System and method for fast Monte Carlo Dose calculation using a virtual source model

Abstract

The present disclosure relates to a method and apparatus for fast Monte Carlo (MC) dose calculation using a virtual source model (VSM). The method includes: receiving three-dimensional (3D) CT images obtained by a CT system; receiving 3D planned dose images, 3D organ segmentation contour images, and radiotherapy plans generated by a treatment planning system (TPS); processing 3D CT images, 3D planned dose images, 3D organ segmentation contour images to have the same spatial resolution and matrix size; further processing 3D CT images to convert image intensity to 3D density maps; processing the radiotherapy plans to generate instructions on how to simulate plan delivery; building VSM using inverse cumulative density function (CDF) tables for the simulation of radiotherapy plans, wherein the step of building VSM comprises: receiving output data files containing phase-space information for the radiation output of a specific medical linear accelerator treatment head; calculating the probability of the inplane and crossplane positions of the radiation particles reverse transported from the phase-space surface back to the treatment head; calculating the Gaussian means and standard deviations of the radiation particles' positions at the treatment head; calculating the probabilities for the source of each radiation particle; calculating the probabilities for the medical linear accelerator treatment head to produce different radiation particle species; binning the inplane position probability information of radiation particles into a single histogram for each source and radiation particle species; binning the crossplane position probability information of radiation particles into histograms for each bin of the inplane position histogram for each source and radiation particle species; binning the inplane direction cosine probability information of radiation particles into histograms for each bin of the inplane position histogram for each source and radiation particle species; binning the crossplane direction cosine probability information of radiation particles into histograms for each bin of the crossplane position histogram for each source and radiation particle species; binning the kinetic energy probability information of radiation particles into radially binned histograms for each source and radiation particle species; converting probability densities for inplane and crossplane positions, inplane and crossplane direction cosines, and kinetic energies histograms into cumulative probability densities for each source and radiation particle species; and inverting cumulative probability densities and converting into probability binned inverse CDF tables; simulating and transporting external beams using VSM through virtual treatment machines to the 3D density maps according to radiotherapy plans to produce 3D simulated dose images; and post-processing the 3D planned dose images, 3D organ segmentation contour images, and the 3D simulated dose images to obtain a final report comparing planned versus simulated dose images.

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