Evaluation of Spatial Resolution for Heavy Ion CT System Based on the Measurement of Residual Range Distribution With HIMAC

We report experimental results from a heavy ion CT system based on the measurement of residual range distribution using an X-ray intensifying screen and a charged coupled device (CCD) camera system. This technique was first investigated by Zygmanski (2000) for proton beams, and they reported that the spatial resolution was significantly degraded by multiple Coulomb scattering (MCS) effects in the irradiated medium. Experiments were done on the spatial resolution phantom by using helium and carbon beams accelerated up to 120 MeV/u and 230 MeV/u by the Heavy Ion Medical Accelerator in Chiba (HIMAC), installed in the National Institute of Radiological Sciences (NIRS) in Japan, using a high performance intensified CCD (ICCD) camera. We show that the MCS blurring effect can be significantly reduced in the reconstructed image by using a carbon beam with this technique. Our results suggest that heavier particles such as carbon would be more useful if this technique is envisioned as a clinical tool to obtain data that would aid proton and/or heavy ion treatment planning.