Feasibility of Three-Dimensional Imaging in Accurately Assessing the Peritoneal Cancer Index for Peritoneal Carcinomatosis

Background Accurate preoperative staging of peritoneal carcinomatosis (PC) is crucial for planning cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC). However, conventional imaging often underestimates disease burden. This study evaluated whether three-dimensional (3D) reconstruction based on multimodality imaging improves estimation of the peritoneal cancer index (PCI) compared with CT. Methods We conducted a retrospective analysis of patients with PC undergoing CRS–HIPEC between February 2022 and February 2025. Preoperative imaging included contrast-enhanced CT and multimodality-based 3D reconstruction (CT, MRI, PET). Imaging-derived PCI (CT-PCI and 3D-PCI) was compared with surgical PCI (reference standard). The primary endpoint was the signed difference (PCI_ref − PCI_index). Agreement was assessed using Bland–Altman analysis. Region-level diagnostic performance (sensitivity, specificity, PPV, NPV) was evaluated. Results Among 62 patients undergoing 3D reconstruction, 42 were included in the final analysis. The median signed difference between imaging and surgical PCI was lower for 3D than for CT (2.0 vs 3.0), although not statistically significant ( P = 0.101). Bland–Altman analysis showed a slightly lower mean bias for 3D compared with CT (+5.3 vs +6.2), indicating a tendency toward underestimation by both modalities. Region-level analysis demonstrated high specificity (>90%) but limited sensitivity, particularly in anatomically challenging areas such as the mesenteric root and small-bowel serosa. Conclusions Multimodality-based 3D reconstruction may improve PCI estimation compared with CT alone, although differences were not statistically significant. Both approaches showed limited sensitivity in critical regions. These findings are exploratory and highlight the need for prospective validation.