ESTRO 2024 - Abstract Book

S3342

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

Jacob G Johansen 1,2 , Esben T Jensen 3 , Eleni Kanouta 1,2 , Cathrine Overgaard 4 , Brita S Sørensen 2,4 , Per R Poulsen 1,2

1 Aarhus University, Department of Clinical Medicine, Aarhus, Denmark. 2 Aarhus University Hospital, Danish Centre for Particle Therapy, Aarhus, Denmark. 3 Aarhus University, Deparment of Physics and Astronomy, Aarhus, Denmark. 4 Aarhus University Hospital, Department of Experimental Clinical Oncology, Aarhus, Denmark

Purpose/Objective:

The depth-dependent relative biological effectiveness (RBE) is one of the most critical issues in proton therapy yet to be fully understood. Small animal studies play a central role in gaining the appropriate knowledge. The steep dose and RBE gradients, however, require accurate positioning of the irradiation target. Especially, since treatments take place at the distal edge of the spread-out Bragg Peak (SOBP), where a few millimetres offset can change the dose dramatically. In this study, we propose a method to validate both the delivered dose and the 3D positional accuracy in RBE mice studies using proton pencil beam scanning (PBS). The method is based on in vivo dosimetry using a small scintillator-based dosimeter with sub-spot time resolution.

Material/Methods:

Time-resolved in vivo dosimetry was performed during RBE studies, where the right hind leg of 126 mice were given 27-47Gy. Three mice were irradiated at a time in a 3x11x3cm3 field (vertical x horizontal x SOBP depth) created with a PBS technique and 8 energy layers, fig. 1. Half of the mice were placed in the middle (~7cm depth) of the SOBP, and the other half were placed close to the distal edge (~8.2cm depth).