Research On The Effect Of Inhomogeneity On The Accuracy Of Various IMRT Dose Calculation Models

3D-IMRT has being widely used in clinical cases while modern radiation oncologytechnology’s developing. Various errors of calculation have been generated by thedifferent algorithms applied in several commentarial TPSs because of the complexity ofbody tissues and dose delivery. It’s a key point to commit the accuracy in diversifiedcomputational conditions and dismiss the errors are beyond clinical scope.The project is based on the research on the effect of inhomogeneity on the accuracyof MONACO, FSPB and XVMC and the discussion of their clinical practices.Firstly, the two-dimensional planar dose and the absolute dose which werecalculated by the two algorithms of MONACO treatment planning system in theuniform phantom were compared by the two-dimensional semiconductor arrays(MapcheckTM) and ion chamber, respectively. Then the dose accuracy of the regularopen fields and IMRT plan which were calculated in the non-uniform artificialanthropomorphic phantom by the two algorithms of the Monaco were measured andcompared with EBT. Moreover, the deviation of dose calculation in a non-uniformanthropomorphic phantom among the lung, bone, and water were compared between6MV and15MV energy rays. The research was supported by the following conclusions:In the homogeneous and equivalent solid water phantom, the errors of thecalculation results by XVMC algorithm and the actual measured values were both lessthan±2%for the6MV and15MV. About the pencil beam algorithm, error was lessthan±3%.The verifications of planning calculated by two algorithms, based on two-dimensional semiconductor arrays showed the pass rates of individual fields were allabove90%with gamma criterion of3%/3mm. The dosimetric verification showed thedeviation between calculated by XVMC and measured by ion chamber was-0.66±1.55%, another was1.67±1.71%as FSPB used.In an anthropomorphic phantom, the deviations between calculated by XVMC andmeasured by films were lower than±2%, with whatever energy and in wherevermedium. While the deviation of FSPB values was as high as6.51%with15MV at thefield as2cm×10cm in lungs, others were in the range of±3%.The verification of individual IMRT beams based on films showed the pass rate of calculated by XVMC and FSPB were larger than90%respectively with gammacriterion of3%/3mm and4%/4mm. At3%/3mm, the rate of FSPB is between80%and90%. At the same time, the pass rates of all individual fields were higher than90%.So the calculation accuracy of XVMC is better than FSPB within multi-segmentsin non-uniform media. The error of algorithm can be controlled beyond3%, whenXVMC used.