Assessing and Modulating Tumor Dose Coverage of Unsealed Radionuclide Therapies using Voxel Dosimetry

<p>This work interrogates absorbed dose metrics for spherical tumors under various configurations with emerging theragnostic radionuclides to understand the true dose being delivered to key points in and around the tumor and how real imaging systems effect the accuracy of these doses. Dose volume kernels (DVK) were generated in TOPAS Monte Carlo for 32P, 64Cu, 67Cu, 90Y, 131I, 153Sm, 161Tb, 166Ho, and 177Lu. These were generated with a fine resolution of (0.1 mm)3, meaning they can be used to generate clinically useful DVKs using the proposed upsampling algorithm. Spherical tumor geometries were generated in TOPAS MC for diameters from 1 mm to 100 mm with varying tumor-to-background ratio (TBR) and then discretized into cubic voxels using MATLAB to generate activity maps. Spatial resolution blurs and different voxel sizes were computed from the discretized MATLAB activity maps. Absorbed dose maps were generated using both DVK and local deposition (LDM) dose algorithms with the different radionuclides for all tumor configurations (diameters and TBR) that additionally included varying spatial resolutions ( 3 mm, 5 mm, 10 mm, 15 mm FWHM Gaussian blurs) and voxel sizes ([3 mm]3 and [5 mm]3). The mean dose, point-dose to rim, and point-dose to the 1 mm and 2 mm outside margins were extracted from these dose maps and compared to the corresponding ground truth. Additionally, an additional phantom scan on a clinical PET/CT system for validation was conducted to compare acquired image data with synthetic data outputs. vi Analytical models were determined for the mean doses as a function of tumor diameter and TBR for ideal, spherical geometries. Voxel size, spatial resolution, radionuclide, TBR, and dose algorithm all influence the accuracy of the inferred dose metrics. Mean tumor doses for all radionuclide affected by the diameter and spatial resolution with increasing accuracy as the tumor diameter increase and spatial resolution improved but was largely unaffected by the voxel size. The point-dose metrics were most susceptible to error for radionuclides with average beta energy exceeding 0.5 MeV (32P, 90Y, 166Ho) with the DVK dose algorithm outperforming the LDM for realistic imaging voxel sizes and resolutions. The LDM dose algorithm slightly outperforms the DVK for mean dose calculation for the energetic beta emitters, but the DVK and LDM-derived doses converge as spatial resolution increases. Across the board, the metrics scale linearly with respect to 1/TBR. Hypoenhancing geometries for key combinations of radionuclide, diameter, TBR, voxel size, and spatial blur were also generated from the solid sphere geometries using a combination of core diameter and core-to-tumor uptake fraction to interrogate the dose consequences of underdosing these regions.</p>

Name thesis:degree_name

Masters of Science (MS)

Level thesis:degree_level

Thesis (MS)

Year dc:date.available

2025

Authors dc:creator

• Kelley, Brian M
• <p>0009-0005-2522-972X</p>

Contributors dc:contributor

• S. Cheenu Kappadath, Ph.D.
• Armeen Mahvash, M.D.
• Richard Wendt III, Ph.D.

• dosimetry theragnostic theranostic therapy radionuclide nuclear medicine imaging
• Other Physics
• Radiology

Repository record dc:identifier

https://digitalcommons.library.tmc.edu/utgsbs_dissertations/1502

OAI identifier oai:identifier

oai:digitalcommons.library.tmc.edu:utgsbs_dissertations-2559