ESTRO 2024 - Abstract Book

S4842

Physics - Quality assurance and auditing

ESTRO 2024

[1] González A, Castro I, Martínez JA. A procedure to determine the radiation isocenter size in a linear accelerator. Med Phys. 2004 Jun;31(6):1489-93. doi: 10.1118/1.1755491. PMID: 15259652.

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Development and validation of an EPID based software for LINAC QA built on a free Python package

Gloria Miori, Matteo Chieregato, Claudio Rancan, Marco Galelli

Fondazione Poliambulanza, Medical Physics Department, Brescia, Italy

Purpose/Objective:

Quality Assurance (QA) of linear accelerators is an important part of the radiotherapy quality assessment. Recommended tests and tolerances for a LINAC QA program are described in the TG-142 AAPM Report (2) .

Material/Methods:

We developed a software for quantitatively evaluating several TG-142 parameters from EPID images, based on the free python package Pylinac(1). The software has an easy GUI and can be run from Windows computers, without the need of any installation. Parameters attentions levels and action levels can be set in a configuration file. Fields delivery order files are used to be able to automatically rename the acquired images.

The program performs different analysis:

• The first tab evaluates field size, flatness and symmetry; • The second tab analyses Winston-Lutz (WL) images to assess gantry, collimator and couch isocenter sizes and the coincidence between mechanical/radiation isocenter or CBCT/radiation isocenter; • The third tab calculates EPID sag; • The fourth tab assesses MLCs performances (leaf position accuracy and repeatability, abutting fields junctions, moving window IMRT). Both relative and absolute MLC position errors can be calculated; • LINAC performances over time are shown in the fifth tab and the results are automatically stored, to be easily accessible outside the software; date, energy, type of analysis and results are automatically saved each time an evaluation is performed in a LINAC specific excel file; • Reports can be created on the last tab;

All evaluations were tested on 2 Elekta LINACs with Agility head.

Results: