The measurement of proton stopping power using proton-cone-beam computed tomography

xA cone-beam computed tomography (CT) system utilizing a proton beam has be en developed and tested. The cone beam is produced by scattering a 160 MeV proton beam with a modifier that results in a signal in the detector system , which decreases monotonically with depth in the medium. The detector syst em consists of a Gd2O2S:Tb intensifying screen viewed by a cooled CCD camer a. The Feldkamp-Davis-Kress cone-beam reconstruction algorithm is applied T o the projection data to obtain the CT voxel data representing proton stopp ing power. The system described is capable of reconstructing data over a 16 x 16 x 16 cm(3) volume into 512 x 512 x 512 voxels. A spatial and contrast resolution phantom was scanned to determine the performance of the system. Spatial resolution is significantly degraded by multiple Coulomb scatterin g effects. Comparison of the reconstructed proton CT values with x-ray CT d erived proton stopping powers shows that there may be some advantage to obt aining stopping powers directly with proton CT. The system described sugges ts a possible practical method of obtaining this measurement in vivo.