title: Speed versus accuracy in a fast convolution photon dose calculation for conformal radiotherapy.
abstract: A convolution dose calculation for megavoltage photon beams is described and the compromise between speed and accuracy examined. The algorithm is suitable for treatment planning optimization, where the need is for a fast, flexible method requiring minimal beam data but providing an accurate result. The algorithm uses a simple tabular beam model, together with a discrete scatter kernel. These beam parameters are fitted either to a measured dose distribution, or to a dose distribution calculated using a more accurate dose calculation algorithm. The calculation is then applied to pelvic and thoracic conformal plans, and the results compared with those provided by a commercial radiotherapy treatment planning system (Pinnacle3, Philips Radiation Oncology Systems, Milpitas, CA), which has been verified against measurements. The calculation takes around 4 s to compute a 100 x 100 mm field, and agreement of the dose-volume histograms with the commercial treatment planning system is to within 5% dose or 8% volume. Use of a grid resolution coarser than 5 x 5 x 5 mm is found to be inaccurate, whereas calculating primary dose on a coarse grid and interpolating is found to increase speed without significantly reducing accuracy. Kernel resolution influences the speed and accuracy, but using 12 discrete points provides a fast result with a limited error. Thus, the algorithm is suitable for optimization applications.
authors.affiliation: Joint Department of Physics, The Institute of Cancer Research and The Royal Marsden NHS Trust, Sutton, Surrey, UK. j.bedford@icr.ac.uk
authors.forename: James L
authors.initials: JL
authors.lastname: Bedford
mesh_terms: D000465:Algorithms; D006801:Humans; D015233:Models, Statistical; D017785:Photons; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods*; D015203:Reproducibility of Results; D013997:Time Factors; D014057:Tomography, X-Ray Computed