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Characterization of the GATE Monte Carlo platform for non-isocentric treatments and patient specific treatment plan verification at MedAustron - Vienna - Austria

Abstract : The goal of this PhD is to develop and validate an independent dose calculation method in order to support the intense commissioning work of a Light Ion Beam Therapy (LIBT) facility, and to validate the Treatment Planning System (TPS) dose calculation. The work focuses on proton therapy treatments and is held as a collaboration between the CREATIS laboratory (Lyon, France) and the MedAustron - Vienna - Austria Ion Therapy Center (Wiener Neustadt, Austria). At MedAustron - Vienna - Austria, in order to exploit a sharp lateral penumbra for the proton beam as well as to improve the accuracy of the TPS dose calculation algorithms, the air gap between the treatment head window and the patient is reduced by moving the patient towards the treatment head. Therefore, non-isocentric treatments have to be accurately taken into consideration during modeling as well as validation phase as moving the target away from the room isocenter may lead to reduced treatment accuracy. In this study, the parametrization of the proton pencil beam follows the recommendations provided in Grevillot et al. (2011), but including a full nozzle description. Special care is taken to model the pencil beam properties in non-isocentric conditions, including the use of a Range Shifter (RaShi). The characterization of the pencil beam is based solely on fluence profiles measured in air and depth dose profile acquired in water. In addition, the presented model is calibrated in absolute dose based on a newly formalism in dose-area-product presented in Palmans and Vatnitsky (2016). Eventually, a detailed validation is performed in water, for three-dimensional regular-shaped dose distributions. Several parameters commonly exploited in proton dosimetry such as range, distal penumbra, modulation, field sizes and lateral penumbra for proton dosimetry are evaluated for validation purposes. The pencil beam optics model reached an accuracy within the clinical requirement of 1mm/10% and it is not affected by the complexity of non-isocentric treatments and the use of a RaShi. Ranges are reproduced within 0.2 and 0.35 mm (max deviation) without and with range shifter, respectively. The dose difference in reference conditions is within 0.5%. The 3D dose delivery validation in water was within 1.2% at maximum. The agreement of distal and longitudinal parameters is mostly better than 1 mm. The obtained results will be used as a reference for the future clinical implementation of the MedAustron - Vienna - Austria independent dose calculation system. As an example of the potential clinical outcome of the presented work, the patient specific quality assurance measurements performed in water have been successfully reproduced within the clinical requirement of 5% accuracy for a few patients.
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Submitted on : Wednesday, September 11, 2019 - 1:03:28 AM
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  • HAL Id : tel-02283555, version 1


Alessio Elia. Characterization of the GATE Monte Carlo platform for non-isocentric treatments and patient specific treatment plan verification at MedAustron - Vienna - Austria. Medical Imaging. Université de Lyon, 2019. English. ⟨NNT : 2019LYSEI002⟩. ⟨tel-02283555⟩



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