The Woodruff School

SUMMARY

In response to radiological or nuclear emergencies, prompt assessment of internal radiation contamination is critical for triage assessment and administration of medical
countermeasures administration. The 2×2” NAIS NaI(Tl) scintillation detectors were selected to construct a scanning system to measure internalized gamma-ray emitting
radionuclide contamination in warfighters. The detector responses were simulated using the Particle and Heavy Ion Transport Code System (PHITS) and validated through benchmark measurements with polymethyl methacrylate (PMMA) slab phantoms that replicated varying human chest wall thicknesses (CWTs) and laboratory check sources to
cover a broad spectrum of gamma energies.
Upon verification, mesh-type anthropomorphic phantoms representing different height and weight groups for both sexes were used to examine correlations of the CWTs in adult
females and chest muscle thicknesses in adult males with the gamma counting efficiencies of detectors positioned at the thoracic region for direct lung contamination. Next, a multi-point detector grid covering critical body areas (cranium, cervical, thoracic, abdomen, and hip) was implemented in PHITS, and gamma depositions from critical radionuclides as defined by the Department of Defense were simulated for all organs of interests. Biokinetic modeling data were incorporated to determine the time-dependent retentions in the organs and the gamma depositions in the detectors.
To optimize the number and position of detectors for contamination characterization, a scoring algorithm was developed by analyzing the pseudo planes across the anterior and posterior of the phantom. The planes were divided into fine meshes, where the gamma fluxes and energies were comprehensively simulated. By applying a convolution matrix to address gamma directionality and an energy-efficiency correction function, the detector array configuration with the most optimal counting statistics were identified for varying radionuclide sources, time post-exposure, and phantom morphometry combinations.

SUBJECT:	Ph.D. Proposal Presentation

BY:	Yi Wei

TIME:	Friday, August 16, 2024, 2:00 p.m.

PLACE:	Boggs Building, 3-47

TITLE:	Design of an In-Vivo Gamma Ray Body Scanner for Assaying Biodistribution of Inhaled Radionuclide Contamination in Warfighters

COMMITTEE:	Shaheen A. Dewji, Chair (NRE) Steven Biegalski (NRE) C.-K. Chris Wang (NRE) Fan Zhang (NRE) Wesley E. Bolch (Biomedical Engineering, University of Florida)

SUMMARY In response to radiological or nuclear emergencies, prompt assessment of internal radiation contamination is critical for triage assessment and administration of medical countermeasures administration. The 2×2” NAIS NaI(Tl) scintillation detectors were selected to construct a scanning system to measure internalized gamma-ray emitting radionuclide contamination in warfighters. The detector responses were simulated using the Particle and Heavy Ion Transport Code System (PHITS) and validated through benchmark measurements with polymethyl methacrylate (PMMA) slab phantoms that replicated varying human chest wall thicknesses (CWTs) and laboratory check sources to cover a broad spectrum of gamma energies. Upon verification, mesh-type anthropomorphic phantoms representing different height and weight groups for both sexes were used to examine correlations of the CWTs in adult females and chest muscle thicknesses in adult males with the gamma counting efficiencies of detectors positioned at the thoracic region for direct lung contamination. Next, a multi-point detector grid covering critical body areas (cranium, cervical, thoracic, abdomen, and hip) was implemented in PHITS, and gamma depositions from critical radionuclides as defined by the Department of Defense were simulated for all organs of interests. Biokinetic modeling data were incorporated to determine the time-dependent retentions in the organs and the gamma depositions in the detectors. To optimize the number and position of detectors for contamination characterization, a scoring algorithm was developed by analyzing the pseudo planes across the anterior and posterior of the phantom. The planes were divided into fine meshes, where the gamma fluxes and energies were comprehensively simulated. By applying a convolution matrix to address gamma directionality and an energy-efficiency correction function, the detector array configuration with the most optimal counting statistics were identified for varying radionuclide sources, time post-exposure, and phantom morphometry combinations.