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Conceptual design of a synchrotron light source used for medical diagnoses at NIRS

A synchrotron light source dedicated to medical applications is designed at NIRS. The synchrotron ring accelerates electrons up to 1.8 GeV and stores them with about 400 mA, and is equipped with two superconducting multipole wigglers to generate sufficient photon flux for medical diagnoses. One of the most interesting applications for us is monochromatic x-ray computed tomography (CT). It plays an important role in advancing heavy ion radiotherapy of cancers which is being performed at NIRS. The radiotherapy is carried out based on a treatment planning which is a protocol for irradiation of the heavy ion beam on a target to maximize dose distribution and a biological advantage. The treatment planning converts CT-number of tissues along paths of the heavy ion beam to electron densities in order to calculated end-of-range of the heavy ion beam. The conventional x-ray CT introduces uncertainty into the CT- numbers due to beam hardening effect. While the monochromatic x-ray makes the CT-scan free from the beam hardening effect. Furthermore, dual energy x-ray CT-scans give the electron density directly without conversion from the CT-number. We focus on the x-ray CT using two monochromatic x-rays, and outline its beamline and the compact ring.