PROTON DOSE MONITORING WITH PET - QUANTITATIVE STUDIES IN LUCITE

The feasibility of using PET for proton dose monitoring is examined he re in detail. First experimental studies in a Lucite phantom have been performed at the medical TRIUMF proton beamline for proton energies o f 62 MeV and 110 MeV. The proton dose delivered to the phantom ranged from 16 Gy up to 317 Gy. The induced activity was analysed 20-40 min a fter the irradiation with a PET scanner.The obtained depth activity pr ofiles were compared to our calculation based on a model using availab le isotope production cross-section data. Both the observed absolute c ount rates and the activity profiles were found to agree very well wit h this model. Effects such as proton range straggling, inelastic nucle ar interactions and the energy spectrum of the emitted positrons were studied in detail and found to change the activities by 5-10%. The lat eral deposition of dose in the phantom could be very well localized by the induced activity. However, the spatial correlation between dose d epth profiles and depth activity profiles was found to be poor, hence the extraction of isodose profiles from activity profiles seems to be very difficult.