Study of spatial resolution and electron density measurement for proton computed tomography

PurposeProton computed tomography (PCT) is an imaging technique using a high-energy proton beam penetrating the human body. Accurate electron density distribution can be derived with PCT. However, the deterioration of the spatial resolution owing to multiple Coulomb scattering is a crucial issue. The spatial resolution of the PCT image is determined by magnitudes of multiple Coulomb scattering in detector material and the resolution of the position measurement of the tracking detector. To avoid deterioration of spatial resolution by multiple Coulomb scattering, reconstructing the single proton trajectory is a promising method to collect as much information as possible. Therefore, we chose a single-sided silicon strip detector as a tracking detector, and we developed a prototype system. In this report, the result of the beam test is introduced.MethodsWe performed the beam test at the HIMAC SB2 beamline, the National Institute of Radiological Sciences, Japan. All measurements were done with a proton beam of 160 MeV. The object for imaging is small(～25 mm in thickness) and made of polyethylene and acrylic. The proton energy was measured with a calorimeter at the most downstream position. Because the data-taking speed of the total system is low(～200Hz), the phantom was not rotated during the data taking. Study of the spatial resolution is done with the projected images. We also confirmed the accuracy of the density resolution of the PCT image.ResultsWe demonstrated an improvement in spatial resolution by reconstructing the proton trajectory. A spatial resolution of 0.45 mm is achieved for a 25-mm-thick polyethylene object.This result implies that those methods are useful for improving spatial resolution.ConclusionWe confirmed that the spatial resolution is improved by reconstructing the proton trajectory. The next step is to drastically improve the data-taking speed.The 7th Korea-Japan Joint Meeting on Medical Physic