Room: AAPM ePoster Library
Purpose: Volumes of the whole liver, left and right hepatic lobes, and GTVs are necessary for the activity calculation of Y90 microspheres for liver radioembolization. Left/right lobe contours can be done based on traditional anatomical landmarks or can be patient-specific based on cone beam CT (CBCT) of the perfused volume during the pre-Y90 study. This work is considering the variation of the prescribed activity based on contouring technique.
Methods: Ten of a proposed 100 post-treatment radioembolization patients were retrospectively analyzed in this work. Clinically, patients were contoured based on the fusion of the CT of the SPECT done immediately after the pre-Y90 study to the CBCT acquired during the study to visualize the perfused volumes to be treated. The whole liver, left/right lobe and GTVs are identified and contoured on this image fusion. Retrospectively, the CT was fused with either an MRI or enhanced CT to identify the middle hepatic vein (MHV). Since the MHV classically divides the liver into left and right, the left and right lobes were re-contoured based on the MHV. Using the BSA model, the Y90 activity was re-calculated with the new volumes and compared with the treatment activity calculations. Whole liver and GTVs were not re-contoured.
Results: On average there is a 7.8% ± 5.1% and 15.1% ± 9.5% discrepancy on the activities calculated for treatment of the right and left lobes, respectively, between the two contouring techniques.
Conclusion: Although an additional 90 patients will be analyzed, preliminary analysis suggests that there are significant differences in the calculated activity based on the contouring technique chosen by the clinician. Smaller practices that do not acquire or do not use the CBCT during treatment planning should consider patient-specific contouring techniques for more accurate activity calculation, especially if the patient has unique blood flow in the liver.