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200605_Philip_Bryant_Gantries

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					                           GANTRIES
                             FOR
                        HADRON THERAPY

                                 May 2006
                        P.J. Bryant – CERN, Geneva


JAI-2006- P.J. Bryant          Slide 1
                                      Contents
            What is a gantry?                  Matching methods…
            A more detailed classification…      Symmetric beam.
              Passive spreading gantries.        Round beam.
              Divergent-beam voxel-              Rotator method.
                scanning gantries.                Equal sigmas method.
              Parallel-beam voxel-               Patents.
                scanning gantries.
                                                GSI therapy complex.
              Exo-centric gantries.
                                                PIMMS.
              Novel designs.
                                                Gantry construction.
            Geometry is not enough…
                                                Superconductivity.
            Gantry matching requirements.
                                                Some controversy.
                                                Riesenrad gantry film.
                                                Conclusions.


JAI-2006- P.J. Bryant                Slide 2
                         If you have a therapy centre,
                        then you will want a gantry or
                                  maybe two!




JAI-2006- P.J. Bryant             Slide 3
                            What is a gantry?
  A gantry directs the beam onto the patient at
   whatever angle is required by the treatment      Accelerator plane
                                                                                     Gantry
   plan. Ideally, the full 2p should be available     (horizontal)                                  Target
                                                                                                    volume
   about the gantry axis.                                                         Horizontal axis
                                                                  Transfer line

  Ideally one should also be able to rotate the                                           Gantry plane
                                                                                            (rotating)
   patient, so as to access the full 4p solid
   angle.
  The requested treatment field is 40  40 cm2.
  The requested beam penetration 27 cm.
  There are two broad classifications :
     Iso-centric gantries.
     Exo-centric gantries.
                                                    Iso-centric                          Exo-centric

JAI-2006- P.J. Bryant              Slide 4
                            A more detailed classification…
             Beam diverges after last dipole:
                         Passive spreading gantries (protons).
                         Divergent-beam voxel-scanning gantries (protons).


             Beam diverges within gantry lattice:
                         Parallel-beam voxel-scanning gantries (light-ions).
                         Exo-centric “Riesenrad” gantry (light ions).



             There is also an extended category of novel
              designs.




JAI-2006- P.J. Bryant                           Slide 5
                        Passive spreading gantries

          The first passive spreading gantry built
           was the “corkscrew” gantry at Loma
           Linda.
                                                              Loma Linda Corkscrew
          Today the accepted conventional design
           is the “conical” gantry as demonstrated
           by IBA.

                                                              IBA Conical

          To understand these gantries it is useful to look
                 at the passive spreading technique.


JAI-2006- P.J. Bryant                 Slide 6
                         Double-scatterer system for protons

 First scatterer significantly
  increases angular divergence.

 Second scatterer is shaped to
  scatter the dense centre to the
  edges while letting the edges pass
  largely unaffected.
                                               Double scatterer

 ~60% of the beam will be lost.
                                                                  Collimator
 Scatterers will be a high Z
   material to favour scattering                                        Quasi-uniform beam
   (copper).                                                             (within 2%) over
                                                                            20  20 cm2


 JAI-2006- P.J. Bryant               Slide 7
         Proton beam preparation before the scatterers
         “Double wedge system”
                                                    34

                         moveable              12

     Beam E0             Beam E1                                          Beam E1   Emin- E1    Beam E1
                                     Beam E1             Beam E3


                fixed                                                    energy                energy
                                     energy                              E1                    E1
                                      E1
                                      E2                  E acc. to
                                      E3                   tumour
                                      E4                  thickness      Emin
                                                                                               Emin
                                      E5                                              time
                                                              time                                            time




    Adjust the beam                 Stepwise energy                   Fast modulation        Static modulation
     energy (Bragg-peak)              modulation to                      by a rotating           by a ‘ridge’ filter
     to the maximum                   define the slices                  propeller to            may be used to
     tumour depth.                    in the tumour.                     create SOBP.            replace propeller.

                         Low-Z materials preferred for less scattering (plexiglass).


JAI-2006- P.J. Bryant                           Slide 8
                        Passive spreading gantries continued
                     The Twiss functions and beam emittances at the entry to the
                      gantry are not critical because the beam is strongly scattered
                      after the last dipole largely destroying the memory of the
                      initial beam.
                     Similarly, the alignment of the incoming beam is not critical
                      because the beam will be spread out and collimated to the
                      correct shape and position just before the patient.
                     The magnets in the gantry can have normal apertures (i.e.
                      weight, cost) because the beam is spread out after the last
                      dipole.
                     This type of beam delivery and gantry is only used for
                      protons. Light ions would fragment in the scatterers and the
                      beam would be heavily polluted by neutrons.




JAI-2006- P.J. Bryant                      Slide 9
                Divergent-beam voxel-scanning gantries

          PSI have a working voxel scanning system for
               protons from a cyclotron.

                                                                     PSI Eccentric

          IBA are promising a replacement nozzle for their
           passive-spreading proton gantries that will perform
           voxel scanning. (The ‘Nozzle’ contains the
           spreading or scanning system and the collimator).
                                                                      IBA Conical

      For voxel scanning, the tumuor is divided into layers and each layer is divided
     into pixels. Each pixel has a width, height and thickness of a few mm, i.e. it is a
       volume pixel or voxel. The beam energy and energy spread are set to match
          the layer depth and thickness and the beam size is set to the voxel size.
JAI-2006- P.J. Bryant                Slide 10
                  Parallel-beam voxel-scanning gantries
         Parallel-beam scanning reduces the surface dose
          given to a patient by divergent-beam scanning.

         Parallel-beam scanning gantries solve the problem of
          lack of space in divergent-beam gantries for the
          scanning magnets for ion beams that have a higher
          magnetic rigidity.

         Gantries specially designed to give parallel scanning
          are the “cylindrical” gantries.

         The disadvantage of the cylindrical gantry is the large   GSI Cylindrical
          aperture needed in the final dipole, which increases
          size, weight and power consumption.




JAI-2006- P.J. Bryant                 Slide 11
                                 Voxel scanning




          Highest precision, but the small beam size makes tumour movement a
           serious limitation.
          Well suited to light ions that scatter less and therefore preserve the small
           beam sizes.
          Synchrotrons offer the best flexibility.
          From full-volume passive spreading through to voxel scanning, there has
           been a reduction in the elementary volumes that are irradiated and a
           corresponding increase of about 3 orders of magnitude in the speed
           required from the on-line dosimetry system to maintain the treatment time
           and accuracy. This makes voxel scanning the highest technology variant.
JAI-2006- P.J. Bryant                 Slide 12
                        Wobbling of an enlarged beam spot




         Consider the above scheme, especially for ions.
         Full passive spreading of ion beams is not recommended as the beam fragments
          and the impurities have different penetrations and RBE values.
         In the above, the scatterer/absorber produces an enlarged beam transversely with
          a momentum spread, typically 2 cm  2 cm  1 cm (spread-penetration).
         The enlarged spot (‘blob’) is rapidly ‘wobbled’ in a circular motion across the
          collimator to give a uniform irradiation field.
JAI-2006- P.J. Bryant                   Slide 13
                             Some comparisons
    To avoid “hot” and “cold” spots in the treatment field, voxel scanning requires
     sub-millimetre precision for the positioning and the size of the beam spot.
     Similarly, it imposes the same precision on the immobilisation of the tumour.
    Passive spreading avoids “hot” and “cold” spots within the treatment area. The
     collimator before the patient “screens” the effect of upstream movements of
     gantry elements and the scatterer “screens” the patient from changes in the
     upstream beam parameters from for instance gantry angle changes.
    Movements of the tumour appears as a blurred edge to the treatment volume.


    Thus voxel-scanning gantries must be more rigid for all gantry angles and
     the beam matching for changing gantry angles is more critical.
    Divergent scanning gantries are limited to protons by the underlying
     technological limits on the scanning elements and the gantry size.



JAI-2006- P.J. Bryant               Slide 14
                                 Some more comparisons
         Cylindrical gantries for ion voxel scanning are of the order of 700 t
          making the specific load on the rollers consequential.
         All the iso-centric gantries roll on large support rings with diameters up
          to 12 m. If a ring is damaged, which occurs, it is virtually impossible to
          replace the ring without completely re-building the gantry.
         Due to the constraints of weight and size, all the iso-centric gantries have
          a limited patient space at the iso-centre.

         In comparison, exo-centric gantries are lighter, less power
          consuming, the support rings are smaller and can be replaced by
          commercially available roller bearings for turrets and the patient
          space is effectively unlimited.

               (IBA have solved the problem of minor damage to the rings, by providing a second precision
               surface on the inside of the ring. This surface is used to guide a mobile grinder that clamps on the
               ring using the inner surface as reference.)




JAI-2006- P.J. Bryant                             Slide 15
                          Exo-centric gantries
  This category is the “engineer’s” solution that
   places the heavy equipment to be rotated
   (magnets, counter-balance weight) on the axis
   and the light equipment (patient, couch, robot
   arm) off axis, BUT the medical community
   does not like this solution.
  Perhaps the first publication is by R.L. Martin.




JAI-2006- P.J. Bryant              Slide 16
                        “Riesenrad” exo-centric gantry

      The “Riesenrad” is named after the famous
       “wheel” in Vienna.
      The heavy dipole magnet (~70 t) is kept on axis
       where it can be more easily balanced and
       supported.
      The patient is in a spacious room which must
       provide a firm support, but need not be positioned
       to high precision.
      The patient’s couch is then aligned with respect to
       the dipole by a robot arm and a photogrammetric
       system.
      The key to this gantry is how to match the
       beam.



JAI-2006- P.J. Bryant               Slide 17
                                 Novel gantries
          The criteria applied by the early gantry designers are not always clear.
           Reducing the the axial length seems to be the most frequent aim and
           surprisingly they seemed insensitive to weight.
          The block of 4 drawings below are taken from the EULIMA study (~1991).
          In general, no optical principles were published for matching the exotic
           gantries apart from the dipole layout.




JAI-2006- P.J. Bryant               Slide 18
                        Novel gantries continued
     The “Planar Gantry” is proposed by M.M. Kats ITEP, Moscow.
     The moving structure is eliminated, but the space around the patient is still
      limited and the total bending is about twice that in the accelerator.
     Two fixed beam lines (one horizontal and one at 60 deg.) is simpler and with
      rotation and limited tilting of a supine or sitting patient nearly all requirements
      can be reasonable met.




JAI-2006- P.J. Bryant                Slide 19
                        Novel gantries continued
     There are some other “mobile-magnet” geometries that
     have been patented”, e.g. by Prof. G. Kraft...




JAI-2006- P.J. Bryant             Slide 20
                             Novel gantries continued
          Another idea is to reduce the overall gantry diameter and weight by inclining the
          final beam at 60 degree (the “alternative gantry” proposed by Marius Pavlovic
          and patented by GSI).




         Note: If two fixed lines are used instead of a gantry then the combination of horizontal +
         60 deg. gives access to more solid angle than horizontal + vertical because rotation about
         the vertical beam brings no gain. If tilting the patient is allowed, then the access becomes
         very good.

JAI-2006- P.J. Bryant                        Slide 21
                        Novel gantries continued
      The “S.C. pipe gantry” that guides and focuses
       a beam like a hose pipe guides water, suggested
       by G. Benincasa.
      The dream of having a flexible beam guide may
       have started with S. Van der Meer, “The Beam
       Guide”, CERN 62-16, 1962. Van der Meer
       studied a coaxial system with the outer
       conductor at infinity and mentioned the use of a
       superconductor.
      A PhD student, A. Maier, tried to improve the
       focusing by shaping the X-section of the
       conductor, adding the return conductor and
       stepping the conductors to get focusing and
       defocusing regions, but a practical scheme could
       not be found.
      In fact, the interest in making charged-particle
       pipes is quite widespread. The next step is to
       add some iron, which leads to the “Pipetron” an
       extruded single or double channel magnet with
       one S.C. cable.
JAI-2006- P.J. Bryant               Slide 22
                             Geometry is not enough...
         Up to this point we have concentrated on the dipole geometry of gantries
          without explaining how the dispersion and focusing could be made to work.
          In fact, many early gantry proposals ignored this point completely.

         To match a gantry ones needs to take care of several aspects:

                The rotational optics (see next slides).

                In some cases, it is necessary to consider the transverse beam distributions, i.e. to
                 distinguish between beams from a resonant slow extraction in a synchrotron and a
                 beam from say a cyclotron.

                For voxel scanning, it is necessary to design the optics of the line and the gantry as
                 an integrated whole e.g. beam size control may be in the line or in the gantry
                 according to the method applied.




JAI-2006- P.J. Bryant                        Slide 23
                        Gantry matching requirements
         The shape and size of the beam spot at the patient must be totally
          independent of the gantry angle.
         There must be no correlation between momentum and position across the
          beam spot.
         For the purposes of scanning, the optics inside the gantry must be
          independent of gantry angle.



                                                             Gantry
                            Accelerator plane
                              (horizontal)                                  Target
                                                                            volume
                                                          Horizontal axis
                                          Transfer line
                                                                   Gantry plane
                                                                    (rotating)




JAI-2006- P.J. Bryant                       Slide 24
                                Matching methods…
 Symmetric beam method with zero dispersion (exact)
          The beam must have zero dispersion and be rotationally symmetric i.e. the same
           distribution (gaussian or KV) with equal Twiss functions and equal emittances in
           both planes at the entry to the gantry.
          The gantry must be designed with a closed dispersion bump in the plane of bending.
 Round-beam method with zero dispersion (partial)
          The beam must have zero dispersion, the same distribution (gaussian or KV) in both
           planes with the condition Exbx=Ezbz at the entry to the gantry. It would also be
           desirable but not absolutely necessary to have x=z=0.
          The gantry must be designed with phase advances of multiples of p in both planes
           (i.e. 1:1 or 1:n matrices) and a closed dispersion bump in the plane of bending.
          The problem in this case is that the optics inside the gantry changes with rotation
           angle. However, it is often possible to “freeze” the last section so that the scanning
           is unaffected.




JAI-2006- P.J. Bryant                     Slide 25
                        Matching methods continued
      Rotator method (exact and completely general)
              This method will rigorously map all Twiss functions and the dispersion
               functions into the gantry coordinate system independent of the gantry
               angle.
              The gantry must be designed to give zero dispersion at the exit, but note
               that it can be finite at the entry. This will be illustrated later with the
               “Riesenrad”.
              This method is essential for slow extracted beams that have extremely
               unequal emittances and control their beam sizes in unconventional ways.
              The rotator appears in a Loma Linda patent, but is not explained!




JAI-2006- P.J. Bryant                    Slide 26
                                           Rotator method

                                                                          Rotator                                              
                                                                      Quadrupole lattice                        v
                                                                     p=3600 q=1800                                     x
                                                                                         q
                                                                                                                         Gantry
                                                                                                  x         u
                                                            z
                                                                                                 
                                                                                             p
                                                                     x
                                                                         Transfer line

                              cos      0 sin  0                      cos      0 sin  0 
                                   2          2
                                                      1 0     0    0       2          2
                                                                                                 1    0   0       0
                                 0    cos  0 sin   0 1     0    0  0       cos  0 sin    0   1   0       0
                        M0               2        2                                 2        2
                                                                                                 
                               sin    0 cos 0  0 0
                                                      
                                                                1   0   sin    0 cos 0   0      0   1      0
                                     2         2
                              0  sin  0 cos  0 0          0    1       2         2
                                                                        0  sin  0 cos   0
                                                                                                       0   0       1
                                                                                                                      
                                          2       2                                2       2


                         Maps the beam 1:1 to the gantry independent of the angle.
                         This is the rotator solution and it maps the dispersion
                          function and the Twiss functions rigorously to the gantry
                          coordinate system.
JAI-2006- P.J. Bryant                            Slide 27
        Appearance of rotator in a Loma Linda patent
    The “rotator” quadrupoles are clearly
     labelled, but the patent does not explain
     the theory or function of the device
     (omission of a non-trivial step should
     invalidate the patent). It is not sure that
     the patent writer realised that the
     “rotator” rotates .
    The “rotator” was invented by Lee Teng of
     Fermilab, but he did not publish the
     design. The detailed derivation appears in
     an internal Loma Linda report and his
     private laboratory notebook.
    The Rotator design shown is clearly a
     FODO design which is not ideal as it
     exhibits large beam changes inside the
     lattice during rotation.



JAI-2006- P.J. Bryant              Slide 28
                        Matching methods continued
      Equal sigma method (partial)
              This method is used in the GSI ion gantry.
              The method has been patented by GSI (EP 1 041 579 A1).
              The validity of this method has not been fully demonstrated.
              The problem can be understood intuitively by first considering the beam
               spot size in terms of sigma and then in terms of the FWHH, for example.
               Although the sigma values may be equal, the FWHH values will be
               different in the two planes because of the different beam distributions.
               Thus, the beam spot will be distorted and its orientation will depend on the
               particular optics.
              This distortion may, or may not, be acceptable after smoothing by
               scattering in the patient’s body.




JAI-2006- P.J. Bryant                   Slide 29
                                          Equal sigma method
 The beam is represented by its sigma
  matrix:
      x2        xx       xz        xz    1,1        1, 2      1,3    1, 4 
                                                                                
      xx       x2       xz       xz    2,1       2, 2      2,3    2, 4 
σ                                       
      zx        zx       z2        zz   3,1          3, 2      3,3    3, 4 
                                                                                 
                                      2               4, 2      4,3    4, 4 
      zx       zx      zz       z   4,1
                                                                                  

 The sigma matrix translates as:
          σ 2  M Overallσ 0 M Overall
                                          T
                                                M Overall  M Gan M Rot                                   r1,1   r1, 2   r1,3    r1, 4 
                                                                                                                                       
                                                                                                          r2,1   r2, 2   r2,3    r2, 4 
 Diagonal terms gives beam widths, e.g.:                                                       M Gan   
                                                                                                           r      r3, 2   r3,3    r3, 4 
                                                                                                          3,1                          
                                                                                                         r                       r4, 4 
           (2)1,1  r1,12 [ (0)1,1 cos 2    (0)3,3 sin 2  ]                                         4,1    r4, 2   r4,3          
                          2r1,1r1, 2 (0)1, 2 cos 2                                            cos          0         sin        0 
                                                                                                                                         
                          r1, 2 [ (0) 2, 2 cos 2    (0) 4, 4 sin 2  ]
                                 2                                                               0           cos          0       sin  
                                                                                       M Rot   
                                                                                                   sin        0         cos        0 
                          2r1,1r1, 2 (0)3, 4 sin 2                                           
                                                                                                 0                                       
                                                                                                             sin         0       cos 
 JAI-2006- P.J. Bryant                                   Slide 30
                        Equal sigma method continued…
    The angular dependence in the beam widths can be removed.
     For example, if the gantry matrix is arranged to give r1,1=0
     and the incoming beam is adjusted to give (0)2,2=(0)4,4, then

                                (2)1,1  r1, 2 2 (0) 2, 2

     The vertical plane and the correlation terms can be similarly
      treated.
     Despite it not being possible to patent equations, this method
      has been patented,
      See European Patent Application EP 1 041 579 A1.
      If one reads carefully, “round” is defined as equal sigmas,
      which does not necessarily mean rotationally symmetric.
JAI-2006- P.J. Bryant                   Slide 31
                                       Patents

         You are probably familiar with the web site:
                         http://ep.espacenet.com
         But maybe you are not familiar with:
                         http://ofi.epoline.org/view/GetDossier
         Try entering for GSI’s therapy system :
                         EP 0 986 070 A1
                         EP 0 986 071 A2




JAI-2006- P.J. Bryant                Slide 32
                          GSI therapy complex
    GSI have recently revamped the patent for their therapy
     complex. The “gist” is quoted below:
     “The new set of claims 1 to 22 concentrates on the
     inventive idea to use a special designed delivery system
     for high energy particles from an accelerator system to
     the isocenter of a treatment field.
     The claimed invention is based on the split of the high
     energy beam transport system into a high energy beam
     transport line and gantry. The high energy beam
     transport line delivers a beam to a coupling point of the
     gantry with special beam properties, so that the gantry
     is able to guide the beam for all angles to the treatment
     field having a circular beam without the need of          GSI gantry matched by the
     adjusting the high energy beam line.”                       equal-sigmas method
    The above is based on the “Equal sigma” method, but the
     patent writer does not understand what “round” really
     means.
    Note. This is the opposite of the PIMMS method (next
     slide) that leaves the gantry unchanged and puts the
     adaptive elements in the line.
JAI-2006- P.J. Bryant              Slide 33
          PIMMS (Proton Ion Medical Machine Study)
 PIMMS, CERN 2000-006, Volume II is a design for a synchrotron-based, light-ion
  therapy centre with various gantries.
 The transfer lines and gantries were designed as an integrated system. The lines are
  assembled from basic modules with 1:1 or 1:n transfer matrices. The phase shifter
  and betatron stepper are placed upstream and can act for all gantries. The rotator can
  usually be placed upstream, but for the “Riesenrad” it is needed next to the gantry.




JAI-2006- P.J. Bryant              Slide 34
                              Horizontal beam size control
     The extracted segment (in blue) is
      called the ‘bar of charge’.
     The bar of charge is about 10 mm
      long and has a very small angular
      spread.
     Horizontally the distribution is quasi
      rectangular and vertically it is
      gaussian.

       Central orbit
      for extraction     X´                      Z´
         channel                                              Fitting an ellipse to this narrow bar is
                                     x                        impractical.
                                                              Instead the bar is regarded as a
                                 X                        Z
                                                               diameter of a larger unfilled ellipse.
                                                              The bar turns at the rate of the phase
                                                               advance.
                    Beam width            Beam height         A phase shifter can be used to turn the
                                                               bar and change the projected beam
JAI-2006- P.J. Bryant                          Slide 35        size.
                         Vertical beam size control
 The vertical beam distribution is the usual gaussian and the beam size is controlled
  in the classic way by varying the betatron amplitude function.
           Classic beam size control              The stepper is a 1:n telescope module that
                                                  keeps all beam parameters constant except
                                                  the vertical betatron amplitude function.




                           In the PIMMS design, the phase shifter and beta stepper are combined
                           in the lattice module illustrated. This module can keep all parameters
                                constant while varying x and bz in any desired combination.
JAI-2006- P.J. Bryant                  Slide 36
               Scanning with the spot shape from a slow
                              extraction

          The spot in PIMMS is NOT round.
           Horizontally the distribution is quasi-
           rectangular and vertically it is
           gaussian.
          It is important that the spot always has
           the same orientation in the gantry
           frame, so that the spot moves with the
           sharp-edged distribution in the
           direction of motion and the gaussian
           tails overlap from row to row.
          The unevenness in the spill in time can
           be smoothed (within limits) by a feed-
           forward that acts on the scan velocity.



JAI-2006- P.J. Bryant                 Slide 37
                        “Riesenrad” gantry matching
  Since the “Riesenrad” has only one dipole it excites dispersion, but cannot close the
   dispersion bump to zero within the gantry itself.
  In the PIMMS design, the bend from the main extraction line excites the dispersion
   function and the gantry is used to close the bump, thus delivering zero dispersion to
   the patient. This is possible because the rotator turns the dispersion function to
   match the gantry’s coordinate system.




JAI-2006- P.J. Bryant             Slide 38
                        Gantry construction – “Riesenrad”

The central cage supports
the three scanning
magnets (1.5 t) and the
large 90° dipole (62 t).
The total weight is ~127 t,
of which 23 t are due to
the counterweight. The
design of the central cage
is driven by the desire to
minimise sagging of the
dipole no matter what
gantry position is
considered.




JAI-2006- P.J. Bryant              Slide 39
                        Gantry construction continued
                                                                                                                         I so c e n tr e d e fo r m a ti o n s d u e to e l a sti c
                                                                                                                             d e fo r m a ti o n s o f th e g a n tr y str u c tu r e

 Top graph shows the
  mechanical movement of the
                                                                                                                                          0,15

                                                                                                                                            0,1

  exo-centre due to elastic




                                                                            D e fo rm a ti o n [m m ]
                                                                                                                                          0,05
                                                                                                                                                                                                             X

  deformations of the gantry while                                                                                                             0                                                             Y


  rotating –p to +p.
                                                                                                        -9 0          -4 5                          0                      45                     90         Z
                                                                                                                                         -0 , 0 5
                                                                                                                                                                                                             Z-c o rr
                                                                                                                                           -0 , 1

                                                                                                                                         -0 , 1 5

                                                                                                                                           -0 , 2

                                                                                                                             G a n tr y r o ta ti o n a n g l e [d e g ]



 Lower graph shows the shift of                                                                                                                           0.2



  the exo-centre in the transverse                                                                                                                      0.175


  plane due to the optical errors                                                                                                                        0.15
                                                                                                                                                                      Dipole+Quads
  caused by the movements of the                                                                                                                        0.125


  magnets during rotation.                      y(iso)_local [mm]                                       All Quads                                          0.1



                                                                                                                                                        0.075



                                                                                                                                                         0.05

                                                                                                                      Dipole                            0.025



                                                                                                                                                            0
                                                                    -0.15                                      -0.1              -0.05                           0               0.05                  0.1              0.15

                                                                                                                                                        -0.025                  Ideal isocentre
                                                                                                                                                x(iso)_local [mm]



JAI-2006- P.J. Bryant                Slide 40
                                   Superconductivity
  It is frequently suggested that S.C. magnets should be used to reduce gantry weight
   and size.
  In practice, it is not trivial:
          To build large bending angle S.C. dipoles, especially with large apertures.
          To either use flexible cryogenic lines that roll on and off a drum on the gantry axis, or to
           mount the helium liquefier on the gantry.
          To ensure the continuous flow of cryogens at all gantry angles.
          To ramp S.C. magnets quickly.
  If the S.C. dipole is iron-free, then the stray field is problematic for the detectors.
  If the S.C. dipole has an iron yoke, then the weight is not so strongly reduced.
  There are also security risks:
          Quenching could frighten patients when the release valve opens.
          There is a risk of oxygen deficiency if large quantities of helium are released.
          There is a risk of cold burns (especially for the lungs) if large volumes of vapour are
           released.
  A reduction in magnetic rigidity or treatment field would bring a more direct
   advantage.

JAI-2006- P.J. Bryant                      Slide 41
                                Some controversy…
                 On the one hand…                           On the other hand…
  Iso-centric gantries are the preferred            Severe engineering problems render the
   solution of the medical community.                 ‘ideal’ gantry expensive.
  And there is considerable reluctance to           Some argue that:
   relax the specifications i.e.                         90% of patients require a treatment
           Treatment field: 40 x 40 cm2.                 field of no more than 10 x 20 cm2.
           Magnetic rigidity corresponding to           A penetration depth of 20 cm is largely
            penetration up to 27 cm.                      sufficient.
                                                         An exo-centric gantry is superior.
                                                         Sufficient angular access can be
                                                          obtained with horizontal and 60 degree
                                                          fixed beam lines by turning, tilting and
                                                          sitting the patient.




JAI-2006- P.J. Bryant                    Slide 42
JAI-2006- P.J. Bryant   Slide 43
                                    Conclusions
 The design of the gantry depends on:
         The method chosen for the rotational optics matching.
         The type of beam delivery: passive spreading, wobbling or voxel scanning.
         The transverse beam distributions: slow extracted beams or fast extracted beams.
         Whether the beam is spread before or after the last dipole.
         The magnetic rigidity: protons or light ions.
 Check the patent situation for the design chosen.
 Be critical of the size of the treatment field and the maximum beam
  penetration, as these two parameters are very expensive.




JAI-2006- P.J. Bryant                 Slide 44
     Post scriptum
 The CD-ROM contains the full CERN Report 2000-006 of the Proton
  Ion Medical Machine Study (PIMMS).
 The optics program used for the design can be copied from the CD-
  ROM and the lattice files for the various gantries can be found in the
  folder “Winagile/Lattices/Optical/Extrline/ for the individual modules
  and “Winagile/Lattices/Engineer/Extrline/ for the gantries set in their
  transfer lines.
 The AutoCad concept design drawings of the elements can be found in
  the Hardware folder.




JAI-2006- P.J. Bryant        Slide 45
 Loma Linda            IBA        IBA

JAI-2006- P.J. Bryant   Slide 46

				
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