High-performance dosimetric gel for low-dose-rate 3D-printed brachytherapy devices

Objective. Gel dosimeters have traditionally been developed for external beam radiotherapy and high-energy photon applications. However, their use in low-energy photon contexts—such as low-dose-rate (LDR) brachytherapy—remains limited by challenges related to temporal and thermal stability, as well as water equivalency. This study aimed to develop a novel dosimetric gel adapted to low-energy photon emissions from isotopes such as 125 I and to evaluate its performance using radioactive seeds incorporated into mock low-dose-rate 3D-printed brachytherapy implants for eye cancer treatments. Approach. A gel formulation composed of methacrylic and ascorbic acid in gelatin, known as MAGIC, was optimized using agarose (MAGIC-a) and paraformaldehyde (MAGIC-pf). The gel’s thermal and temporal stability and self-polymerization were assessed using magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) relaxometry. Water equivalency was evaluated using Monte Carlo (MC) simulations. The radiation sensitivity of MAGIC-pf gel to 125 I seeds was experimentally measured over two-days, followed by MRI readouts at 1.5T and 3T. For comparison, the gel’s sensitivity to a high-energy, high-dose-rate (HDR) 192 Ir source was also assessed. Dose distributions were evaluated using 3D-printed polymer episcleral plaques. Main results. MAGIC-pf demonstrated superior thermal and temporal stability, along with enhanced MRI readout performance. Sensitivity values of MAGIC-pf exposed to 125 I seeds ranged from 0.155 to 0.388 Gy -1 .s -1 at 1.5T, and from 0.1 to 0.386 Gy -1 .s -1 at 3T. The gel’s sensitivity to a 192 Ir source yielded 0.786 Gy -1 .s -1 at 1.5T. 3D-printed polymer episcleral plaques containing three 125 I seeds with asymmetric radiation emission profiles produced highly reproducible and geometrically precise dose distributions, visualized in 2D and 3D. Significance. MAGIC-pf gel demonstrated excellent temporal and thermal stability, compatibility with HDR and LDR brachytherapy applications, and water equivalency under investigated conditions. The sub-millimetric dose profiles it enables are well-suited to the precision demands of next-generation personalized 3D-printed brachytherapy implants.