ESTRO 2024 - Abstract Book

S3401

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

Comparable G-values are obtained applying both methods for generating inter-track interactions in TOPAS-nBio using the IRT chemistry approach, whereas difference can be up to 4% at the end of the chemical stage of the simulation depending on the examined molecule type. Thus, both methods are suitable tools for investigating inter-track interactions. However, applying the IRT chemistry instead of the SBS approach with the phsp method, can lead to differences in the G-values of 22%. For this reason, the phsp method offers a considerable advantage compared to the TsIRTInterTrack methods since the latter cannot be simulated with the SBS approach. This approach is in general considered as more accurate for chemical simulations but requires significantly more computing time.

Keywords: inter-track interaction, FLASH, Monte Carlo

References:

[1] Derksen, L., Flatten, V., Engenhart-Cabillic, R., Zink, K., & Baumann, K. S. (2023). A method to implement inter-track interactions in Monte Carlo simulations with TOPAS-nBio and their influence on simulated radical yields following water radiolysis. Physics in Medicine and Biology.

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Digital Poster

Determination of the correction factor k Q of PTW Semiflex3D for reference dosimetry at ZAP-X system

Katrin Saße 1 , Karina Albers 1 , Daniela Eulenstein 2 , Georg Weidlich 3 , Björn Poppe 1 , Hui Khee Looe 1

1 Carl von Ossietzky University, University Clinic for Medical Radiation Physics, Oldenburg, Germany. 2 PTW Freiburg, PTW, Freiburg, Germany. 3 ZAP Surgical, ZAP, San Carlos, USA

Purpose/Objective:

The ZAP-X system is a fully shielded radiosurgery system for the treatments of small brain lesions. The system consists of a 3 MV linear accelerator and eight collimators with diameters between 4 and 25 mm. According to manufacturer’s recommendation, reference dosimetry is performed with the largest 25 mm collimator at a source-to-surface distance (SSD) of 45 cm using a PTW Semiflex 3D ionization chamber (Type 31021, PTW Freiburg, Germany). The chamber is usually positioned at a measurement depth of 7 mm in water, which corresponds to the depth of the dose maximum. Since existing dosimetry protocols do not provide correction factor to account for the influence of beam quality for these measurement conditions, Monte Carlo simulations are performed in this study to quantify the associated beam quality correction factor k Q for this purpose.

Material/Methods:

The absorbed dose to water D W for the beam quality Q can be obtained as D W = M ⋅ N D,W ⋅ k Q , where M is the measured signal, corrected for influence quantities, and ND,W is the chamber-specific calibration coefficient obtained with a