|
When trying to understand the optical design of an existing Medical Gantry for Proton-Therapy, then the
compactness (e.g. no space-consuming modular waist to waist transport system is acceptable here) and the large
90 to 135 degree bending magnet (focusing properties, momentum-dispersion) at the end of the gantry is
usually causing some headache to newcomers in this field. Especially the fact, that the dispersion at the beginning
(matching- or rotation-point) and at the end (iso-center, location of the tumor to be irradiated) must be zero
(D=D'=0) or (R16=R26=0). The first order input files for the Graphic Transport Framework for three types of gantries
will be presented here. In order to ease the search for an optical solution of the problem, the principle of
beam line inversion (BLI) will be applied here. The reasons for this are the following facts: It is much
easier to start with the requested beam properties at the end (values for x , x', y=x, y'=x', dp/p and D=D'=0)
and then apply some amplitude-limiting constraints in backward direction (heuristic trial and error method)
along the beam line and again D = D' = 0 after the last bending magnet before the rotation-point of the gantry.
Additional constraints are also  x=y
and x'=y' (and preferably a double-waist)
at the rotation-point of the gantry. (To fullfil the later requirements see the notes about
Algebraic combination constraints).
Important inputs are the signs and strengths of the starting values (guesses) for the quadrupole lenses.
The different groups (2 to 5 quads) should always have alternating gradients. The sign of the 1st quad from the
end (near the 90 or 135 degrees bending magnet) is given by keeping primarily the most critical one of either
the x-amplitude, the y-amplitude or the dispersion nearby at a limited size. Of course, the different
parameters in these 3 files may be altered and adapted to your special needs. Care has then to be taken,
that the beam size values of the different fit-constraints (fit code digits i, j equal 1, 1 for x or 3, 3 for y)
are adapted manually and eventually moved to other z-coordinates.
The 3 presented input samples for Transport will demonstrate this approach:
The 1st one describes the large IBA-GA-gantry used at the MGH in Boston. The data for it
were mainly extracted from publications by J. Flanz et al. [1] and [2].
For having a look at the Transport input file
click here
and for viewing the produced transport envelopes
click here .
A Cosy Infinity [6] input procedure and its
graphic plot
(4th order, bending plane only) for a higher order check with the IBA-GA type of gantry is also available.
The 2nd one describes the PSI-type gantry (isocentric version) designed by E. Pedroni and H. Enge [3][4].
For having a look at the Transport input file
click here
and for viewing the produced transport envelopes
click here.
A Cosy Infinity [6] input procedure and its
graphic plot
(4th order, bending plane only) for a higher order check with the PSI type of gantry is also available.
The 3rd one describes an early PSI-study gantry designed by M. Daum and B. Jost [5].
For having a look at the Transport input file
click here
and for viewing the produced transport envelopes
click here .
A Cosy Infinity [6] input procedure and its
graphic plot
(4th order, bending plane only) for a higher order check with the M.Daum et al. type of gantry is also available.
References:
[1] J. Flanz et al., Overview of the MGH-NPTC plans and progress, Nucl. Instr. and Meth. in Phys. Res. B99 (1995) 830-834
[2] J.B. Flanz (NPTC-MGH Boston), Large Medical Gantries, 1995 Particle Accelerator Conference.
[3] E. Pedroni, Beam line data for an isocentric PSI-Gantry, via private communication.
[4] H. Enge, Report on Ion-Optical Work on a Proton-Therapy Gantry for the Paul Scherrer Institute. (1990)
[5] SIN-Jahresbericht 1984, JB21 and MED31/32.
[6] M. Berz, COSY INFINITY, an arbitrary order beam dynamics simulation and analysis code,
downloadable via the web from the Department of Physics and Astronomy at the Michigan
State University.
see also: Treating Cancer with Protons in Physics Today, September 2002, pages 45-50.
Other Proton Beam Therapy Application Examples:
Degrader Design for a 250 MeV Medical Cyclotron
Isotope Production Yield Optimization at PSI
Double Scattering Computations for Proton Beam Spreading
Last updated by
Urs Rohrer on 13-Feb-2007
|
back to: About Graphic Transport
