Assessing chest wall thickness sensitivity on <i>in-vivo</i> lung counting efficiency in military-specific mesh-type computational phantoms for warfighter radiation triage

In radiological and nuclear emergencies, military personnel and first responders are at elevated risk of internal contamination via inhalation of airborne radionuclides. Rapid<i>in-vivo</i>assessments are required for efficient triage, regulatory compliance, and medical intervention. This study investigates the impact of chest wall thickness (CWT) on lung counting efficiency using military-specific mesh-type human computational phantoms that represent the current standards and anthropomorphic parameters of U.S. members of the military. A 2″ × 2″ NaI(Tl) scintillation detector with digital base was modeled and benchmarked against experimental measurements using polymethyl methacrylate slab phantoms to assess attenuation effects. Monte Carlo simulations in Particle and Heavy Ion Transport code System were employed to characterize lung deposition of radionuclides, with variations in CWT examined across different anthropometric models. Results demonstrated an inverse exponential relationship between CWT and detector peak counting efficiency, with minor deviations in female phantoms due to geometric constraints. These results support improved calibration approaches for<i>in-vivo</i>radiation detection systems and enable more consistent internal contamination assessments across a range of body types during emergency response operations.