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

Abstract

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 _max thresholds ranging from 20 to 60% (MTV ₂₀-MTV ₆₀) with bladder masking and manual adjustment when required. Method 2 created an isocontour around the tumour prior to different SUV _max 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 ₂₅ and MTV ₃₀ were closest to the MRI volumes for both readers (mean percentage change from MRI volume of 2.9% and 13.4% for MTV ₂₅ and − 13.1% and − 2.0% for MTV ₃₀ for readers 1 and 2). 70% of lesions required manual adjustment at MTV ₂₅ compared with 45% at MTV ₃₀. There was excellent inter-observer agreement between MTV ₃₀ to MTV ₆₀ (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 ₂₀ and MTV ₂₅ with wide 95% CIs). Bladder masking was performed in 86% of cases overall. For method 2, excellent correlation was demonstrated at MTV ₂₅ and MTV ₃₀ (mean % change from MRI volume of −3.9% and − 8.6% for MTV ₂₅ and − 16.9% and 19% for MTV ₃₀ 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 ₃₀ provides the optimal correlation with MRI volume taking into consideration the excellent inter-reader agreement and less requirement for manual adjustment.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-020-05136-8.