Biomedical Engineering Reference
In-Depth Information
that the lattice design of EMMA could not be transferred directly to a proton/carbon
machine [
8
] as it was difficult to achieve the packing density with a realistic magnet
design, making the space in the straight sections insufficient for the RF acceleration
cavities. A new lattice design has been proposed [
9
] to overcome these difficulties.
This design offers extraction energies up to 250 MeV for protons and 68 MeV/amu
for carbon ions and consists of 12 cells on a radius of 6.25 meters.
30.2.4
Linear Accelerators
Another interesting concept merging the continuous beam production of a cyclotron
and the flexibility in energy selection offered by RF acceleration systems has been
proposed and developed by U. Amaldi from the TERA (TErapia con Radiazioni
Adroniche) Foundation. A beam extracted from a cyclotron at an energy of 30 - 60
MeV is chopped at 200 - 400 Hz and injected into a 3 GHz side coupled linac (SLC)
for acceleration from 30 to 210 MeV. One of the advantages of the cyclotron/linac
combination, named Cyclinac, is the availability of direct beams from the cyclotron
for the production of radio pharmaceuticals, as well as for eye tumor treatments.
Hospitals which already own a radio pharmacy could add a linear accelerator to
provide an energy boost to the output of the cyclotron and add proton therapy to
their program.
The ensuing beam consists of a sequence of 5
sec pulses with a delay time
between pulses of 2.5 - 5 ms. The number of particles per pulse can be varied
from pulse to pulse within milliseconds by changing the power delivered to the
accelerating modules of the linear accelerator and by changing the charge injected
into the acceleration chain from a computer controlled ion source. The output energy
of the system is variable as it is in a synchrotron, the time structure of the beam is
ideal for spot scanning, and the transverse emittance is about 10 times smaller than
found in cyclotrons and synchrotrons.
Latter allows for smaller gaps in focussing and deflection magnets, reducing the
cost of beam delivery systems and gantries. The original design for the SLC called
for a 11 m long structure with 24 tanks and permanent quadrupole magnets, an
RF peak power of 30 MW, and a beam current of 33
A[
10
]. A four tank proto-
type named LIBO (LInear BOoster) was constructed and tested at CERN. Each of
the tank consisted of 15-16 accelerating cells and between two successive tanks
a FODO structure of permanent magnetic quadruploe magnets was installed for
beam focussing. This system achieved an acceleration of protons from 62 to 74
MeV in 1 meter distance [
11
]. Based on this success a complete design has been
finished. The first fast cycling accelerator is planed for the Institute for Diagnostics
and RAdiotherapy (IDRA) in Biella, Italy. The same concept can be applied to the
production of carbon ion beams for therapy, and a design of a Carbon BOster for
Therapy in Oncology (CABOTO) has been developed. Using 18 modules with 3
tanks consisting of 17-21 acceleration modules each, carbon ions and hydrogen
molecules can be accelerated from 120 MeV/amu to 400 MeV/amu.
