Session Item

Tomographic proton imaging is now increasingly being regarded by the international scientific community as a powerful, innovative  tool for the direct measurement of Relative Stopping Power (RSP) maps in proton therapy. To this purpose, a proton computed tomography  (pCT) system, composed by a microstrip silicon tracker and a YaG:Ce calorimeter, has been designed and manufactured by the I.N.F.N. CSN5 PRIMA/IRPT/RDH Collaboration. Measurements carried out with our pCT system at the Trento proton Therapy Center using a 211 MeV proton beam with a certified electron density calibration phantom, provided RSP tomography images reconstructed by customized iterative algebraic reconstruction algorithms. Results show that our system is able to correlate measured and expected RSPs with discrepancies less than 1%. A quantitative comparison of artifacts produced by metal prosthesis in X-CT and pCT using an anthropomorphous head phantom carrying a titanium spinal bone prosthesis and a tungsten dental filling is presented. Reconstructed pCT images evidence a significant reduction of artifacts in the proximity of prosthesis against those found in X-CT ones. Hounsfield Units (HU) standard deviations normalized to mean values up to 12% and 6% have been found for X-CT in ROIs distant about 2cm from titanium spinal bone and 1 cm from tungsten dental filling respectively. In same ROIs of pCT images, RSP standard deviations, normalized to mean, are reduced to about 2-3%. These results evidence the potential benefit of using pCT as a tool for improving tumor targeting precision in hadron therapy. An outlook on future perspectives in the  radiographic / tomographic proton imaging research is finally discussed.