ESTRO 2021 Abstract Book

S197

ESTRO 2021

OC-0289 Comparison of side effects at 2 years in the randomised PACE-B trial (SBRT vs standard radiotherapy) A.C. Tree 1 , E. Hall 2 , P. Ostler 3 , H. van der Voet 4 , A. Loblaw 5 , W. Chu 5 , D. Ford 6 , S. Tolan 7 , S. Jain 8 , A. Martin 9 , J. Staffurth 10 , P. Camilleri 11 , K. Kancherla 12 , J. Frew 13 , D.H. Brand 14 , A. Chan 15 , I.S. Dayes 16 , S. Brown 2 , J. Pugh 2 , S. Burnett 2 , A. Dufton 17 , C. Griffin 2 , M. Mahmud 2 , O. Naismith 1 , N. van As 1 , O.B. of the 18 1 The Royal Marsden NHS Foundation Trust, Department of Oncology, London, United Kingdom; 2 The Institute of Cancer Research, Clinical Trials and Statistics Unit, London, United Kingdom; 3 Mount Vernon Cancer Centre, Department of Oncology, Northwood, United Kingdom; 4 The James Cook University Hospital, Department of Oncology, Middlesbrough, United Kingdom; 5 Odette Cancer Centre, Sunnybrook Health Sciences Centre, Department of Oncology, Toronto, Canada; 6 University Hospitals Birmingham, Department of Oncology, Birmingham, United Kingdom; 7 The Clatterbridge Cancer Centre, Department of Oncology, Birkenhead, United Kingdom; 8 Queen's University Belfast, Department of Oncology, Belfast, United Kingdom; 9 West Suffolk and Addenbrooke’s Hospitals, Department of Oncology, Cambridge, United Kingdom; 10 Velindre Cancer Centre, Department of Oncology, Cardiff, United Kingdom; 11 Churchill Hospital, Department of Oncology, Oxford, United Kingdom; 12 University Hospitals of Leicester, Department of Oncology, Leicester, United Kingdom; 13 Freeman Hospital, Department of Oncology, Newcastle, United Kingdom; 14 The Institute of Cancer Research, Uro-Oncology Unit, London, United Kingdom; 15 University Hospitals Coventry & Warwickshire, Department of Oncology, Coventry, United Kingdom; 16 Juravinski Cancer Centre, Division of Radiation Oncology, Hamilton, Canada; 17 Beatson West of Scotland Cancer Centre, Department of Oncology, Glasgow, United Kingdom; 18 PACE , Trial Investigators, London, United Kingdom Purpose or Objective Prostate stereotactic body radiotherapy (SBRT) is associated with low levels of toxicity but randomised data comparing SBRT with standard radiotherapy schedules is lacking. Here we present late toxicity, to 2 years after treatment, for men treated in the PACE-B trial. Materials and Methods Men with NCCN low/lower intermediate risk prostate cancer (Gleason 4+3 excluded) were randomised (1:1) to 62Gy in 20 fractions/78Gy in 39 fractions over 4-8 weeks (collectively called SOC) or 36.25Gy in 5 fractions (concomitant boost to CTV to 40Gy) over 1-2 weeks (SBRT). Androgen deprivation therapy was prohibited. Patients were recruited from 37 centres across the UK, Ireland and Canada. After 12 weeks post-treatment, men were assessed for side effects 3-monthly for the first 2 years according to CTCAE and RTOG scales. Follow up is ongoing prior to analysis of the primary endpoint of freedom from biochemical/clinical failure. Proportion of participants with grade 2 or higher (G2+) gastrointestinal (GI) and genitourinary (GU) RTOG toxicity and CTCAEs at 2 years are compared between groups using chi-squared test. Kaplan-Meier estimates of cumulative late G2+ toxicity rate at 2 years are presented. Results 874 men were randomised (441 SOC; 433 SBRT); follow-up is complete to two years post treatment. 9% of participants had low risk and 91% had intermediate risk prostate cancer. Median PSA at trial entry was 8.0 ng/ml. Baseline characteristics were similar in both groups. Worst grade CTCAE GI and GU toxicities at 2 years are shown in Table 1. The incidence of G2+ GI toxicities was low with no differences between groups at 2 years: CTCAE: SOC 3.8% v SBRT 4.0%; p=0.87; RTOG: SOC 3.1% vs SBRT 2.0%; p=0.35. Two-year cumulative incidence rates of G2+ CTCAE GI toxicity were 10.0% (95% CI: 7.5% to 13.3%, 42 events) for SOC and 12.2% (9.4% to 15.8%, 51 events) for SBRT. Two-year cumulative incidence rates of G2+ RTOG GI toxicity were 7.6% (95% CI: 5.5% to 10.6%, 32 events) for SOC and 8.4% (95% CI: 6.1% to 11.5%, 35 events) for SBRT. At 2 years, the incidence of CTCAE G2+ GU toxicity was higher with SBRT (6.4% vs 11.1%, p=0.02); the increase in RTOG G2+ GU toxicity was not statistically significant: SOC 2.3% vs SBRT 4.6%; p=0.08. Two-year cumulative incidence rates of G2+ CTCAE GU toxicity were 18.8% (95% CI: 15.4% to 22.8%, 79 events) for SOC and 29.1% (95% CI: 25.0% to 33.7%, 122 events) for SBRT. Two year cumulative incidence rates of G2+RTOG GU toxicity were 12.9% (95% CI: 10.0% to 16.5%, 54 events) for SOC and 20.8% (95% CI: 17.2% to 25.0%, 87 events). The most frequently reported CTCAE GU G2+ toxicity was urinary frequency which peaked at 4.5% at 9 months for SOC and at 8.3% at 15 months for SBRT. Rates of CTCAE and RTOG G3+ GI and GU toxicities at 2 years were <1% for both groups.

Conclusion Side effects from radiotherapy were low in both groups. With 2 years follow-up, SBRT was associated with a higher rate of late G2+ GU toxicities. G3+ toxicity was rare.

OC-0291 IMPORT HIGH trial: Dose escalated simultaneous integrated boost radiotherapy in early breast