Dosimetry of Proton Beams

Dosimetry in proton beam therapy (PBT) is a technology that delivers a precise determination of the physical dose for a therapeutic exposure. The physical dose is a basic quantity that determines two derivative quantities of biological dose in Gy and radiological protection dose in Sv. Field dosimeters and dose monitors in PBT and radiation therapy (RT) are calibrated by measuring a calibration factor of the absorbed dose in water according to the IAEA TRS 398, the standard dosimetry method. In the usual PBT or RT facility, the thimble-type ionization chamber is a standard dosimeter commonly used worldwide. The calibration factor must be calibrated for the primary (reference) dosimeter at least once a year at SSDL, traced to other dosimeters and dose monitors in each PBT or RT facility. Importantly, daily treatment for dose monitors is to be calibrated to assure the stability of the calibration factor and dose precision.