Fig. 6From: Monitoring of breathing motion in image-guided PBS proton therapy: comparative analysis of optical and electromagnetic technologiesMeasurement distortion during EM tracking in close proximity of a CT scanner. Topogram (top-left panel) divided in CT preparation (PREP) and acquisition (X-RAY) stages, and 3D CT imaging (bottom-left panel) acquisition protocols. Probability density function of measurement error is shown in the right hand panel Back to article page