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 as¹²⁵I and to evaluate its performance using radioactive seeds incorporated into mock LDR 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 simulations. The radiation sensitivity of MAGIC-pf gel to¹²⁵I seeds was experimentally measured over two-days, followed by MRI readouts at 1.5 T and 3 T. For comparison, the gel's sensitivity to a high-energy, high-dose-rate (HDR)¹⁹²Ir 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 to¹²⁵I seeds ranged from 0.155 to 0.388 Gy^-1·s^-1at 1.5 T, and from 0.1 to 0.386 Gy^-1·s^-1at 3 T. The gel's sensitivity to a¹⁹²Ir source yielded 0.786 Gy^-1·s^-1at 1.5 T. 3D-printed polymer episcleral plaques containing three¹²⁵I 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.