ESTRO 2023 - Abstract Book

S376

Sunday 14 May 2023

ESTRO 2023

214 patients were treated between 10-2019 and 03-2022, 108 (50%) receiving IMPT, 106 (50%) receiving VMAT and 135 (63%) receiving adjuvant immunotherapy. With IMPT, mean lung dose and mean esophagus dose were significantly lower compared to VMAT (Table 1). In VMAT patients, observed rates of RP and AE corresponded well with predictions (mean NTCP) indicating that the model can be used without adjustment for the model-based clinical evaluation (Table 2). The observed rates of RP and AE after IMPT were significantly lower than predicted both from their VMAT plans made for plan comparison (RP: OR 0.35, 95% CI 0.11-0.61; AE: OR 0.54, 95% CI 0.34-0.81) and IMPT plans (Table 2). After adjusting for confounders, IMPT patients had lower observed RP (OR 0.28, 95% CI 0.09-0.92; p=0.04) and AE rates (OR 0.37, 95% CI 0.17-0.80; p=0.01) compared to observed rates of VMAT patients. The observed RP and AE rates after IMPT were significantly lower than expected based on the NTCP-model, indicating model adjustment is needed for IMPT plans.

Conclusion The observed rates of RP and AE for patients treated with IMPT were significantly lower compared to the predicted rates from their VMAT-plans made for plan comparison and, based on multivariable analysis, compared to the observed rates of VMAT patients. The photon-based NTCP-models for RP and AE predict the NTCP for VMAT accurately but overestimated the risk of RP and AE for IMPT plans. MO-0471 Post-radiotherapy G3+ esophageal toxicity predictors: Pooled data from 2,131 lung cancer patients A. Abravan 1 , H. Mistry 2 , A. Mcwilliam 1 , C. Faivre-Finn 1 , A. Vega 3 , J. López-Guerra 4 , D. de Ruysscher 5 , C. West 6 , A. Salem 7 1 The University of Manchester and The Christie Hospital, Division of Cancer Sciences, School of Medical Sciences, Faculty of Biology, Medicine and Health and Department of Radiotherapy Related Research, MANCHESTER, United Kingdom; 2 The University of Manchester, Division of Cancer Sciences, School of Medical Sciences, Faculty of Biology, Medicine and Health, MANCHESTER, United Kingdom; 3 Instituto de Investigación Sanitaria de Santiago de Compostela, Fundación Pública Galega de Medicina Xenómica, Santiago de Compostela, Spain; 4 University Hospital Virgen del Rocio, Department of Radiation Oncology, Sevilla, Spain; 5 Maastricht University Medical Center, Department of Radiation Oncology (MAASTRO), GROW School for Oncology and Developmental Biology, Maastricht , The Netherlands; 6 The University of Manchester, Division of Cancer Sciences, Translational Radiobiology Group, MANCHESTER, United Kingdom; 7 Hashemite University, Faculty of Medicine, Zarqa, Jordan Purpose or Objective Esophageal toxicity is relatively common following lung cancer radiotherapy. Severe esophageal toxicity (G3+) often necessitates hospital admission and significantly detriments quality-of-life. There are no robust predictors for G3+ esophageal toxicity. We investigated predictors of post-radiotherapy acute G3+ esophageal toxicity from a large lung cancer dataset. Materials and Methods 2,687 patients from 5 studies (2 randomized trials: RTOG-0617 and CONVERT and 3 prospective datasets: MAASTRO, REQUITE and Spanish) were reviewed. Inclusion criteria were lung cancer patients treated with curative-intent radiotherapy (prescribed dose ≥ 40Gy) who were followed-up prospectively. Acute toxicity (within 90 days of radiotherapy completion) was assessed according to Common Terminology Criteria for Adverse Events [versions 3.0-4.0]. The primary endpoint was acute G3+ esophageal toxicity. Univariable and multivariable logistic regression analyses of complete cases were performed using a priori selected variables including sex, age, study, lung cancer type, dose per fraction, planning target volume, smoking status, concurrent chemotherapy and esophageal V35Gy (volume receiving ≥ 35Gy), mean and maximum dose. Both physical dose and EQD2,10 (equivalent dose in 2Gy fractions with α / β =10Gy) were tested. Due to low incidence of the outcome, data from all studies were pooled, and sensitivity analyses were performed by removing one study at a time. Model performance was assessed by calibration plots and receiver operating characteristic area under the curve. Results Of 2,131 patients analyzed, 202 (9.5%, range 2.0-16.5%) developed acute G3+ esophageal toxicity (Table 1). There was a strong correlation between esophageal mean dose and V35Gy (90%, range 83-96%). As the CONVERT trial did not collect mean esophageal dose, V35Gy was selected for analyses of all 5 studies. On multivariable analysis, acute G3+ esophageal toxicity was associated with concurrent chemotherapy (OR=2.9, p=0.03) and esophageal V35Gy (OR=1.02, p<0.0001).