Proton and Ion Cancer Therapy

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Proton and Ion Cancer Therapy
Ideally, proton and ion therapy require very
small, intense and mono-energetic beams. The
energy is particularly important, as this
controls the depth at which the main energy
deposition takes place. In general, the protons
used for this therapy are accelerated using
cyclotrons, which can only give a single proton
energy. To produce the correct energy, this must
be degraded using absorbers and this can produce
an undesirable spread.
FFAGs, on the other hand, can produce particle
beams with a variety of energies. A prototype
under test in Japan is designed for three, but
more may be possible. This will reduce, if not
eliminate, the need for absorbers. Furthermore,
FFAGs produce very intense particle bunches, so
in principle it will be possible to select from
these intense bunches of exactly the right
characteristics and perform a 3D scan of the
tumour.
Boron Neutron Capture Cancer Therapy
Accelerator Driven Sub-critical Reactors
BNCT is a possible method for treating one of the
deadliest forms of cancer, a type of brain tumour
called a "glio-blastoma multiforme". This
afflicts 12500 people in the USA each year, for
example, and is always fatal. In BNCT, a compound
containing boron-10, a non-radioactive isotope,
is introduced into the brain and preferentially
absorbed by the tumour. This is then exposed to
intense neutron beam which causes the boron-10 to
fission, releasing an alpha particle and lithium
nucleus. Both of these have a very short range
and hence destroy the malignant cells that the
boron is in without damaging healthy cells.
Accelerator Driven Systems address two main, but
related, issues to do with nuclear power
generation. The first is to drive sub-critical
nuclear reactors based on thorium-232 (Th-232).
There has been interest in using thorium for many
years as it is 3 times more abundant in the
Earth's crust than uranium and in principle all
of it can be used in a reactor, compared to 0.7
of natural uranium. It works by absorbing a
neutron to become Th-233 which decays to U-233,
which fissions. The problem is there are
insufficient neutrons generated to sustain the
reaction. In ADS, a high intensity proton
accelerator is used to generate the neutrons
required to sustain the reaction by spallation.
It has a big advantage over conventional
reactors, in addition to burning thorium if the
accelerator is turned off, the reactor stops
without the need to employ moderators to absorb
neutrons.
BNCT has been investigated in a number of
countries with very positive results. Most
studies have employed reactors as the neutron
source, which is not practical for treating many
patients on a day-to-day basis. FFAGs provide a
possible solution for producing enough neutrons
to treat patients in hospital and a study of this
has recently started in Japan.
Tests of BNCT have employed nuclear reactors, but
these are impractical for large scale
day-to-day treatment. An FFAG could provide the
neutrons rather than a reactor.
The second issue is the transmutation of
radioactive waste. Along with safety, the
disposal and storage of the waste is one of main
problems of nuclear power generation. In
transmutation, the long-lived waste is bombarded
with neutrons which in most cases causes fission
and gives (in general) short-lived products. This
also generates energy and transmutation could be
combined with a sub-critical reactor.
FFAGs are ideal for this application due to the
high beam intensity and rapid cycling. A five
year project started at Kyoto University Research
Reactor Institute in 2002 to develop an FFAG and
a reactor to test the feasibility of this form of
energy generation and nuclear waste transmutation.
A drawing of an ADS scheme using a linear
accelerator. There are a number of benefits to
using an FFAG for the proton acceleration instead.
What still needs to be done ?
Physics research applications currently under
study for FFAGs
There are two types of FFAG envisaged. All those
built or under construction so far are so-called
"scaling" FFAGs in which the orbits of particles
around the machine are the same, except they
scale with energy. The problem with this is the
magnets required tend to be large and complex,
and hence quite expensive.
? high power proton drivers FFAGs are being
considered in relation to a number of future,
high power proton drivers. ? eRHIC a 10 GeV
electron FFAG is being investigated as part of
the project to create electron-ion collisions at
the Brookhaven Laboratory.
The second type is a "non-scaling" FFAG, in which
the orbit shapes change as a function of energy.
This allows the apertures of the magnets to be up
to 10 times smaller than for a scaling machine,
making the FFAG much more compact. In addition,
the non-scaling magnets are less complex. Taken
together, these could make a non-scaling machine
considerably cheaper than a scaling machine for
the same performance.
A magnet for the prototype 150 MeV scaling FFAG
built at KEK. The magnets for a non-scaling FFAG
could have a 10 times smaller aperture, making
them smaller and cheaper.
The current Neutrino Factory layout in the USA.
The orbit shape in scaling FFAG cells is the same
at each energy, but varies with non-scaling
machines. This allows the apertures of the
magnets to be much smaller in the latter,
reducing the cost for the same performance.
The non-scaling nature of the second type of FFAG
introduces a number of problems, however. In
particular, there are a number of features which
are entirely novel to this type of machine and
never before tested in an accelerator. As a
result, it is planned to build a small electron
non-scaling FFAG, the first of this type ever
built, to check that none of these features will
stop the machine working.
We are seeking collaborators to work with us on
the development of this novel form of accelerator
for any of the potential applications !