ESTRO 2023 - Abstract Book

S212

Saturday 13 May

ESTRO 2023

1 CHU Bordeaux, Radiation Oncology, Bordeaux, France; 2 Montpellier Cancer Institute (ICM) , Radiation Oncology, Montpellier, France; 3 Fédération Francophone de Cancérologie Digestive, university of Burgundy, Biostatistics, Dijon, France; 4 Antoine Lacassagne Cancer Center, Radiation Oncology, Nice, France; 5 Tenon University Hospital, APHP, Sorbonne University, Radiation Oncology, Paris, France; 6 Léon Bérard Cancer Center, Radiotherapy, Lyon, France; 7 Tivoli Clinic, Radiotherapy, Bordeaux, France; 8 Saint-Joseph Hospital group, Oncology, Paris, France; 9 Azuréen Cancer Center, Radiotherapy, Mougins, France; 10 Université Paris Cité, INSERM U1160, Paris, France; 11 Saint Louis Hospital, APHP, Radiotherapy, Paris, France; 12 Hospital of Vendée, Medical Oncology, La Roche sur Yon, France; 13 Daniel Hollard Institute, Radiotherapy, Grenoble, France; 14 Rennes University Hospital, Gastroenterology, Rennes, France; 15 Rennes 1 University, Inserm U1242 COSS, Rennes, France; 16 Poitiers University hospital, Hepatology and Gastroenterology , Poitiers, France; 17 Université Claude Bernard Lyon 1, Radiation Oncology, Lyon, France; 18 Cancer institute, North Paris, Radiation Oncology, Paris, France; 19 Catalan Oncology Center, Medical Oncology, Perpignan, France; 20 University of Bordeaux, BRIC (BoRdeaux Institute of onCology), UMR1312, INSERM, Bordeaux, France Purpose or Objective Chemoradiotherapy (CRT) with intravenous 5-fluorouracil (5FU-IV) and mitomycin C (MMC) is the standard treatment for anal canal cancer. Capecitabine, an oral precursor of 5FU, can be proposed (option) as an alternative to 5FU-IV but its equivalence is not validated. Our study evaluates the efficacy and toxicity of capecitabine compared to 5FU-IV in combination with MMC and conformal intensity modulated radiotherapy (IMRT) in patients treated for squamous cell carcinoma of the anal canal (SCCA) from the FFCD-ANABASE cohort. Materials and Methods Based on the FFCD-ANABASE cohort, a French national prospective multicenter observational study, we compared patients treated with CRT in IMRT, using MMC and 5FU-IV or MMC and capecitabine. The primary endpoint was 3-year recurrence- free survival (RFS). Secondary endpoints included overall survival (OS), anal cancer specific survival (ACSS), colostomy-free survival (CFS), tumor control rate, and toxicity (grade ≥ 3). Results Among 1015 patients treated for non-metastatic SCCA with IMRT between January 2015 and April 2020 in the FFCD-ANABASE cohort, 542 patients (401 women and 141 men) had a concomitant chemotherapy with 5FU-IV and MMC (n=404) or capecitabine and MMC (n=138). The median age was 64 years (35-92). Patient and tumor characteristics were not significantly different between groups. The median radiation dose was 60 Gy (IQ 59.4-64.8). The median follow-up was 35.94 months (95% CI 35.25-36.86). The 3-year RFS was 76.8% for the 5FU-IV-MMC group (95% CI 71.89-80.96%) and 76.59% for the capecitabine-MMC group (95% CI 66.92-83.77%) with no statistically significant difference. The 3-year OS was 85.35% and 82.89%, 3-year ACSS was 90.96% and 89.93%, CFS was 81.7% and 86.2%, respectively for the 5FU-IV-MMC and capecitabine-MMC groups. The tumor control rate was 83.4% for the 5FU-IV-MMC group and 84.8% for the capecitabine-MMC group. Acute toxicity grade 3 or higher was more frequent in the 5FU-IV-MMC group (n=189; 46.8%) compared to the capecitabine-MMC group (n=49; 35.5%), p=0.02. Radiotherapy interruption was required for 41.3% patients in the 5FU-IV- MMC group versus 17.4% in the capecitabine-MMC group, p<0.001. Conclusion Although there is no prospective randomized trial, our observational study showed in a large population of patients treated for SCCA, a similar efficacy of capecitabine compared to 5FU-IV in combination with MMC and IMRT. Treatment with 5FU- IV-MMC appeared to be more toxic, with a significantly higher number of treatment interruptions. Capecitabine is not only equivalent but also has reduced toxicity and should be recommended in combination with MMC and IMRT. OC-0278 Real-time clinical decision-making using motion including dose calculation E. Goodwin 1 , B. Eiben 1 , E. Persson 1 , S. Nill 1 , U. Oelfke 1 1 The Royal Marsden Hospital and the Institute of Cancer Research, The Joint Department of Physics, Sutton, United Kingdom Purpose or Objective We have developed a framework for calculating real-time motion-including dose for Unity MR-Linac patients (Elekta AB, Stockholm). Using this framework we aim to predict whether to intervene during treatment. Intervention may be as simple as pausing delivery to wait for anatomy to revert to a baseline state, or may be complex, such as initiating online replanning. We investigate whether dose data provides a better basis for a prediction model than the motion data alone. Materials and Methods 18 prostate cancer patients (36.25Gy/5#) treated using 9 field IMRT on an MR-Linac were selected. The 3D centroid shift of the CTV was extracted from cine images taken during treatment using an optical flow algorithm. Motion-including and zero-motion real time dose reconstruction were performed as in [1]. After each beam, DVHs for clinical structures were calculated. The CTV coverage and the near-maximum dose to the rectum were selected to determine dose delivery quality. Reduced quality was defined if the motion-including CTV D95% was more than 2% lower, or the rectum D2% more than 2% higher the zero-motion parameter at the end of treatment. A model was made for each DVH parameter (DVHp). The models used 8 separate logistic regressions (LR) scored at the end of delivery of each of the first 8 beams to predict reduced quality. Three approaches to training the models were used: a dose model, using the DVHp for the current and all previous beams, a position model, using the average CTV position during delivery of each beam up to the current, and a dual model, where both dose and position data were used. The models were trained using a leave-one-out method on a per patient basis. If any of the LR predicted reduced quality with a probability >0.75, the overall result for that fraction was scored as reduced quality, and later beams were not assessed. Results For the dose, position, and dual models respectively the CTV D95 prediction sensitivities were 0.47, 0.67 and 0. 47, the specificities were 0.96, 0.91 and 0.96. The Rectum D2% prediction sensitivities were 0.55, 0.90 and 0.54 and specificities Proffered Papers: MR-Linac