JAERI-Conf 95-021

3a1-4
DESIGN OF A COMPACT PROTON ACCELERATOR FACILITY
DEDICATED FOR CANCER THERAPY
Akira NODA, Mak:oto INOUE, Yoshihisa IWASHITA, Toshiyuki SHIRAI
Masatsugu NISHI*, Kamo HIRAMOTO* and Jyunichi HIROTA**Accelerator Laboratory, Institute for Chemical Research, Kyoto University, Uji, Kyoto, Japan*Hitachi Research Laboratory, Hitachi Ltd., Hitachi, Ibaraki, Japan**Hitachi Works, Hitachi Ltd., Hitachi, Ibaraki, JapanAbstract
A compact proton accelerator facility dedicated forA combined function
cancer therapy is designed.
synchrotron with the maximum energy of 250 MeV is
A ferrite-loaded untuned cavity with theadopted.
frequency range of 1.6-8 MHz is utilized for beam
accelerauon. Combination of a horizontal beam line anda gantry in the same treatlnent room will realize multiport irradiation. The beam efficiency will be improvedby positioning outside the treaunent room even with asmgle treaunent room. Scanning method for beam
spreading also increases beam utilization efficiency.

center hospital of somewhat larger size. For thispurpose, a proton accelerator facility entirely dedicated forcancer thera_Ry has been designed. Because of the merit ofvariability of the output beaiD energy, proton synchrotron
is adopted. In order to avoid the complex control ofmagnet power supplies, a combined function lattice isadopted2Y. As the RF accelerating cavity, a ferrite loaded
untuned cavity with the frequency range of 1.6~8 MHz isadopted for the merit of easy operation'). For the
medically dedicated machine, it should be operated withminimum possible down time without any professionalsof accelerator. From this point of view, the RF powersource of the injector linac is to be optimized.

1. Introduction

2. Total Scheme

Recently it becomes to be known that cancer
therapy with use of charged particles as proton and heavyions IS very promising from the view-point of quality oflife of the patient due to the merit of no erasion. As thenational center for cancer therapy with heavy ions,
HIMAC has been constructed at National Insutute ofRadiological Sciences and clinical treatlnents have alreadybeen started with good results!). However, the number ofpatients who need such treatlnents is overwhelmingly
large compared with the curable patients at such a limited
faCility and it is inevitable to realize a proton therapy
facility of such a size as can be operated with an areal-

As the main accelerator, a proton synchrotron asshown in Fig. 1 is adopted because of the merit ofenergy varia0ility2). The charged particle therapy is
considered to orient the pin-point irradiation to thevolume spread in three dimensions. In this case, thedepth of the irradiation is to be controlled by the beamenergy and then variable energy accelerator is inevitable.
The pencil beam is to be scanned in two directions in thetransverse phase spaces. In order to realize flat dose
distribution by this scanning method, good time structureof the beam is required.
~ Extracted Beam

Electrostatic
Deflector

Trim Quadrupole~Magnetoccr
BF
Electrode for RF knockoutin transverse direction
RF Accelerating
Cavity (untuned)

Bending Magnet
with n-value(BF: Horizontallyfocusing)!TrimMagnet
Bending Magnet
with n-value(BD: Horizontallydefocusing)

Injector Linac

Fig 1. Layout of the Proton Accelerator System.
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100.0 .--~---;------,---,;----,------,-----,:j 9~able 1 .Main Parameters of the Proton Therapy Facility,a-~,80.0 ~ --<>-- Accelerating Voltage (V)t~/
60.0 ~/Proton70-250MeV
0.5Hz
5 Gy per Min. (Max.)c

1

Horizontal and Rotatable
Scanning~orI

2o.o F-/ ·E_0.0 ~jo-· ..-r

For tJ?.e efficient :use of the beam, posi~oning ofthe next pattent IS reqwred to be performed m parallelwith the present treatment. Usually, several treatment
rooms are provided to make preparation in the otherrooms. It, however, requires rather larger number ofoperators. So we propose such a system that positioningof the patients is ~ormed outside the treatment roomwith use of X-ray cr and so on. Mter entering into thetreatment room, the precise positioning of the patient tothe beam is realized with mechanical alignment of thepositioning stage with use of knock-IJins4>- Thus, only
one treatment room will be provided. The required beamspecification by the medical use is listed up in Table 1.

I-2o.n4. SynchrotronWith use of combined function lattice, complexity
related to the tracking between power supplies of dipoleand quadrupole magnets can be avoided. AD.other element
which requires complex control is an RF accelerating
cavity, beCause its frequency changes according to thebeam acceleration. In ordinary proton synchrotron, theresonant frequency of the accelerating cavity is tuned by

00.1

0.8D

1.3

•

~..\~5'~\.
~- .-- Revolution Frequency (MHz)

l7..

·llll

<2.

~

0is ;'"',.. -~8_,-s..

i4 'i..,:::s'<~3~2:I:!:!..

~ 1.__r- - - - - ' - - - - ' - - - - - - - ' - - - - - ' - - - - - - - - "

-0.2

0.0

0.2

0.4

0.6

0.8t (sec)Fig. 3 Sweeping Pattern of RF frequency and Voltage.

Stainless Duct

In order to make the injector linac to be compact,
rather higher frequency of 433 MHz is adopted. In order
to attain the required maximum dose rate of 5 Gv permin., proton beam with the intensity of 5 x IOI'tl per
pulse IS needed for irradiation with scanning instead ofscatterer. If this intensity of the proton bearii is injected
into the synchrotron ring_ with the kinetic energy of 7MeV, the betatron tune shift due to space charge force isestiinated to be 0.09 assuming that the emittance of theinjected beam are 145n mmmrad and lOJt mm-mrad inhorizontal and vertical directions, respectively. This tune
shift seems tolerable and the injection energy of 7 MeV
is acceptable. The scanning method has rather hil!her
beam efficiency in producing wide irradiation fiefd5),
which makes the beam injection into the synchrotron
with necessary intensity much easier.
As the injector linac, we propose the combinationof the RFQ and Alvarez Drift Tube linac, which aresimilar to the one already O(~<tted at ICR, Kyoto
University since 19926). As the RF source, the system
based on the klystron as the existing one and that basedon parallel planar triode arrays should be carefullycompared from the point of view of reducing the beam
down time as short as possible and attaining the easy
operation. The latter system commercially av3ilable cangenerate up to 360 kW while the current J>I()posed systemneeds ~500 kW of peak power. Some R&D is necessaryfor this power source.

:::~ZI.

..·

3. Injector linac•mt_'';\-.-- .-- •- •)2.0

Fig. 2 Excitation Pattern of the Synchrotron.

t(sec)

400mm

Fig. 4 The really fabricated untuned cavity.
the bias magnetic field of the ferrite loaded cavity. In theprop<>sed case, the required voltage is fairly low and thepossibility of the untuned cavity is stnilied. If thesynchrotron ring as shown in Fig. 1 is operated as shownin Fig. 2, the acceleration voltage and revolution
frequency should satisfy the relation shown in Fig. 3.
Onfy a few hundreds vOlts is needed as the gap voltage
and untuned RF cavity driven by a solid state amplifier IS
adopted to make the operation easy, which eliminates thecontrol of the biasing current for the ferrite. A powermodel of the untuned cavity has been fabricated and its
structure is shown in Fig. 4. We have devised a new
driving method for the untuned cavity by coupling theRF power to each winding of the ferrite nng. Owing tothe good efficiency of power feeding, necessary gap
voltage of several hundreds volts can be attained With thepower less than 1 kW which can be easily generated by asolid stale amplifier7).
·_·
Further a dig!tal synthesizer is utilized as the_signal source of the RF because its. purity in frequency
component is known to contribute easy acceleration
control from the experience of HIMACS). It is expectedthat no feed back for phase and radial position differences
might be necessary if the B dot dock for frequency
control is precise enough (~.2G), once the sweep patternof the RF frequency is fixed. So the RF feed bacK withbeam signal will be utilized only for fixing the new
excitation pattern, which makes daily operation veryeasy.
.
In order to provide the beam with long durationfrom the synchrotron, slow beam extraction with thirdorder resonance is to be utilized. In th~ _proposed system,
the new method to utilize transverse RF electric field is
to be utilized9.10). The betatron amplitude of the beam
which initially .locates inner side of the separatrix isenlarged by this RF electric field. This method iseffecttve to realize the small emittance extracted beam andsynchronization with breathing.
In Table 2, the main parameters of the proton
synchrotron are listed up.

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IUdiation
MonitoringEmergency

ExitConsultatioa

Fig. 5 Layout of the proposed KUMPF as the example of the irradiation facility with a single treatment room.
5. Irradiation System
It is needed to enlarge the irradiation field to somesize as 15 em in diameter to cover the region of thetumor to be treated. For this purpose, we propose toutilize the scanning method2). The scatterer reduces thebeam utilization efficiency to ~ 114, while the present
method is ex~ted to utilize the extracted beaffi morethan 85 %5). This reduced the necessary beam intensityfrom the synchrotron to 5 x 1010 at the needed dose rateof 5 Gy/min. Due to this reduction of the beam
intensity, the space charge tune shift is under 0.01 even if
the injection energy is 7 MeV, which is considered tocontribute the injector system to be compact.
In order to make efficient irradiatiOn to the tumor
with smallest possible damage to the surrounding normal
For thiscells, multi-port irradiation is inevitable.
purpose, we propose a combination of a single horizontal
beam line and a rotating gantry in the same treatment
room4). With this configuration, concentration of theirradiated dose to the tumor is considered to be wellrealized.

As already mentioned, a single treatment room
equipped with both a horizontal and a rotatable gantry isprovided which keeps the needed operator as smalf as
The positioning of the patients will bepossible.
performed outside the treatment room relying on themechanical precision of alignment In Fig. 5, the layoutof the KUMPF is shown as an example of such
medically dedicated facility.
The present authors at Kyoto University are proposing torealize such a facility at first at their umversity in order tomake R&D research with real facility4).
6. Acknowledgements
The authors would like to present their sincere
thanks to the group of the HIMAC at National Instituteof Radiologicil Scrences in Chiba for providing them alot of valuable information based on the ex'R_Crience ofoperation of the HIMAC. They are also grateful to Prof.
K. Ono at Research Reactor Institute, Kj'oto Universityfor his fruitful discussion on the KUMPF. This work is
supported by Grant-in-Aid for Scientific Research from
the Ministry of Education, Science and Culture.

Table 2 Main Parameters of the Proton Synchrotron
7MeVInjection Energy
250MeV
Maximum Energy
22.9 mCircumference
4
Superperiod
Numoer of Betatron Oscillations per Tum
1.75
Horizontal Direction
0.85
Vertical Direction
Magnet System
Dipole Magnet (combined function)
8
Number of Magnets
45°
Deflection Angle
1.62 mRadius of Curvature
1.5 T
Maximum Field Strengthn-value-0.599
at the horizontally focusing section
0.904
At the vertically focusing section
RF System
1.59-8.04 MHz
Frequency Range~ 100 V
AcceleratiOn Voltage
Ferrite LoadedCavity
untunedDigital Synthesizer
Signal Source

7. References
1. S. Yarnada, Invited talk at the 1995 Particle
Accelerator Conference, Dallas, USA (1995) in print.
2. K. Hiramoto et al., Contribution to PfCOGXXI,Chiba, Japan (1994) in print.
3. J. Hirota et al., Contnoution to the 1995 Particle
Accelerator Conference, Dallas, USA (1995) in print.
4. A. Noda et al., Contribution to PfCOGXXI,Chiba, Japan (1994) in print.
5. K. Hiramoto et al., Bull. lust. Chern. Res.,Kyoto University, 73, No.1 (1995) ppll-18.
6. M. Inoue et al., Bull. Instr. Chern. Res., Kyoto
University, 71, No.1 (1993) pp57-61.
7. J. Hirota et al., Contribution to this symposium.
8. M. Kanazawa et al.,Proc. Of the 4tli EuropeanParticle Accelerator Conf., London, UnitedKingdom(1994), pp1972-1974.
9. K. Hiramoto and M. Nishi, Nucl. Instr. AndMeth. A322 (1992) pp154-160.
10. M. Tomizawa et al., Nucl. Instr. And Meth. A326
(1993) pp399-406.

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