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Development of an ultrasmall -band linear accelerator guide for a four-dimensional image-guided radiotherapy system with a gimbaled x-ray head
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Image of FIG. 1.
FIG. 1.

The gimbaled x-ray head is composed of a -Band accelerator guide, multi-leaf collimator, and gimbals mechanism.

Image of FIG. 2.
FIG. 2.

The gimbaled x-ray head is mounted on the O-ring with x-ray tubes and two flat panel detectors. The O-ring rotation provides portal selection around the isocenter and the O-ring skew provides the noncoplanar beam angles around the isocenter. The pan and tilt motions of the gimbals provide active compensation for the mechanical distortion and quick beam motion to compensate for the movement of the target around the isocenter.

Image of FIG. 3.
FIG. 3.

The accelerator guide is composed of the electron gun section with a cathode, an injector section, and a side-coupled standing wave acceleration cavity section.

Image of FIG. 4.
FIG. 4.

The maximum electric field appears on the nose cone of the nose reentrant cavity. The ratio of maximum electric field to the acceleration gradient on the axis is 4.3.

Image of FIG. 5.
FIG. 5.

The injector section is composed of five cavities. Cavity No. 1 is a prebuncher cavity. Cavity No. 3 and cavity No. 5 are buncher cavities. Cavity No. 2 and Cavity No. 4 are coupling cavities and do not contribute to acceleration. Cavity No. 1 through Cavity No. 4 are axial coupling cavities, which are coupled via beam holes. Cavity No. 5 is a side-coupled cavity and is fed from the acceleration cavity.

Image of FIG. 6.
FIG. 6.

The accelerating cavities and the coupling cavities have bipartite structure.

Image of FIG. 7.
FIG. 7.

The cavity parts are made of oxygen-free high conductivity copper (ASTM F68 Class 1) and the inner surfaces are machined with an ultraprecision lathe.

Image of FIG. 8.
FIG. 8.

One unit of the accelerating guide is composed of an accelerating cavity and a coupling cavity.

Image of FIG. 9.
FIG. 9.

The electron gun is composed of an anode electrode, cathode assembly, focusing electrode, and ceramic insulator.

Image of FIG. 10.
FIG. 10.

The accelerator guide assembled on the test stand.

Image of FIG. 11.
FIG. 11.

Outline of the accelerator test bench. The beam profile scanner has slits movable in two axes on the plane perpendicular to the beam line. Current monitor No. 1 is used to measure the output beam current and the beam profile. The beam is magnetically analyzed with the beam bending magnet. The beam energy distribution is measured with the energy analyzing slit and current monitor No. 2.

Image of FIG. 12.
FIG. 12.

Beam profile of the electron beam of the electron gun measured at , .

Image of FIG. 13.
FIG. 13.

Beam profile measured from the output beam hole of the accelerator guide.

Image of FIG. 14.
FIG. 14.

Beam energy distribution measured for , 75, 100, and with a microwave input . The normalized beam current is the percentage of the current in a window with respect to the total current.

Image of FIG. 15.
FIG. 15.

Beam energy distribution measured for a microwave input , 1.74, 2.0, and with . The normalized beam current is the percentage of the current in a window with respect to the total current.

Image of FIG. 16.
FIG. 16.

Beam loading characteristics calculated from the beam energy distribution in Fig. 14. The theoretical beam loading line is also shown. Error bars show the measurement error caused by the resolution of the energy analyzing setup (i.e., the bending magnet and the energy analyzing slit).

Image of FIG. 17.
FIG. 17.

Leakage radiation from the accelerator guide measured with a Farmer ionization chamber with a 15-cm-long lead collimator at from the axis of the accelerator guide. The ionization chamber was scanned along the axis of the accelerator guide with the axis of the collimator perpendicular to the axis of the accelerator guide and in the looking-down direction in Fig. 11.


Generic image for table

Transmission efficiency of the accelerator guide calculated by dividing the reading of current monitor No.1 in Fig. 11 by the cathode current supplied to the electron gun.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Development of an ultrasmall C-band linear accelerator guide for a four-dimensional image-guided radiotherapy system with a gimbaled x-ray head