ESTRO 2024 - Abstract Book

S3267

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

This study demonstrates accurate absolute dose measurements using EBT3, EBT-XD, and OC-1 films in conventional electron beams, with the rigorous protocol implemented. To our knowledge, this is the first comparative study of these three film types in an electron beam. In future works, these films will be characterized in FLASHKNiFE's UHDR beams.

Keywords: Film dosimetry, absolute dose mesasurement

References:

(1)Petersson K, Jaccard M, Germond JF, Buchillier T, Bochud F, Bourhis J, Vozenin MC, Bailat C. High dose-per-pulse electron beam dosimetry - A model to correct for the ion recombination in the Advanced Markus ionization chamber. Med Phys. 2017 Mar;44(3):1157-1167. doi: 10.1002/mp.12111. Epub 2017 Feb 28. PMID: 28094853. (2)Jaccard M, Petersson K, Buchillier T, Germond JF, Durán MT, Vozenin MC, Bourhis J, Bochud FO, Bailat C. High dose per-pulse electron beam dosimetry: Usability and dose-rate independence of EBT3 Gafchromic films. Med Phys. 2017 Feb;44(2):725-735. doi: 10.1002/mp.12066. Epub 2017 Feb 8. PMID: 28019660.

1576

Digital Poster

General aS1200 EPID reading-to-dose conversion

Antonella Fogliata 1 , Jack B Liver 2 , Giacomo Reggiori 1 , Luca Cozzi 1

1 Humanitas Research Hospital IRCCS, Radiotherapy, Milan-Rozzano, Italy. 2 Radiqa Development, Physics, Bellinzona, Switzerland

Purpose/Objective:

The most popular electronic portal imaging device EPID currently available on Varian linacs is the Portal Vision aS1200, an amorphous silicon detector. The response of such a detector varies with the beam spectrum and consequently with field size for the entire range of field sizes used in radiotherapy. This is an important characteristic to take into account in the case of the use of those detectors for dosimetric purposes. This work aims to find a general reading to-dose conversion in the primary beam, dependent on field size, valid for any aS1200.

Material/Methods:

Similar to the GLAaS algorithm [1], the EPID reading-to-dose conversion refers to an isocentric set-up at the depth of the maximum dose in a hypothetical water phantom. Output EPID measurements were obtained for different field sizes from 3x3 to 30x30 cm 2 , on a 5 mm central region of interest (ROI) of the aS1200 image irradiated with 50 MU; the detector was positioned at isocentre distance. The same measurements were acquired with an ion chamber in a