Physical and engineering aspect
of carbon beam therapy
Tatsuaki Kanai*, Nobuyuki Kanematsu*, Shinichi Minohara*, Ken Yusa*,
Eriko Urakabe*, Hideyuki Mizuno†, Yasushi Iseki¶, Mitsutaka Kanazawa*,
Atsushi Kitagawa*, Takehiro Tomitani*
*Research center of charged particle therapy,National Institute of Radiological Sciences, 4-9-1,
Anagawa, Inage-ku, Chiba-shi, 263-8255 CHIBA, JAPAN
†
Saitama Cancer Center, Ina-machi, Saitama, Japan
¶
Dept. of Energy Sciences, Tokyo Institute of Technology, Nagatsuta, Yokohama, Japan
Abstract. Conformal irradiation system of HIMAC has been up-graded for a clinical trial using a technique of a
layer-stacking method. The system has been developed for localizing irradiation dose to target volume more
effectively than the present irradiation dose. With dynamic control of the beam modifying devices, a pair of wobbler
magnets, and multileaf collimator and range shifter, during the irradiation, more conformal radiotherapy can be
achieved. The system, which has to be adequately safe for patient irradiations, was constructed and tested from a
viewpoint of safety and the quality of the dose localization realized.
A secondary beam line has been constructed for use of radioactive beam in heavy-ion radiotherapy. Spot scanning
method has been adapted for the beam delivery system of the radioactive beam. Dose distributions of the spot beam
were measured and analyzed taking into account of aberration of the beam optics. Distributions of the stopped
positron–emitter beam can be observed by PET.
Pencil beam of the positron-emitter, about 1 mm size, can also be used for measurements ranges of the test beam in
patients using positron camera. The positron camera, consisting of a pair of Anger-type scintillation detectors, has
been developed for this verification before treatment.
Wash-out effect of the positron-emitter was examined using the positron camera installed.
In this report, present status of the HIMAC irradiation system is described in detail.
INTRODUCTION
since June 1994. Now we have already treated over
1000 patients using our carbon beams. During these
Clinical trials of carbon beam radiotherapy have
eight years, the irradiation system at HIMAC has been
been started using heavy-ion accelerator complex,
improved. In our system, a passive method has been
HIMAC (Heavy Ion Medical Accelerator in Chiba) at
adapted for spreading the Bragg peak in depth direction
NIRS (National Institute of Radiological Sciences)
and for broadening the narrow accelerated beam in
CP680, Application of Accelerators in Research and Industry: 17th Int'l. Conference, edited by J. L. Duggan and I. L. Morgan
© 2003 American Institute of Physics 0-7354-0149-7/03/$20.00
1146
lateral direction. Through this passive method, the
conformal irradiation using layer-stacking. Another
irradiation system can be applicable to moving target,
development of the irradiation technique is use of
for example, lung or liver.
positron emitter as the therapeutic beam.
In this method, large
In this
fraction of dose is sometimes given to the skin of the
report, the improvements at HIMAC system will be
patient.
presented.
In order to increase dose localization and
then to decrease dose to skin, we have developed
Multi-leaf
Collimator
Target
Wobbler Scatterer
Magnets
Compensator
Monitors
Ridge Filter
Range Shifter
Figure 1. Illustration of the conformal irradiation using layer-stacking method
cannot be changed. With dynamic control of the beam
CONFORMAL IRRADIATION SYSTEM
USING A LAYER-STACKING METHOD
modifying devices during the irradiation, more
conformal radiotherapy can be achieved. Uniform
fields can be made by a pair of wobbler magnets and a
Conformal irradiation system of HIMAC has been
scatterer. The Bragg peak of the mono-energetic beam
up-graded for a clinical trial using a technique of a
is
layer-stacking method [1,2]. Fig. 1 illustrates the layer
gaussian-modulating ridge filter is adapted to prevent
stacking method for the conformal irradiation. The
hot or cold spot due to moving of target volume during
system has been developed for localizing irradiation
the irradiation [3]. Width of the broadened Bragg peak
dose to target volume more effectively than the present
was designed to be 2.5 mm. The mini-peak is swept
irradiation dose. In a present passive irradiation method
longitudinally by inserting a range shifter for making a
using a ridge filter, a scatterer, a pair of wobbler
SOBP. The target volume is divided parallel to distal
magnets, and multileaf collimator, the width of a
edge of the target volume. The curved layer of the
spread-out Bragg peak (SOBP) in the radiation field
mini-peak according to the divided target is made by
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slightly
broadened
by
a
ridge
filter.
A
the compensator placed just up-stream of the patient.
Fig. 2 shows typical example of the result of dose
Each layer is sequentially irradiated from the deepest
distribution realized by installed system, in which
one by the mini-peak. By this longitudinal sweep of
uniform dose distribution is planned to put on the target
the Bragg peak, SOBP can be made and covered the
for test of the system.
whole target volume. When irradiating the mini-peak
SPOT SCANNING SYSTEM FOR 11C
BEAM
by layer by layer, the irradiation field is shrunk along
the target volume by a multileaf collimator. By this
procedure, unwanted irradiation to normal tissues can
be avoided. In order to safely perform treatments by
An irradiated volume can be verified by observing
this conformal therapy, moving devices should be
annihilation-pair gamma rays from the stopping
watched during the irradiation and the synchronousness
position in the patient when positron emitter beams,
among the devices should be checked. The system,
such as
which has to be adequately safe for patient irradiations,
irradiation system of the radioactive beam has been
was constructed and tested from a viewpoint of safety
installed in HIMAC for using positron emitter as the
and the quality of the dose localization realized.
therapeutic beams [4]. A spot scanning technique is
11
C, are used as therapeutic beam. An
adopted for spreading the radioactive beam because of
considerably low intensity. In the spot scanning, the
position of each spot is controlled by excitation of a
pair of scanning magnets and inserting range shifter.
Because 11C spot beams have a wide momentum spread
(2%), the aberration should be taken into account to
calculate their dose distribution. We measured the
beam envelope and the dose distribution of the
spot-beam. Based on these measurements, the dose
distributions of
11
C beams are calculated and the
irradiation volume is designed in water phantom. Fig. 3
and 4 show the optimized dose distribution using the
11
C beam for a concave target. Fig. 3 shows
two-dimensional dose distribution in a central plane.
Fig. 4 shows dose distributions at the depth of 164 mm
and 184 mm. Gap of the concave target is 30 mm in
this case. As shown in these figures, penumbra size
Figure 2 Typical example of the dose distribution
was relatively large size because of the large emittance
realized by the layer-stacking method.
of the radioactive beam.
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In the application of the probing beam, it is very
(a)
important to know washout effect of the positron
x [mm]
emitter in the patient because of blood flow. The
washout
z [mm]
effect
is
experimentally
examined
by
measuring the stopped positron emitter in the brain and
muscle of rabbit using developed positron camera. We
164 184
observed three components of the washout effect [6].
Biological decay constants for the fast, middle and
Figure. 3. Iso-dose contour for a concave target
(b)
slow components of a brain and a thigh muscle were 2
1.2
sec., 140 sec., 10191 sec. and 10 sec., 195 sec., 3175
Dose (arbitrary units)
1
sec., respectively.
0.8
0.6
CONCLUSIONS
0.4
z=164
z=184
0.2
0
-60
-40
-20
0
x [mm]
20
40
Recent developments at HIMAC beam delivery system
are described. The conformal therapy using the layer
60
stacking method will soon be applied for patient
Figure 4. Dose distributions at 164 and 184 mm depth.
treatments.
Utilization of the positron emitter beam for therapy is
DEVELOPMENT OF POSITRON
CAMERA
still at a stage of feasibility study. Now, experimental
evidences of the merit should be shown for the real
treatment of the patient.
A probing beam of positron emitters is injected into
REFERENCES
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dose. Thus, the crystal size was optimized as a function
of the range accuracy by numerical simulation [5]; 600
mm in diameter and 30 mm thick.
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