Fuminori Soga

Biophysical characteristics of HIMAC clinical irradiation system for heavy-ion radiation therapy

PURPOSE The irradiation system and biophysical characteristics of carbon beams are examined regarding radiation therapy. METHODS AND MATERIALS An irradiation system was developed for heavy-ion radiotherapy. Wobbler magnets and a scatterer were used for flattening the radiation field. A patient-positioning system using X ray and image intensifiers was also installed in the irradiation system. The depth-dose distributions of the carbon beams were modified to make a spread-out Bragg peak, which was designed based on the biophysical characteristics of monoenergetic beams. A dosimetry system for heavy-ion radiotherapy was established to deliver heavy-ion doses safely to the patients according to the treatment planning. A carbon beam of 80 keV/microm in the spread-out Bragg peak was found to be equivalent in biological responses to the neutron beam that is produced at cyclotron facility in National Institute Radiological Sciences (NIRS) by bombarding 30-MeV deuteron beam on beryllium target. The fractionation schedule of the NIRS neutron therapy was adapted for the first clinical trials using carbon beams. RESULTS Carbon beams, 290, 350, and 400 MeV/u, were used for a clinical trial from June of 1994. Over 300 patients have already been treated by this irradiation system by the end of 1997.

Heavy ion synchrotron for medical use —HIMAC project at NIRS-Japan—

Abstract A heavy ion synchrotron complex for medical use is being constructed at Chiba, Japan. General feature and present status of this project are described.

Dosimetry and Measured Differential W Values of Air for Heavy Ions

Heavy-ion irradiation systems were designed and constructed at two cyclotron facilities in Japan for use in various fields of radiation physics and radiation biology. A 135 MeV/u carbon beam as well as 12 MeV/u carbon and helium-3 beams were first used in experiments. We have established a systematic method for heavy-ion dosimetry at both high and low incident energies involving measurements of fluences. We also obtained differential W values (w) of air for those beams by comparing the results of fluence measurement dosimetry with ionization chamber dosimetry. The differential W values of air were found to be 36.2 +/- 1.0, 34.5 +/- 1.0, and 33.7 +/- 0.9 eV for 6.7 MeV/u carbon ions, 10.3 MeV/u 3He ions, and 129.4 MeV/u carbon ions, respectively. The w value for high-energy heavy ions approaches the W value for high-energy electron or photon beams. In ionization chamber dosimetry for a heavy-ion beam, we found a track-size effect. A difference in the track sizes of heavy ions in the gas and solid phases affected the output current of the ion chamber in the case of high-energy heavy ions.

Performance of HIMAC

Abstract The NIRS heavy-ion two-synchrotron medical facility, HIMAC, was approved in the 1987 fiscal year and clinical trials were started in late June 1994 as previously arranged. The operation experiences show that the entire HIMAC facility can work well with high stability and excellent reproducibility. For example, the intensity of beam extracted slowly from the rings can be reduced as low as 500 particles per pulse because stable and reproducible acceleration can be achieved in the rings in spite of no beam feedback. This performance enables direct counting of the beam and its fragments in the preparatory experiments toward clinical treatments and provides a promising basis for acceleration and storage of radioactive beams toward simultaneous treatment and diagnosis in future.

Design of synchrotron light source and its beamline dedicated to dual-energy x-ray computed tomography

A synchrotron light source dedicated to medical applications has been designed at National Institute of Radiological Sciences. The storage ring, with circumference of 80 m, is designed for acceleration of 2.3 GeV and a stored current of 420 mA. It is equipped with two multipole wigglers to produce sufficient photon flux in a hard x-ray region required for medical applications. The purposes of the synchrotron light source are clinical performance of medical diagnoses clinically and research and development relating with medical applications. One of the most interesting applications for us is dual-energy x-ray computed tomography (CT). It gives the information about electron density of human tissue. The information plays an important role in advancing heavy-ion radiotherapy of cancers. Electron density can be derived from attenuation coefficients measured by different energy x rays. In this paper, a practical method of the dual-energy x-ray CT with synchrotron radiation is proposed with the theoretical consideration. The primitive experiment using monochromatic x rays emitted from radioisotopes proved the procedure of analysis mentioned here effective to derive electron densities from linear attenuation coefficients for two x rays of a different energy. The beamline dedicated to dual-energy x-ray CT is also proposed. It has a multipole wiggler as a light source and it mainly consists of a dual crystal monochromator and a rotating filter for attenuating photon flux of x rays and two-dimensional detector.

Single particle irradiation system to cell (SPICE) at NIRS

Selective irradiation by an ionizing particle of a targeted cell organelle may disclose such mechanisms as signal transaction among cell organelles and cell-to-cell communication in the processes toward an endpoint observed. Bystander effect, existence of which has been clearly evidenced by application of the particle microbeam to biological experiments, suggests potential deviation from the conventional risk estimation at low particle fluence rates, such as in an environment of space radiation in International Space Station. To promote these studies we started the construction of a microbeam facility (named as SPICE) by using our HVEE Tandem accelerator (3.4 MeV proton and 5.1 MeV 4 He 2þ ). For our primary goal, ‘‘irradiation of cell organelle with a single particle with a position resolution of 2 l mi n a reasonable irradiation time’’, special features are considered. Usage of a triplet Q-magnet for focussing the beam to micrometer levels is an outstanding feature compared to facilities of other institutes. Other features are almost similar to those of other institutes. Those are precise position control of a cell dish holder, design of the cell dish, data acquisition of microscopic image of a cell organelle (cell nucleus), data processing, reliable particle detection, soft and hard wares to integrate all these related data and system to control and irradiate a targeted spot with exactly determined number of particles.

Application of 6 MeV/n heavy‐ion beams to biophysical experiments

A new accelerator facility and two irradiation methods using 6 MeV/n heavy‐ion beams are described along with preliminary results concerning their applications to biophysical investigations. The beams are obtained from the injector linac installed at the Heavy Ion Medical Accelerator in Chiba. Various ion species (He–Xe) having different charge states are accelerated to the same velocity, which is suitable for comparing the charge effects of heavy ions in the high linear energy transfer region. An attempt has been made to test the usefulness of the apparatus for studying track structure by using pBR322 plasmid DNA and spores as targets in vacuum. Newly constructed equipment with a molecular‐beam source (water vapor) placed on this beam line is also described.

Secondary Electrons from Water Vapor with the Impact of 6.0 MeV/u He2+ Ions: Atomic Data and their Application to Biomedical Investigations

We measured the energy and angular distributions (7 eV–10 keV and 20°–160°) of secondary electrons produced in collisions of 6.0 MeV/u He2+ ions with water vapor. Binary‐encounter collision peaks were clearly observed at the calculated energies at angles of 3keV. To assess the new cross sections, these values were incorporated in the kurbuc Mont...

Present status of HIMAC at NIRS

Since 1994 clinical trials have been performed successfully with carbon beam. To improve the clinical result further, new irradiation systems are under development such as a 3D-irradiation system and a verification system of range with positron emitter. There are also improvements on the accelerator performances. One is the wide range of ion species; the others are concerned with the machine devices and new beam monitors to get good machine operation. In this report we present current status of HIMAC.

Inactivation measurements of yeast along the path of 135 MeV/amu carbon for a beam monitor in medical applications

Abstract The survival ratios of yeast cells as a function of carbon beam penetration into a plastic block were evaluated at an initial energy of 135 MeV/amu. The cells were inserted into holes at several depths along the beam path. We estimated the inactivation ratios of both the haploid and the budding response of the haploid cell for the wild and the sensitive strain at stationary and growth phase. The ratios along the beam path were applicable as a method of beam adjustment in the planning of heavy ion therapy