SU-E-J-102: Performance Variations Among Clinically Available Deformable Image Registration Tools in Adaptive Radiotherapy: How Should We Evaluate and Interpret the Result?

Abstract

Purpose: To evaluate the performance variations in commercial deformable image registration (DIR) tools for adaptive radiation therapy. Methods: Representative plans from three different anatomical sites, prostate, head-and-neck (HN) and cranial spinal irradiation (CSI) with L-spine boost, were included. Computerized deformed CT images were first generated using virtual DIR QA software (ImSimQA) for each case. The corresponding transformations served as the “reference”. Three commercial software packages MIMVista v5.5 and MIMMaestro v6.0, VelocityAI v2.6.2, and OnQ rts v2.1.15 were tested. The warped contours and doses were compared with the “reference” and among each other. Results: The performance in transferring contours was comparable among all three tools with an average DICE coefficient of 0.81 for all the organs. However, the performance of dose warping accuracy appeared to rely on the evaluation end points. Volume based DVH comparisons were not sensitive enough to illustrate all the detailed variations while isodose assessment on a slice-by-slice basis could be tedious. Point-based evaluation was over-sensitive by having up to 30% hot/cold-spot differences. If adapting the 3mm/3% gamma analysis into the evaluation of dose warping, all three algorithms presented a reasonable level of equivalency. One algorithm had over 10% of the voxels not meeting this criterion for the HN case while another showed disagreement for the CSI case. Conclusion: Overall, our results demonstrated that evaluation based only on the performance of contour transformation could not guarantee the accuracy in dose warping. However, the performance of dose warping accuracy relied on the evaluation methodologies. Nevertheless, as more DIR tools are available for clinical use, the performance could vary at certain degrees. A standard quality assurance criterion with clinical meaning should be established for DIR QA, similar to the gamma index concept, in the near future.