Proton radiographs improve range prediction

Proton therapy planning relies upon estimates of particle range in the patient, typically derived from a stoichiometric calibration that converts Hounsfield units (HU) in an X-ray CT scan to relative stopping powers (RSP). This approach uses literature values of tissue composition, however, and patient-to-patient variations can result in RSP errors of over 2%, placing a lower limit on treatment planning margins. Researchers, including a team at University College London, have devised a patient-specific calibration approach. Their strategy uses a proton radiograph to improve estimates of range that are quantified using water equivalent path lengths (WEPL)