Dosimetric evaluation of metallic eye shield using flexible dummy eye shield for electron radiotherapy

Abstract

Accurate dosimetry in electron radiotherapy using metallic eye shields is crucial yet challenging, primarily due to limitations of commercial treatment planning system (TPS) algorithms in handling high-density materials and the difficulty of obtaining artifact-free imaging. This study aimed to address these issues by developing a novel tungsten shield design with an off-center handle and a complementary flexible, biocompatible silicone dummy shield fabricated via cast-and-mold techniques using 3D-printed molds. The dummy shield was engineered to enable artifact-free computed tomography (CT) imaging and improve patient comfort. A comprehensive dosimetric evaluation compared Monte Carlo (MC) simulations (TOPAS toolkit, CAD-based models with Al backscatter covers), TPS calculations using the artifact-free CT data, and direct physical measurements (MOSFET detectors at eyelid/lens points, EBT4 Gafchromic film). MC simulations exhibited superior agreement with film dosimetry (gamma passing rate approx. 95 % for 3mm/3 % criteria), significantly outperforming TPS calculations (approx. 74 %). MOSFET measurements further corroborated the accuracy of MC simulations compared to TPS. The findings underscore the clinical utility of the flexible dummy shield for improved simulation and patient comfort and validate the necessity of rigorous MC modeling for precise dose computations around metallic eye shields, thereby overcoming critical limitations in conventional TPS.