The Feasibility Study Of Mri-Based Dose Calculation With Look-Up Table In Radiation Treatment Planning

Computed tomography (CT) has been the basis for the radiation treatment planning (RTP) because of converted Hounsfield units. In the brain regions, an accurate delineation of the target volume, however, has been difficult with only the CT data due to the poor soft tissue contrast of CT images. Therefore, the magnetic resonance images (MRI) for the delineation of the target volumes were used. In this study, MRI-based treatment planning was developed by generated electron density through the use of diagnostic MRI. To evaluate of the MRI-based dose calculation, the look up table from diagnostic MRI images were generated. The look up table is similar to image value to density table (IVDT). To evaluate the MRI-based RTP, the dose distributions from the MRI-based RTP were compared to the CT-based calculation. For the precise evaluation, the distortion of MR images was corrected and the geometrical registrations between CT images and MR images were performed. One MRI set has ED information from look up table. Another set was generated with voxel values assigned with a homogeneous density of water. To evaluate the accuracy of the MRI-based dose calculation, ten clinical cases are studied. For each case, IMRT plans are computed with the same beam configuration but different image basis: CT, MRI with look up table, and MRI with voxel values replaced by that of water. The dose distributions from the three types of calculations are compared. In all cases, the MRI with look up table yielded very close dose values as compared with the CT-based calculation. The maximum discrepancy between the two is found to be less than 3.0% in the maximum dose. Compared to the MRI with look up table, the MRI with uniform water voxel value yielded quite different dose distributions in all regions, and the dose discrepancy can be as large as 5-8% for all cases. The differences of maximum dose of the MRI with uniform water voxel value were lower than the MRI with look up table, because the air cavity was not calculated in the MRI with uniform water. The MR images with look up table yield similar treatment plan compared with the CT-based calculations. The approach has potential to eliminate simulation CT by planning a patient treatment with only simulation MRI.