Biophysical impact of custom shield materials and apertures on electron beam dosimetry: a Monte Carlo study for clinical applications

PurposeThis study aims to evaluate how different shield materials and aperture sizes impact dosimetric properties within the planning target volume (PTV) across various electron beam energies.Material and MethodsMonte Carlo simulations were performed using a 30 × 30 × 30 cm3 solid water phantom covered with a custom bolus-shield assembly. The phantom was irradiated with 6, 9, and 16 MeV electron beam energies. Shield materials included polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), and lead alloy, while the bolus was made of ABS. Three configurations were tested, each pairing a fixed 0.5 cm thick ABS bolus with one of the shield materials (thicknesses were adjusted based on material properties). For each configuration, aperture sizes of 2 × 2, 5 × 5, and 8 × 8 cm2 were evaluated. Reference simulations were conducted for each energy using a 0.5 cm ABS bolus covering the entire phantom.ResultsOur findings demonstrate that although ABS and PLA require thicker layers and result in wider penumbras than other materials, they are promising shield materials for low- and medium-energy electron beams. These materials improved surface dose coverage, offered superior deep-tissue protection, and eliminated dual hot spots yielding more favorable distributions. Moreover, sensitivity tests confirmed the model's robustness against setup errors up to ± 5°. However, larger angles introduced obliquity effects, establishing a 5° tolerance limit for reliable clinical applications.ConclusionThis study demonstrates that traditional lead shields can be effectively replaced by a custom 3D-printed ABS or PLA unit that functions simultaneously as a bolus and shield. This approach is particularly effective for low and medium electron energies with small-to-moderate apertures, where it enhances surface dose and protects deep tissues more effectively. Ultimately, these findings confirm that tissue-equivalent polymer shields can satisfy clinical radiobiological requirements, offering a viable, non-toxic alternative to lead to optimizing patient safety during superficial cancer treatments.