ESTRO 2022 - Abstract Book

S1309

Abstract book

ESTRO 2022

This work presents alanine dosimetry for validating a simple setup for small-field localized irradiations of subcutaneous tumors implanted in the flank or in the hind limbs in mice. The setup has a large degree of reproducibility between irradiations, and spares the contralateral side of the mouse, allowing investigation of abscopal effects. Alanine is easy and flexible to use, its size comparable to subcutaneous mouse tumors, which makes it ideal for dosimetric validation in vivo studies.

PO-1528 Investigation on beam quality verification with a detector array in combination with quad wedges

D. Czarnecki 1 , M. Alissa 1,2 , A.A. Schoenfeld 3 , V. Flatten 4,5 , K. Zink 1,5

1 University of Applied Sciences, Institute of Medical Physics and Radiation Protection, Giessen, Germany; 2 University Medical Center Giessen-Marburg, Department for Radiotherapy and Radiooncology, Giessen, Germany; 3 Sun Nuclear Corp., research, Giessen, Germany; 4 University of Applied Sciences, Institute of Medical Physics and Radiation Protection, Giessen, Germany; 5 University Medical Center Giessen-Marburg, Marburg Ion Beam Therapy Center, Marburg, Germany Purpose or Objective Multi-axis ionization chamber arrays can be used for quality assurance and acquisition of linear accelerator specific data. The multi-axis ionization chamber array IC PROFILER (Sun Nuclear Corp., Melbourne, Florida) in combination with quad- wedge accessories can be used to determine the beam quality specifier. In this work, we have investigated the ability of the IC PROFILER to measure the photon beam quality specifier %dd(10) x . For this purpose, a Monte Carlo based model of the detector array was developed and compared against measurements at a clinical linear accelerator (linac). Materials and Methods A Monte Carlo based model of the IC Profiler detector array with 251 cavities and quad wedge accessories was developed in detail according to manufactory drawings using the egs++ class library from the EGSnrc code system. The cross sections of the developed model are presented in Figure 1. The calculated dose distributions in principal D p,x and D p,y as well as diagonal directions D d,p and D d,n behind the wedges were investigated in a 6 MV Elekta Precise radiation field to calculate the dose area ratio DAR : DAR = ( D p,x + D p,y ) / ( D d,p + D d,n ) In addition to the Monte Caro simulations, measurements were performed at a clinical 6 MV linac at the University Medical Center Marburg, Germany. To vary the photon beam quality of the Elekta 6 MV linac, the current of the bending magnet was adjusted.

Figure 1: Monte Carlo based model of the IC PROFILER. A cross section with two of the four quad wedges is shown on the left and a cross section through the chambers on the right. The cross sections are not scaled. Results Figure 2 shows the Monte Carlo calculated dose area ratio DAR as a function of %dd(10) x using linac head models with electron beam spot sizes from 1 to 3 mm full-width-at-half-maximum (FWHM) with electron energies in the range from 5.75 to 6.3 MeV. Figure 2 also presents the measured %dd(10) x values as a function of DAR .