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-Tyr(3)-octreotide (DOTATOC) treatment for mNET (EudraCT no. 2008–007965–22) underwent WB-DWI MRI and gallium 68 ((68)Ga)–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 (68)Ga-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), ADCratio(7w) of the least-responding lesion (ADCratio(7w-least)) (HR = 0.94, P < .001), and baseline mean standardized uptake values (SUV(mean)) (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 ADCratio(7w-least) (HR = 0.97, P < .001), with pretreatment volume and ADCratio(7w-least) remaining significant at multivariable analysis (P = .005, P = .002, respectively). CONCLUSION: The ADCratio(7w) after start of PRRT for mNET was an independent predictor of patient outcome. Keywords: MR–Diffusion-Weighted Imaging, Radionuclide Therapy, Whole-Body Imaging, Metastases, Tumor Response, Treatment Effects EudraCT no. 2008-007965-22 © RSNA, 2022