title: Feasibility of a multigroup deterministic solution method for three-dimensional radiotherapy dose calculations.
abstract: OBJECTIVE
  To investigate the potential of a novel deterministic solver, Attila, for external photon beam radiotherapy dose calculations.
  
  
  METHODS
  Two hypothetical cases for prostate and head-and-neck cancer photon beam treatment plans were calculated using Attila and EGSnrc Monte Carlo simulations. Open beams were modeled as isotropic photon point sources collimated to specified field sizes. The sources had a realistic energy spectrum calculated by Monte Carlo for a Varian Clinac 2100 operated in a 6-MV photon mode. The Attila computational grids consisted of 106,000 elements, or 424,000 spatial degrees of freedom, for the prostate case, and 123,000 tetrahedral elements, or 492,000 spatial degrees of freedom, for the head-and-neck cases.
  
  
  RESULTS
  For both cases, results demonstrate excellent agreement between Attila and EGSnrc in all areas, including the build-up regions, near heterogeneities, and at the beam penumbra. Dose agreement for 99% of the voxels was within the 3% (relative point-wise difference) or 3-mm distance-to-agreement criterion. Localized differences between the Attila and EGSnrc results were observed at bone and soft-tissue interfaces and are attributable to the effect of voxel material homogenization in calculating dose-to-medium in EGSnrc. For both cases, Attila calculation times were <20 central processing unit minutes on a single 2.2-GHz AMD Opteron processor.
  
  
  CONCLUSIONS
  The methods in Attila have the potential to be the basis for an efficient dose engine for patient-specific treatment planning, providing accuracy similar to that obtained by Monte Carlo.
authors: Department of Radiation Physics, MD Anderson Cancer Center, Houston, TX 77030, USA.
authors: Oleg N
authors: ON
authors: Vassiliev
authors: Todd A
authors: TA
authors: Wareing
authors: Ian M
authors: IM
authors: Davis
authors: John
authors: J
authors: McGhee
authors: Douglas
authors: D
authors: Barnett
authors: John L
authors: JL
authors: Horton
authors: Kent
authors: K
authors: Gifford
authors: Gregory
authors: G
authors: Failla
authors: Uwe
authors: U
authors: Titt
authors: Firas
authors: F
authors: Mourtada
mesh_terms: D000465:Algorithms; D005240:Feasibility Studies; D020342:Finite Element Analysis; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D009010:Monte Carlo Method; D010315:Particle Accelerators; D017785:Photons / Q000627:therapeutic use; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011859:Radiography; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*