title: Electron pencil-beam redefinition algorithm dose calculations in the presence of heterogeneities.
abstract: The electron pencil-beam redefinition algorithm (PBRA) is currently being refined and evaluated for clinical use. The purpose of this work was to evaluate the accuracy of PBRA-calculated dose in the presence of heterogeneities and to benchmark PBRA dose accuracy for future improvements to the algorithm. The PBRA was evaluated using a measured electron beam dose algorithm verification data set developed at The University of Texas M. D. Anderson Cancer Center. The data set consists of measurements made using 9 and 20 MeV beams in a water phantom with air gaps, internal air and bone heterogeneities, and irregular surfaces. Refinements to the PBRA have enhanced the speed of the dose calculations by a factor of approximately 7 compared to speeds previously reported in published data; a 20 MeV, 15 x 15 cm2 field electron-beam dose distribution took approximately 10 minutes to calculate. The PBRA showed better than 4% accuracy in most experiments. However, experiments involving the low-energy (9 MeV) electron beam and irregular surfaces showed dose differences as great as 22%, in albeit a small fractional region. The geometries used in this study, particularly those in the irregular surface experiments, were extreme in the sense that they are not seen clinically. A more appropriate clinical evaluation in the future will involve comparisons to Monte Carlo generated patient dose distributions using actual computed tomography scan data. The present data also serve as a benchmark against which future enhancements to the PBRA can be evaluated.
authors.affiliation: Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston 77030, USA.
authors.forename: R A
authors.initials: RA
authors.lastname: Boyd
authors.forename: K R
authors.initials: KR
authors.lastname: Hogstrom
authors.forename: G
authors.initials: G
authors.lastname: Starkschall
mesh_terms: D000465:Algorithms; D001842:Bone and Bones / Q000528:radiation effects; D004583:Electrons; D006801:Humans; D015233:Models, Statistical; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011874:Radiometry / Q000379:methods*; D011882:Radiotherapy, High-Energy / Q000295:instrumentation / Q000379:methods*; D013997:Time Factors; D014867:Water
chemical_list: D014867:Water