ESTRO 2022 - Abstract Book

S1372

Abstract book

ESTRO 2022

This study investigated how to deal with the presence of breast expanders in the radiotherapy treatment process. The high density materials affects the image quality and accuracy of dose calculations. This study shows that a density override of magnet and port with titanium is in best agreement with radiochromic film measurements.

Poster (digital): Imaging acquisition and processing

PO-1591 A simple proton-radiography system for accurate RSP measurements in proton therapy

F. Olivari 1 , E. van der Graaf 1 , M. van Goethem 1 , S. Brandenburg 1

1 University Medical Center Groningen (UMCG), CRCG, Groningen, The Netherlands

Purpose or Objective Proton radiography (pRG) can be used to optimize proton relative stopping power (RSP) predictions from X-ray-imaging- based techniques to improve the quality of proton therapy treatment plans. In this work, we present a simulation study for a simple pRG-system with the potential of being routinely used in the clinic and with sufficient RSP accuracy to be used for improving X-ray-based RSP predictions. Materials and Methods The simulated pRG-system consists of a thin and finely 2D-pixelated detector measuring the energy deposited by primary protons (protons produced at the source) and their fluence distribution. The mean energy deposited per primary proton is converted into residual range in water with a calibration function. By irradiating the detector without and with a sample placed before the screen the RSP of the material is obtained from the residual range difference and sample thickness. The RSPs of 12 different materials (Gammex human-tissue-equivalent materials, plastics, metals, and carbon) have been determined from Monte Carlo simulations. To estimate the accuracy of our method in the simulation framework, the RSPs obtained with the screen are compared with reference RSPs obtained from simulations of irradiations of a water tank in which the residual range of protons is determined: the RSP of a material is derived from the range shift with a sample before the tank and the sample thickness. The system is realized experimentally with a scintillator screen coupled with a CCD camera (Figure 1): the light yield, which is proportional to the energy deposit in the screen, is measured. The mean light yield per incident primary proton is calculated using the data of the fluence distribution scored with simulations as a proxy of the real fluence distribution, and it is converted into residual range in water. For the materials considered in simulations, the experimental RSPs are determined with the screen and compared with reference RSPs derived from residual range measurements in a water tank.