Proceedings of IBIC2012, Tsukuba, Japan

MOPB58BEAM QUALITY ENSURING INSTRUMENTS AT THE GUNMAUNIVERSITY HEAVY-ION MEDICAL CENTER
E. Takeshita#, T. Kanai, S. Yamada, K. Yusa, M. Tashiro, H. Shimada,K. Torikai, A. Saito, Y. Kubota, A. Matsumura, M. Kawashima,
Gunma University Heavy-Ion Medical Research Center
3-39-22, Showa, Maebashi, Gunma 371-8511 JAPAN

Since carbon beam based cancer therapy started at the
Gunma University Heavy-ion Medical Center in the year
2010, the total number of treated patients increased to 306
by the end of 2011. This fiscal year, already 164 patients
have been treated. In order to control the medical beam
qualities, i.e., position, size and intensity of the beam,
monitoring devices were mounted on the high-energy
beam transport line. The beam position and size can bemeasured and tuned with a screen monitor, which consistsof a fluorescent screen and a CCD camera. Just before
starting the treatment, the operators check for a proper
beam position by strip-line monitor measurements placed
close to the isocenter. The irradiation dose is controlledusing two secondary electron emission monitors placed
before wobbling magnets. This dose monitor is helpful asfor high beam intensities it’s less affected by therecombination effect. The technical layout of all beam
monitors are described.

________________________________________#eriuli@gunma-u.ac.jp

INTRODUCTION OF GHMC
The Gunma University Heavy Ion Medical Center(GHMC) [1] is located at the Gunma University Hospital.
Basic and accelerator building designs started in April andJuly 2006, respectively. The construction works started in
February 2007 and were completed in October 2008. The
facility's dimension is about 65 m × 45 m, approximately
1/3 of the Heavy Ion Medical Accelerator in Chiba(HIMAC) [2]. The layout of the bottom floor is shown in
Figure 1. The facility contains three treatment rooms withfour irradiation ports (horizontal; Room A, horizontal +vertical; Room B, and vertical; Room C) and a room witha vertical port intended for R&D of beam delivery systemand biology experiments.

Accelerator Complex
The injection part consists of a compact ECR ion
source and two linear accelerators, which are the radio
frequency quadrupole linac (RFQ linac) and thealternating phase focusing linac (APF linac) [3]. The RFQ
linac accelerates the carbon ion beam up to 600 keV/u

Figure 1: Layout of B1 floor in GHMC.
ISBN 978-3-95450-119-9

Overview and Commissioning of Facilities1c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○AbstractMOPB58

Proceedings of IBIC2012, Tsukuba, Japanand the APF linac accelerates the carbon beam up to 4
MeV/u.
The maximum carbon beam energy achieved by thesynchrotron [4] is 400 MeV/u, and the extracted beam isdelivered through a high energy beam transfer line
(HEBT) to the isocenter. The excitation pattern cycle ofthe synchrotron is normally 2.7 seconds: Injection time is
0.1 seconds, acceleration and deceleration are 0.7 seconds,
respectively, and 1.2 seconds are needed for the
extraction. The maximum beam intensity is 1 × 109
particles/seconds, which is equivalent to 5 GyE/min.

problem for the treatment. As the beam's shape is very
narrow and the beam size is about >10 mm on theisocenter, the irradiation field is not sensitive due to thebeam motion. Every morning, the beam profile on theisocenter is inspected and adjusted to the center within 2
mm.

Verification beam before and during treatment

Beam Delivery System
The beam delivery system guides the high-energy
carbon beams generated by the accelerator complex to thetherapeutic usage and delivers them to the patient lying in
the treatment room. A beam delivery system comprises ofseveral devices, i.e., dose monitors, wobbler magnets, ascatterer, a ridge filter, a range shifter set, a multi-leaf
collimator, a compensator and a patient positioner system,
for precise aiming of the therapeutic beams on theplanned target volume by adopting a beam wobbling
method.

c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○CHECK BEAM POSITION AND SIZE
Screen Monitors for HEBT Tuning
The HEBT section includes 19 screen monitors (SC)and 4 strip line monitors (SLM) beam profile
measurements. A screen monitor consists of a fluorescentscreen (Al2O3) and a CCD camera. The beam profile isobserved as motion picture with 30 frame/sec. Aftertaking profile data, the position and size are manuallycalculated during measurement time. To tune the beam
position, the beam profile is measured using the screen
monitor and the position of the beam manually modified
using steering magnets in order to decrease beam axis
misalignments. Figure 2 shows a result obtained by thescreen monitor data. The position was calculated applying
the center of gravity method. It can be seen that the beam
positions have a few millimetres time dependence during
extraction. However, in a broad beam irradiation
technique, position time dependence is not a serious

Figure 3: Season variation of the beam position measured
by the SLM in room B (BHC and BVC).
The SLM is mounted on every irradiation port close to
the isocenter in order to verify the position and size of thebeam just before treatment begins. Each of the horizontal
and vertical planes is covered by 30 strips with 1.5 mm
spacing and the effective area is 45 mm × 45 mm. The
beam position variation depends on the season as shownin Figure 3. The maximum difference for the position ineach port, measured at several beam energies, stay within~4 mm in a year.

380MeV/u

Figure 2: Position of the extracted beam at the isocenter
measured by SC as a function of time.

Figure 4: Schematic view of “flatness monitor”.

ISBN 978-3-95450-119-9
2

Overview and Commissioning of Facilities

Proceedings of IBIC2012, Tsukuba, JapanCONTROL INTENSITY
Spill Profile
Every morning, the extracted beam intensity is counted
using a FC placed on the entrance of the HEBT. The
efficiencies of the injection, acceleration, capture andextraction of the beam are measured by the DCCT inside
the synchrotron. Figure 4 shows the spill structure (greenline) and the beam current (blue line) at an energy of 380
MeV/u. The average intensity of the extracted beam isalmost 1.0 × 109 particles/seconds, which satisfies theinitial design criterion.

treatment, the linearity of the response is acceptablewithin 0.3 %.
x 10

-13

0.79
Chamber Outout/Monitor (C/Count)

Also during treatment beam position and size arecontrolled using the SLM and the flatness of theirradiation field is verified by a parallel plate typeionization chamber called “flatness monitor”. Figure 4
shows the schematic view of the flatness monitor. The
effective area is I 220 mm and the electrode gap is 9 mm.

MOPB58

0.785
0.78
0.775

~0.3%

0.77
0.765
0.76
0.755

Area used for the treatment

0.75
0.745
3

10
10
Main Monitor Preset(Count)

4

CONCLUSIONSThe presented data show that the beam diagnostics ofthe GHMC facility provide all necessary equipment forcommissioning and machine operation, especially forbeam quality verification during medical treatment. The
HEBT devices deliver high resolution data and allow
fine-tuning of synchrotron extraction and HEBT lines.
Any device, most importantly the isocenter diagnostics,
can be integrated into therapy protocols.
Figure 5: Spill structure of the extracted carbon beam on
380MeV/u.

Dose monitors
Two secondary emission monitors (SEM) are set up
upstream of the wobbler magnets to control the irradiationdose for the treatment. The detection efficiency of thedose monitor for the treatment should not change due tothe irradiation condition of the beam wobbling method. Inorder to measure the dose of the pencil beam before
wobbling, the SEM as the dose control monitor isemployed. The SEM is very helpful for high beam
intensities, as it’s less affected by the recombination
effect. Main monitor is used for the dose control mainly
and the leak current of the beam continue to measureusing sub monitor during the treatment. If the leak current
surpasses a threshold value (~1% of preset count), thebeam is stopped immediately by an interlock systemusing a fast quadrupole magnet set up within thesynchrotron. Figure 5 shows the linearity of the dose
response on the SEM depending on the irradiation presetcount. From 1 to 5 × 104 counts, which was used for the

ACKNOWLEDGMENT
The authors would like express their thanks to the
Mitsubishi Electric Corporation staff members for their
dedicated operation and support of our facility. We also
would like to thank all members of medical doctors,
clinical nurses and medical radiology technicians at the
GHMC for their valuable advices and encouragement.

REFERENCES[1] T. Ohno et al., “Carbon Ion Radiotherapy at the Gunma
University Heavy Ion Medical Center: New Facility Setup”, Cancers 2011, 3, 4046-4060.
[2] K. Noda et al., "HIMAC and new facility design for wide
spread use of carbon cancer therapy", APAC'04, Korea,
March 2004, p. 552-556.
[3] Y. Iwata et al., "THE COMPACT INJECTOR AS THE
SECOND INJECTOR OF THE HIMAC", LINAC2010,
Japan, 2010, p. 190-192.
[4] T. Furukawa et al., "Design of synchrotron and transportline for carbon therapy facility and related machine study at
HIMAC", Nucl. Instr. and Meth. A 542 (2006) 1050-1053.

ISBN 978-3-95450-119-9
Overview and Commissioning of Facilities3

c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○Figure 6: Linearity of the dose response by the SEM as afunction of number of the irradiation preset counts.