Systems, devices and methods related to calibration of a proton computed tomography scanner

A proton computed tomography system comprising:

• a calibration device comprising a plurality of degrader plates configured to be introduced into a beam of protons along a beam axis, each of the plurality of degrader plates having a known water-equivalent thickness (WET) value;
• a particle detection system configured to generate signals in response to interaction between a proton and the particle detection system comprising:
• a front tracker detector positioned so that the beam axis intersects the front tracker detector prior to the calibration device;
• a rear tracker detector positioned so that the beam axis intersects the rear tracker detector after the calibration device;
• and
• an energy detector positioned so that the beam axis intersects the energy detector after the calibration device;
• a processor configured to determine, for each of a plurality of protons that interact with the particle detection system:
• a path through the calibration device, the path determined by analyzing signals generated by the front tracker detector and the rear tracker detector;
• an energy measurement determined by analyzing signals generated by the energy detector;
• and
• a calibration factor relating the energy measurement to a water-equivalent path length (WEPL), the WEPL based on the known WET values and the path through the calibration device.