MEDICAL PROTON SYNCHROCYCLOTRON
E. Toyota, T. Hori, Y. Hirao* and S. Fukumoto**
Sumitomo Heavy Industries, Ltd.
*Institute for Nuclear Study, University of Tokyo**National Laboratory for High Energy Physics
Abstract
Nowadays the synchrocyclotron is not newly built because of
its lower beam intensity compared with the isochronous cyclotron.
But its proton beam intensity can fill the demands requiredin diagnostics and treatment for cancer. It is worth while
designing a synchrocyclotron dedicated to medical use when
taking into consideration the merits such as easiness ofoperation and rather a little space occuoation of the machine.
The conceptual design of 230 MeV proton synchrocyclotron has
been made and its main parameters are presented.
Introduction
The proton beam is used both for radiotherapy diagnostics
and for therapy of cancer. When we provide 35 em f,or the necessary penetration depth, the energy of 230 MeV is required andsimultaneously this becomes the maximum acceleration energy.
The required intensity is 1.35 x 10 10 pps (2.2 nA) when the dose
rate of 600 rad·liter/min is needed to be provided for the maximum
value in therapy. A synchrocyclotron is adoPted for the accelera•
tor suitable to such intermediate energy regioB.
Outline of Synchrocyclotron
The most important factors for a medical accelerator are
stability of the machine and easiness of operation and maintenance. When the range of frequency-modulation is taken to bewide, various difficulties are brought in design of the variablecapacitor. On the other hand, according to reduce the widthof frequency-modulation, the magnetic field must be set up to
more isochronous one and the control of the magnetic fieldtends to be complicated by the need of trim coils.
In this design, the magnetic field is to increase according
to the enlargement of radius, within the range in which trim
coils are of no use and in the result the width of frequencyThe focus
modulation is suppressed to 15% of initial RF.
strength is produced by the AVF method. For the simplicity ofmechanism, the single dee type is adopted and acceleration is
In order to protect the axle-bearing
made with first harmonics.
of the rotating capacitor from the damage caused by induced
current, the rotating shaft is insulated electrically and therotating capacitor consists of rotor plates in serial connection
floated from the earth side.
The solid-core magnet, the largest and most costly componentof the synchrocyclotron, is estimated to 800 ton in total weightThis heavy weightas the result of the safty first design.
brings the difficulties in overhaul of the heavy iron yoke
But this matter is of no problem byat the time of maintenance.
the consideration of a dedicated overhauling procedure. By this-121-reason the possibi lity of reducing the total weight is not beinginvestig ated further.
An idea of effectiv e usage of iron core
as a shieldin g material should be consider ed hereafte r.
The main paramete rs of the synchroc yclotron are listed
below together with the figure of design drawings .
Paramete r List of 230 MeV Synchro cyclotro nMaximum Energy
Intensit y
Magnet System
AVF Field
Pole Diameter
Average Field Strength
Main Coils PowerWeight
RF SystemFrequenc y Range
Dee Voltage
PowerVacuum SystemProton

230 MeV>lfi A
3 Sector
3,200 mm
16.3 kGauss
36.0 kW
800 Ton23......., 20 MHz
30 kV
60 kW20,000 1/sec
5 x lo-6 Torrll~OKE

8)

DEFLECTOR

2)

POLE

9)

OIL DIFFUSION PUMI'

3)

MAIN COIL

10)BEAM PROBE

4)

DEElll

UI::I:: S'l'l::M

12)

RF CAVIT'l'Sl

DUMMll' DEE

6)

10"

1)

VACUUM PUMP

SOURCE

l3lt<O'l'ARY CONDENSER

l4)

Rf

POWER FEEDER

w-~----·i!

0~~--JOQQ -----------l_~8"'N0005?

"11"'....

12)

230 MeV PROTON SYNCHROCYCL01RON-122-