks), MHRT was 60Gy/20 f in 4 wks. Acute toxicity was assessed at baseline, 2-weekly during MHRT/final day of SBRT, and at 2, 4, 8 & 12 wks post-treatment. Primary acute toxicity outcomes were percentage of pts with grade 2 or higher (G2+) RTOG genitourinary (GU) and gastrointestinal (GI) toxicities during the acute period, compared by Χ 2 test (α 0.025 for each outcome), analysis by treatment received. Other key outcomes were percentage G2+ CTCAE GI and GU toxicities (collected post-treatment only) and percentage of pts with minimally clinically important difference (MCID) in EPIC-26 subdomain scores urinary incontinence (UI) (8 points), urinary irritative or obstructive (UO) (6 points) and bowel (5 points).

Results:

Characteristics of the MHRT (608 treated/601 allocated) and SBRT (584/607) groups respectively were: median age: 72.4 vs 73.1 years; NCCN intermediate risk 63.3% vs 64.6%, high risk 36.7% vs 35.4%; Gleason score≤3+4: 62.4% vs 59.9%, 4+3: 30.8% vs 35.6%, 4+4: 6.8% vs 4.5%; PSA median (IQR) 8.3 (6-12.4) vs 8.5 (6-12.4). RTOG G2+ toxicity was not significantly different for GI events (MHRT 69/606 (11.4%) vs SBRT 75/581 (12.9%), p=0.422; G3+ 3/606 (0.5%) vs 2/581 (0.3%)), nor GU events (MHRT 166/605 (27.4%) vs SBRT 160/579 (27.6%) p=0.94; G3+ 10/605 (1.7%) vs 12/579 (2.1%)). There were differences in CTCAE G2+ GI toxicity: MHRT 60/604 (9.9%) vs SBRT 90/584 (15.4%) p=0.004) but not GU: MHRT 170/604 (28.2%) vs SBRT 194/582 (33.3%) p=0.053. Percentage of pts