Figure 1.

Schematic illustration of the first-generation pCT scanner. Protons are individually recorded by the four planes of position-sensitive silicon detectors which form the scanner reference system. These four planar detectors provide positions as well as angles of the protons in front and behind the object. A signal proportional to the energy of each outgoing proton is recorded with a segmented calorimeter in coincidence with its position and angle information. For a complete scan, the object is traversed by broad proton cone beam from many different projection angles