Title:
[The influence of energy on X-ray voxel Monte Carlo algorithm based on kilovoltage cone beam computed tomography images for dose calculation].

Abstract:
This paper is to investigate how the different energy impact the accuracy of X-ray Voxel Monte Carlo (XVMC) algorithm when it is applied for dose calculation in Kilovoltage cone beam CT(kv-CBCT) images. The CIRS model 062 was used to calibrate the CT numbers-relative electron density table of CT and CBCT images. CT and CBCT scans were performed when simulation model of human head-and-neck placed in same position to simulate locally advanced nasopharyngeal carcinoma. 6MV and 15MV photon were selected in Monaco TPS to design intensity-modulated radiotherapy (IMRT) plans. XVMC algorithm was selected for dose calculation then the calculation results were compared and the impact of energy on the calculation accuracy was analyzed. The comparison results of dose volume histograms (DVHs), dose received by targets, organs at risk, conform index and uniform index of targets indicate a high agreement between CT based and CBCT based plans. More evaluation indicators show higher accuracy when 15MV photon was selected for dose calculation. gamma index analysis with the criterion of 2mm/2% and threshold of 10% was used for comparison of dose distribution. The average pass rate of each plane was 99.3% +/- 0.47% on the base of 6MV and 99.4% +/- 0.44% on the base of 15MV. CBCT images after calibration has high accuracy of dose calculation and has higher accuracy when 15MV photon was selected.