Deformation-Aware Monte Carlo Assessment of a Bi2O3/Thermoplastic Polyurethane Shielding Surrogate Under Tensile Strain and Local Thickness Loss

Flexible shielding polymers may undergo geometric thinning during tensile use or localized damage, but flat-sheet attenuation measurements cannot resolve the resulting spatial loss of protection. A radiation-transport surrogate comprising 60 wt% thermoplastic polyurethane and 40 wt% Bi2O3 (modeled density, 1.835 g cm−3) was investigated using prescribed deformation, Geant4, PHITS, Phy-X/XCOM, and 60–120 kVp SpekPy spectra. This is a computational transport model, not a mechanically or experimentally validated formulation. Geant4 mass attenuation coefficients were verified against Phy-X at six energies (30–100 keV) and against XCOM at 90, 91, 92, and 95 keV across the Bi K-edge. Constant-volume uniform strain of 50% raised whole-field transmission by 14.8–32.8%; an illustrative transverse-response sensitivity quantified the dependence of thickness and attenuation on the prescribed kinematics. At 50% local thinning, whole-field transmission increased by only 5.66–15.0%, whereas 5-million-history event-based ROI scoring gave dose enhancement factors of 2.435±0.106, 1.823±0.064, 1.508±0.048, and 1.395±0.042 at 60, 80, 100, and 120 kVp, respectively. Additional 60 kVp calculations varied the defect dimensions, ROI size, and detector position, revealing the influence of spatial averaging. Beer–Lambert attenuation accounts for the primary response to prescribed uniform thinning; the Monte Carlo framework additionally resolves polychromatic scatter, spectral changes, and localized dose enhancement. These numerical results characterize idealized geometric perturbations and should not be interpreted as measurements of real garment durability or clinical dose.