Author: Sabrina Campelo, Sandun Y. Jayarathna, Adam D. Melancon, Paige L. Nitsch, Christopher Ryan Peeler, Julianne M. Pollard-Larkin, Ramaswamy Sadagopan, Xiaochun Wang, George Zhao 👨🔬
Affiliation: The University of Texas MD Anderson Cancer Center 🌍
Purpose: Development of an in-house analytical simulation for streamlining photon counting detector (PCD) system protocols through measuring transmitted photon energy spectra through a Hafnium (Hf)-loaded phantom and estimating percent attenuations. This work advances quantitative material decomposition techniques for novel Hf-based imaging/dose enhancement applications.
Methods: An analytical simulation method was developed using MATLAB™ (R2024a) to model X-ray interactions in a two-dimensional phantom (6 cm diameter/2 cm diameter vials loaded with either Hafnium (15-/5-/3-/1-wt%) or cortical bone). Transmitted X-ray energy-spectra were scored on a 2D PCD (12-crystals, 1 cm width) array. Ray tracing was performed (0.5 mm steps) to calculate interaction coordinates inside the phantom with energy-dependent interaction probabilities derived from NIST Compton and photoelectric cross-sections. For comparison, a comprehensive GEANT4 Monte Carlo (G4MC) simulation was performed in the same setup configuration. The filtered 140kVp X-ray beam (3 mm thick fan-beam, 107 incident photons) irradiated the phantom, and transmitted energy spectra were scored (1 keV energy resolution) on each PCD element. Both simulations were repeated on a homogeneous water phantom providing baseline measurements for deriving signal attenuations for each PCD element.
Results: Analytical simulations performed on an Apple M1 MaxTM personal computer (8 performance/2 efficiency cores) agreed with G4MC (performed on a dedicated computing cluster) within ~10% for lower Hf concentrations. MC transmitted X-ray spectrums showed a maximum 100% gamma (3 keV/5% tolerance) passing rate for 1 wt% Hf solution, and ~25% for a 15 wt% Hf solution compared to analytical calculations. Percent attenuation differences for 1 wt% Hf was found to be ~11% between MC/analytical and significantly increased to ~75% for 15 wt% Hf in 65-70 keV energy bins.
Conclusion:
The analytical simulation model enables rapid feasibility checks for early-phase preclinical development of novel contrast agents/radioenancers (Hf-based NBTX3) based phantom studies, detector configurations, reserving the resource-intensive GEANT4 approach for detailed validations.