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It is desirable not only that cancers be cured, but also
that the therapies cause minimal damage to the patient's organs and physical
form in consideration of the patient's rehabilitation.
An advanced charged particle therapy for cancer
is expected to be a human friendly therapy that places fewer physical burdens
on patients.
It has a powerful therapeutic effect, especially
on intractable cancers, and has been approved as a highly advanced medical
technology by the Ministry
of
Health, Labour and Welfare.
The Research Center for Charged Particle Therapy,
as a leading research institute in this field, undertakes research and development
for the further
advancement
and dissemination of this therapy.
A cutting-edge radiation therapy system based on the achievements
of the NIRS
The National Institute of Radiological Sciences (NIRS)
started cancer therapy in 1961 using x-rays, gamma rays and other modalities.
Since then, it has gained worldwide recognition for 45 years of achievements.
Fast neutron beam therapy using a cyclotron and proton therapy, which were
introduced in 1975 and 1979, respectively, were found to be effective against
some cancers that were difficult to treat with conventional radiation therapies
such as x-rays and gamma rays.
However, for certain types of cancer difficult to cure
with fast neutron or proton beams, the goal has been to develop a new therapy
using a beam that
has a better biological effect than the fast neutron beam and also the sharp
intensity of the proton beam.
The NIRS therefore decided to promote the medical application of heavy ions, taking advantage of its accumulated research results, and constructed the world's first heavy ion medical accelerator, HIMAC. Charged particle therapy was started in 1994 and the number of patients exceeded 6000 by May 2011. It was approved as a highly advanced medical technology by the Ministry of Health, Labour and Welfare in October 2003 during the first 5 year project of the NIRS. The NIRS is now in a new stage to promote the construction of a compact version of the system for dissemination of the therapy.
Use of charged particle therapy for resistant and deep seated
cancers
In order to realize a better radiation therapy, it is
essential to use a type of radiation with higher therapeutic effect. There
are two indicators for therapeutic effects: relative biological effectiveness
(RBE) and oxygen enhancement ratio (OER).
When the therapeutic effects of charged particles (carbon
atoms) are compared with those of gamma rays, the charged particles have an
advantage of about
three times the RBE value (a larger value indicates greater effects) and
an OER, where a smaller value is better, of about half that of gamma rays,
as
shown in Fig. 1.
When radiation is used as a therapy, it is also important
to use a type of radiation that causes less damage to normal tissues. Therefore,
it is necessary
to know how the radiation intensity (dose) will distribute in the body.
Both gamma ray and fast neutron beams are strongest near the surface of the
human
body and are attenuated in deeper areas of the tissues, as shown in Fig
2. This suggests that when a deep cancer is treated with these types of radiation,
normal tissues between the surface and the target are susceptible to damage
and a deep area beyond the target will be also affected. In contrast, the
use of protons or charged particle beams can reduce damage to the tissues
by focusing
the peak of the beam on the location of the tumor, as the beam becomes
dramatically
intense at a certain depth according to the energy applied but is weak
before and after that depth. The NIRS is engaged in research and development
for
an ideal radiotherapy using charged particle (carbon) beams which has a
greater therapeutic effect on cancer but causes less damage to normal tissues.
Cancer therapy with HIMAC, the world's most advanced charged
particle cancer therapy system
Particle beam therapy is used in various parts of the
world, mostly using hydrogen ions (protons), which are the lightest atoms.
However, more than 10 years of clinical studies by the NIRS have revealed that
a beam of carbon atoms has excellent properties, additional to those of the
proton beam.
Since 1994 the NIRS has conducted clinical studies in
cancer treatment using carbon ion beams obtained from HIMAC, the world's first
medically-dedicated
heavy ion accelerator. Based on the results, carbon beam therapy was approved
as a highly advanced medical technology by the Ministry of Health, Labour
and Welfare in October 2003, marking a significant step from an experimental
treatment
to regular clinical use.
Now there are growing expectations for charged particle
therapy. The NIRS is currently working to provide technical support for dissemination
of modern
radiation therapy technologies, fostering human resources, and further
developing advanced charged particle therapies for the future.
Proliferation of charged particle therapy
The NIRS completed research and development for a compact
charged particle therapy system in 2005. We now have prospects that a beam
performance comparable
to that used in cancer therapy at the NIRS can be realized in a system
about one third of the size of HIMAC. In order to make charged particle therapy
available to more people by using the compact system, the NIRS has given
technical support to Gunma University, which starts the construction of
a
charged particle cancer therapy system in 2006. The NIRS will continue
to assume a central role in providing human resources including charged particle
therapists, clinical radiological technologists and medical physicists.
The NIRS, in collaboration with external research institutes
and universities, is currently developing new technologies including laser
acceleration and
conducting research and development on therapeutic systems small enough
to install in
existing hospitals.
Cancer therapy using energetic heavy ions produced
with HIMAC
has been performed at NIRS since June 1994. The HIMAC complex
consists of heavy-ion accelerators and four irradiation ports,
and can accelerate heavy ions up to approximately 80% of the speed of light.
There are only a few such heavy-ion accelerator
complexes in the world, and a number of overseas researchers are interested
in using heavy-ion beams produced by HIMAC for their research.
HIMAC is used for cancer treatments from 7 a.m.
to 7 p.m. on weekdays, and provides heavy-ion beams for fundamental research
at night and on weekends. These research projects involve biology, chemistry
and physics as well as medical physics. To perform experiments, one may need
to submit a proposal. Calls for proposals for experiments using HIMAC are posted
twice a year, and submitted proposals are reviewed by a Proposal Advisory Committee
consisting of researchers outside of NIRS to ensure fair judgment.
This program of soliciting outside heavy ion research
proposals began in October 1994. Currently more than 100 research proposals
a year are submitted resulting
in over 60 papers a year, and the number of visiting researchers exceeds
500 a year. Many graduate students do experiments using HIMAC for their thesis,
and NIRS plays an important role in educating young scientists.
More Information >> Research Project with Heavy
Ions at NIRS-HIMAC
HIMAC Building