A study on multiplex proton imaging using GEANT4

Treatment planning systems in proton therapy facilities employ X-ray CT images for dose calculation of a patient. Since the interactions of X-ray in matter are fundamentally different from those of proton, the X-ray image has to be translated into the stopping power map of protons for dose calculation. This conversion induces intrinsic discrepancy and known as the limitation of proton treatment plan based on X-ray imaging. Proton imaging is considered to be a direct measurement of stopping power map and is expected to improve the treatment accuracy. In this paper, we report on a study about the multiplex proton imaging using the GEANT4 simulation. The multiplex proton images have been reconstructed by using 250 MeV mono energetic proton beam. Two imaging schemes were proposed i.e. the range scan imaging scheme and the multiple-scattering imaging scheme. The range scan imaging scheme used a range modulator in variable thickness, in order to obtain energy dependent proton images. The proton images were reconstructed by accumulating energy deposits in a water equivalent detector of which thickness was 1 cm. The multiple-scattering imaging scheme was reconstructed by calculating the spatial displacement due to multiple Coulomb scattering in the object. Both methods successfully reconstructed the image of artificial organs in a water phantom.