@misc{oai:repo.qst.go.jp:00078977,
 author = {Inaniwa, Taku and Inaniwa, Taku},
 month = {Dec},
 note = {Radiation therapy for cancer by using heavy ions has attracted considerable attention. The accelerated heavy ions can deliver a high dose to a tumor while sparing surrounding normal tissue from undesired exposure because of their superior dose distribution around the Bragg peak near the beam range. In addition, due to the high linear energy transfer (LET) of heavy ions, heavy-ion beams show high relative biological effectiveness (RBE) in cell killing as compared to conventional low-LET radiations, especially around the Bragg peak.
Following the pioneering clinical studies of heavy-ion therapy with helium-, carbon-, and neon-ion beams at the Laurence Berkley Laboratory, University of California (LBL) in the USA, the National Institute of Radiological Sciences (NIRS) in Japan started carbon-ion radiotherapy in 1994 based on the argument that carbon ions reasonably behave as low-LET radiation in the entrance normal tissue region and as high-LET radiation in a deep-seated tumor. The NIRS employed a wobbler method for field formation and customization. The system consists of pair of orthogonal bending magnets (wobbler magnets) and a scatter to broaden the beam laterally in conjunction with a ridge filter to broaden the beam longitudinally. This method requires patient specific beam customization devices, i.e., a beam collimator and a range compensator. In the NIRS, carbon-ion radiotherapy has been applied for various tumors, and the optimal dose-fractionation protocols have been established for each tumor through dose escalation clinical studies. Besides these clinical studies, new treatment techniques, e.g., a synchronized gating and a layer-stacking, have been developed and used in clinical treatments. Four more carbon-ion radiotherapy facilities have been constructed and are operating in Japan.
In Germany, the GSI Helmholtz Center for Heavy-Ion Research (GSI) performed clinical studies from 1997 to 2009. The GSI employed a pencil-beam scanning method. In this method, a narrow carbon-ion beam is scanned three dimensionally by a pair of orthogonal magnets (scanning magnets) and a beam energy changing from a synchrotron. This method realizes a better dose distribution. In addition, this method does not require patient specific devices. The technologies developed at the GSI have been transferred to three European facilities (HIT) Marburg Ion-Beam Therapy Center (CNAO) and one Chinese facility (SPHIC). The HIT equipped a world first rotating gantry for carbon-ion radiotherapy, which will be useful for intensity modulated carbon-ion radiotherapy.
The most acute disadvantage of the scanning method is that the method is extremely sensitive to organ motion during treatment. Therefore, in the past decade, one of the biggest research topics in the particle therapy community was how to treat the moving tumor with the scanned ion beams. To deal with this topic, the NIRS initiated a project to construct the New Particle Therapy Research Facility for scanned carbon-ion radiotherapy. The project revealed a rescanning with a synchronized gating is the realistic and effective method for moving tumor treatment with the scanned ion beams. Nowadays, many scanning facilities employed this method for moving tumor treatments in conjunction with real-time respiratory motion monitoring systems.
Ongoing developments include extension of carbon-ion radiotherapy to radiotherapy with multiple ion species to realize simultaneous optimization of dose and radiation quality such as LET or RBE and facility downsizing to expand the availability of carbon-ion radiotherapy by using superconducting magnet technologies., ESTRO meets Asia 2019},
 title = {Current status and future perspective of carbon-ion radiotherapy},
 year = {2019}
}