ESTRO 2024 - Abstract Book

S3217

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

fluence perturbations between f clin and f ref . The PTW microSilicon and microSilicon X can be used down to the 0.5 x 0.5 cm 2 field size fulfilling the tolerance of 5% (IAEA TRS483) which was not necessarily the case with previous models.

Keywords: silicon diodes, component fluence perturbation

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Digital Poster

Dependence on the calibration field in treatment verifications using the 1600SRS liquid array

Roberto Gómez Pardos, MªAurora Vicedo González, MªTrinitat García Hernández, Domingo Planes Meseguer, Domingo Granero Cabañero, Juanjo Rovira Escutia, José Bea Gilabert, Rafael García Mollá, Begoña Bordería Navarro, Patricia Cuesta Calatayud, Maria Luisa Alcaraz Lozano, Álvaro Fernández bernal, Miguel Ángel Beltrán Bonet, Noelia Hidalgo Llopis

Consorcio Hospital general universitario de Valencia, Medical Physics, Valencia, Spain

Purpose/Objective:

2D arrays of ionization chambers or diodes have become an important tool in the verification of patient treatments. An alternative to these are liquid chamber arrays which allow increasing the ratio between the active detection area and the detector area (fill-factor) in order to improve the spatial resolution and to ensure a correct measurement of complex dose distributions containing high dose gradients. These detectors, however, present a dependence on field size and dose rate [1] that manifests itself in VMAT/IMRT treatments, generally highly modulated and consisting of small variable-rate fields that often differ from the calibration field. The aim of this work is to evaluate the dependence on the field size of the PTW 1600SRS liquid chamber array and the influence of the chosen calibration size in order to develop a calibration procedure to verify the doses delivered in radiotherapy treatments.

Material/Methods:

Measurements were carried out on an Elekta Versa_HD with the 1600SRS array consisting of 1521 liquid chambers of 0.003 cm 3 active volume covering an area of 15x15 cm 2 . The detector array was inserted into the PTW Octavius4D phantom. Detector output factors were measured under patient verification conditions for all energies (6MV, 6FFF, 10MV and 10FFF) and for different field sizes (1x1cm 2 to 10x10cm 2 ) normalized to the PTW recommended 4x4cm 2 field. Output factors were measured with the Pinpoint chamber (PTW,Freiburg,Germany) at the isocenter of the Octavius4D phantom applying the TRS-483 factors. All measurements were performed for the maximum nominal rate of each energy.