S2967
Late-Breaking
ESTRO 2026
United Kingdom. 11 The Clatterbridge Cancer Centre NHS Foundation Trust, The Clatterbridge Cancer Centre, Liverpool, United Kingdom. 12 Cardiff University, School Of Medicine, Cardiff, United Kingdom. 13 The Christie NHS Foundation Trust, The Christie, Manchester, United Kingdom. 14 Tata Memorial Centre, Tata Memorial Centre, Mumbai, India. 15 Cancer Trials Ireland, Bon Secours Radiotherapy Cork in Partnership with UPMC Hillman Cancer Centre, Cork, Ireland Purpose/Objective: The role of elective pelvic nodal radiotherapy in prostate cancer remains unclear but has been explored with moderate hypofractionation1,2. SBRT is well-established in low and intermediate-risk prostate cancer3. PACE-NODES (NCT05613023) is a phase 3 randomised trial comparing 5 fraction (f) prostate SBRT (P-SBRT) with 5f prostate and pelvic nodal SBRT (PPN-SBRT) in high-risk patients. Primary outcome is time to biochemical or clinical failure, for which data are not yet mature. Here, we present acute adverse events (AEs) to 12 weeks. Material/Methods: Eligible participants had high-risk localised prostate cancer, defined by T3a-T4 and/or Gleason 8-10 and/or PSA>20ng/ml, receiving 12-36 months hormone therapy. Participants were randomised 1:1 to P-SBRT receiving 36.25Gy/5f or PPN-SBRT, additionally receiving 25Gy/5f to pelvic nodes. Dose guidance followed PACE-C with additional PPN-SBRT constraints based on SPORT. Target sample size was 1128. Clinician-reported acute AEs included CTCAE and RTOG grading at final fraction, then 2, 4, 8 and 12 weeks post-treatment. Primary endpoints for this analysis were CTCAE grade ≥ 2 (G2+) gastrointestinal and genitourinary AEs. Patient-reported outcomes included EPIC-26, IPSS and EQ-5D at baseline and 4 weeks. Results: 1166 patients were recruited (September 2022-July 2025) across 42 UK, 4 Irish and 1 New Zealand sites. Median age was 72.7 years (IQR 67.7-76.5), median baseline PSA 12.2ng/ml (IQR 7.9-21.7). 18 patients did not receive radiotherapy; a further 60 (17 P-SBRT, 43 PPN-SBRT) did not receive allocated treatment, most commonly because dose constraints couldn’t be met. Acute AE data to 12 weeks post-treatment from 1066 participants were analysed by treatment received (555 P-SBRT, 511 PPN-SBRT). The proportions of patients with CTCAE G2+ gastrointestinal AEs within the 12- week period were 20.9% (116/555) P-SBRT and 27.8% (142/511) PPN-SBRT (difference 6.9%, 95% CI 1.7%,12.0%, p=0.009). CTCAE G2+ genitourinary effects were reported for 40.2% (223/555) and 36.0% (183/511) respectively (difference -4.0%, 95% CI - 10.2%,1.5%, p=0.14). Both gastrointestinal and
genitourinary side effects peaked at 2 weeks and were similar between groups by 12 weeks (figure 1). The proportion of patients with minimum clinically important reductions in EPIC-26 bowel scores at 4 weeks was lower for P-SBRT than PPN-SBRT (208/379, 54.9% vs 239/365, 65.5%, difference 10.6%, 95% CI 1.4%,19.8%, p=0.003) but similar for other domain scores (figure 2).
Conclusion: P-SBRT and PPN-SBRT are feasible in a multicentre RCT. PPN-SBRT increases gastrointestinal, but not genitourinary, side effects in the short term but differences resolve by 12 weeks. Ongoing follow-up will yield data on longer-term side effects and cancer control. References: 1. Syndikus, I., et al., PIVOTALboost: A phase III
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