Peritoneal Cancer Index Correlates with Radiographic Assessment of Colorectal Carcinomatosis

Background. The Peritoneal Cancer Index (PCI), calculated intraoperatively, has previously yielded mixed results when correlated with computed tomography. This study aimed to quantify variation in this scoring method comparing radiologists' and surgeons' radiologic PCI (rPCI) assessment. Methods. The rPCI of 104 patients treated at a single institution for peritoneal carcinomatosis was calculated by an abdominal radiologist and a surgeon. An additional 36-patient cohort was studied to compare preoperative rPCI with intraoperative gold standard PCI. Agreement was compared using kappa statistics. Results. The rPCI of the 104 patients studied ranged from 2 to 39 (median, 12; interquartile range [IQR], 6-23) by the radiologist's analysis and 2 to 37 (median, 9; IQR, 6-15) by the surgeon's analysis. There was good agreement for PCI cutoffs of 15 (77.48%; kappa, 0.40) and 20 (78.63%; kappa, 0.24). The 36-patient cohort undergoing surgical exploration showed a median rPCI of 4 (IQR, 2-5.75) and a median intraoperative PCI of 11 (IQR, 6-12), with a significant difference in score by method (p < 0.001, Wilcoxon signed-rank test). Conclusions. For rPCI cutoffs greater than 15 and 20, the surgeon's and radiologist's rPCI showed strong concordance, denoting the interobserver reproducibility of rPCI. Moreover, concordance with intraoperative PCI translated to radiographic assessment. The rPCI consistently underestimated intraoperative PCI, suggesting that rPCI may be a useful conservative tool for assessing peritoneal burden. Although surgical exploration is needed to "rule in" patients as candidates for CRS, the authors suggest that rPCI can be used to "rule out" patients as CRS candidates based on institutional PCI cutoffs.