Evaluation of dose calculations with inhomogeneity correction in intensity-modulated radiation therapy for esophagus cancer.

BACKGROUND: Differences often exist in the dose calculation accuracy caused by using different dose calculation algorithms in non-uniform tissues.

OBJECTIVE: To evaluate the accuracy of dose calculation with inhomogeneity correction in intensity-modulated radiation therapy (IMRT) by comparing dose calculated in Monaco with measurements in lung-chest phantom for esophagus cancer treatments.

METHODS: Finite size pencil beam (FSPB) and X-ray voxel Monte Carlo (XVMC) were used respectively for IMRT dose recalculations. Ten IMRT plans were recalculated and measured in the chest-lung phantom. The dose measurements using the Gafchromic ® (EBT3) dosimetry films were validated with open fields in the interfaces of materials with various physical densities. The accuracy of dose calculations was then evaluated by both point dose comparison and Gamma analysis against the film measurements.

RESULTS: For regular open fields, the discrepancies of the point doses were less than 3.0% and 2.0% between measurement and calculations by FSPB and XVMC, respectively. For 6 MV IMRT plans, the average passing rates based on 3% /3 mm Gamma criteria were 82.8±1.0% and 96.4±0.7% for FSPB and XVMC, respectively.

CONCLUSIONS: The XVMC algorithms more accurate in IMRT dose calculations with inhomogeneity correction for esophagus cancer.