ESTRO 2021 Abstract Book

S414

ESTRO 2021

Conclusion This analysis suggests that cCRT leads to delayed but substantially more rapid accelerated tumour repopulation late in radiotherapy treatments of LA-NSCLC. Consequently, overall treatment time should be carefully considered when designing such cCRT treatments. This analysis partly explains the poorer overall survival seen for protracted dose-escalation schedules such as 74 Gy in 7.5 weeks in the Phase III randomised clinical trial - RTOG-0617 . Based on the modelling results, dose-escalation of LA-NSCLC cCRT should be limited to 6 weeks to prevent accelerated tumour repopulation. OC-0528 Model-based assessment of hypoxia dose painting in NSCLC patients treated with PBS proton therapy A. Köthe 1,2 , N. Bizzocchi 1 , S. Safai 1 , A.J. Lomax 1,2 , D.C. Weber 1,3,4 , G. Fattori 1 1 Paul Scherrer Institute, Center for Proton Therapy, Villigen, Switzerland; 2 ETH Zürich, Department of Physics, Zürich, Switzerland; 3 Inselspital Universitätsspital Bern, Radiation Oncology Department, Bern, Switzerland; 4 University Hospital of Zürich, Radiation Oncology Department, Zürich, Switzerland Purpose or Objective To assess the clinical benefit of targeting tumour hypoxia by dose escalation using pencil-beam scanning proton therapy (PBSPT) compared to volumetric modulated arc therapy (VMAT) in NSCLC patients. Materials and Methods