ICDA-5

Comparative study of the interaction between electron and photon beams in nPAG dosimeter

Jun 9, 2026, 3:44 PM

2m

CTU in Prague, Faculty of Nuclear Sciences and Physical Engineering (Prague, Czechia)

Poster Dosimetry and radiation protection in medicine and biology Poster session

Speakers

Dr Leandro Mariano (Federal Institute of Parana) Anna Luiza Malthez (Federal University of Technology – Paraná)

Description

Dosimetry employing normoxic polyacrylamide gel (nPAG) dosimeters is a promising tool for recording and evaluating three-dimensional (3D) dose distribution in clinical linear accelerators (LINACs). Also, nPAG dosimeters can evaluate several informations required in quality assurance in radiotherapy treatments with photon and electron beams, such as beam profile, flatness and symmetry.
Aiming the application of nPAG dosimeters in clinical dosimetry, we study the interaction of electron and photon beams in nPAG dosimeters. Experimental setup included nPAG dosimeter samples (20 mm diameter, 70 mm height, and mass of 70 g) exposure to 18 MV photon and 18 MeV electron beams from a LINAC (Varian CX), using two orthogonal incident fields (30 Gy in the entrance for each). The Varian’s Eclipse treatment planning system provided the reference dose distribution over nPAG dosimeter samples.
The nPAG dosimeters present 3D polymerization patterns, according to the absorbed dose, that are evaluated via magnetic resonance imaging (MRI). T2-weighted nPAG dosimeter images were acquired with a 1.5 T medical magnetic resonance imaging (MR) (GE Signa). Through post-processing (Matlab 2023 software), 3D reconstruction techniques and slice analysis were performed to evaluate beam divergence and dose deposition in the samples. These results were compared with the simulations from the treatment planning software (Eclipse) and Monte Carlo (Penelope Code System for Monte Carlo Simulation of Electron and Photon Transport).
Reconstructed images allowed examining dose profiles for both photon and electron beams, and 3D distribution of dose, since polymerization in nPAG dosimeter is proportional to absorbed dose. The preliminary experimental results from image reconstruction dosimeter polymerization demonstrate that the electron beam exhibits less scattering in the incident field compared to the photon beam and, as expected, show that dose deposition for the photon beam is more uniform along the interaction path when compared to the electron beam.