Assembling and test of a proton computed radiography apparatus

Proton computed tomography (pCT) is a medical imaging method, based on the use of proton beams with kinetic energy of the order of 250 MeV, aimed to directly measure the stopping power distribution of tissues (presently calculated from X-rays attenuation coefficients), thus improving the accuracy of treatment planning in hadron therapy. A pCT system should be capable to measure tissue electron densities with an accuracy better than 1% and with a spatial resolution better than 1 mm. The blurring effect due to multiple Coulomb scattering can be circumvented by single proton tracking. As a first step toward pCT, we designed a proton computed radiography (pCR) prototype capable to carry out a single projection. The pCR apparatus includes a tracker (based on identical tracker modules, each including a silicon microstrip detector) to measure proton trajectory and a calorimeter (made of four YAG:Ce optically separated crystals) to measure residual energy. The tracker modules have been extensively tested and calibrated with beta particles and 62 MeV protons. The calorimeter has been tested with 62 MeV and 200 MeV protons, as well. The tracker assembly and the test of the tracker modules coupled to the calorimeter are presently under way. Results from these experiments are presented in this contribution.