How the Rigid and Deformable Image Registration Approaches Affect the Absorbed Dose Estimation Using Images Collected before and after Transarterial Radioembolization with 90Y Resin Microspheres in a Clinical Setting

Background: Transarterial radioembolization (TARE) relies on directly injected Y-90- or Ho-166-loaded microspheres in the hepatic arteries. The activity to be injected is generally based on pre-TARE Tc-99m-macro-aggregated-albumin (MAA) imaging, while the actual dose distribution is based on post-treatment images. The volume of interest (VOIs) propagation methods (i.e., rigid and deformable) from pre- to post-TARE imaging might affect the estimation of the mean absorbed dose in the tumor and non-tumoral liver (NTL), i.e., D-T and D-NTL, respectively. Methods: In 101 consecutive patients, liver and tumor were delineated on pre-TARE images and semi-automatically transferred on Y-90-PET/CT images with a rigid or deformable registration approach. Pre- and post-TARE volumes and D-T/D-NTL/D-L were compared using correlation coefficient (CC) indexes, such as intra-class (ICC), Pearson's (PCC), concordance (CCCo) and Bland-Altman analyses. The Kaplan-Meier curves of overall survival (OS) were calculated according to D-T. Results: All computed CCs indicated very good (>0.92) agreement for volume comparison, while they suggested good (ICC >= 0.869, PCC >= 0.876 and CCCo >= 0.790) and moderate agreement in the intra- and inter-modality D-T/D-NTL/D-L comparisons, respectively. Bland-Altman analyses showed percentage differences between the manual and deformable approaches of up to about -31%, 9% and 62% for tumoral volumes, D-T and D-NTL, respectively. The overall survival analysis showed statistically significant differences using D-T cutoffs of 110, 90 and 85 Gy for the manual, rigid and deformable approaches, respectively. Conclusions: The semi-automatic transfer of VOIs from pre- and post-TARE imaging is feasible, but the selected method might affect prognostic D-T/D-NTL constraints.