Diffusion-weighted MRI Is Superior to PET/CT in Predicting Survival of Patients Undergoing ⁹⁰Y Radioembolization of Hepatic Metastases

Purpose To determine the relationship between diffusion-weighted (DW) liver MR images obtained 4-6 weeks after lobar yttrium 90 (⁹⁰Y) treatment and overall survival in comparison with PET/CT or established oncologic factors known to affect survival. Materials and Methods The institutional review board approved this prospective intraindividual comparative study in 36 consecutive patients (25 women) with liver-dominant metastases (20 colorectal, 14 breast, two other) (mean age, 60 years ± 10 [standard deviation]) who underwent fluorine 18 (¹⁸F) fluorodeoxyglucose (FDG) PET/CT and DW MRI before and 4-6 weeks after ⁹⁰Y radioembolization. DW MRI response was defined as a mean minimal apparent diffusion coefficient increase of more than 30%; PET/CT response was defined as a mean maximal standardized uptake value decrease of more than 30%. Kaplan-Meier curves, log-rank test, and multivariable Cox regression analyses were used to compare patient survival as a function of imaging and Response Evaluation Criteria in Solid Tumors (RECIST) response, pretreatment Eastern Cooperative Oncology Group (ECOG) performance status (PS) (0 vs 1), hepatic tumor load (<25% vs ≥25%), and presence versus absence of extrahepatic disease. Results Thirty-five of the 36 patients were observed until death (median survival, 36 weeks). Response was observed with PET/CT in 18 of 36 patients (50%). Median survival was 39 weeks in patients who responded to PET/CT versus 27 weeks in those who did not (P = .60). Response was observed with DW MRI in 24 of 36 patients (67%). Median survival was 53 weeks in DW MRI responders versus 20 weeks in nonresponders (P = .01). At multivariable analysis, DW MRI response was the only independent predictor of survival (P < .01). Response based on RECIST parameters, ECOG PS, hepatic tumor load, and presence of extrahepatic metastases did not correlate with survival. Conclusion In patients with hepatic metastases undergoing ⁹⁰Y radioembolization, prediction of response to therapy with DW MRI was superior to that with PET/CT and established oncologic factors.