The compact electron cyclotron resonance ion source KeiGM for the carbon ion therapy facility at Gunma University

Evaluation of a therapeutic carbon beam using a G2000 glass scintillator

A G2000 glass scintillator (G2000-SC) was used to determine the carbon profile and range of a 290-MeV/n carbon beam used in heavy-ion therapy because it was sensitive enough to detect single-ion hits at hundreds of mega electron Volts. An electron-multiplying charge-coupled device camera was used to detect the ion luminescence generated during the irradiation of G2000-SC with the beam. The resulting image showed that the position of the Bragg peak can be determined. The beam passes through the 112-mm-thick water phantom and stops 5.73 ± 0.03 mm from the incident side to the G2000-SC. Additionally, the location of the Bragg peak was simulated when irradiating G2000-SC with the beam using the Monte Carlo code particle and heavy ion transport system (PHITS). Simulation results show that the incident beam stops at 5.60 mm after entering G2000-SC. The beam stop location obtained from images and the PHITS code is defined at 80% distal fall-off from the Bragg peak position. Consequently, G2000-SC provided effective profile measurements of therapeutic carbon beams.

Development of 1.2-GHz ECR ion source and Wien filter for inexpensive ion beam processing system

A desktop-sized ion beam processing system with an inexpensive electron cyclotron resonance (ECR) ion source has been developed for industrial applications at the National Institute of Technology, Toyama College. A commercially available 1.2- to 1.3-GHz transceiver is adopted as a microwave source to generate the ECR plasma. The minimum-B magnetic field is formed by arranging small rectangular permanent magnets. A Wien filter with orthogonal electric and magnetic fields is employed as a beam separator. At the end of the beam line, a processing chamber with a substrate stage for ion beam applications, such as ion implantation and microfabrication, is installed. Here, we report the results of the first experiment. Ar ion beams with a current of approximately 62 µA were obtained at an extraction voltage of 4 kV. In addition, we demonstrate that Ar and Xe ions can be separated by the Wien filter.

Development of a compact ECR ion source for various ion production

There is a desire that a carbon-ion radiotherapy facility will produce various ion species for fundamental research. Although the present Kei2-type ion sources are dedicated for the carbon-ion production, a future ion source is expected that could provide: (1) carbon-ion production for medical use, (2) various ions with a charge-to-mass ratio of 1/3 for the existing Linac injector, and (3) low cost for modification. A prototype compact electron cyclotron resonance (ECR) ion source, named Kei3, based on the Kei series has been developed to correspond to the Kei2 type and to produce these various ions at the National Institute of Radiological Sciences (NIRS). The Kei3 has an outer diameter of 280 mm and a length of 1120 mm. The magnetic field is formed by the same permanent magnet as Kei2. The movable extraction electrode has been installed in order to optimize the beam extraction with various current densities. The gas-injection side of the vacuum chamber has enough space for an oven system. We measured dependence of microwave frequency, extraction voltage, and puller position. Charge state distributions of helium, carbon, nitrogen, oxygen, and neon were also measured.

A review of ion sources for medical accelerators (invited)

There are two major medical applications of ion accelerators. One is a production of short-lived isotopes for radionuclide imaging with positron emission tomography and single photon emission computer tomography. Generally, a combination of a source for negative ions (usually H- and/or D-) and a cyclotron is used; this system is well established and distributed over the world. Other important medical application is charged-particle radiotherapy, where the accelerated ion beam itself is being used for patient treatment. Two distinctly different methods are being applied: either with protons or with heavy-ions (mostly carbon ions). Proton radiotherapy for deep-seated tumors has become widespread since the 1990s. The energy and intensity are typically over 200 MeV and several 10(10) pps, respectively. Cyclotrons as well as synchrotrons are utilized. The ion source for the cyclotron is generally similar to the type for production of radioisotopes. For a synchrotron, one applies a positive ion source in combination with an injector linac. Carbon ion radiotherapy awakens a worldwide interest. About 6000 cancer patients have already been treated with carbon beams from the Heavy Ion Medical Accelerator in Chiba at the National Institute of Radiological Sciences in Japan. These clinical results have clearly verified the advantages of carbon ions. Heidelberg Ion Therapy Center and Gunma University Heavy Ion Medical Center have been successfully launched. Several new facilities are under commissioning or construction. The beam energy is adjusted to the depth of tumors. It is usually between 140 and 430 MeV∕u. Although the beam intensity depends on the irradiation method, it is typically several 10(8) or 10(9) pps. Synchrotrons are only utilized for carbon ion radiotherapy. An ECR ion source supplies multi-charged carbon ions for this requirement. Some other medical applications with ion beams attract developer's interests. For example, the several types of accelerators are under development for the boron neutron capture therapy. This treatment is conventionally demonstrated by a nuclear reactor, but it is strongly expected to replace the reactor by the accelerator. We report status of ion source for medical application and such scope for further developments.

Status of ion sources at National Institute of Radiological Sciences

The National Institute of Radiological Sciences (NIRS) maintains various ion accelerators in order to study the effects of radiation of the human body and medical uses of radiation. Two electrostatic tandem accelerators and three cyclotrons delivered by commercial companies have offered various life science tools; these include proton-induced x-ray emission analysis (PIXE), micro beam irradiation, neutron exposure, and radioisotope tracers and probes. A duoplasmatron, a multicusp ion source, a penning ion source (PIG), and an electron cyclotron resonance ion source (ECRIS) are in operation for these purposes. The Heavy-Ion Medical Accelerator in Chiba (HIMAC) is an accelerator complex for heavy-ion radiotherapy, fully developed by NIRS. HIMAC is utilized not only for daily treatment with the carbon beam but also for fundamental experiments. Several ECRISs and a PIG at HIMAC satisfy various research and clinical requirements.

Cost-effectiveness of carbon ion radiation therapy for locally recurrent rectal cancer

The aim of this study was to evaluate the cost-effectiveness of carbon ion radiotherapy compared with conventional multimodality therapy in the treatment of patients with locally recurrent rectal cancer. Direct costs for diagnosis, recurrent treatment, follow-up, visits, supportive therapy, complications, and admission were computed for each individual using a sample of 25 patients presenting with local recurrent rectal cancer at the National Institute of Radiological Science (NIRS) and Gunma University Hospital (GUH). Patients received only radical surgery for primary rectal adenocarcinoma and had isolated unresectable pelvic recurrence. Fourteen and 11 patients receiving treatment for the local recurrence between 2003 and 2005 were followed retrospectively at NIRS and GUH, respectively. Treatment was carried out with carbon ion radiotherapy (CIRT) alone at NIRS, while multimodality therapy including three-dimensional conformal radiotherapy, chemotherapy, and hyperthermia was performed at GUH. The 2-year overall survival rate was 85% and 55% for CIRT and multimodality treatment, respectively. The mean cost was yen4 803 946 for the CIRT group and yen4 611 100 for the multimodality treatment group. The incremental cost-effectiveness ratio for CIRT was yen6428 per 1% increase in survival. The median duration of total hospitalization was 37 days for CIRT and 66 days for the multimodality treatment group. In conclusion, by calculating all direct costs, CIRT was found to be a potential cost effective treatment modality as compared to multimodality treatment for locally recurrent rectal cancer.

Isotopic anomaly for carbon ions in an electron cyclotron resonance ion source

In many experiments methods were applied to increase the highly charged ion output from an electron cyclotron resonance ion source; the gas-mixing method is still generally being applied. The dominant role of the masses of the ions in the gas-mixture was apparent. Two basically differing mechanisms could to first order explain most of the observations. A significant mass effect showed up in a mixture of oxygen isotopes, the so-called oxygen anomaly; so far that effect could be explained in zeroth order only. The anomaly was observed later for nitrogen isotopes as well. In the present experiment it is shown that the anomaly also exists for carbon isotopes, where the necessity of feeding the source with carbon-hydrogen compounds brings about an essential different experimental fact.

Review on heavy ion radiotherapy facilities and related ion sources (invited)

Heavy ion radiotherapy awakens worldwide interest recently. The clinical results obtained by the Heavy Ion Medical Accelerator in Chiba at the National Institute of Radiological Sciences in Japan have clearly demonstrated the advantages of carbon ion radiotherapy. Presently, there are four facilities for heavy ion radiotherapy in operation, and several new facilities are under construction or being planned. The most common requests for ion sources are a long lifetime and good stability and reproducibility. Sufficient intensity has been achieved by electron cyclotron resonance ion sources at the present facilities.