Association of Tumor [F]FDG Activity and Diffusion Restriction with Clinical Outcomes of Rhabdomyosarcomas.

PURPOSE

To evaluate whether the extent of restricted diffusion and 2-deoxy-2-[F] fluoro-D-glucose ([F]FDG) uptake of pediatric rhabdomyosarcomas (RMS) on positron emission tomography (PET)/magnetic resonance (MR) images provides prognostic information.

PROCEDURE

In a retrospective, IRB-approved study, we evaluated [F]FDG PET/CT and diffusion-weighted (DW) MR imaging studies of 21 children and adolescents (age 1-20 years) with RMS of the head and neck. [F]FDG PET and DW MR scans at the time of the initial tumor diagnosis were fused using MIM software. Quantitative measures of the tumor mass with restricted diffusion, [F]FDG hypermetabolism, or both were dichotomized at the median and tested for significance using Gray's test. Data were analyzed using a survival analysis and competing risk model with death as the competing risk.

RESULTS

[F]FDG PET/MR images demonstrated a mismatch between tumor areas with increased [F]FDG uptake and restricted diffusion. The DWI, PET, and DWI + PET tumor volumes were dichotomized at their median values, 23.7, 16.4, and 9.5 cm, respectively, and were used to estimate survival. DWI, PET, and DWI + PET overlap tumor volumes above the cutoff values were associated with tumor recurrence, regardless of post therapy COG stage (p = 0.007, p = 0.04, and p = 0.07, respectively).

CONCLUSION

The extent of restricted diffusion within RMS and overlap of hypermetabolism plus restricted diffusion predict unfavorable clinical outcomes.