Author: Omer Abdulaziz Ali, Robin Hill, Nathan Huntelerslag 👨🔬
Affiliation: Waikato Hospital, Hamilton, New Zealand, Central Coast Cancer Centre, Gosford, Australia 🌍
Purpose: Characterizing transmission through eye shields is essential to understanding dose distribution in underlying tissues. This study aims to utilize Monte Carlo (MC) simulations to model and characterize tungsten eye-shield for electron beams.
Methods: The TOPAS MC package (v3.9) was employed to model Varian’s TrueBeam LINAC for 6 and 9 MeV electron beams and tungsten eye-shield with varying thicknesses of Aluminum (AL) caps. The LINAC beam model was validated by comparing percent depth-dose (PDD) and profiles for 4x4 and 10x10 cm² fields measured in a 3D-water phantom using the IBA CC13 ionization chamber and PTW microDiamond detectors. A 2 mm-thick tungsten eye shield (Radiation Products Design, Inc., Albertville, USA) with 0.5 mm and 1 mm-thick AL caps was modeled. PDDs and profiles beneath the eye shield were calculated for the same field sizes and beam energies, both with and without AL caps. Dose distribution beneath the eye shields was measured in a Solid-Water phantom at a 3 mm depth using Gafchromic EBT3 film.
Results: The MC model for the LINAC demonstrated excellent agreement with the measured PDDs and beam profiles with an average gamma passing rate of 98% using a 2%/1mm criterion for both beam energies. Regarding eye-shield simulations, results showed significant dose increases at shield edges were observed at shallower depths. Beam profiles under the shield agreed well with film measurements. For a 10x10 cm² field, transmission values calculated by MC were 3.0% and 2.0% compared to MicroDiamond measurements, without and with a 1 mm AL cap, for 6 and 9 MeV, respectively. Overall, dose distributions beneath the eye-shield generated by MC simulations closely agreed film measurements to within 3%.
Conclusion: This study demonstrates the feasibility of MC simulations for a detailed understanding of dose distributions beneath tungsten eye shields, highlighting their feasibility for accurate dosimetry characterization.