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Evaluation of a Grid-Based Boltzmann Solver for Nuclear Medicine Voxel-Based Dose Calculations

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J Mikell

J Mikell1*, S Kappadath1 , T Wareing2 , F Mourtada3 , (1) The University of Texas Graduate School of Biomedical Sciences at Houston and MD Anderson Cancer Center, Houston, TX (2) Transpire Inc., Gig Harbor, WA, (3) Christiana Care Hospital, Newark, DE


WE-A-17A-7 Wednesday 7:30AM - 9:30AM Room: 17A

Purpose: Grid-based Boltzmann solvers (GBBS) have been successfully implemented in radiation oncology clinics as dose calculations for external photon beams and 192Ir sealed-source brachytherapy. We report on the evaluation of a GBBS for nuclear medicine voxel-based absorbed doses.

Methods: Voxel-S-values were calculated for monoenergetic betas and photons (1, 0.1, 0.01 MeV), 90Y, and 131I for 3 mm voxel sizes using Monte Carlo (DOSXYZnrc) and GBBS (Attila 8.1-beta5, Transpire). The source distribution was uniform throughout a single voxel. The material was an infinite 1.04 g/cc soft tissue slab. To explore convergence properties of the GBBS 3 tetrahedral meshes, 3 energy group structures, 3 different square Chebyschev-Legendre quadrature set orders (Sn), and 4-7 spherical harmonic expansion terms (Pn) were investigated for a total of 168 discretizations per source. The mesh, energy group, and quadrature sets are 8x, 3x, and 16x, respectively, finer than the corresponding coarse discretization. GBBS cross sections were generated with full electron-photon-coupling using the vendors extended CEPXS code. For accuracy, percent differences (%Δ) in source voxel absorbed doses between MC and GBBS are reported for the coarsest and finest discretization. For convergence, ratios of the two finest discretization solutions are reported along each variable.

Results: For 1 MeV, 0.1 MeV, 0.01 MeV, Y90, and I-131 beta sources the %Δ in the source voxel for (coarsest,finest) discretization were (+2.0,-6.4), (-8.0, -7.5), (-13.8, -13.4), (+0.9,-5.5), and (-10.1,-9.0) respectively. The corresponding %Δ for photons were (+33.7,-7.1), (-9.4, -9.8), (-17.4, -15.2), and (-1.7,-7.7), respectively. For betas, the convergence ratio of mesh, energy, Sn, and Pn ranged from 0.991-1.000. For gammas, the convergence ratio of mesh, Sn, and Pn ranged from 0.998-1.003 while the ratio for energy ranged from 0.964-1.001.

Conclusions: GBBS is promising for nuclear medicine voxel-based dose calculations. Ongoing work includes evaluating GBBS in bone, lung, and realistic clinical PET/SPECT-based activity distributions.

Funding Support, Disclosures, and Conflict of Interest: Research reported in this publication was supported by the National Cancer Institute of the National Institutes of Health under Award Number R01CA138986. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

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