Fig. 3From: Monitoring of breathing motion in image-guided PBS proton therapy: comparative analysis of optical and electromagnetic technologiesTesting of tracking system technologies in the Gantry 2 facility at PSI (couch in treatment position), the arrows point to 3 EM sensors (left panel) and 5 optical markers (right panel). The detail view in right panel shows the gantry configuration VI from Table 1 Back to article page