ESTRO 2022 - Abstract Book

S96

Abstract book

ESTRO 2022

Conclusion The proposed method constitutes the first successful attempt for an evaluation and assessment of MLC modelling with TPS- independent tests. Our study demonstrates that it is feasible to obtain information on the MLC characteristics with simple measurements. Only small variations were observed in the measurements within a given MLC type, while high variations were found in TPS dose calculations, which highlights the challenges faced by the community to configure MLCs in TPSs. This procedure can be readily incorporated in IMRT audits performed by national and international groups as part of the credentialing required for QA and clinical trials.

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Kerns, IJROBP 2017 Glenn, MedPhys 2019 LoSasso, MedPhys 1998 Arnfield, MedPhys 2000 Hernandez, PMB 2017

Saez, PMB 2020

OC-0121 Improving QA: Increasing resolution of detector arrays in dosimetry systems using a simple add-on

M. van den Bosch 1 , S. van het Schip 1 , H. van Velzen 1 , W. de Kruijf 1

1 Institute Verbeeten, Department of Medical Physics & Instrumentation, Tilburg, The Netherlands

Purpose or Objective In radiotherapy, dosimetry systems with diodes or ionization chambers are commonly used to verify whether the linear accelerator can deliver the treatment plan correctly. By adding more detectors, the measurement resolution can be increased. Another way to increase the measurement resolution is to shift the dosimetry system slightly after the first measurement, repeat the measurement and combine both results. For example, this method is used for the Delta4 (Scandidos; cylindrical solid PPMA phantom with two orthogonal planes with diodes) in the craniocaudal direction. Due to its cylindrical shape the outer contour does not change when shifting the dosimetry system in that direction. Unfortunately, a shift in the other directions will result in a change of the outer contour. This results in a change of the attenuation of the incident beam and consequently a dosimetric error. In this study, we introduce shells that prevent geometry changes when shifting the dosimetry system between measurements (patent pending). By combining the measurement values the resolution can be improved. Materials and Methods Two shells were printed with a 3D printer. They were made of Acrylonitril Butadieen Styreen (1.01g/cc) and printed in 3 parts to ensure an easy (un)mount of the shell onto the Delta4.

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