Linear Accelerator Technology - Data Management
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Transcript Linear Accelerator Technology - Data Management
Linear Accelerator Technology
State of the Art Platforms for Advanced
Image Guidance
Theodore Thorson, Ph.D.
Senior Advisor
Elekta
Outline
Historical development of treatment delivery equipment
Linear accelerator components, alternative engineering approaches &
clinical influence
Precision delivery features
Image guided capabilities
Evolving Strategies in Radiation Oncology - 2
History of Radiation Delivery
Orthovoltage: 1920-1950
High energy systems: 1930-1950
Van de Graff
Resonant transformer
Betatron
Radioactive isotope units
Evolving Strategies in Radiation Oncology - 3
Van De-Graaff
Radium
Cesium
Cobalt 60
Resonant Transformer
History of Radiation Delivery
Linear Accelerators: 1950 to present
Traveling wave systems
Standing wave systems
Microtron
Reflexotron
Evolving Strategies in Radiation Oncology - 4
Linear Accelerator System Overview
Shielding
Electron
Gun
Bending
System
Accelerator Wave Guide
HV Pulse
Control
System
µ Wave Pulse
Dosimetry
Collimation
RF
Power
Source
HV Pulse
Modulator
X-Ray or Electron Beam
for Treatment
AC
Line Power
Evolving Strategies in Radiation Oncology - 6
Support Structure
Basic Accelerator Technology
Microwave
Power sources
Acceleration structures
Beam transport systems
Support structures
Evolving Strategies in Radiation Oncology - 7
Power Source Options
Klystron
Evolving Strategies in Radiation Oncology - 8
HV Pulse
Linear Amplifier
Requires frequency stabilized oscillator
High Voltage (140kV)
High Power (7+MW)
Typical 10,000 hr life
High cost
Electromagnet (solenoid)
Phase and power amplitude independent
of reflections
Klystron
HV Pulse
Operational Trade-offs
Characteristics
Amplifier
Phase and power amplitude
stability
Longer life (6-10 yrs)
High power applications
Fixed PRF
Evolving Strategies in Radiation Oncology - 9
Initial Cost
Additional Components
RF Driver
Rotating RF joint
Oil tank
Solenoid
Power supplies
(T drive)
Size
Replacement time
Higher operating voltages
Power Source Options
Magnetron
+
Evolving Strategies in Radiation Oncology - 10
HV Pulse
Simple Oscillator
Low Power operation (3-6MW)
5000 hr typical life
Low cost
Permanent or electromagnet
Low Voltage (45 kV)
Power amplitude phase and frequency
dependent on reflections
Electromagnetic tuning
Magnetron
Characteristics
HV Pulse
Operational Trade-offs
Self-oscillator
Shorter life (5-8 yrs)
Low initial cost
Frequency stability
Small size
Subject to RF reflections
Short replacement time
Lower power operation
Simple RF system
Fewer components
Variable PRF
Evolving Strategies in Radiation Oncology - 11
Accelerator Structures
HV Pulse
Short section
SW accelerator
Short section - TW accelerator
Evolving Strategies in Radiation Oncology - 12
Long section - SW accelerator
Accelerator Options
HV Pulse
TW ACCELERATOR STRUCTURE
SW ACCELERATOR STRUCTURE
Moderate shunt impedance, longer structure for
equivalent energy gain
High Shunt Impedance, shorter structure for equivalent
energy gain
Short fill time
Circulator not required
Longer fill time
High accelerating beam capacity
Circulator required
Spectrum insensitive to accelerating field
Low accelerating beam capacity
Bunching less sensitive to accelerating field
Spectrum sensitive to accelerating field
Generally low vacuum requirement
Bunching highly sensitive to accelerating field
High vacuum requirement
Evolving Strategies in Radiation Oncology - 13
Electron Beam Bending - 90
o
HV Pulse
Magnet Pole
Energy Spread
Evolving Strategies in Radiation Oncology - 14
Position Change
Angular Change
Achromatic Magnet Designs
Evolving Strategies in Radiation Oncology - 15
HV Pulse
Bending system trade-offs
HV Pulse
h1
r1
h2 > h1
r2 > r2
Evolving Strategies in Radiation Oncology - 16
h2
r2
Support System Designs
Stand
and Gantry
Compact packaging
Support for beamstopper
Requires shorter accelerator
structure
Single unit floor imbedded
baseframe
Evolving Strategies in Radiation Oncology - 17
Support System Designs
Drum
and Arm
Small backwall to isocenter
distance
High degree of patient access
Structural support for other
components
Easy access for service
Easily accomodates longer
accelerator structure
Evolving Strategies in Radiation Oncology - 18
Enhanced delivery technology
1980-90
Multileaf
collimation
Information
Computer
technology
Control systems
Evolving Strategies in Radiation Oncology - 19
Multileaf Collimation
Trade-Offs
Leakage
Geometry
Field Size Capability
Number of leaves
Leaf pitch
Evolving Strategies in Radiation Oncology - 20
Multileaf Collimation
Geometry
Internal
External
Internal
•Lower collimator replacement
•Moveable carriage & leaves
•Upper collimator replacement
•Full thickness leaves
•Backup diaphragms
•Backup diaphragms
•Focus - Double, straight leaf
ends
•Focus - divergence + leaf ends
•Focus - divergence + leaf
ends
Evolving Strategies in Radiation Oncology - 21
Double Focus Collimation
Geometric Trade-Off
3.0
mm
error
3.8
mm
error
Evolving Strategies in Radiation Oncology - 22
Multileaf Field Sizes
Maximum Leaf Travel
Comparisons (1 cm leaves)
40 cm
1 cm leaf
area
12.5 cm
A
Max Field
Size
40
} x 40
Max Field Size
Max Field Size
1 cm leaves
1 cm leaves
Single Field
Single Field No center leaf gap
40
40
32.5cm
40
40
32.5
10cm
B
} x 27
30 cm
C
14.5 cm
27
40
14.5 cm
27
} x 40
30
40
40
40
40
40
Evolving Strategies in Radiation Oncology - 23
40
29
14.5
Multileaf Collimation
Leaf Pitch Trade-Off
Upper Collimator
Replacement
Lower Collimator
Replacement
External Collimator
Evolving Strategies in Radiation Oncology - 24
Multileaf Collimation
MicroMLC
• Maximum field size: 72 x 63 mm
•Number of leaves: 40 per side
•Leaf thickness: 1 mm
•Material: tungsten
Evolving Strategies in Radiation Oncology - 25
• Maximum field size: 100 x 100
mm
•Number of leaves: 26 per side
•Leaf thickness: 5.5, 4.5, 3 mm
•Material: tungsten
Clinical Setups
Distance
a – gantry to isocentre
b – head to isocentre
c – head size
d – floor to isocentre
Evolving Strategies in Radiation Oncology - 26
Varian – Clinac
EX
104cm
41cm (30 with
wedge)
90cm
131cm
ELEKTA PRECiSE
124cm
SIEMENS PRIMUS
97.3cm
45cm
62cm
124cm
43cm
75cm
133cm
Expanding Data Requirements
For Treatment Delivery
115,000
120,000
100,000
Number of Data Elements
Basic Data Parameters
X-Jaw
Y-Jaw
Collimator Rotation
Gantry Rotation
Blocks
Wedges
80,000
60,000
40,000
Expanded Parameters
Couch Positions (4)
20,000
Asymmetric Jaws (4)
MLC Leaf Positions (80) 0
Patient Coordinates (4-6)
Evolving Strategies in Radiation Oncology - 27
23,000
7
14
28
44
52
91
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Control of Radiation Delivery
Hardware
Electronics
Linac
Linac
MLC
MLC
Linac
MLC
Linac
MLC
Control
Control
Control
Control
Console
User
Interface
User
Interface
Linac
MLC
Linac Common MLC
Control Memory Control
User
Interface
Added
GUI
Record/Verify
DB
Evolving Strategies in Radiation Oncology - 28
Treatment Planning
Image Guidance Technology
Electronic portal imaging
Motion management
Evolving Strategies in Radiation Oncology - 29
Advanced Image Guidance
Varian Trilogy
Elekta Synergy
Evolving Strategies in Radiation Oncology - 30
Image Guidance - Components
Solid state imaging panel
Clearance
90cm
Evolving Strategies in Radiation Oncology - 31
Kilovoltage X-ray source
Volume Data Acquisition
Evolving Strategies in Radiation Oncology - 32
Reconstructed Volume Image
Evolving Strategies in Radiation Oncology - 33
Transverse view
Evolving Strategies in Radiation Oncology - 34
CT section sequence
Evolving Strategies in Radiation Oncology - 35
Comparison to Planning CT
Evolving Strategies in Radiation Oncology - 36
Target Volume Definition
Evolving Strategies in Radiation Oncology - 37
3D Volume information
Rando Head Phantom
Note resolution in
all dimensions
Evolving Strategies in Radiation Oncology - 38
Synergy “double-exposed”
Cone Beam CT
Evolving Strategies in Radiation Oncology - 39
3.5 cGy skin dose, 3.0 cGy prostate dose
Synergy “double-exposed” Cone Beam CT - Patient 1
3.5 cGy skin dose, 3.0 cGy prostate dose
Evolving Strategies in Radiation Oncology - 40
Patient 2
Clear delineation of borders of the bladder
(B), prostate (P), seminal vesicles (SV), and
rectum (R) with modest increase in imaging
dose.
B
P
R
SV
3.8 cGy skin dose;
3.5 cGy isocenter dose
Evolving Strategies in Radiation Oncology - 41
3D Patient Motion
Respiratory correlated CT (RCCT)
Serial or spiral CT with external surrogates
Imaging at many phases of breathing cycle
Free breathing cone-beam CT (no surrogates)
3D Motion
• 3 images/sec, 1000 projections, 6 phases/cycle
Evolving Strategies in Radiation Oncology - 42
Summary
Beam bending systems should be achromatic - all manufacturers comply
All types of power sources are used and can be made to work in most applications
There is no ideal accelerator design
All designs include trade-offs, most are minor, but may have significance to clinical applications
All accelerator systems will work in a variety of clinical situations
Consider your clinical practice requirements and consider how various trade-offs affect your needs
Advanced image guidance will allow precision capabilities of treatment systems to achieve accuracy
in delivery
Evolving Strategies in Radiation Oncology - 43
With thanks to the
Elekta Synergy™ Research Group
NKI, Amsterdam, Netherlands
Christie, Manchester, UK
Princess Margaret, Toronto, Canada
William Beaumont, Royal Oak, USA
Evolving Strategies in Radiation Oncology - 44
Evolving Strategies in Radiation Oncology - 45