Voxel-based dosimetry with integrated Y-90 PET/MRI and prediction of response of primary and metastatic liver tumors to radioembolization with Y-90 glass microspheres.

Purpose: In this study, we aimed to evaluate the response of the primary and metastatic liver tumors to radioembolization with ⁹⁰Y glass microspheres and investigate its correlations with dosimetric variables calculated with ⁹⁰Y PET/MRI.

Methods: In this ambispective study, 44 patients treated with ⁹⁰Y glass microspheres and imaged with ⁹⁰Y PET/MRI were included for analysis. Dosimetric analysis was performed for every perfused lesion using dose-volume histograms. Response was assessed by comparing pre-treatment and follow-up total lesion glycolysis (TLG) values derived from ¹⁸F-FDG PET imaging. The relationship between ΔTLG and log-transformed dosimetric variables was analyzed with linear mixed effects regression models. ROC analyses were performed to compare discriminatory power of the variables in predicting response and complete response.

Results: Regression and ROC analyses demonstrated that mean tumor dose and almost all D values were statistically significant predictors of treatment response and complete treatment response. Specifically, D60, D70 and D80 values exhibited significantly higher discriminatory power for predicting treatment response compared to the mean dose (D_mean) delivered to tumor. High specificity cut-off values to predict response were determined as 160.75 Gy for D_mean, 95.50 Gy for D60, 89 Gy for D70, and 59.50 Gy for D80. Similarly, high-specificity cut-off values to predict complete response were 262.75 Gy for D_mean, 173 Gy for D70, 140.5 Gy for D80, and 100 Gy for D90.

Conclusion: In this study, we demonstrated that voxel-based dosimetry with post-treatment ⁹⁰Y PET/MRI can predict response to treatment. D60, D70 and D80 variables also did have greater discriminatory power compared to D_mean in prediction of response. In addition, we present high-specificity cut-offs to predict response (CR + PR) and complete response (CR) for both D_mean and several D variables derived from dose-volume histograms.