Mitsubishi Heavy Industries Technical Review Vol. 46 No. 1 (Mar. 2009)29

State-of-the-Art Medical Treatment Machine MHI-TM2000

ETSURO HIRAIKAZUHIRO TSUKUDAYUICHIRO KAMINOSADAO MIURA

KENJI TAKAYAMATATSUFUMI AOI|1. Introduction
The combination of the aging population and the declining birthrate means that theproportion of aged patients with cancer is increasing rapidly. An improved quality of life (QOL) isrequired so that patients can go about their daily lives, finding fulfillment on their own and feeling
content while they are treated. The three main approaches for treating cancer are radiotherapy,surgery, and chemotherapy. Of these, radiotherapy is considered the most patient-friendly therapy,
meeting the goals of our aging society. Mitsubishi Heavy Industries, Ltd. (MHI) is actively
involved in the development and manufacture of a cancer treatment machine, working jointly with
Kyoto University and the Institute Biomedical Research and Innovation laboratory based on MHI’s
experience and technology in the field of industrial machines.
This paper introduces a state-of-the-art medical treatment machine developed by MHI.

|2. Composition and features
The MHI-TM2000 radiotherapy machine developed by MHI is a device to realize
image-guided radiotherapy (IGRT) that combines x-ray imaging and treatment.
Its design adopts a unique configuration that incorporates to a maximum extent theknowledge accumulated by MHI, such as the micro-positioning technology required by machine
tools, image processing technology developed for printing machines, and system control
technology used in steel-making machines, manufacturing, and the development of large
1accelerators (Figure 1) .

Figure 1 Diagram showing the configuration of the MHI-TM2000(1) As the structure main body frame, we adopted a ring-shaped gantry with high rigidity.
Because distortion deformation can be minimized, we can realize high-precision positioning
while simultaneously enabling x-ray irradiation from all radial directions to the diseased partat the center location that is called isocenter of the machine without moving the couch on
which the patient is lying.

Mitsubishi Heavy Industries Technical Review Vol. 46 No. 1 (Mar. 2009)30(2) The device uses a compact C-band standing wave type accelerator that was jointly developedby the Institute of Physical and Chemical Research, the High Energy Accelerator Research
Organization (KEK), and MHI. Its acceleration frequency (5.712 GHz) is two times higher
than that used in general therapy devices, and microminiaturization and weight saving areachieved while maintaining the stability of the beam, making the device one third the size oftypical therapy devices. This is the first C-band type of therapy device. This allowed its
installation on gimbals mechanism, as mentioned below. In addition, it is necessary to adjust
the acceleration frequency in accordance with the thermal expansion of the accelerator during
operation, and output stability is ensured by adopting a new automatic wide-band frequency
2control .
(3) Two pairs of kV x-ray imaging systems are installed. An imaging function is used to confirm
the precise irradiation location, and high-quality three-dimensional static images of the patient
can be taken from every angle. Furthermore, our machine can obtain cone-beam computed
tomography (CT) images quickly and of a quality comparable to conventional slice CT bytaking images while rotating one pair of imaging systems. The machine is also equipped withan algorithm to automatically identify the diseased organ from the radioscopy images.
(4) The head used for generating therapeutic x-rays can be swiveled on gimbals mechanism(Figure 2). The accelerator is installed on gimbals to realize high-precision positioning bycorrecting deviation of the irradiation site due to mechanical flexion of the gantry.
(5) The couch on which the patient lies can be moved in 3- (Figure 3) or 5-axial directions withhigh precision, enabling correct positioning of the isocenter. High-precision correction isenabled by using a system that combines an infrared (IR) marker on the body surface and anIR camera.
(6) The therapeutic x-rays are formed into a beam of the desired shape by using a multi-leaf
collimator (MLC) with high precision and rapid response that has been newly developed,
enabling irradiation with the optimal irradiation pattern. In addition, x-ray images can be taken
and recorded using an electronic portal imaging device (EPID).

Figure 2 Schematic of the gimbals mechanism
The movement of the gimbals mechanism and theirrelationship with the change in beam position are shown.

Figure 3 Photograph showing the directionof couch movement in three axes

As mentioned above, irradiation of normal tissues during therapy is avoided, and theexposure dose is reduced because the radiation irradiation therapy can be done with high precisionfrom multiple directions with this machine.
Furthermore, because ample image support functions are provided and the therapy can bedone quickly, one machine can be used to treat many patients.

|3. Performance of the machine
Figure 4 shows a typical flow chart for irradiation therapy with the MHI-TM2000. Wepresent examples of the main performance features of this machine:Mitsubishi Heavy Industries Technical Review Vol. 46 No. 1 (Mar. 2009)31

1. Pre-positioning
using alaser
pointer and >bodysurface
marking

2. Confirmation oftheirradiationsite using
kV x-ray
images3. Calculat4. Correcting
5. Confirma6. Radia7. Monitoring thethe location oftion of thetion
ing theamount of
the isocenterradiation
treatmentdiseasedcorrection
using thefield bypart during(automatic
three-axis
usingthe>>>>> irradiationor manual)
couch or fineelectronicwith kVcorrection withportal
x-ray
the gimbals
imaging
imagingmechanism
device(EPID)

Figure 4 Flowchart showing a typical therapeutic procedure using our machine(1) Irradiation location precision
As the accelerator head rotates along the ring, some flexion is generated due to its deadweight. This is corrected automatically by fine adjustments of the accelerator head with thegimbals mechanism so that the irradiation is focused on the isocenter. The threshold value ofthe correction deviation can be set arbitrarily. We have achieved an effective precision of staticirradiation positioning of the x-ray of 0.1 mm or less when the isocenter is within the 360°
rotation field of the ring type gantry. This is a specification that allows irradiation of diseasedorgans that require high precision, such as the brain.
(2) Image fusion function
Because a monitor is used to display a composite of the CT image used for therapeuticplanning and the x-ray image from the imaging system, any deviation in the location of theisocenter can be calculated quickly. The composite image can be produced manually orautomatically. When it is done by manual fusion, the reference image (left side) and imaging
system image (right side) are both displayed, and the amount of deviation can be calculated
when a part of the image is selected using a mouse (Figure 5).
(3) Safety countermeasures
Any medical treatment machine must be assurance of safety. With regard to radiation, thedevice ensures radiation leakage of 1/1000 or less in the patient plane. Furthermore, ascountermeasures against failure, the device has redundant main and auxiliary systems that areindependent of each other, so that there is no possible room for failure. Safety is further ensured
by using independent interlock controls for the electric power source, dosimeter system, controlsystem, etc.

Figure 5 Example of fused
x-rays images(manual)The reference image(left side) and imaging
system image (right side) areboth displayed.

|4. System specifications
Table 1 shows the system specifications. The device uses an x-ray energy of 6 MeV, which
does not generate neutrons. This system can be used for treating lesions in the brain, head and neckregion, and lungs for radiosurgery procedures, and for treating deep organs, such as the prostateand pancreas by combination with intensity modulated radiation therapy (IMRT). We canMitsubishi Heavy Industries Technical Review Vol. 46 No. 1 (Mar. 2009)32

provide as option the latest software that increases the efficiency of therapeutic planning andsupports high-precision therapy.
Table 1 Major specifications of the system
Item
Electron acceleration energy
Absorbed x-ray dose
X-ray radiation field (maximum)
Rated therapy distance
High-frequency electric power source
Head rotation angle
Head rotation speed
Ring swing angle
Gimbals driving range
External dimensions of the couchMLC type
Weight(MeV)(cGy/min)
(mm)
(MW)
(°)
(°/ s)(°)(°) / [(mm)]
(mm)
(kg)

Specification
6500
150×150
1 000
Klystron 4−185 to +185
7±60±2.5 / [±44]450 × 2 200 × 1,100
Single focus
Approximately 12,000|5. Conclusion
The MHI-TM2000 has received approval by the U.S. Food and Drug Administration (FDA)
and by the Japanese Ministry of Health Labor and Welfare as a new pharmaceutical products andhas been marketed since April 2008. It is now being used clinically in the Institute of Biomedical
Research and Innovation laboratory located in Kobe, and we are accumulating clinical experienceand obtaining reliability data. In the future, we plan to develop a system that can identify a moving
diseased organ automatically from radioscopy images, and we anticipate further addition of the saidfunction and developments that meet the needs of patients and physicians.
We are sincerely grateful to Dr. Masahiro Hiraoka, Professor of the Graduate School ofMedicine, Kyoto University, and Dr. Masaki Kokubo, Leader of the Radiotherapy Research Group,Institute of Biomedical Research and Innovation laboratory, and the staff of the Kyoto Universityand Institute of Biomedical Research and Innovation Laboratory, who gave us considerable
guidance and encouragement.

References
1.
2.

Y. Kamino, et.al, Development of a Four-dimensional Image-guided Radiotherapy System with aGimbaled X-ray Head, Int. J. Radiat. Oncol., Biol., Phys. 66, (2006) p. 271-p.278
Y. Kamino, et.al, Development of a New Concept Automatic Frequency Controller for an Ultra-small
C-band Linear Accelerator Guide, Med. Phys. 34,（2007） p.3 243-p.3 249

Authors
Etsuro Hirai
Manager,
Machinery Engineering
Department,
Hiroshima Machinery Works

Kazuhiro TsukudaManager,Machinery Engineering Department,
Hiroshima Machinery Works

Yuichiro Kamino
Manager
Nagoya Aerospace Systems
Works

Sadao MiuraManager,
Joining & Welding Product Section,
Plant and Transportation Systems
Engineering & Construction Center

Kenji Takayama
Machinery Engineering
Department,
Hiroshima Machinery Works

Tatsufumi Aoi
Manager,
Control Systems Laboratory,
Hiroshima Research & Development
Center, Technical Headquarters