Optimising FDG-PET/CT Segmentation in Metastatic Breast Cancer: Comparison of SUVmax Thresholds Using syngo.via

Objectives: Semi-automated lesion delineation in FDG-PET/CT is sensitive to the maximum standardised uptake value (SUVmax) threshold used, but its effect on quantitative outputs and image-quality surrogates is not standardised. We compared commonly used thresholds to identify a practical setting for workstation-based SUVmax-threshold segmentation in syngo.via, within a PERCIST-consistent clinical workflow. Material and Methods: We retrospectively reviewed FDG-PET/CT scans from 37 women with metastatic breast cancer, each with a single metastatic lesion. Lesions were contoured in syngo.via using fixed isocontours at 20%, 30%, 40% and 50% of lesion SUVmax. For each threshold, we calculated SUVmean, metabolic tumour volume (MTV), total lesion glycolysis (TLG), signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). Medians and percentage changes were summarised, and trends were visualised with line charts. Differences across thresholds were assessed using Friedman tests; associations between metrics were examined with Spearman correlation. Results: Increasing the threshold from 20% to 50% increased median SUVmean by 52% (3.35 to 5.09), SNR by 59% (52.00 to 82.64), and CNR by 62% (48.25 to 78.09), while reducing MTV by 81% (4.51 to 0.84 cm 3 ) and TLG by 69% (14.35 to 4.49) (all p <0.001). SUVmean, SNR, and CNR were strongly positively correlated (ρ>0.9), whereas MTV and TLG were strongly negatively correlated (ρ<−0.9) as the threshold increased. The 40% threshold provided a workable middle ground, improving conspicuity without an excessive loss of volumetric burden. Conclusion: A 40% SUVmax threshold appears to offer the most balanced overall workstation-based setting in syngo.via, supporting lesion detection while preserving clinically meaningful estimates of disease extent for staging and treatment monitoring.