ESTRO 2020 Abstract Book

S323 ESTRO 2020

depends on LET as well as tissue type, dose, dose-rate, fractionation scheme etc. The purpose of this work was to characterize the particle field produced by proton pencil beam at different positions in water to validate Monte

Carlo (MC) simulations. Material and Methods

A hybrid semiconductor pixel detector was used to characterize the energy deposition spectra of mixed radiation field produced by therapeutic proton beams. The Timepix ASIC enables to measure the energy deposition, position and direction of energetic charged particles by high-resolution spectrometric tracking of single particles. In-situ measurements were performed with a Timepix detector equipped with a 300 um silicon sensor in a miniaturized MiniPIX-Timepix camera placed in an in- house designed, thin and waterproof PMMA holder (Fig. 1) and positioned inside a water phantom (BluePhantom, IBA). The calibration was performed with the primary beam in air and was followed by the energy deposition measurements along longitudinal and lateral pencil beam profiles in water. The energy deposition spectra acquired with Timepix were compared to MC simulations performed with GATE MC and GPU-accelerated MC code FRED.

Conclusion We externally validated new Dutch prediction models for dysphagia, grade 2+ and grade 3+, at 6 and 12 mo after treatment. The original grade 2+ model at 6 mo matched the Danish patients well, even though the patient cohorts are substantially different, and will be used to select patients for the DAHANCA35 trial.

Proffered Papers: Proffered papers 30 - Protons and ions

Fig. 1.Experimental setup. Results

OC-0576 Timepix for characterization of mixed radiation field produced in proton radiotherapy P. Stasica 1,2 , J. Baran 1 , J. Gajewski 1 , C. Granja 3 , C. Oancea 4 , M. Pawlik-Niedźwiecka 1 , M. Rydygier 5 , A. Schavi 6 , A. Ruciński 1 1 Institute of Nuclear Physics PAN, Proton Radiotherapy Group, Krakow, Poland ; 2 AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, Krakow, Poland ; 3 ADVACAM s.r.o, ADVACAM s.r.o, Prague, Czech Republic ; 4 ADVACAM s.r.o., ADVACAM s.r.o., Prague, Czech Republic ; 5 Institute of Nuclear Physics PAN, Institute of Nuclear Physics PAN, Krakow, Poland ; 6 Sapienza University of Rome, Sapienza University of Rome, Rome, Italy Purpose or Objective The dosimetric advantage of proton radiotherapy is due to depth-dose distribution (Bragg peak, BP), which enables minimizing deposited dose in healthy tissue and maximizing it in the tumor region. Proton linear energy transfer (LET), characteristic with depth is not precisely reflected in radiobiological effectiveness (RBE) of 1.1, which is currently used in clinical routine and causes uncertainties in biological dose calculations. In fact, RBE

Fig. 2 (top) shows the spectrum of energy deposited by therapeutic proton beams obtained from calibration measurements in air. Fig. 2 (bottom) shows spectrum of energy deposited by all particles produced by 150 MeV proton beam, at ¾ of its range (117 mm), and 6 cm away from the beam core. The corresponding MC simulation shows energy deposited by charged particles, gammas and electrons. The summary of 40 measurements performed at different depths along the pencil beam lateral profiles for primary protons of 100, 150 and 200 MeV will be reported and the discrepancy between experimental and simulation results will be discussed.