Reliability of 3 Strategies of Orbital Tumor Volume Measurement Using Phantom Modeling

The reliability of 3 volume measurement strategies was investigated using MRI and a simple method for creating phantom orbit tumors.

Water-based starch was molded into orbital "tumors" of 3 shapes (sphere, ovoid, diffuse); water displacement was used to calculate volume. "Tumors" were placed into 3D-printed orbit phantoms, MRIs were obtained and volume analysis was performed. Observers measured tumor volume using ellipsoid volume (EV), manual segmentation, and semi-automated segmentation strategies. Intraclass correlation coefficients were calculated comparing observer measurements to true volumes. The coefficient of repeatability determined the percentage of tumor volume change required for each method to detect tumor growth.

Intraclass correlation coefficients comparing measured volumes to true volumes using EV, manual segmentation, and semi-automated segmentation were 0.61, 0.98, and 0.99 for spherical, 0.64, 0.97, and 0.98 for ovoid, and 0.18, 0.82, and 0.87 for diffuse tumors. Semi-automated segmentation followed by manual segmentation had the highest correlation between measured and true tumor volume for all 3 tumor geometries. EV had low correlation with true volume for all tumor geometries. Diffuse tumors had high variability and low correlation for all 3 measurement techniques.

This study shows the reliability of 3 strategies to measure orbital tumor volume with MRI based on tumor geometry, using a simple phantom model. EV, the most commonly employed strategy in clinical practice, had low correlation and high variability across tumor shapes. Using manual segmentation and semi-automated segmentation, a measured change in volume greater than 25% may be considered true growth, while the EV strategy required a 40%-400% change in volume to reliably measure tumor growth.