ACCELERATOR DEVELOPMENTS FOR CANCER THERAPY
Satoru Yamada, Gunma University Heavy-Ion Medical Center, Maebashi, Japan
Abstract
Japanese accelerator developments in heavy-ion cancer
therapy can trace its history back to the R&D studies ofNUMATRON project, which was proposed for nuclear
physics research in the mid 1980s. As a direct extensionof these studies, the world’s first dedicated heavy-ion
synchrotron, Heavy Ion Medical Accelerator in Chiba,
HIMAC, was constructed in the beginning of the 1990s.
Systematic clinical studies with carbon beams show
excellent results even for radio-resistive cancers such as
sarcomas on bones and soft tissues. Based on the successof HIMAC, a newly designed carbon therapy facility has
been constructed at Gunma University and will open up a
new era of the carbon therapy.

ions, on the other hand, make a very sharp peak called theBragg peak at the end of their paths. Protons form asimilar Bragg peak having a rather broad width due to themultiple Coulomb scattering with atoms in water.

INTRODUCTION
There are a variety of accelerators used in cancer
therapy, such as electron linacs in conventional photon
therapy, PET cyclotrons, and synchrotrons and cyclotrons
in charged-particle therapy. In this paper, I will restrict tothe accelerators mainly used in carbon therapy in Japan.
In the early stage of this field, the basic research on
cancer therapy had been performed using high-energy
cyclotrons constructed for nuclear physics research.
RIKEN has been one of the most active laboratories ofthis field.
In 1979, the first proton treatment was initiated at NIRS
with 70 MeV cyclotrons for eye melanoma. Four years
later, proton therapy for deeply seated cancers wasinitiated with KEK-booster synchrotron by a Tsukuba
University Group. In 1994, carbon therapy was initiatedwith HIMAC at National Institute of RadiologicalSciences, NIRS. The success of the cancer treatment withHIMAC stimulated radiation therapeutists, and many
particle therapy facilities have been constructed in Japan.
Now we have seven working therapy facilities in Japan,
whereas we had only 30 therapy facilities working in theworld at the end of last year. Seven of the 30 facilities arelocated in Japan, and five of the seven Japanese facilities
are using protons for the therapy, one is using carbon ions,and the last one at Hyogo Prefecture can provide bothprotons and carbons.
A new carbon therapy facility was put into operation in
March 2010 at Gunma University, three more proton
facilities are now under construction, and two morecarbon facilities are now in detailed design stage; so, wewill have a total of 13 particle therapy facilities in Japanby the end of the fiscal year 2015. The rapid increase in
the number of facilities is mainly due to the excellent
dose localization of the particle beams. Figure 1 shows
the depth-dose curves for various radiations in water. The
dose distribution of X-ray shows a broad peak near thesurface, and then it exponentially decreases. The carbon

Figure 1: Dose distribution of various radiations.
In transverse directions, the boundary of the irradiatedparticle beam becomes obscure at the end of its trajectory
mainly due to multiple scattering. Since the effects ofmultiple scattering are more serious for lighter ions, theboundary of the irradiated area is clearer for carbon ionsthan for protons. The dose distribution of carbon ions will
be much better than that of protons both in the axial andtransverse directions.
In order to realize a carbon therapy facility having theexcellent characters described above, researches on heavy
ion accelerators have been carried out in Japan. In thispaper, a brief history of accelerator developments incancer therapy is described.

NUMATRON PROJECTThe NUMATRON project[1] is the origin of Japanesedevelopmental studies on heavy-ion synchrotrons forcancer treatment. NUMATRON is the abbreviation for
the NUclear MAtter TRON and was proposed to study thecharacteristics of high-temperature and high-density
nuclear matter in the middle of the 1970s. The basic
researches on cancer treatments with high-energy heavy
ions were also included in the project. The design and theR&D studies on the accelerator had been performed by
the Institute for Nuclear Study, University of Tokyo,
since 1976.
Figure 2 indicates a layout of the NUMATRON
accelerator complex; it has a big injector linac, a storage
ring to accumulate low-intensity heavy ion beams, and asynchrotron ring to accelerate heavy ions up to a
relativistic energy of 670 MeV/u. A variety of R&D
studies were performed on the injector linacs,

accumulator ring, and other components of the accelerator
complex.

Figure 2: NUMATRON was designed to accelerate heavy
ions such as Uranium ions up to 670 MeV/u.
In the R&D studies, a Test Accumulation Ring for
Numatron, TARN[2] was constructed to study thetechnical feasibility of the accumulator ring. The injector
was an existing sector-focused cyclotron used in studies
of nuclear physics. The vacuum pressure of the ring isrequired to be better than 10-11 Torr. To increase thecirculating beam intensity, we adopted the multi-turninjection plus RF-stacking method as an injection scheme.
For further acceleration, we introduced a stochastic
cooling system for momentum cooling. A photograph ofTARN is shown in Fig. 3.

Figure 4: World’s first heavy-ion RFQ linac LITL on theright and world’s longest RFQ linac TALL on the left.
In 1985, we constructed a synchrotron, TARN2, which
accelerates protons up to 1 GeV, as the final R&D studiesof the NUMATRON project. The mean radius of thesynchrotron ring is 12 m, and the vacuum is also better
than 10-11 Torr. A layout of TARN2 is given in Fig. 5.

Figure 3: Test accumulation ring for NUMATRON,TARN.
We have another round of studies for injector
developments. Figure 4 shows the world’s first heavy-ion
RFQ linac, Lithium Ion Test Linac, LITL[3] constructedin 1982. This linac adopted a single-loop coupler for
high-power coupling, and after LITL, this couplingsystem has become the standard for the RFQ linac. Andthen, we constructed the world’s longest RFQ linac,TALL, whose vane length is 7.2 m. We introduced
inductive block tuners to tune the gap voltage distribution
along the beam axis. The LITL[4] is shown on the righthand side of Fig. 4, and TALL is on the left.

Figure 5: Layout of the TARN2 synchrotron.
The TARN2 synchrotron was designed to accelerate
heavy ions, and we need an RF acceleration cavity having
a very wide frequency range of 0.6 to 7.5 MHz. As theextraction method, we adopted an RF knockout method;
this is very powerful in switching the beam on and beam
off within a very short time of around 1 ms. We adopted
an electron cooling system to reduce the momentum
spread of the circulating beams. In Fig. 6, a ferrite-loaded
RF cavity having a wide frequency range is shown. A2

photograph of the NUMATRON accelerator groupmembers is given in Fig. 7.

charge-to-mass ratio greater than 1/2. The maximum
range in water is designed to be 30 cm for silicon ions.

Figure 6: RF cavity with a wide frequency range of 0.6 to7.5 MHz.

Figure 8: A layout of HIMAC.

Figure 9: HIMAC Synchrotron.
Figure 7: NUMATRON accelerator group members.

MEDICAL SYNCHROTRON HIMAC
On the basis of the R&D studies on the NUMATRON
accelerator,
aheavy-ion
medicalsynchrotron,
HIMETRON, has been proposed by the INS group. In
1985, National Institute of Radiological Sciences, NIRS,
started the conceptual design study of Heavy Ion Medical
Accelerator in Chiba, HIMAC[5], in collaboration withINS. NIRS organized a study group for this purpose
including the INS group and the four private companies,
Mitsubishi Electric, Hitachi, Toshiba, and Sumitomo
Heavy Industries. The construction of the HIMAC wasstarted in 1988 and was completed in 1993.
A layout of HIMAC is given in Fig. 8. The accelerator
consists of three different types of ion sources, an RFQ
linac with 7 m length, a 25-m-long Alvarez type linac, apair of synchrotron rings, and a beam transport system.
We have three treatment rooms having a horizontal beamport, a vertical beam port, and both horizontal and verticalbeam ports to a single iso-center. HIMAC can accelerateions ranging from protons to xenon ions. The maximum
energy is designed to be 800 MeV/u for light ions with aFor HIMAC, we adopted a PIG-type ion source[6] anda 10 GHz ECR source[7] developed by the NIRS people.
With these two different types of ion sources, we canproduce heavy ions from protons to argon ions. To
accelerate heavier ions, such as iron, krypton, and xenon
ions, we added a 18 GHz ECR source. As injector, aconventional four-vane-type RFQ linac and a very big
Alvarez-type drift tube linac were adopted. Both linacs
are operated at 100 MHz, and the diameter of the drift
tube linac exceeds 2 m[8].
In Fig. 9, a part of the synchrotron ring is given. The
average diameter of the ring is about 40 m, and a ferriteloaded RF cavity having exactly the same size andstructure of an RF cavity is installed in the ring.
Figure 10 shows the indications for carbon therapy.
There are lots of organs treated by carbon ions, forexamples, the brain and skull base, head-and-neck region,eye, lung and liver, pancreas, rectum, prostrate and uterus,
and bone and soft tissues.

3carbon facility at Maebashi in 2007. The facility is thefirst example of the new cost-effective design in hospitalenvironments. Figure 11 shows a cut-away view of theGunma-University Heavy-ion Medical Center, GHMC.
We have three treatment rooms in the facility, and afourth irradiation room is being prepared for basic
experiments in physics and biological fields. The size ofthe building is 45  60 m2, whereas HIMAC building is
as large as 65  120 m2.

Figure 10: Indications for carbon therapy.
After more than 5,000 clinical experiences at HIMAC,
carbon ions show excellent characteristics in cancer
therapy: (1) the excellent dose localization reduces theside effects appreciably, (2) we can reduce the number ofthe fractionation without increasing the side effects andrisks of reoccurrence, and (3) carbon therapy is effective
for some kind of radio-resistive cancers such as bone andsoft-tissue sarcoma.

GUNMA MODEL
Through systematic clinical studies with HIMAC, thecarbon ions are recognized to be effective for curing
deeply seated human cancers. The high construction andoperation costs of facilities, however, are the big
obstacles in the wide use of the carbon therapy. So, R&D
studies have been carried out at NIRS to obtain a costeffective design of carbon therapy facility[9]. Gunma
University has been collaborating on these R&D studies
since 2004.

Figure 11: Cut-away view of Gunma University Heavy
Ion Medical Center. Rooms A, B, and C are used forcancer treatment and Room D is being prepared for future
developments.
A wide variety of R&D studies include ion source andinjector developments. On the basis of these studies,
Gunma University had initiated the construction of a new

(a)

(b)
(c)
Figure 12: (a) Injector linacs and ion source. (b) The
inside view of the RFQ linac. (c) The inside view of theIH linac.
The ion source is a permanent-magnet-type ECR
source[10], and it generates carbon 4+ ions with morethan 250 eμA. An injector[11] consists of a four-vanetype RFQ and Interdigital-H-type linear accelerator with
Alternating Phase Focusing. Both linacs are operated in
200 MHz and use the RF field both for beam acceleration
and beam focusing. Since we do not need any extra
focusing elements in the cavities, the injector is very easy
to handle and works stably. The output energy of theinjector is determined to be 4 MeV/u so that a charge
stripping efficiency from carbon 4+ to 6+ exceeds 90% at
the end of the IH linac. The maximum surface field isadopted at rather low value of 1.6 Kilpatrick to reduce therisks of sparking problem. A photograph of the injector
and the ion source is shown in Fig. 12.

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The lattice structure of the synchrotron is conventional
FODO-type[12] and the circumference of the ring is 63 m.
Fully striped carbon ions are injected into the ring by amulti-turn injection method. The pulse length of theinjected beam can be varied by a chopper system in theinjector. We can form a circulating hollow beam bytuning the timing and time duration of the pulse length inorder to reduce the tune shift caused by space-charge
effects at a rather low injection energy of 4 MeV/u. The
synchrotron accelerates carbon ions up to an energy
ranging from 160 to 400 MeV/u. A slow beam-extraction
technique using 1/3 resonance is adopted. The maximum
bending field is designed to be 1.5 T. The weight of eachbending magnet is about 8 t, and the total weight of thering magnets is about 150 t. An overview of thesynchrotron is given in Fig. 13.

Usually, the therapy accelerator is switched on in themorning and switched off in the evening; so, the start-up
time of the therapy accelerator is a very importantparameter. Now, we realized 1 h for the start-up time, but
we would like to reduce this time to 30 min. The timerequired for changing synchrotron energy and switching atreatment room to the next should be less than 3 min, andthis has already been realized. The reproducibility of thebeam intensity and beam position is expected to be better
than 10% and 0.5 mm, respectively, without any tuning,
and this has also been realized. So, the short scheduled
shutdown time is 4 weeks per year in the early stage, andmaybe a few years later, we will not need any scheduled
shutdown time. This is desired to increase the number oftreated patients.
In February 2007, the construction of the Gunma
facility was initiated. The building was completed in
October 2008. We started the accelerator commissioningin August 2009. In March 2010, we accepted the firstpatient. From June, we started the charged treatment. Thecarbon treatment costs about 3 million yen.
New plans for carbon therapy facilities are going on
especially in Europe and East Asia. The success of theGunma facility is expected to open up a new era ofcharged-particle therapy.

ANOTHER APPLICATION OF HEAVYION BEAMS

Figure 13: Synchrotron ring with a circumference of 63 m.
We adopted the Wobbler technique to form a wide
uniform irradiation field of 15 cm2, because therequirements for the properties of the extracted beams arenot so tight. The details of the beam-shaping technique inthe beam delivery system are out of the scope of thispaper. In Fig. 14, the inside view of the treatment room B
is shown.

Figure 14: Inside view of the treatment room B.

The ion-beam plant-breeding performed by RIKEN
group is another successful application of heavy-ion
beams. When heavy ions are irradiated on biomedical
cells, the DNA ladder in the nucleus gets damaged byheavy-ion irradiation. When the damage is serious, thebiological cells will be killed by the irradiation. But when
the damage is not so serious, a part of the characteristicsof the cells can be changed. This is an example of such acase: by the irradiation using the heavy-ion beams, thecolor of flowers can be changed. In Fig. 15, someexamples of new colors of flowers in the market are given.

Figure 15: Examples of commercial cultivars produced byion-beam breeding (data provided by RIKEN).

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