Optimal method for metabolic tumour volume assessment of cervical cancers with inter-observer agreement on [18F]-fluoro-deoxy-glucose positron emission tomography with computed tomography.

PURPOSE

Cervical cancer metabolic tumour volume (MTV) derived from [18F]-FDG PET/CT has a role in prognostication and therapy planning. There is no standard method of outlining MTV on [18F]-FDG PET/CT. The aim of this study was to assess the optimal method to outline primary cervical tumours on [18F]-FDG PET/CT using MRI-derived tumour volumes as the reference standard.

METHODS

81 consecutive cervical cancer patients with pre-treatment staging MRI and [18F]-FDG PET/CT imaging were included. MRI volumes were compared with different PET segmentation methods. Method 1 measured MTVs at different SUV thresholds ranging from 20 to 60% (MTV-MTV) with bladder masking and manual adjustment when required. Method 2 created an isocontour around the tumour prior to different SUV thresholds being applied. Method 3 used an automated gradient method. Inter-observer agreement of MTV, following manual adjustment when required, was recorded.

RESULTS

For method 1, the MTV and MTV were closest to the MRI volumes for both readers (mean percentage change from MRI volume of 2.9% and 13.4% for MTV and - 13.1% and - 2.0% for MTV for readers 1 and 2). 70% of lesions required manual adjustment at MTV compared with 45% at MTV. There was excellent inter-observer agreement between MTV to MTV (ICC ranged from 0.898-0.976 with narrow 95% confidence intervals (CIs)) and moderate agreement at lower thresholds (ICC estimates of 0.534 and 0.617, respectively for the MTV and MTV with wide 95% CIs). Bladder masking was performed in 86% of cases overall. For method 2, excellent correlation was demonstrated at MTV and MTV (mean % change from MRI volume of -3.9% and - 8.6% for MTV and - 16.9% and 19% for MTV for readers 1 and 2, respectively). This method also demonstrated excellent ICC across all thresholds with no manual adjustment. Method 3 demonstrated excellent ICC of 0.96 (95% CI 0.94-0.97) but had a mean percentage difference from the MRI volume of - 19.1 and - 18.2% for readers 1 and 2, respectively. 21% required manual adjustment for both readers.

CONCLUSION

MTV provides the optimal correlation with MRI volume taking into consideration the excellent inter-reader agreement and less requirement for manual adjustment.