BLUE RIBBON POSTER RADIOPHARMACEUTICALS: A Comprehensive Validation of an In-House Preclinical Alpha Irradiation Platform
Abstract
Purpose
This study is to report our recent comprehensive validation of an in-house preclinical alpha irradiation platform with versatile control over fluence rate, energy, temporal, and spatial irradiation patterns.
Methods
We validated the fluence-rate control via linear modulation of source-to-aperture distance for an Am-241 alpha source operated under vacuum and delivered through a fixed 2×2 mm2 Si3N4 exit aperture. Both Monte Carlo (MC) integration over the source-aperture geometry and experimental measurements using CR-39 track counting were performed. Downstream sample-plane fluence rate was determined using an analytical geometric model as a function of aperture-to-sample distance. Alpha-particle energy at the sample plane was validated via CR-39 track diameter measurement, Geant4 and SRIM MC simulations under three conditions: 1) 1mm air gap+0µm Mylar layer; 2) 1mm air gap+2.5µm Mylar layer; and 3) 1mm air gap+7.5 µm Mylar layer. Temporal control using a programmable pneumatic gate-valve system was was tested under different programmed irradiation patterns, and spatial control was validated using a programmable motion stage to generate reproducible irradiation patterns.
Results
MC calcuated fluence rates spanned approximately 101.2 to 2.6 decays·s⁻¹·mm-2 by varying source-to-aperture distance from 57 to 381 mm with source activity of 4.8 MBq. CR-39 measured fluence rates at distances of 279 and 381 mm are 4.8 and 2.6 decays·s⁻¹·mm-2, closely agreeing with MC predictions. Effective sample-plane dose rates decreased with increasing aperture-to-sample distance, consistent with geometric beam expansion. For the three energy conditions, measured alpha track diameters are 17.23±0.48µm, 17.32±0.52µm, and 18.40±0.50µm, which matches with calculated diameters of 17.23±0.02µm, 17.42±0.03µm, and 17.88±0.04µm within 1 standard deviation. Corresponding energies are 4.456±0.041, 4.412±0.046, and 3.456±0.057MeV. Temporal and spatial irradiation tests demonstrated reproducible delivery and pattern fidelity.
Conclusion
The alpha irradiation platform's control of dose rate, energy, temporal delivery, and spatial irradiation patterns has successfully been validated.