Author: David P. Adam, Bryan Bednarz, Tyler J Bradshaw, Wesley S. Culberson, Clifford G. Hammer, Sean Jollota, Ohyun Kwon, Jordan Teague 👨🔬
Affiliation: Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin - Madison, Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University, Department of Radiology, University of Wisconsin - Madison 🌍
Purpose: To quantify absorbed dose to water from 90YCl using thermoluminescent dosimeters (TLDs) and to acquire partial volume corrections for 90YCl positron emission tomography (PET).
Methods: Six hollow spheres (16, 8, 4, 2, 1, 0.5 mL) filled with 1.46 mCi/mL 90YCl solution were placed in a water-filled, cold background Jaszczak phantom. Activity measurements were obtained using a Capintec 55tr radionuclide calibrator whose dial setting for 90YCl has been determined with a NIST-traceable 90Y source. The Jaszczak phantom was imaged 11 hours on a GE Discovery MI PET/CT and reconstructed with three different methods (VPFX-S 192x192, VPFX 192x192, VPFX 256x256). VPFX-S is time-of-flight (TOF) with resolution recovery (SharpIR), and VPFX is TOF without SharpIR. ROI-based recovery coefficients (RC) were evaluated for each sphere. In addition, three waterproof probes containing stacks of 4 TLD-100(LiF) chips were placed at increasing distances from the 16 mL sphere while maintaining the phantom’s imaging geometry. TLDs were passively irradiated for 21 days (501 hours) before readout.
Results: The RC range was ~0.5-0.8 of administered activity concentration depending on the reconstruction method of choice. The TLD dose measurements were [5.0+/-0.1, 4.1+/-0.2, and 2.1+/-0.1] cGy at increasing distance from the 16 mL sphere.
Conclusion: This work lays the foundation for improving 90Y image-based dosimetry by providing physical measurement for future comparison with simulation results.