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.