Comparison Between Diffusion-Weighted MRI and I-mIBG Uptake in Primary High-Risk Neuroblastoma.

Background: High-risk neuroblastoma (HR-NB) has a variable response to preoperative chemotherapy. It is not possible to differentiate viable vs. nonviable residual tumor before surgery.

Purpose: To explore the association between apparent diffusion coefficient (ADC) values from diffusion-weighted magnetic resonance imaging (DW-MRI), I-meta-iodobenzyl-guanidine ( I-mIBG) uptake, and histology before and after chemotherapy.

Study Type: Retrospective.

Subjects: Forty patients with HR-NB.

Field Strength/sequence: 1.5T axial DW-MRI (b = 0,1000 s/mm ) and T -weighted sequences. I-mIBG scintigraphy planar imaging (all patients), with additional I-mIBG single-photon emission computed tomography / computerized tomography (SPECT/CT) imaging (15 patients).

Assessment: ADC maps and I-mIBG SPECT/CT images were coregistered to the T -weighted images. I-mIBG uptake was normalized with a tumor-to-liver count ratio (TLCR). Regions of interest (ROIs) for primary tumor volume and different intratumor subregions were drawn. The lower quartile ADC value (ADC ) was used over the entire tumor volume and the overall level of I-mIBG uptake was graded into avidity groups.

Statistical Tests: Analysis of variance (ANOVA) and linear regression were used to compare ADC and MIBG values before and after treatment. Threshold values to classify tumors as viable/necrotic were obtained using ROC analysis of ADC and TLCR values.

Results: No significant difference in whole-tumor ADC values were found between different I-mIBG avidity groups pre- (P = 0.31) or postchemotherapy (P = 0.35). In the "intratumor" analysis, 5/15 patients (prechemotherapy) and 0/14 patients (postchemotherapy) showed a significant correlation between ADC and TLCR values (P < 0.05). Increased tumor shrinkage was associated with lower pretreatment tumor ADC values (P < 0.001); no association was found with pretreatment I-mIBG avidity (P = 0.17). Completely nonviable tumors had significantly lower postchemotherapy ADC values than tumors with >10% viable tumor (P < 0.05). Both pre- and posttreatment TLCR values were significantly higher in patients with >50% viable tumor than those with 10-50% viable tumor (P < 0.05). DATA CONCLUSION: I-mIBG avidity and ADC values are complementary noninvasive biomarkers of therapeutic response in HR-NB.

Level Of Evidence: 4.

Technical Efficacy Stage: 3.