A novel method for quantitative assessment of irregularity of FDG uptake in head-and-neck carcinoma for prediction of outcome

Objectives: The prognostic value of SUV is unsatisfactory in head-and-neck carcinoma. The aim of the present study was to evaluate a new measure for the irregularity of the tumor`s shape in the FDG image as prognostic factor in this cancer type.

Methods: FDG PET/CT had been performed in 32 patients (61.3±10.1y) with advanced head-and-neck cancer prior to therapy. The FDG image of the primary tumor was segmented using the ROVER 3D segmentation tool based on thresholding at the volume-reproducible intensity threshold after subtraction of local background. The novel irregularity measure (IRREG) is defined as the deviation of the tumor's shape from sphere symmetry, computed as the ratio of the third power of the tumor's surface divided by the second power of its volume. Kaplan-Meier curves with respect to both overall (OAS) and progression-free survival (PFS) were separated by the best discrimination threshold according to ROC analysis and then compared by log-rank tests.

Results: Four patients died during follow-up, 11 experienced tumor progression. Median PFS was 11.3 mo. IRREG was prognostic for OAS (p=0.016), as was the glycolytic volume (GV, p=0.003). Statistical significance for the prediction of PFS was very high for both IRREG (p=0.0003) and GV (p=0.0006). Total mean glycolytic volume was also predictive for PFS, although significance was somewhat lower (p=0.029). Higher tumor irregularity was associated with a higher risk of progression and reduced survival. Pts. with IRREG >2 showed 3-year OAS rate of 58% compared to 92% in pts. with IRREG< 2. Neither SUVmax nor SUVmean was predictive for OAS or PFS.

Conclusions: The irregularity of the pretherapeutic FDG uptake pattern in the primary tumor as quantitatively characterized by the novel measure is predictive for tumor recurrence and survival in patients with head-and-neck carcinoma. The measure should be further evaluated for risk stratification in these patients.