Caren van Roekel

214 Chapter 8 Quantitative analysis was performed using Simplict 90 Y (Mirada Medical Ltd, Oxford, United Kingdom) software. Activity calculations were performed using volumes drawn on contrast-enhanced CT (CECT) images that were registered to low-dose CT images of nuclear imaging datasets. In this process, only rigid transformations were used. Volumes of interest (VOI) were delineated using the axial reconstruction of a portal venous phase CECT. VOIs of the perfused volume of all injection locations, all measurable tumors (defined as having a diameter ≥ 20mm), and the dependent segment were drawn. The dependent segment VOIs were preferably drawn using cone-beam CT imaging, otherwise segmentation was performed based on the Couinaud classification of segmental hepatic anatomy. The non-dependent segment VOI was created by subtracting the dependent segment from the whole liver VOI. The activity concentrations were calculated using the net administered activity (i.e. corrected for residual activity). Activity concentrations in patients treated with holmium were also calculated using Simplicit 90 Y software. As part of this study, activity measurements obtained in Simplicit 90 Y were compared with measurements made using in-house developed dosimetry software in order to validate the use of Simplicit 90 Y for 166 Ho-microspheres.(9) The differences were found to be negligible. Patients in whom not all above mentioned VOIs could be delineated were excluded from this analysis, as well as cases where accurate registration of CECT to post-treatment imaging was impossible. Sequential lobar therapy cases Patients receiving sequential lobar therapy underwent post-treatment imaging twice (i.e. once for every radioembolization procedure) but were counted as one case. In the visual analysis, both post-treatment scans (i.e. the left and right hemi-liver scans) were assessed separately and the results were subsequently merged, counting the highest score. In the quantitative analysis, the activity concentrations of all VOIs were calculated on both scans and the results were averaged.