ESTRO 2024 - Abstract Book

S3416

Physics - Dose calculation algorithms

ESTRO 2024

Keywords: Monte Carlo, Linac Bunker Shielding

References:

Rijken, J., et al., Conservatism in linear accelerator bunker shielding. Australasian physical & engineering sciences in medicine, 2019. 42(3): p. 781-787.

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Differences between clinical 6 MV unflattened dose distributions and pre-treatment dose control

Marcus Krantz 1 , Alma Blombäck 2 , Roumiana Chakarova 1,2

1 Sahlgrenska University Hospital, Department of Medical Physics and Biomedical Engineering, Gothenburg, Sweden. 2 Sahlgrenska Academy at the University of Gothenburg, Department of Medical Radiation Sciences, Gothenburg, Sweden

Purpose/Objective:

An independent check of the planned dose before radiation treatment is an important part of the pre-treatment quality control (QC). Availability of advanced dose calculation algorithms in treatment planning systems (TPS) and implementation of complex treatment techniques, such as 6 MV flattening filter free beams (6FFF), enhance the need to perform 3D dose verification based on patient CT data with an adequate accuracy [1]. The independent dose calculation software used for verification may be commissioned in a similar way as the TPS. However, differences may be observed in the computed dose distributions, particularly in non-homogeneous regions or regions with secondary electron disequilibrium. Analysis of such differences is of interest to be able to understand their origin, to detect errors and systematic dose uncertainties.

The objective of this work was to evaluate clinical 6FFF dose distributions obtained by five established dose calculation algorithms, focusing on quantifying differences from pre-treatment dose control.

Material/Methods:

Dose calculations were performed in patient geometry using clinical plans with 6FFF beams designed in the Eclipse™ TPS for Varian TrueBeam ® accelerators. Eight plans were included: two plans for treatment of prostate cancer, two plans for treatment of brain tumors and four plans for treatment of cancer in the thorax region. All plans, except one, involved a dynamic treatment delivery technique. A Monte Carlo (MC) accelerator model for 6FFF beams was built and validated against experimental measurements from accelerator commissioning. The model was implemented in the MC system developed earlier for pre-treatment QC [2].