Biomedical Engineering Reference
In-Depth Information
press organs, several hospitals have placed an option on this system and the first
installation is expected to take place in 2011 at the Siteman Cancer Center at
Barnes-Jewish Hospital and Washington University School of Medicine in St. Louis,
MO. [
3
]
30.2.2
Miniaturization of Standard Accelerators
Cyclotrons are not the only system which can benefit from modern technology.
Using superconducting materials cyclotrons today are much more compact than
systems of the same output energy 20 or 30 years ago. Similar developments are
foreseeable for synchrotrons, and attempts to compactify medical synchrotrons
exist, mostly in Russia.
The patents for one such system has been purchased by Texas based ProTom
International, Inc. Offered under the name Radiance 330 it is a compact proton
synchrotron with fully variable beam energy ranging from 30-330 MeV, has an
external ring diameter of approximately 5 meter and weighs only 15 tons. The
system is offered in a standard configuration of separate accelerator room and
treatment room(s), but has not yet been FDA approved.
But this must by no means be the smallest size. At the Budker Institute for
Nuclear Physics in Novosibirsk a table top synchrotron has been designed with a
footprint of only 1.6 x 1.6 m
2
for an energy range from 12 to 200 MeV and an
RF sweep from 7.4 to 26.5 MHz in 3.5 milliseconds. Multi-turn injection had been
demonstrated but the stored beam was 2 orders lower in intensity than expected.
Also, at the time no RF was installed and no extraction was provided. The project
was abandoned for unknown reasons, but a system like this could easily rival the
compact cyclotrons, and could even be mounted on a gantry, similar to the Still
River system.
30.2.3
Fixed Field Alternating Gradient (FFAG) accelerators
Aside from the standard cyclotrons and synchrotrons, used nowadays for virtually
all hospital based particle therapy installations, the fixed-field alternating gradient
accelerator (FFAG) promises to combine the advantages of continuous operation
found in cyclotrons with the flexibility of active energy change available in a
synchrotron. In a FFAG variable energy extraction at kHz rate is possible.
The FFAG closely resembles a synchrotron, using a specific combination of fo-
cussing and deflecting magnets to steer the particles onto a closed orbit, intersecting
acceleration cavities on each loop. The main difference consists of the fact that
instead of varying the magnetic field strength during the acceleration process in
order to keep the particles on the prescribed orbit, the FFAG uses a temporally fixed
field with a strong radial gradient. Particles with larger energies move to slightly
