A coarse mesh transport method for photons and electrons in 3-D

• Main Author: Hayward, Robert M.
• Other Authors: Rahnema, Farzad
• Language: en_US
• Published: Georgia Institute of Technology 2014
• Subjects: Monte Carlo; Treatment planning; Transport theory; Radiotherapy; Radiation Dosage; Monte Carlo method; Medical physics
• Online Access: http://hdl.handle.net/1853/51928

A hybrid stochastic-deterministic method, COMET-PE, is developed for dose calculation in radiotherapy. Fast, accurate dose calculation is a key component of successful radiotherapy treatment. To calculate dose, COMET-PE solves the coupled Boltzmann Transport Equations for photons and electrons. The method uses a deterministic iteration to compose response functions that are pre-computed using Monte Carlo. Thus, COMET-PE takes advantage of Monte Carlo physics without incurring the computational costs typically required for statistical convergence. This work extends the method to 3-D problems with realistic source distributions. Additionally, the performance of the deterministic solver is improved, taking advantage of both shared-memory and distributed-memory parallelism to enhance efficiency. To verify the method’s accuracy, it is compared with the DOSXYZnrc (Monte Carlo) method using three different benchmark problems: a heterogeneous slab phantom, a water phantom, and a CT-based lung phantom. For the slab phantom, all errors are less than 1.5% of the maximum dose or less than 3% of local dose. For both the water phantom and the lung phantom, over 97% of voxels receiving greater than 10% of the maximum dose pass a 2% (relative error) / 2 mm (distance-to-agreement) test. Timing comparisons show that COMET-PE is roughly 10-30 times faster than DOSXYZnrc. Thus, the new method provides a fast, accurate alternative to Monte Carlo for dose calculation in radiotherapy treatment planning.