High-density shielding materials reduced modeled radiotherapy vault footprint by up to 34%

KEY POINTS

• TOPAS Monte Carlo simulations compared conventional concrete with Bi₂O₃ concrete, magnetite-lead, steel-magnetite, datolite-galena, and Yb₂O₃ polymer for shielding 6 MV and 18 MV linac vaults.
• Conventional concrete required a modeled footprint of 165.84 m² per vault. At 6 MV, alternative materials reduced floor area by 17.5–32.3%; at 18 MV, reductions ranged from 21.9–33.9%.
• At 18 MV, modeled areas were 129.52 m² with Bi₂O₃ concrete, 119.65 m² with magnetite-lead, 118.58 m² with steel-magnetite, 114.34 m² with datolite-galena, and 109.66 m² with Yb₂O₃ polymer.
• For the 18 MV worst-case geometry, conventional concrete required a 2.50 m primary barrier, compared with 1.06 m for steel-magnetite, 0.91 m for datolite-galena, and 0.74 m for Yb₂O₃ polymer after dose-based refinement.
• All evaluated materials remained below the 0.1 mSv/week NCRP-151 controlled-area design goal. Worst-case calculated doses were approximately 0.061–0.063 mSv/week, similar to conventional concrete.
• Neutron-dose components for 18 MV remained much smaller than total dose, on the order of 10⁻⁵ mSv/week, although compositions containing lead or other high-Z materials produced somewhat higher neutron components than concrete or Yb₂O₃ polymer.
• The largest space reduction came from Yb₂O₃ polymer, but the authors note that rare-earth content may make it substantially more expensive. Steel-magnetite and datolite-galena concrete may offer more realistic construction pathways.
• This remains a computational design study. Narrow-beam attenuation data required correction for realistic scatter and leakage, and no full-scale experimental vault, construction-cost analysis, mechanical validation, or regulatory implementation was performed.

CLINICAL TAKEAWAY

SOURCE

Journal of Applied Clinical Medical Physics