MEASUREMENT OF RENAL TUMOR SIZE ON MEDICAL IMAGING: THE IMPACT OF 2D VERSUS 3D METHODS ON THE T-STAGE
Abstract
Introduction When resecting a localized kidney tumour, surgeons should understand the patient-specific complexity. T-staging helps by classifying the tumour based on its maximal diameter: T1a (≤4cm), T1b (>4-7cm), T2a (>7-10cm) or T2b (>10cm). These thresholds were based on post-op measurements of resected tumours. For treatment planning, however, diameters are measured on pre-op medical images (e.g. CT). Radiologists use three manual methods, varying in accuracy and speed. In this study, these pre-op methods are examined and compared to post-op staging and three new methods are proposed. Materials and Methods Six measurements methods were tested to calculate the tumour diameter in 173 patients. 3D models were segmented on CT for automatic analysis with PyRadiomics. Paired t-tests were used to compare all methods. To identify the method correlating best with surgical complexity, operation time (OT) and estimated blood loss (EBL) were compared (T1a vs. T1b) using unpaired t-tests. Effect sizes (Cohen's d) were used to check their relevance. Results Comparing T-stages to the 2D oblique method (most accurate method currently used), the 3D diameter method upstages 4.0% of the cases, while all other methods downstage several cases (3D volume: 16.8%; 2D ellipsoid: 13.9%; 2D axial: 5.2%; 2D perpendicular: 4.0%). The result of the 3D diameter method is on average 16.9% larger than the post-op diameter. All methods significantly differ between T1a and T1b regarding surgical complexity. For EBL, 2D axial has the largest effect size (d = 0.75), followed by 3D volume (d=0.73). For OT, the post-op diameter has the largest effect size (d=1.35), followed by 3D volume (d=1.26). Discussion and Conclusions This investigation is part of a larger scale project to develop a pre-op planning platform for (partial) nephrectomies. This study shows that the measurement method influences the T-staging, which may directly impact the preferred treatment plan. Hence, surgeons should be aware of the used method.