title: Evaluation of a deterministic grid-based Boltzmann solver (GBBS) for voxel-level absorbed dose calculations in nuclear medicine.
abstract: To evaluate the 3D Grid-based Boltzmann Solver (GBBS) code ATTILA (®) for coupled electron and photon transport in the nuclear medicine energy regime for electron (beta, Auger and internal conversion electrons) and photon (gamma, x-ray) sources. Codes rewritten based on ATTILA are used clinically for both high-energy photon teletherapy and (192)Ir sealed source brachytherapy; little information exists for using the GBBS to calculate voxel-level absorbed doses in nuclear medicine. We compared DOSXYZnrc Monte Carlo (MC) with published voxel-S-values to establish MC as truth. GBBS was investigated for mono-energetic 1.0, 0.1, and 0.01 MeV electron and photon sources as well as (131)I and (90)Y radionuclides. We investigated convergence of GBBS by analyzing different meshes ([Formula: see text]), energy group structures ([Formula: see text]) for each radionuclide component, angular quadrature orders ([Formula: see text], and scattering order expansions ([Formula: see text]-[Formula: see text]); higher indices imply finer discretization. We compared GBBS to MC in (1) voxel-S-value geometry for soft tissue, lung, and bone, and (2) a source at the interface between combinations of lung, soft tissue, and bone. Excluding Auger and conversion electrons, MC agreed within  ≈5% of published source voxel absorbed doses. For the finest discretization, most GBBS absorbed doses in the source voxel changed by less than 1% compared to the next finest discretization along each phase space variable indicating sufficient convergence. For the finest discretization, agreement with MC in the source voxel ranged from  -3% to  -20% with larger differences at lower energies (-3% for 1 MeV electron in lung to  -20% for 0.01 MeV photon in bone); similar agreement was found for the interface geometries. Differences between GBBS and MC in the source voxel for (90)Y and (131)I were  -6%. The GBBS ATTILA was benchmarked against MC in the nuclear medicine regime. GBBS can be a viable alternative to MC for voxel-level absorbed doses in nuclear medicine. However, reconciliation of the differences between GBBS and MC at lower energies requires further investigation of energy deposition cross-sections.
authors.affiliation: Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA. The University of Texas Graduate School of Biomedical Sciences, Houston, TX, USA.
authors.forename: Justin
authors.initials: J
authors.lastname: Mikell
authors.forename: S
authors.initials: S
authors.lastname: Cheenu Kappadath
authors.forename: Todd
authors.initials: T
authors.lastname: Wareing
authors.forename: William D
authors.initials: WD
authors.lastname: Erwin
authors.forename: Uwe
authors.initials: U
authors.lastname: Titt
authors.forename: Firas
authors.initials: F
authors.lastname: Mourtada
mesh_terms: D065638:Absorption, Radiation; D001822:Body Burden; D001918:Brachytherapy / Q000592:standards*; D006801:Humans; D009010:Monte Carlo Method; D009683:Nuclear Medicine / Q000379:methods / Q000592:standards*; D011829:Radiation Dosage; D011877:Radionuclide Imaging / Q000592:standards*