BLUE RIBBON POSTER RADIOPHARMACEUTICALS: Development of a Traceable Am-241 on ZnS Phantom for Quantitative Alpha-Particle Imaging
Abstract
Purpose
With advances in Targeted Alpha Therapy (TAT) preclinical and clinical research, the importance for accurate and traceable dosimetry with sub-organ resolution becomes critical. Current limitations in verifying imaging resolution and activity quantification hinder the standardization of these therapies. This work evaluates the use of a modern digital autoradiography system combined with a printed, traceable 2D reference standard to simultaneously verify imaging resolution and validate activity quantification.
Methods
A Jetlab-4 benchtop dispenser was used for gravimetric drop-on-demand inkjet printing of a 2D phantom. A solution of 241Am in 0.1mol/L HCl, with activity traceable to primary standards at the National Institute of Standards and Technology (NIST), was deposited directly onto a ZnS phosphor screen used in an ionizing-radiation Quantum Imaging Detector (iQID). A bitmap profile of a Derenzo phantom was imported to define the deposition pattern, consisting of 3,338 droplets (approximately 60pL each). The total activity was established using precise gravimetry linked to a standard solution, and the phantom was imaged in the iQID to characterize spatial resolution, activity linearity, and image uniformity.
Results
The Derenzo pattern, with six varying feature sizes, was printed with high precision. iQID calibration parameters, including minimum pixel threshold and camera gain, were optimized to match the known activity to within 0.5%. Subsequently, the imaged activity across the phantom sectors agreed with the dispensed activity to within 1%. Analysis also identified a first-drop effect, characterized by increased droplet mass initially dispensed after idle periods, highlighting a variable for future refinement to improve reproducibility.
Conclusion
The successful printing of 241Am onto ZnS phosphor confirms the feasibility of using inkjet deposition to create quantitative 2D standards for alpha-particle imaging. The agreement to within 1% between dispensed and imaged activity demonstrates both the accuracy of the fabrication method and the reliability of iQID calibration for standardized TAT dosimetry.