title: Fast Pencil Beam Dose Calculation for Proton Therapy Using a Double-Gaussian Beam Model.
abstract: The highly conformal dose distributions produced by scanned proton pencil beams (PBs) are more sensitive to motion and anatomical changes than those produced by conventional radiotherapy. The ability to calculate the dose in real-time as it is being delivered would enable, for example, online dose monitoring, and is therefore highly desirable. We have previously described an implementation of a PB algorithm running on graphics processing units (GPUs) intended specifically for online dose calculation. Here, we present an extension to the dose calculation engine employing a double-Gaussian beam model to better account for the low-dose halo. To the best of our knowledge, it is the first such PB algorithm for proton therapy running on a GPU. We employ two different parameterizations for the halo dose, one describing the distribution of secondary particles from nuclear interactions found in the literature and one relying on directly fitting the model to Monte Carlo simulations of PBs in water. Despite the large width of the halo contribution, we show how in either case the second Gaussian can be included while prolonging the calculation of the investigated plans by no more than 16%, or the calculation of the most time-consuming energy layers by about 25%. Furthermore, the calculation time is relatively unaffected by the parameterization used, which suggests that these results should hold also for different systems. Finally, since the implementation is based on an algorithm employed by a commercial treatment planning system, it is expected that with adequate tuning, it should be able to reproduce the halo dose from a general beam line with sufficient accuracy.
authors.affiliation: Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, UK; Department of Oncology, University of Cambridge, Cambridge, UK.
authors.forename: Joakim
authors.initials: J
authors.lastname: da Silva
authors.affiliation: Cavendish Laboratory, Department of Physics, University of Cambridge , Cambridge , UK.
authors.forename: Richard
authors.initials: R
authors.lastname: Ansorge
authors.affiliation: Department of Oncology, University of Cambridge , Cambridge , UK.
authors.forename: Rajesh
authors.initials: R
authors.lastname: Jena
keywords: adaptive radiotherapy; dose calculation; double Gaussian; graphics processing unit; pencil beam; proton therapy