Role of diffusion-weighted MRI in assessing Ewing sarcoma treatment response: Findings from a COG phase III trial.

RATIONALE AND

OBJECTIVES

To correlate quantitative measures of tumor cell density, derived from diffusion-weighted magnetic resonance imaging (MRI), with quantitative measures of tumor glucose metabolism, derived from 18F-FDG positron emission tomography (PET), and post-induction event-free survival (EFS) in patients with metastatic Ewing sarcoma.

MATERIALS AND

METHODS

We performed a secondary review of 21 patients (mean age 14.1 years ±4.67, 12 females) with metastatic Ewing sarcoma who were enrolled in a prospective, multicenter phase III clinical trial by the Children's Oncology Group (AEWS1221) and underwent paired diffusion-weighted MRI and 18F-FDG PET scans at baseline and post induction chemotherapy (after 6 cycles). Tumor size, apparent diffusion coefficient (ADC)mean and ADCmin (whole tumor, viable, and necrotic portions), and standardized uptake values (SUVmax) were measured. Pearson's correlation coefficient was used to assess relationships between continuous imaging biomarkers.

RESULTS

Baseline ADCmean of the viable tumor inversely correlated with SUVmax (R = -0.51, p = 0.022). After induction, SUVmax inversely correlated with whole tumor ADCmin (R = -0.59, p = 0.028) but not with viable tumor ADCmean (R = -0.15, p = 0.62). Both whole tumor ADCmin and viable tumor ADCmean post-induction correlated with tumor volume changes (R = -0.56, p = 0.008; R = -0.5, p = 0.022). None of these biomarkers were associated with EFS risk.

CONCLUSION

Baseline ADCmean (excluding necrosis) may serve as a surrogate for SUVmax, while post-induction ADCmin correlates with metabolic activity but not survival outcomes. Further studies are needed to validate these findings.