A Heterogeneous Coarse Mesh Method for Coupled Photon Electron Transport Problems

A hybrid Monte Carlo/deterministic coarse mesh transport method (COMET-PE) has been developed for pure photon or coupled photon and electron transport in heterogeneous problems. The accuracy of the method was evaluated in two highly stylized 2D benchmark problems: (1) a homogeneous rectangular water phantom and (2) a heterogeneous problem that is typical of a 2D vertical slice of lung. It was found that the method produces results that are very close to those of direct Monte Carlo with significantly higher computational efficiency (2–3 orders of magnitude). In both test problems, the maximum and the average energy deposition differences between COMET-PE and the reference Monte Carlo solutions for the pure photon transport case ranged from 2.0%–2.4% and 1.0%–1.2%, respectively. The corresponding differences for the coupled photon and electron transport case ranged from 1.1%–2.2% and 0.5%–0.9%, respectively. The COMET-PE computation time was more than 200 and 700 times shorter than EGSnrc in the homogeneous and the heterogeneous problems, respectively. Therefore, it is concluded that the new incident flux response expansion method is highly accurate and efficient for energy deposition calculation in heterogeneous tissues.