ESTRO 2023 - Abstract Book

S375

Sunday 14 May 2023

ESTRO 2023

Conclusion The quantified ICB contribution corroborates the PACIFIC trial finding that ICB provides significant OS improvement following standard cCRT regardless of disease stage and histology, with 8.6% (95% CI: 5.3-12.2%) 2-year OS gain. Intended ICB duration, fraction of tumour PDL1%, and age were significantly associated with the treatment outcomes. Tumour biology and molecular features need to be studied to facilitate patient selection as the benefits from cCRT-ICB may be greater for specific subgroups. MO-0470 IMPT reduces esophageal and pulmonary toxicity compared to VMAT in stage II-IV NSCLC patients A. Hessels 1 , R. Stoffers 1 , A. Niezink 1 , O. Chouvalova 1 , F. Ubbels 1 , A. van der Leest 1 , M. Woltman - van Iersel 1 , P. Deseyne 1 , Purpose or Objective The objective of this study was to evaluate whether observed rates of grade ≥ 2 radiation pneumonitis (RP) and grade ≥ 2 acute esophagitis (AE) in NSCLC patients treated with chemoradiotherapy using either IMPT or VMAT matched predicted rates of toxicity according to the Dutch National Indication Protocol Proton Therapy for Thoracic tumors that is used to select patients for IMPT. Materials and Methods Patients were selected for IMPT or VMAT based on expected reduction of normal tissue complication probabilities ( Δ NTCP) for grade ≥ 2 RP, grade ≥ 2 AE, and/or 2-year mortality based on a treatment plan comparison (VMAT vs IMPT). Toxicity rates of RP and AE were prospectively collected as part of our standard follow-up program (SFP) for lung cancer patients (Clinicaltrials.gov: NCT02421718). To assess the benefit of IMPT over VMAT, model-based clinical evaluation was applied, comparing the observed toxicity rates after IMPT to the expected rates calculated from the VMAT plans made for plan comparison for each patient treated with IMPT. Additionally, observed RP and AE rates were compared with expected rates of the same technique to validate the NTCP-models. Multivariable logistic regression analysis was performed to adjust for potential confounders (WHO performance score, age, smoking status, tumor stage, immunotherapy use and mean radiation doses for heart, lungs and esophagus). H. Elzinga 1 , E. Haan - Stijntjes 1 , E. Korevaar 1 , P. Pisciotta 1 , H. Langendijk 1 , R. Wijsman 1 1 University Medical Center Groningen, Radiation Oncology, Groningen, The Netherlands

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