Evaluation of radiotherapy treatment planning with mega-voltage cone beam CT

The prospective use for MV CT for patient treatment planning are for consecutive phase plans in 3D conformal and intensity modulated radiotherapy, patients with metal implants, adaptive radiation therapy and single fraction palliative treatment. This study is to validate the authors´ previous work on MV cone beam CT (MV CBCT) images reconstructed with bespoke FDK algorithm based 3D reconstruction software for treatment planning. MV CBCT images were fused with planning CT images to include complimentary data which help elucidate visualization and segmentation of different anatomical structures for better treatment planning. The landmark based manual registration of planning CT and MV CBCT images was done. The registration was validated using quantitative and qualitative measures. A relative dose calculation was done where the whole brain was delineated as the target volume. Forward planning with parallel oppose fields with micro multi-leaf collimator shaping and 6 MV beam was performed on both kV and MV CBCT images. Dose volume histograms and volume comparisons of the target were done. The volumes of the target were measured on kV and MV CBCT. The relative dose for the points in the target volume in MV CBCT was within 3% difference from dose calculated with planning CT. The results of this study show that MV CBCT images could be effectively used for planning in a commercial treatment planning system, if the necessary corrections mentioned are incorporated.