We are developing a four-dimensional image-guided radiotherapy system with a gimbaled x-ray head. It is capable of pursuing irradiation and delivering irradiation precisely with the help of an agile moving x-ray head on the gimbals. Requirements for the accelerator guide were established, system design was developed, and detailed design was conducted. An accelerator guide was manufactured and basic beam performance and leakage radiation from the accelerator guide were evaluated at a low pulse repetition rate. The accelerator guide including the electron gun is long and weighs about . The length of the accelerating structure is . The accelerating structure is a standing wave type and is composed of the axial-coupled injector section and the side-coupled acceleration cavity section. The injector section is composed of one prebuncher cavity, one buncher cavity, one side-coupled half cavity, and two axial coupling cavities. The acceleration cavity section is composed of eight side-coupled nose reentrant cavities and eight coupling cavities. The electron gun is a diode-type gun with a cerium hexaboride direct heating cathode. The accelerator guide can be operated without any magnetic focusing device. Output beam current was with a transmission efficiency of 58%, and the average energy was . Beam energy was distributed from 4.95 to . The beam profile, measured from the beam output hole on the axis of the accelerator guide, was full width at half maximum (FWHM) width. The beam loading line was , where is output beam current. The maximum radiation leakage of the accelerator guide at from the axis of the accelerator guide was calculated as at the rated x-ray output of from the measured value. This leakage requires no radiation shielding for the accelerator guide itself per IEC 60601-2-1.
We are very thankful to Dr. Tsumoru Shintake of the RIKEN Harima Institute and Dr. Hiroshi Matsumoto of the Japanese National Organization for High Energy Accelerator Research (KEK). The technology for the -band standing wave-type accelerator guide came from a joint research and development program with Dr. Shintake and Dr. Matsumoto conducted in 1998 and 1999. We depend a lot on them for other -band accelerator technology including klystron and -band devices. Related presentations were made at the 46th annual meeting of the American Association of Physicists in Medicine (AAPM) (Pittsburgh, Pennsylvania, July 2004) by Kamino et al.; at the 46th annual meeting of the American Society for Therapeutic Radiology and Oncology (ASTRO) (Atlanta, Georgia, October 2004) by Takayama et al.; and at the 47th meeting of ASTRO (Denver, Colorado, October 2005) by Takayama et al.
II. METHODS AND MATERIALS
II.A. Establishment of the requirements for the accelerator guide
II.A.1. Electron beam energy
II.A.2. Dose rate
II.A.3. Short settling time of beam energy spectrum
II.A.4. Minimization of penumbra
II.A.5. Requirements on the mechanical property
II.B. System design of the accelerator guide
II.B.1. Frequency band selection
II.B.2. Output beam energy and beam current
II.B.3. Beam loading
II.B.4. Beam optics
II.C. Overall structure of the accelerator guide
II.D. Detailed design of the accelerator guide
II.D.1. Detailed design of the electron gun
II.D.2. Detailed design of the accelerating structure
II.E. Manufacturing the accelerator guide
II.F. Evaluation of the accelerator guide
II.F.1. Evaluation of the electron gun
II.F.2. Evaluation of the whole accelerator guide
III. RESULTS AND DISCUSSION
III.A. Beam characteristics of the electron gun
III.B. Beam characteristics of the whole accelerator guide
III.B.1. Beam current and transmission efficiency
III.B.2. Beam profile
III.B.3. Beam energy distribution
III.B.4. Beam loading characteristics
III.B.5. Leakage radiation from the accelerator guide
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