Abstract
90Y radioembolization is an established treatment modality for hepatic malignancies. Successful radioembolization requires optimal dose delivery to tumors while minimizing dosages to parenchyma. Post-treatment positron emission tomography (PET)/computed tomography (CT) dosimetry is the established benchmark, whereas PET/magnetic resonance (MR) is an emerging modality. The goal of this study was to assess the intermodality agreement between PET/MR and PET/CT 90Y dosimetry. In this single-institution study, 18 patients (20 treatment sessions) with a primary or metastatic hepatic malignancy underwent both PET/MR and PET/CT after 90Y radioembolization. Patients were randomized to undergo one modality first, followed by the other. The region of interest was delineated using MR images and tumor and liver dosimetry was calculated. Intermodality agreement was assessed using the Bland-Altman method. A generalized linear model was used to assess the effect of baseline variables on intermodality dose differences. PET/MR underestimated tumor and liver absorbed doses when compared to PET/CT by -3.7% (P=0.042) and -5.8% (P=0.029), respectively. A coverage probability plot demonstrated that 80% and 90% of tumor dose measurements fell within intermodality differences of 11% and 18%, respectively. PET/MR underestimated tumor dose at both low (<1 GBq) and high (>3 GBq) injected activity levels (P<0.001) by -22.3 [standard deviation (SD) =13.5] and -24.3 (SD =18.7), respectively. Although PET/MR significantly underestimated the absorbed dose when compared to PET/CT, the intermodality agreement was high and the degree of underestimation was better than previously reported. Intermodality differences were more pronounced at low and high injected doses. Additional studies are required to assess the clinical implications of these findings.
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