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Motion in Radiotherapy
Martijn Engelsman
Contents
• What is motion ?
• Why is motion important ?
• Motion in practice
• Qualitative impact of motion
• Motion management
• Motion in charged particle therapy
2
What is motion ?
3
Motion in radiotherapy
• Aim of radiotherapy
– Deliver maximum dose to tumor cells and
minimum dose to surrounding normal tissues
• “Motion”
– Anything that may lead to a mismatch between
the intended and actual location of delivered
radiation dose
4
Radiotherapy treatment process
1)
2)
3)
4)
5)
6)
7)
Diagnosis
Patient immobilization
Imaging (CT-scan)
Target delineation
Treatment plan design
Treatment delivery (35 fractions)
Patient follow-up
5
Why is motion important ?
6
PTV concept (1)
(ICRU 50 and 62)
GTV (Gross Tumor Volume):  = 5 cm, V = 65 cm3
CTV (Clinical Target Volume):  = 6 cm, V = 113 cm3
PTV (Planning Target Volume):  = 8 cm, V = 268 cm3
High dose region
7
PTV concept (2)
• Margin from GTV to CTV
– Typically 5 mm or patient and tumor specific
– Improved by:
• Better imaging
• Physician training
• Margin from CTV to PTV
– Typically 5 to 10 mm
– Tumor location specific
– Improved by:
• Motion management
• Smart treatment planning
GTV
CTV
PTV
High Dose
8
Example source of motion
35 Fractions
=
35 times patient setup
www.pi-medical.gr
9
Sources of motion
•
•
•
•
•
•
•
•
Patient setup
Patient breathing / coughing
Patient heart-beat
Patient discomfort
Target delineation inaccuracies
Non-representative CT-scan
Target deformation / growth / shrinkage
Etc., etc. etc.
10
Subdivision of motion
• Systematic versus Random
• Inter-fractional versus Intra-fractional
• Treatment Preparation versus Treatment Execution
– Less commonly used
11
Systematic versus Random
• Systematic
– Same error for all fractions (possibly even all patients).
• Random
– Unpredictable. Day to day variations around a mean.
• Known but neither
– Breathing, heartbeat
12
Setup errors for three patients
y
Beam’s Eye View
x
13
Setup errors for a single patient
Random (x)
Random (y)
Systematic (y)
Systematic (x)
14
Inter-fractional versus Intra-fractional
• Inter-fractional
– Variation between fractions
• Intra-fractional
– Variation within a fraction
15
Treatment preparation versus treatment execution
Always systematic
2)
3)
4)
5)
6)
Patient immobilization
CT-scan
Target delineation
Treatment plan design
Treatment delivery (35 fractions)
Treatment
preparation
Treatment
execution
Systematic and/or random
16
Motion in practice
17
Target delineation
Steenbakkers et al.
Radiother Oncol. 2005; 77:182-90
Systematic
Inter-fractional
Treatment preparation
Random
Intra-fractional
Treatment execution
18
Patient setup
y
x
Systematic
Inter-fractional
Treatment preparation
Random
Intra-fractional
Treatment execution
19
Target deformation / motion
1/3
Bladder
Target
Systematic
Inter-fractional
Treatment preparation
Random
Intra-fractional
Treatment execution
20
Target deformation / motion
2/3
Bladder
Target
Systematic
Inter-fractional
Treatment preparation
Random
Intra-fractional
Treatment execution
21
Target deformation / motion
2)
3)
4)
5)
6)
3/3
Patient immobilization
CT-scan
Target delineation
Treatment plan design
Treatment delivery (35 fractions)
22
Breathing motion
Movie by
John Wolfgang
Systematic
Inter-fractional
Treatment preparation
“ Random”
Intra-fractional
Treatment execution
23
Qualitative impact of motion
24
Importance of motion
Raise your hand to vote
• Breathing motion / heart beat
Almost least
• Systematic errors
Most
• Random errors
Least
Let’s “prove” it
25
Simulation parameters (1)
To enhance the visible effect of motion:
High dose conformed to CTV
GTV
CTV
PTV
High Dose
GTV
CTV
High Dose
26
Simulation parameters (2)
CTV
100
GTV
CTV
High Dose
Dose (% of prescribed dose)
95 %
90
80
70
60
50
-60 -50 -40 -30 -20 -10
0
10 20 30 40 50 60
distance from beam axis (mm)
Parallel opposed beams
Direction of motion
27
A m plitude of breathing m otion:
35
0 mm
5 mm
30
10 m m
Volume a.u.
25
20
15
10
5
0
80
85
90
95
100
105
D ose, % of IC R U reference dose
28
Standard deviation of random errors:
35
0 mm
5 mm
30
10 m m
Volume a.u.
25
20
15
10
5
0
80
85
90
95
100
105
D ose, % of IC R U reference dose
29
System atic error:
35
0 mm
5 mm
30
10 m m
Volume a.u.
25
20
15
10
5
0
80
85
90
95
100
105
D ose, % of IC R U reference dose
30
DVH reduction into:
• Tumor Control Probability (TCP)
• Assumption: homogeneous irradiation of the CTV to 84 Gy results in
a TCP = 50 %
1.0
0.8
TCP
0.6
0.4
0.2
0.0
0
20
40
60
80
D ose (G y)
100
120
31
Tumor motion and tumor control probability
Amplitude of
breathing motion
(mm)
Random setup errors
(1SD)
(mm)
Systematic setup
error
(mm)
TCP
(%)
0
0
0
47.3
5
-
-
47.0
10
-
-
46.3
15
-
-
44.3
-
5
-
46.8
-
10
-
43.5
-
15
-
36.9
-
-
5
45.5
-
-
10
40.1
-
-
15
6.0
Typical motion:
32
Importance of motion
Therefore …
• Breathing motion / heart beat
Almost least
• Systematic errors
Most
• Random errors
Least
33
Why are systematic errors worse ?
Random errors / breathing blurs the cumulative dose distribution
dose
Systematic errors shift the cumulative dose distribution
CTV
Slide by
M. van Herk
34
In other words…
• Systematic errors
- Same part of the tumor always underdosed
• Random errors / Breathing motion / heart beat
- Multiple parts of the tumor underdosed part of the time,
correctly dosed most of the time
But don’t forget: Breathing motion and heart beat can have systematic
effects on target delineation
35
Motion management
36
Radiotherapy treatment process
2)
3)
4)
5)
6)
Patient immobilization
CT-scanning
Target delineation
Treatment plan design
Treatment delivery
37
Patient immobilization
Leg pillow
Intra-cranial mask
www.sinmed.com
GTC frame
Breast board
www.sinmed.com
www.massgeneral.og
38
Benefits of immobilization
• Reproducible patient setup
• Limits intra-fraction motion
39
Radiotherapy treatment process
2)
3)
4)
5)
6)
Patient immobilization
CT-scanning
Target delineation
Treatment plan design
Treatment delivery
40
CT-scanning
• Multiple CT-scans prior to treatment planning
- Reduces geometric miss compared to single CT-scan
• 4D-CT scanning
- Extent of breathing motion
- Determine representative tumor position
• See lecture “Advances in imaging for therapy”
41
Radiotherapy treatment process
2)
3)
4)
5)
6)
Patient immobilization
CT-scanning
Target delineation
Treatment plan design
Treatment delivery
42
Target delineation
• Multi-modality imaging
- CT-scan, MRI, PET, etc.
• Physician training and inter-collegial verification
• Improved drawing tools and auto-delineation
43
Radiotherapy treatment process
2)
3)
4)
5)
6)
Patient immobilization
CT-scanning
Target delineation
Treatment plan design
Treatment delivery
44
Treatment plan design
• Choice of beam angles
- e.g. parallel to target motion
• Smart treatment planning
• Robust optimization
• IMRT
• See, e.g., lecture “Optimization with motion
and uncertainties”
45
Radiotherapy treatment process
2)
3)
4)
5)
6)
Patient immobilization
CT-scanning
Target delineation
Treatment plan design
Treatment delivery
46
Magnitude of motion in treatment delivery
• Systematic setup error
– Laser: S = 3 mm
– Bony anatomy: S = 2 mm
– Cone-beam CT: S = 1 mm
• Random setup errors
– s = 3 mm
• Breathing motion
– Up to 30 mm peak-to-peak
– Typically 10 mm peak-to-peak
• Tumor delineation
– See next slide
47
Tumor delineation
• 22 Patients with
lung cancer
• 11 Radiation
oncologists from 5
institutions
• Comparison to
median target
surface
Rad. Onc. #
Mean volume
(cm3)
Mean distance
(mm)
Overall SD
(mm)
1
36
-6.4
15.1
2
48
-3.7
11.6
3
53
-4.3
13.9
4
55
-2.4
7.0
5
58
-3.3
12.7
6
67
-1.6
10.0
7
69
-1.2
6.2
8
72
-1.0
6.6
9
76
-0.2
7.4
10
93
0.9
5.7
11
129
0.4
6.1
All
69 ( 25)
-1.7
10.2
5?
Steenbakkers et al.
Radiother Oncol. 2005; 77:182-90
48
Motion management
49
Motion management for setup errors
• Portal imaging
50
Portal imaging
Obtained from Treatment
Planning System
Obtained in
treatment room
51
Setup protocol
• NAL-protocol (No Action Level)
– Portal imaging for first Nm fractions
– Calculate a single correction vector compared to
markers for laser setup
de Boer HC, Heijmen BJ.
Int J Radiat Oncol Biol Phys.
2001;50(5):1350-65
Lasers only
52
Motion management for breathing
• In treatment plan design
-
Margin increase
Overcompensating dose to margin
Robust treatment planning
See, e.g., lecture “Optimization with motion and
uncertainties”
• Control patient breathing
- Breath-hold
- Gated radiotherapy
53
Breathing traces
Trace
PDF =
Probability
Density
Function
1)
2)
3)
54
Margin increase
55
Effect of blurring on dose profile (conformal)
Only a limited shift
in 95% isodose level
Conformal beam
1.0
Dose (relative)
0.8
0.6
Unblurred
Breathing
Random setup errors
Both
0.4
0.2
0.0
0
10
20
30
40
50
60
70
distance (from central axis, mm)
56
Margin for breathing (conformal)
5
10
15
57
Margin for breathing (IMRT)
IMRT
beam
Conformal
beam
1.0
1.0
Dose
Dose(relative)
(relative)
0.8
0.8
0.6
0.6
Hypothetically
Sharp
Dose
Distribution
Unblurred
Breathing
Random setup errors
Both
0.4
0.4
0.2
0.2
0.0
0.0 0
0
10
20
30
40
50
60
70
10
20 (from
30 central
40 axis,
50 mm)60
distance
70
distance (from central axis, mm)
58
Margin for breathing (IMRT)
IMRT
5
10
15
59
Breath hold
60
Control / stop patient breathing
• Exhale position most reproducible
• Inhale position most beneficial for sparing
lung tissue
61
Breath hold techniques
• Voluntary breath hold
•
Rosenzweig KE et al. The deep inspiration breath-hold technique in the treatment of inoperable
non-small-cell lung cancer. Int J Radiat Oncol Biol Phys. 2000;48:81-7
• Active Breathing Control (ABC)
•
Wong JW et al. The use of active breathing control (ABC) to reduce margin for breathing
motion. Int J Radiat Oncol Biol Phys. 1999;44:911-9
• Abdominal press
–
Negoro Y et al. The effectiveness of an immobilization device in conformal radiotherapy for
lung tumor: reduction of respiratory tumor movement and evaluation of the daily setup
accuracy. Int J Radiat Oncol Biol Phys. 2001;50:889-98
62
Gating
63
Gated radiotherapy
Gating window
• External or internal markers
• Usually 20% duty cycle
• Some residual motion
64
Gating benefits and drawbacks
• Less straining for patient than breath-hold +
• Increased treatment time • Internal markers
– Direct visualization of tumor (surroundings) +
– Invasive procedure / side effects of surgery -
• External markers
– Limited burden for patient +
– Doubtful correlation between marker and tumor
position
-
• Intra-fractional
• Inter-fractional
65
Motion in charged particle therapy
66
T. Bortfeld
67
Range sensitivity
Spherical tumor in lung
Paralell opposed photons
Single field photons
Single field protons
Displayed isodose levels: 50%, 80%, 95% and 100%
68
Range sensitivity
Spherical tumor in lung
Paralell opposed photons
Single field photons
Single field protons
Displayed isodose levels: 50%, 80%, 95% and 100%
69
Range sensitivity
Spherical tumor in lung
Paralell opposed photons
Single field photons
Single field protons
Displayed isodose levels: 50%, 80%, 95% and 100%
70
Dose-Volume Histogram (protons)
PTV (static)
CTV
GTV
CTV-GTV
71
SOBP Modulation
High-Density
Structure
Target
Volume
Beam
Critical
Structure
Range
Compensator
A
p
e
r
t
Body
Surface
u
r
e
72
Passive scattering system
Aperture
Range Compensator
+
Lateral
conformation
=
Distal
conformation
73
Smearing the range compensator
High-Density
Structure
Target
Volume
Beam
Critical
Structure
Range
Compensator
A
p
e
r
t
Body
Surface
u
r
e
74
Smearing the range compensator
High-Density
Structure
Target
Volume
Beam
Critical
Structure
Range
Compensator
A
p
e
r
t
Body
Surface
u
r
e
75
Setup
Smear Error
Displayed isodose levels: 50%, 80%, 95% and 100%
C
D
A
0
0
B
0
10
C
10
0
D
10
10
76
Motion management in particle therapy
• Passive scattered particle therapy
• For setup errors and (possibly) breathing motion
- Lateral expansion of apertures
- Smearing of range compensators
• IMPT
- See, e.g., lecture “Optimization with motion and
uncertainties”
77
Thank you for your attention
78

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