PRIMA proton imaging for clinical application

PRIMA project is an Italian project funded by INFN and MIUR (PRIN 2006), which developed a proton Computed Tomography (pCT) prototype based on tracking the single proton. PRIMA approaches to the pCT consist in the use of silicon detectors, which measure the energy and position of individual protons before and after they traverse the object. The device consists of a silicon microstrip tracker, used to reconstruct the trajectory of each proton, and a calorimeter that measure the particle residual energy. It is characterized by an active area of 5 × 5 cm² and by an acquisition rate of 10kHz. PRIMA prototype was tested, under 62 MeV proton beam at Laboratory Nazionali del Sud, (Catania Italy) and under 180 MeV proton beam at Svedberg Laboratories, Uppsala Universitet, (Uppsala Sweden). Several experiments concerning proton imaging, tomography and radiography images, were carried out during these beam tests. In particular in this paper will be reported the PRIMA experience on the data acquired using special phantoms. The performed tests aimed to evaluate the clinical applicability of proton radiography in terms of image quality. In order to test spatial resolution, electron density resolution and energy resolution of the system, PRIMA group has developed suitable phantoms for radiography. The phantoms are custom-made and suitable for high-contrast spatial resolution. They are PolyMetilMetacrilate (PMMA) cylinders with holes of different size and depth. In particular, the phantom diameter was chosen accordingly with the tracker field of view while the phantom length depends on the beam quality: it was 20mm and 150mm for 60MeV and 180MeV proton beam respectively. In this paper the experimental setup will be described, radiographic images will be shown and quantitative results on spatial resolution will be reported.