Early Whole-Body Diffusion-weighted MRI Helps Predict Long-term Outcome Following Peptide Receptor Radionuclide Therapy for Metastatic Neuroendocrine Tumors

Purpose: To evaluate the predictive value of 7-week apparent diffusion coefficient change from baseline (ADCratio(7w)) at whole-body diffusion-weighted MRI (WB-DWI MRI) after one peptide receptor radionuclide therapy (PRRT) cycle to predict outcome in patients with metastatic neuroendocrine tumor (mNET). Materials and Methods: From April 2009 to May 2012, participants in a prospective clinical trial investigating yttrium 90-DOTA Phe1-Tyr3-octreotide (DOTATOC) treatment for mNET (EudraCT no. 2008-007965-22) underwent WB-DWI MRI and gallium 68 (Ga-68)-DOTATOC PET/CT before and 7 weeks after one PRRT cycle. ADCratio 7w response was compared with the 7-week Response Evaluation Criteria in Solid Tumors version 1.1 and Ga-68-DOTATOC PET/CT quantitative responses to predict overall survival (OS) and progression-free survival (PFS) with Cox regression analysis. Results: Forty participants were analyzed (mean age, 60 years +/- 11 [SD]; 21 men). Median PFS and OS were 10.5 months (range, 2-36 months) and 18 months (range, 3-81 months), respectively. Survival analysis showed significantly positive effects on PFS by age (hazard ratio [HR] = 0.96, P =.007), tumor grade (HR = 2.84, P =.006), Ki-67 index (HR = 1.05, P =.01), ADC(ratio) 7w of the leastresponding lesion (ADCratio 7w-least) (HR = 0.94, P < .001), and baseline mean standardized uptake values (SUVmean) (HR = 0.89, P =.02), with ADCratio 7w-least and SUV mean remaining significant in multivariable analysis (P,.001, P =.02, respectively). There were significantly positive effects on OS by pretreatment lesion volume (HR = 1.004, P =.004), tumor grade (HR = 2.14, P =.04), Ki-67 index (HR = 1.05, P =.01), and ADC(ratio) 7w-least (HR = 0.97, P,.001), with pretreatment volume and ADC(ratio) 7w-least remaining significant at multivariable analysis (P =.005, P =.002, respectively). Conclusion: The ADC(ratio) 7w after start of PRRT for mNET was an independent predictor of patient outcome. (C)RSNA, 2022.