Development of a Proton Computed Radiography Apparatus

There is today a growing up interest in proton therapy for tumor treatment, because these particles permit to tightly shape the dose to the target. Anyway, the accuracy in the determination of dose distribution for proton therapy is presently limited by the uncertainty in stopping power distribution, which is calculated from the photon attenuation coefficients measured by X-ray tomography. A proton computed tomography apparatus (pCT) could be used to directly measure stopping power and reduce this uncertainty. The main problem with proton imaging is the blurring effect introduced by multiple Coulomb scattering, but single proton tracking is a promising technique to face this difficulty. As a first step toward a pCT system, we designed a proton radiography (pCR) prototype based on a silicon microstrip tracker to characterize particle trajectories and on a segmented YAG:Ce calorimeter to measure their residual energy. The target is to detect protons with initial kinetic energy in the range 250-270 MeV and with a particle rate of ∼1MHz. Design and development of the pCR prototype, as well as the characterization of its single components, are described in this article. Status of development of reconstruction algorithms capable to account for Coulomb scattering is reported too.