ESTRO 2024 - Abstract Book

S3183

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

189

Digital Poster

Impact of spatial resolution on VMAT pre-treatment verification with gamma index analysis.

Andrea González Rodríguez, Sara Jiménez Puertas, Sergio Lozares Cordero, Raquel Castro Moreno, Javier Diez Chamarro, Marta Sánchez Casi, Tomás González González, David Villa Gazulla, Mónica Hernández Hernández, Almudena Gandía Martínez, José Antonio Font Gómez

Hospital Universitario Miguel Servet, Physics and Radiological Protection Department, Zaragoza, Spain

Purpose/Objective:

Analysis of the effects of spatial resolution in gamma index for VMAT pre-treatment verification plans in radiotherapy.

Material/Methods:

Nine VMAT plans, calculated with Monte-Carlo algorithm for linear accelerator VersaHD (Elekta) in the Monaco TPS, are retrospectively selected. The pre-treatment verification is measured in a matrix1500, with 1405 ionization chambers separated 10 mm in the x and y direction axes, and 7.1 mm diagonally (Figure 1). The gamma index analysis is performed with Verisoft (PTW) software.

Figure 1

The same plan is measured twice with the matrix1500, first time with the phantom located at the isocenter point and secondly with the phantom shifted longitudinally and perpendicular to MLC movement by 5mm. Verisoft software offers a tool, a merge option to increase the spatial resolution of the matrix1500 up to 5 mm using the both measurements. Two gamma index are analyzed, one with the isocenter irradiation shot, and one with the merge option using the both measurements. The gamma index criteria evaluated are Γ(2mm,3%) and Γ(3mm,2%), with a threshold > 10% of the maximum dose. The percentage of points that pass the Γ criterion (GP) or passing rates must be over 95%.