ESTRO 2023 - Abstract Book

S704

Monday 15 May 2023

ESTRO 2023

Conclusion The OPERA trial is the first to demonstrate that a CXB dose escalation is increasing the OP rate with good bowel function. This benefit is optimal if starting treatment in T < 3cm using CXB first. Such a planned rectal preservation appears as a valid option to discuss in MDT and with well informed patient for select tumor and prolonged surveillance after watch and wait. OC-0833 Randomised phase II trial of adaptive image guided bladder radiotherapy: Disease control data R. Huddart 1,2 , A. Birtle 3 , K.C. Cheung 4 , A. Choudhury 5 , F. Foroudi 6 , H. Gribble 7 , C. Griffin 7 , S. Hafeez 7,8 , E. Hall 7 , A. Henry 9 , B. Hindson 10 , R. Lewis 7 , D. McLaren 11 , H. McNair 12,8 , A. Nikapota 13 , A. Omar 7 , O. Parikh 14 , L. Philipps 7 , I. Syndikus 15 , M. Varughese 16 , C. Vassallo-Bonner 17 , A. Webster 18 1 The Institute of Cancer Research, Division of Radiotherapy and Imaging, London, United Kingdom; 2 Royal Marsden Hospital NHS Foundation Trust, Radiotherapy Department, London, United Kingdom; 3 Lancashire Teaching Hospitals NHS Foundation Trust, Cancer Oncology, Preston, United Kingdom; 4 The Institute of Cancer Research , Clinical Trial and Statistics Unit, London, United Kingdom; 5 The Christie NHS Foundation Trust, Translational Radiobiology, Manchester, United Kingdom; 6 Austin Health, Radiation Oncology, Austin, Australia; 7 The Institute of Cancer Research, Clinical Trial and Statistics Unit, London, United Kingdom; 8 The Royal Marsden NHS Foundation Trust, Radiotherapy Department, London, United Kingdom; 9 Leeds Teaching hospitals NHS Trust, Division of Cancer Studies and Pathology, Leeds, United Kingdom; 10 Canterbury District Health Board, Department of Oncology Services, Christchurch, New Zealand; 11 NHS Lothian, Department of Oncology, Edinburgh, United Kingdom; 12 Institute of Cancer Research, Division of Radiotherapy and Imaging, London, United Kingdom; 13 Brighton and Sussex University Hospitals NHS Trust, Clinical Oncology, Brighton, United Kingdom; 14 Lancashire Teaching Hospitals NHS Trust, Oncology, Burnley, United Kingdom; 15 The Clatterbridge Cancer Centre, Department of Radiotherapy, Liverpool, United Kingdom; 16 Royal Devon and Exeter NHS Foundation Trust, Department of Oncology, Exeter, United Kingdom; 17 The Institute of Cancer Research, Patient representative, London, United Kingdom; 18 University College Hospital (UCLH), National Radiotherapy Trials Quality Assurance Group (RTTQA), London, United Kingdom Purpose or Objective Radiotherapy (RT) delivery to the bladder is challenging as it is a mobile, deformable structure. Plan of the day (POD) adaptive image-guided RT and tumour boost dose escalation can optimise treatment of bladder cancer (BC). RAIDER aims to define a feasible, safe schedule for muscle-invasive BC using modern techniques. Materials and Methods RAIDER (ISRCTN 26779187) is an international phase II trial. Participants (pts) had unifocal T2-T4a urothelial BC and were randomised (1:1:2) to standard whole bladder RT (WBRT), standard dose adaptive tumour focused RT (SART) or dose- escalated adaptive tumour boost RT (DART). Two fractionation (f) schedules recruited independently. WBRT & SART dose was 64Gy/32f or 55Gy/20f and DART was 70Gy/32f or 60Gy/20f. For SART & DART, POD (small, medium, large) was chosen daily. Neo-adjuvant chemotherapy (NAC) and concomitant radiosensitising therapy (CTh) were permitted. Primary endpoint is the proportion of RT related CTCAE grade ≥ 3 (G ≥ 3) toxicity occurring 6-18 months (m) after RT. A non-comparative design planned to rule out >20% G ≥ 3 toxicity in DART pts, required 57 evaluable DART pts in each fractionation cohort (90% power, 5% 1-sided alpha). Adverse events (AE) are treatment emergent with RT relatedness assessed blind to treatment. Toxicity analysis is by treatment received in the evaluable population (pts with at least one toxicity assessment 6-18m) and is independent by fractionation. Disease control data (3m local control assessed by cystoscopic biopsy; overall survival) are reported by allocated treatment group for both fractionation cohorts combined. Results 345 patients were randomised between Oct 2015 and Apr 2020: 46/41 WBRT, 46/41 SART and 90/81 DART pts in 32f/20f cohorts respectively. Baseline characteristics were balanced across groups: median age 73/72 years; 85/78% T2; 46/52%