Purpose: The purpose of this study is to investigate the utility of contrast-enhanced magnetic resonance imaging (CE-MRI), diffusion-weighted MRI (DW-MRI), and (68)Ga-DOTATOC positron emission tomography/computer tomography ((68)Ga-DOTATOC PET/CT) in the assessment of response to loco-regional peptide receptor radiotherapy (PRRT) with (90)Y-/(177)Lu-DOTATOC in patients with hepatic metastases from gastro-entero-pancreatic neuroendocrine tumors (GEP-NET).
Procedures: CE-MRI, DW-MRI, and (68)Ga-DOTATOC-PET/CT images were acquired before and 3 months after one to two cycles of intra-arterial (90)Y-/(177)Lu-DOTATOC therapy in 14 patients (nine female, five male; mean age, 54 ± 9 years; range, 41-69 years) with hepatic metastases from GEP-NET. A total of 38 liver metastases were defined as target lesions for which the longest diameter, mean apparent diffusion coefficient (ADCmean) and maximum standardized uptake value (SUVmax) were assessed. Based on changes in size on follow-up imaging, target lesions were classified as responding (RL) or nonresponding (NRL). Relative changes in tumor size, ADCmean, and SUVmax were compared between the two subgroups.
Results: A total of 27 responding and 11 nonresponding lesions were successfully evaluated. Mean ADCmean increased significantly in RL (p = 0.011) as well as NRL (p = 0.025). A significant correlation was found between baseline ADCmean and both the percent ADCmean change (p = 0.033) and decrease in lesion size after therapy (diameter p = 0.006; volume p = 0.002). SUVmax of RL declined significantly by 24.1 % (p = 0.014) and remained nearly unchanged in NRL. The change of SUVmax correlated significantly with the pretreatment SUVmax (p < 0.001) and the change in lesion diameter (p = 0.009). NRL with an ADCmean change >0.31 × 10(-3) mm(2)/s on first follow-up imaging showed a decrease in size in the long-term course.
Conclusion: These results suggest that both DW-MRI and DOTATOC-PET imaging provide potential biomarkers for early assessment of treatment and stratification of therapy response, but that DW-MRI should be interpreted only in combination with SSTR expression and morphologic changes.