ESTRO 2023 - Abstract Book

S795

Monday 15 May 2023

ESTRO 2023

Results Results: Twenty patients with pelvic sarcomas/chordomas treated with CIRT at MedAustron from November 2020 to February 2022 were analyzed. Median follow up was 11.4 months (range, 4.6-25.3). Majority of patients had sacral chordomas (17/20). Sharper penumbra, smaller spot of carbon-ions and PBS technique permitted to limit doses to sacral nerves without significantly compromising target dose coverage (figure 1b). SNSo-CIRT plans were feasible in all patients and robustly optimized against different scenarios. Early follow-up revealed a cumulative incidence of RILSN (grade 1-3) of 15.7% at 2-years. Two (10%) patients developed grade 3 RILSN (CTCAE v5). Median time to develop RILSN was shorter, 4.8 months (range, 2-6)., partly because of curettage surgery for sacral chordoma in one and type II diabetes in another. Higher average maximum doses, Dmax to sacral nerves (76.41 +/- 3.78 vs 68.63 ± 25.24 Gy RBE) and dose to 2cc of nerves, D2cc (71.42 ± 1.19 vs 64.27 ± 23.71 Gy RBE) were observed on mMKM recalculation in RILSN patients (Table 1). Log rank test showed, (LEM) D0.5cc, D1cc and D2% as significant predictors Actuarial 1-year local control rate was 95% and none of the local recurrences could be correlated to nerve sparing strategy. None developed other grade >2 toxicities.

Conclusion Conclusion: RILSN is a potentially serious long-term toxicity. Our preliminary data suggest that sacral nerve sparing is technically feasible and could minimize RILSN. Longer follow up is required to establish local control and RILSN risk analysis. The optimal dose constraints have still to be determined. MO-0947 Lessons learned from RT toxicity outcomes from UK VorteX and IMRiS trials for limb sarcoma R. Simoes 1 , H. Dehbi 2 , S. Gulliford 3 , B. Seddon 4 , M. Robinson 5 , P. Hoskin 6 , S. Forsyth 7 , L. White 8 , P. Gaunt 9 , A. Hughes 9 , E. Miles 10 , K. Harrington 11 , A. Miah 12 1 The Institute of Cancer Research; The Royal Marsden Hospital; University College London Hospitals; RTTQA group, Radiotherapy, London, United Kingdom; 2 Comprehensive Clinical Trials Unit at University College London, Inst of Clinical Trials & Methodology, London, United Kingdom; 3 University College London Hospital NHS Foundation Trust, Radiotherapy Physics, London, United Kingdom; 4 University College London Hospital NHS Foundation Trust, Sarcoma Unit, London, United Kingdom; 5 University of Sheffield, Department of Oncology, Sheffield, United Kingdom; 6 University of Manchester, Division of Cancer Sciences, Manchester, United Kingdom; 7 Cancer Research UK & UCL Cancer Trials Centre, UCL Cancer Trials Centre, London, United Kingdom; 8 Cancer Research UK & UCL Cancer Trials Centre, Cancer Trials Centre, London, United Kingdom; 9 Cancer Research UK Clinical Trials Unit, Clinical Trials Unit, Birmingham, United Kingdom; 10 National Radiotherapy Trials Quality Assurance Group (RTTQA), Mount Vernon Hospital, Northwood, United Kingdom; 11 The institute of Cancer Research, Radiotherapy and Imaging, London, United Kingdom; 12 The Royal Marsden Hospital, Sarcoma Unit, London, United Kingdom

Purpose or Objective