Practical Challenges and
Opportunities for
Proton Beam Therapy
M. F. Moyers
Loma Linda University Medical Center
Outline
I.
II.
III.
IV.
V.
VI.
VII.
Introduction
Registration and Immobilization
Beam Shaping
Localization
Uncertainties, Margins, and Motion
Interoperability
Summary
References
O
O
O
O
Moyers, M. F. “Proton Therapy” The Modern Technology of
Radiation Oncology: A Compendium for Medical Physicists and
Radiation Oncologists ed. van Dyk, J. (Wisconsin: Medical
Physics Publishing, 1999) p. 823 - 869.
Moyers, M. F. Miller, D. W. Bush, D. A. Slater, J. D. Slater, J. M.
“Methodologies and tools for proton beam design for lung
tumors” International Journal of Radiation Oncology, Biology,
Physics 49(5) (2001) p. 1431 - 1440.
Moyers, M. F. "LLUPTF: eleven years and beyond" Nuclear Physics
in the 21st Century (New York: American Institute of Physics, 2002)
p. 305 - 309.
Shanazi, K. Moyers, M. F. Yuh, G. Miller, D. Slater, J. Loredo, L.
"Cerebrospinal irradiation using proton beams for the treatment of
medulloblastoma" Medical Physics 29(6) (2002) p. 1216.
LOMA LINDA UNIVERSITY MEDICAL CENTER
COMPLETED PROTON PATIENT SUMMARY
FROM INCEPTION THROUGH JANUARY TO MARCH 2003
DIAGNOSIS CATEGORY 1990
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
1991
Choroidal Melanoma
Pituitary
Acoustic Neuroma
Meningioma
Astrocytoma
Other Brain
Head & Neck
Prostate
Other Pelvis
Craniopharyngioma
Orbital
Paraspinal Tumors
Chordoma/Chondrosarcoma
Sarcoma
Other Chest
AVM
Other Abdominal
SNVM
3
TOTAL BY YEAR
3
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
TOTAL
7
10
3
8
4
6
3
4
1
0
3
1
0
3
0
13
17
3
16
26
6
26
198
8
3
2
11
13
3
0
4
6
0
8
4
7
20
234
10
0
0
8
26
3
7
1
13
5
3
8
6
9
26
234
4
1
0
6
21
12
11
31
5
21
8
1
3
7
5
15
27
308
0
1
1
4
25
2
34
17
7
29
8
7
4
7
17
3
49
476
8
2
2
7
28
4
16
14
9
20
13
2
2
19
9
17
41
507
3
4
11
7
38
8
34
6
4
35
9
2
2
12
7
31
43
631
8
4
13
12
51
15
44
21
9
30
1
7
9
9
10
36
55
447
5
2
12
15
44
9
27
12
23
57
10
6
7
17
13
41
65
491
7
2
0
14
34
17
49
12
13
101
13
13
10
9
18
30
75
649
12
16
2
10
9
11
39
64
694
15
3
9
6
193
3
5
18
40
4
46
11
23
57
4
10
50
10
49
4
21
27
1
8
2
6
4
5
3
53
345
338
416
494
681
760
944
780
899
1033
1035
245
1
1
121
78
57
130
130
249
500
5066
84
19
53
114
378
92
323
133
119
380
%
1.5%
1.0%
0.7%
1.6%
1.6%
3.1%
6.2%
63.1%
1.0%
0.2%
0.7%
1.4%
4.7%
1.1%
4.0%
1.7%
1.5%
4.7%
8,026 100.0%
Conformal Avoidance Therapy
Cerebro-spinal Irradiation
standard protons
standard x rays
Heart
1.2
Esophagus
1.2
0.8
1
0.6
0.4
0.2
0
0
5
10
15
20
25
30
35
Dose (Gy)
Thyroid
Fraction of Volume
Fraction of Volume
1
0.8
0.6
0.4
0.2
1.2
0
Fraction of Volume
1
0
5
10
15
20
25
30
35
40
Dose (Gy)
0.8
0.6
Vertebral Body
1.2
0.4
0.2
0
0
5
10
15
20
25
30
35
Dose (Gy)
Bowel
1.2
Fraction of Volume
1
0.8
0.6
0.4
Fraction of Volume
1
0.2
0.8
0
0.6
0
5
10
15
20
25
30
35
40
Dose (Gy)
0.4
DVHs:
0.2
0
0
10
20
Dose (Gy)
30
40
pink - standard x rays
blue - standard protons
45
The Caveat of Proton Beam Therapy
O
More precise but less forgiving than x rays
and electrons
» sharper lateral gradient
» sharper distal gradient
» lower integral dose
» if miss-used, can lead to geometrical miss of
target
» if miss-used, can damage normal tissue
» if target unknown, can lead to geometrical miss
of target
Standard Headrest and Facemask Frame
Problems with Standard
Headrest and Facemask Frame
O
O
O
O
O
magnified FOV CT circle does not include table top and
mask frame preventing design of bolus
common headrest shape does not conform to individual
patient resulting in patient discomfort and fulcrum points
for motion
support sides of common headrest produce large
perturbations in proton dose distribution
facemask frame produces large perturbations in proton
dose distribution
large skin-to-aperture distance results in large penumbra
Headrest Perturbations (Wake Effect)
0o and 10o Incidence
↑ CAX
↑ support
↑ CAX
↑ support
Penumbra Example
149 MeV - Center of Modulation at Isocenter
16
76 mm bolus, ApID = 380 mm
38 mm bolus, ApID = 380 mm
80-20 % Penumbra Width [mm]
no bolus, ApID = 380 mm
12
no bolus, ApID = 210 mm
8
4
0
0
20
40
60
80
100
Bolus Thickness + Patient Depth [mm water]
120
140
Flat Table Top
O
O
Perturbation from
table edge
Large gap between
aperture/bolus and
patient resulting in
large penumbra
Whole Body Pod
O
O
minimize perturbation
from edge
minimize gap between
aperture/bolus and
patient resulting in
smaller penumbra
Picture of Pod with C-arms
Aperture and Aperture Frame
Bolus and Bolus Frame
Bolus and Aperture Requirements
O
minimize skin-to-aperture distance
» penumbra versus air gap
O
minimize scatter
» penumbra versus thickness of bolus
O
minimize weight
» lifting restrictions for therapists
O
accurately place into beamline
» lateral margin
Methods to Satisfy Bolus and
Aperture Requirements
O
exchangeable cones for different field sizes
» similar to electron cones
» scatter or scan beam only to final size
O
O
O
successive stages of pre-collimator trimmers
and a final patient aperture
aperture thickness split into several layers
that are installed separately
large number of accelerator energies
» portal specific energy
O
O
extendable snout
multi-leaf collimator
Snout Extension with Pre-collimator
Plates and Exchangeable Cone
Multi-leaf Collimator (Chiba)
O
O
eliminates lifting of
heavy apertures
provides ability to
do IMPT
Prostate Field using MLC
(Berkeley MLC and LLUMC proton beam)
surface
29 cm deep
26 cm scattering diameter
Depth Profiling Techniques
(Range Modulation)
TECHNIQUE
energy stacking
LOCATION
accelerator
rangeshifters
accelerator exit
nozzle entrance
nozzle exit
propellors
nozzle middle
nozzle entrance
ridge filters
nozzle middle
COMMENTS
a. no mechanical movements, no generation of neutrons
d. accelerator retuning, switchyard retuning, scatterer adjustment
a. no accelerator retuning
d. switchyard retuning, lower dose rate at lower energies,
generation of neutrons, scatterer adjustment
a. no accelerator retuning, no switchyard tuning
d. lower dose rate at lower energies, generation of neutrons,
scatterer adjustment
a. no accelerator retuning, no generation of neutrons, no
scatterer adjustment
d. increased penumbra
a. easy to make, no scatterer adjustment
d. installed by hand, easy to break
a. small, automatically installed
d. complex design to compensate for scattering
a. time independent
d. difficult to make
Modulator Propellors
43 cm diameter
large beam
mid-nozzle
11 cm diameter
small beam
nozzle entrance
Ridge Filters (Kashiwa)
Dynamic Scattering System
Scanning Definitions
O
Wobbling: a non- or slowly-repeating pattern
» ex. circular with modulating radius - perpendicular sine
waves with identical frequencies 90o out of phase
» ex. Lissajous - perpendicular triangle waves of
different frequencies (non-multiple)
O
Raster: a spatially and temporally constant scan
pattern pre-defined for use with all patients
» ex. repeating triangle wave
» ex. rectilinear
O
Spot: a customized scan pattern for an individual
patient defined spatially and or temporally
Film of Small Spot Scan
Orthogonal X Ray Tubes and Imagers on
Rotating Gantry (Hyogo)
↑extended
retracted→
Alignment in Tx Room Using Orthogonal
Pairs of DRRs and Electronic Images
O
Identical landmarks identified on
treatment planning DRRs and
treatment room images.
Alignment in Tx Room Using Orthogonal
Pairs of DRRs and Electronic Images
O
O
Alignment algorithm calculates
translations and rotations.
Aperture projection with x ray
magnification also transmitted
for comparison with double
exposure.
Authorization to Treat
O
O
O
precision treatments use small margins from
tumors and critical structures
therapist versus MD versus computer algorithm
turnaround time
Proton Beam Treatment Planning General Comments
Planning is the core of proton beam therapy.
“The devil is in the details”.
XCT
O
CT# versus tissue
» scanner dependent
» protocol dependent
(FOV, kVp, slice
width, filter)
» patient specific
scaling
O
CT# to proton RLSP
conversion curve
Relative Linear Stopping Power
2.0
1.5
1.0
Battista et al 1980 fit
MGH model c1980
LLUMC model 1996
Moyers et al 1992 measured
Schneider et al 1996 calculated
0.5
0.0
0
500
1000
1500
Scaled CT Number
2000
2500
3000
Relative Linear Stopping Power
Assignments
O
O
O
O
O
O
registration / immobilization
devices
gas bubbles
contrast agents
metal implants
artifacts
tissue motion
Margins and Uncertainties
O
target coverage
» CTV only, no PTV
O
O
O
normal tissue
avoidance
lateral penumbra
lateral alignment
uncertainty
» target, 90% (1.5 σ)
» normal, average position
O
O
distal gradient
penetration uncertainty
» target, 90% (1.5 σ)
Motion Example: Moving Target
Solution: expand aperture, design target for bolus with
WE of bolus target set to match real target tissue
Motion Example: Moving Normal Tissue
Solution: replace tissue volume with
highest density tissue
Interoperability
XCT
Siemens
Treatment
Planning
System
home
grown
Permedics
Toshiba
CMS
Phillips
MDSNordion
Varian
GE
Shimadzu
Aperture
Manuf.
Bolus
Manuf.
Beam
Delivery
System
home
grown
Optivus
Positioner
Imager
home
grown
Par
Scientific
Huestis
Fanuc
home
grown
ABB
home
grown
Trixell
IBA
Siemens
HEK
Hitachi
Oncolog
PerkinElmer
Cares
Built
Fanuc
Mitsubishi
IBA
Accel
Mitsuibishi
Hitachi
DICOM-RT WG-7
Ion Beam Sub-Group
O
Dec, 1999
Aug, 2000
O
Feb, 2000
O
O
Jul, 2001
Nov, 2001
O
May, 2002
O
throughout
O
Varian proposal to add tags to support protons
LLUMC proposal to define and test parallel RT Proton
Beam Module that would later be incorporated into standard
RT Beams Module
WG-6 proposal for RT Ion Plan Object parallel to RT Plan
Object
formation of Ion Beam sub-committee of DICOM WG-7
first formal meeting of ion beam sub-committee at NEMA
headquarters in Arlington
second formal meeting in conjunction with PTCOG meeting
in Cantania
numerous telephone and web conferences
Summary
O
O
O
O
O
O
O
O
O
reduce motion and assure repeatable set-ups
avoid edges within beam path
avoid objects that do not lie on the CT conversion curve
minimize air gaps between beamline devices and patient
minimize bolus thickness or rangeshifter thickness at patient
explicitly account for lateral and penetration uncertainties on
a beam by beam basis
explicitly account for penumbra and distal gradient on a
beam by beam basis
avoid collisions with localization devices
provide communication between devices involved in
planning and delivering treatments