Defining region boundaries to assess the peritoneal cancer index on imaging: a Delphi study

Background: The gold standard for evaluating the presence and extent of peritoneal lesions is determining the surgical peritoneal cancer index (PCI). However, there is a growing need for non-invasive methods to assess peritoneal lesions. While the standardised and quantified PCI scoring system can be applied to imaging, the region definitions used for surgical PCI assessment are not directly applicable to radiological assessment. Purpose: To define region boundaries applicable to radiological PCI assessment. Materials and methods: A Delphi study was conducted among 88 international experts, including radiologists, surgeons and gynaecologists. Within a questionnaire, the proposed regions for radiological PCI evaluation were shown as overlays on a CT scan and 3D volumes. Participants rated their level of agreement for each structure and region boundary on a 5-point Likert scale in iterative rounds. Consensus was defined as > 75% agreement and < 15% disagreement, and major agreement was defined as 60–75% agreement. Results: In the first Delphi round, 45 experts participated, leading to consensus on 45 of 52 statements. Regions 3, 5, 7, and 9–12 required further refinement. In the second round, 40 experts participated, resulting in consensus on three additional structures/boundaries. For all remaining structures/boundaries, a major agreement was obtained. Final adjustments involved revising terminology for the lower boundaries of regions 5 and 7 and adopting more practical boundaries for regions 9–12 to ensure equal small bowel volumes in these regions. Conclusion: This study defined region boundaries for radiological PCI assessment, facilitating a structured and practical approach for objective evaluation of peritoneal lesions on imaging. Key Points: Question There is a growing need for a non-invasive and standardised imaging method to assess the presence and extent of peritoneal lesions. Findings This Delphi study achieved expert consensus on most region boundaries for evaluating the radiological PCI, providing structured guidelines for imaging-based assessment of peritoneal lesions. Clinical relevance This study establishes imaging guidelines for assessing peritoneal lesions, enabling more consistent and objective patient evaluations in clinical practice, potentially reducing the need for invasive procedures.