Measurements of proton beam attenuation radiographs at a clinical facility

Abstract

In recent years, a proton computed tomography (pCT) demonstrator was installed and tested at the MedAustron facility in Wiener Neustadt, Austria. It consists of four double-sided silicon strip detectors (DSSDs) for particle tracking and a range telescope to obtain the residual range of the protons that passed through the object to be imaged. Besides conventional pCT, which uses the energy loss information of the single ions, the tracker of the demonstrator also allows for other imaging modalities such as beam attenuation imaging (also referred to as fluence loss imaging). When a proton beam passes through a medium, a certain fraction of the incident primary particles gets absorbed due to the inelastic scattering with the atomic nuclei of the material. Recent studies investigating proton imaging based on inelastic nuclear scattering at clinical energies with single-particle tracking used Monte Carlo simulations and lack additional experimental validation. In this work, proton radiographs based on beam attenuation were measured at clinical beam energies (100.4 MeV, 145.4 MeV) and, for the first time, at 800 MeV. As phantom, an aluminum stair profile was imaged at two different rotation angles to investigate material thicknesses between 2 mm and 10 mm. The recorded beam attenuation was compared to existing reference data from prior measurements and the inelastic nuclear cross sections as incorporated in the Geant4 database. Furthermore, the measurement at 800 MeV could be compared to an existing measurement of the inelastic nuclear cross section of aluminum at a similar energy (792.9 MeV).