ESTRO 2021 Abstract Book

S388

ESTRO 2021

Conclusion The pilot study of the DAHANCA 35 has demonstrated that the plan comparison in local treatment centres can be used to select patients for proton treatment based on ΔNTCP. However, the comparative proton plan seems to slightly overestimate the benefit of the clinical proton plan, perhaps due to the precautionary principle of a clinical treatment plan and due to variations in target and OAR contouring. Continuous quality assurance of the delineation procedures and an optimal patient flow is crucial in this randomized clinical trial setting. OC-0506 Ultra-fast scintillator-based dosimeter for pencil beam scanning proton FLASH therapy E. Kanouta 1 , J. Johansen 1 , G. Kertzscher 1 , M. Sitarz 1 , B. Sørensen 1,2 , P. Poulsen 1 1 Aarhus University Hospital, Danish Centre for Particle Therapy, Aarhus, Denmark; 2 Aarhus University Hospital, Department of Experimental Clinical Oncology, Aarhus, Denmark Purpose or Objective FLASH is a novel radiotherapy modality where the radiation dose is delivered with ultra-high dose rates (>40Gy/s). It has received massive attention since pre-clinical FLASH studies have shown remarkable normal tissue sparing, with unaltered tumor response, when compared to conventional dose rates. Proton FLASH is currently being investigated due to the possibility of treating deep-seated tumors. Dose rate monitoring with a