Kidney Tumor Location Measurement Using the C Index Method

Purpose: Tumor location assessment is essential to plan nephron sparing kidney surgery. We describe a method to quantify the proximity of kidney tumors to the renal central sinus for reporting and surgical management. Materials and Methods: Centrality index scoring was done using standard 2-dimensional cross-sectional computerized tomography images in 133 consecutive patients undergoing transperitoneal laparoscopic partial nephrectomy between September 2003 and November 2005. The Pythagorean theorem was used to calculate the distance from tumor center to kidney center. The distance was divided by tumor radius to obtain the centrality index. We assessed the correlation of the centrality index with laparoscopic partial nephrectomy operative parameters and the urological complication rate. Centrality index accuracy and interobserver variability were assessed. Results: A centrality index of 0 equates to a tumor that is concentric with the center of the kidney. A centrality index of 1 equates to a tumor with its periphery touching the kidney center. As the centrality index increases, the tumor periphery becomes more distant from the kidney center. Multivariate regression analysis revealed an association of the centrality index with warm ischemia time (p = 0.004), which is a surrogate for technical complexity. Interobserver correlation of centrality index values was greater than 93% with an estimated learning curve of 14 cases required for measurement variability to decrease below 10% of the mean centrality index of 10 consecutive cases. Conclusions: Centrality index scoring provides a clinically useful measure of tumor centrality. This system may allow improved clinical and radiological assessment of kidney tumors, and improved reporting of quantitative tumor site.