Towards new response criteria in neuroendocrine tumors: Which changes in MRI parameters are associated with longer progression-free survival after radioembolization of liver metastases?

Purpose: To evaluate the association of therapy-related changes in imaging parameters with progression-free survival (PFS) of patients with unresectable liver metastases from neuroendocrine tumors (NETLMs). Materials and Methods: Forty-five radioembolized patients (median age: 62 years; range: 43-75) received a pre- and 3 months posttherapeutic magnetic resonance imaging (MRI) examination. The latter were evaluated for tumor size, arterial enhancement, and necrosis pattern. Influences of therapy-related changes on PFS were analyzed. Statistical analysis included Student's t-test, Wilcoxon test, Cox regression analysis, and Kaplan-Meier curves. Results: The median percentage decrease in sum of diameters was 9.7% (range: 43.9% decrease to 15.4% increase). Twenty-one patients (47%) showed increased necrosis. Three parameters were associated with significantly longer PFS: a decrease of diameter (hazard ratio [HR]: 0.206; 95% confidence interval [CI]: 0.058-0.725; P = 0.0139), a decrease in tumor arterial enhancement (HR: 0.143; 95% CI: 0.029-0.696; P = 0.0160), and an increase in necrosis after 3 months (HR: 0.321; 95% CI: 0.104-0.990; P = 0.0480). Multivariate analysis revealed that changes in diameter and arterial enhancement have complementary information and are associated independently with long PFS. Conclusion: A decrease both in sum of diameters and arterial enhancement of metastases, as well as an increase in necrosis, are associated with significantly longer PFS after radioembolization.