# External Validation of an Open-Source Model for Automated Muscle Segmentation in CT Imaging of Cancer Patients

## TL;DR

This study validates an open-source AI model for automatically segmenting muscles in CT scans of cancer patients, showing high accuracy but noting limitations at low BMI.

## Contribution

The study provides external validation of an open-source AI model for muscle segmentation in CT scans using an independent dataset.

## Key findings

- The AI model achieved a median Dice Similarity Coefficient of 0.978 and a median Segmentation Surface Error of 3.863 cm².
- Segmentation errors were more frequent in abdominal wall muscles and at lower BMI values.
- The model showed robustness to variations in arm positioning during scans.

## Abstract

Computed tomography (CT) at the third lumbar vertebra (L3) is widely used for muscle quantification, but manual segmentation is labor intensive. This study externally validates an AI model, trained on a public dataset, for automated L3 muscle segmentation using an independent cohort, including a subgroup analysis of subject characteristics (e.g., age and a history of cancer). The AI model was trained on 900 CT scans with expert annotations from a publicly available repository. Validation was performed on 232 PET CT scans from the University Hospital Brussels, each manually segmented by an expert. Segmentation post-processing employed a density-based clustering algorithm to discard arm muscles and Hounsfield unit (HU) thresholding to refine the muscle segmentation. Performance was assessed using the Dice Similarity Coefficient (DSC) and Segmentation Surface Error (SSE). The model achieved a median DSC of 0.978 and a median SSE of 3.863 cm2 across the validation set. At lower BMI values, the model was more prone to overestimation of muscle surface area. Most segmentation errors occurred in the abdominal wall muscles. Analysis showed no significant difference between arm positioning above the head and alongside the body, indicating robustness to minor artifacts from arm positioning. The AI model delivers accurate, automated L3 muscle segmentation, supporting larger-scale body composition studies. However, diminished accuracy at low BMI values and limited demographic diversity of the data highlight the need for broader validation.