Comparison of whole-body DW-MRI with 2-[18F]FDG PET for staging and treatment monitoring of children with Langerhans cell histiocytosis

Purpose To assess and compare the diagnostic accuracy of whole-body (WB) DW-MRI with 2-[ 18 F]FDG PET for staging and treatment monitoring of children with Langerhans cell histiocytosis (LCH). Methods Twenty-three children with LCH underwent 2-[ 18 F]FDG PET and WB DW-MRI at baseline. Two nuclear medicine physicians and two radiologists independently assessed presence/absence of tumors in 8 anatomical areas. Sixteen children also performed 2-[ 18 F]FDG PET and WB DW-MRI at follow-up. One radiologist and one nuclear medicine physician revised follow-up scans and collected changes in tumor apparent diffusion (ADC) and standardized uptake values (SUV) before and after therapy in all detectable lesions. 2-[ 18 F]FDG PET results were considered the standard of reference for tumor detection and evaluation of treatment response according to Lugano criteria. Sensitivity, specificity, positive and negative predictive values, and diagnostic accuracy of WB DW-MRI at baseline were calculated, and the 95% confidence intervals were estimated by using the Clopper-Pearson (exact) method; changes in tumor SUVs and ADC were compared using a Mann–Whitney U test. Agreement between reviewers was assessed with a Cohen’s weighted kappa coefficient. Analyses were conducted using SAS software version 9.4. Results Agreement between reviewers was perfect (kappa coefficient = 1) for all analyzed regions but spine and neck (kappa coefficient = 0.89 and 0.83, respectively) for 2-[ 18 F]FDG PET images, and abdomen and pelvis (kappa coefficient = 0.65 and 0.88, respectively) for WB DW-MRI. Sensitivity and specificity were 95.5% and 100% for WB DW-MRI compared to 2-[ 18 F]FDG PET. Pre to post-treatment changes in SUV ratio and ADC mean were inversely correlated for all lesions ( r : -0.27, p = 0·06) and significantly different between responders and non-responders to chemotherapy ( p = 0.0006 and p = 0·003 for SUV ratio and ADC mean , respectively). Conclusion Our study showed that WB DW-MRI has similar accuracy to 2-[ 18 F]FDG PET for staging and treatment monitoring of LCH in children. While 2-[ 18 F]FDG PET remains an approved radiological examination for assessing metabolically active disease, WB DW-MRI could be considered as an alternative approach without radiation exposure. The combination of both modalities might have advantages over either approach alone.