Post on 28-Mar-2015
Motion in Radiotherapy
Martijn Engelsman
2
Contents
• What is motion ?
• Why is motion important ?
• Motion in practice
• Qualitative impact of motion
• Motion management
• Motion in charged particle therapy
3
What is motion ?
4
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
5
Radiotherapy treatment process
1) Diagnosis
2) Patient immobilization
3) Imaging (CT-scan)
4) Target delineation
5) Treatment plan design
6) Treatment delivery (35 fractions)
7) Patient follow-up
6
Why is motion important ?
7
PTV concept (1)
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
(ICRU 50 and 62)
8
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
GTVCTVPTVHigh Dose
9
Example source of motion
www.pi-medical.gr
35 Fractions=
35 times patient setup
10
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.
11
Subdivision of motion
• Systematic versus Random
• Inter-fractional versus Intra-fractional
• Treatment Preparation versus Treatment Execution– Less commonly used
12
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
13
x
y
Setup errors for three patients
Beam’s Eye View
14
Systematic (x)
Random (y)
Random (x)
Setup errors for a single patient
Systematic (y)
15
Inter-fractional versus Intra-fractional
• Inter-fractional– Variation between fractions
• Intra-fractional– Variation within a fraction
16
Treatment preparation versus treatment execution
2) Patient immobilization
3) CT-scan
4) Target delineation
5) Treatment plan design
6) Treatment delivery (35 fractions)
Treatment preparation
Treatment execution
Always systematic
Systematic and/or random
17
Motion in practice
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Systematic Inter-fractional Treatment preparation
Random Intra-fractional Treatment execution
Target delineation
Steenbakkers et al.
Radiother Oncol. 2005; 77:182-90
19
Systematic Inter-fractional Treatment preparation
Random Intra-fractional Treatment execution
Patient setup
x
y
20
Systematic Inter-fractional Treatment preparation
Random Intra-fractional Treatment execution
Target deformation / motion 1/3
Target
Bladder
21
Systematic Inter-fractional Treatment preparation
Random Intra-fractional Treatment execution
Target deformation / motion 2/3
Target
Bladder
22
2) Patient immobilization
3) CT-scan
4) Target delineation
5) Treatment plan design
6) Treatment delivery (35 fractions)
Target deformation / motion 3/3
23
Breathing motion
Systematic Inter-fractional Treatment preparation
Random Intra-fractional Treatment execution
Movie by John Wolfgang
“ ”
24
Qualitative impact of motion
25
Importance of motion
• Breathing motion / heart beat
• Systematic errors
• Random errors
Raise your hand to vote
Let’s “prove” it
Most
Least
Almost least
26
Simulation parameters (1)
GTVCTVPTVHigh Dose
GTVCTV
High Dose
To enhance the visible effect of motion: High dose conformed to CTV
27
GTVCTV
High Dose
Parallel opposed beamsDirection of motion
Simulation parameters (2)
-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 6050
60
70
80
90
10095 %
Do
se
(%
of
pre
sc
rib
ed
do
se
)
distance from beam axis (mm)
CTV
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80 85 90 95 100 1050
5
10
15
20
25
30
35
Dose, % of ICRU reference dose
Vo
lum
e a
.u.
Amplitude of breathing motion:
0 mm
5 mm
10 mm
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80 85 90 95 100 1050
5
10
15
20
25
30
35
Dose, % of ICRU reference dose
Vo
lum
e a
.u.
Standard deviation of random errors:
0 mm
5 mm
10 mm
30
80 85 90 95 100 1050
5
10
15
20
25
30
35
Dose, % of ICRU reference dose
Vo
lum
e a
.u.
Systematic error:
0 mm
5 mm
10 mm
310 20 40 60 80 100 120
0.0
0.2
0.4
0.6
0.8
1.0
Dose (Gy)
TC
P
DVH reduction into:
• Tumor Control Probability (TCP)
• Assumption: homogeneous irradiation of the CTV to 84 Gy results in a TCP = 50 %
32
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:
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Importance of motion
• Breathing motion / heart beat
• Systematic errors
• Random errors
Therefore …
Most
Least
Almost least
34
Why are systematic errors worse ?
dose
CTV
Random errors / breathing blurs the cumulative dose distribution
Systematic errors shift the cumulative dose distribution
Slide byM. van Herk
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• 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
In other words…
36
Motion management
37
Radiotherapy treatment process
2) Patient immobilization
3) CT-scanning
4) Target delineation
5) Treatment plan design
6) Treatment delivery
38
Patient immobilization
Breast board
Intra-cranial mask
GTC frame
www.massgeneral.og
www.sinmed.com
www.sinmed.com
Leg pillow
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Benefits of immobilization
• Reproducible patient setup
• Limits intra-fraction motion
40
Radiotherapy treatment process
2) Patient immobilization
3) CT-scanning
4) Target delineation
5) Treatment plan design
6) Treatment delivery
41
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”
42
Radiotherapy treatment process
2) Patient immobilization
3) CT-scanning
4) Target delineation
5) Treatment plan design
6) Treatment delivery
43
Target delineation
• Multi-modality imaging
- CT-scan, MRI, PET, etc.
• Physician training and inter-collegial verification
• Improved drawing tools and auto-delineation
44
Radiotherapy treatment process
2) Patient immobilization
3) CT-scanning
4) Target delineation
5) Treatment plan design
6) Treatment delivery
45
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”
46
Radiotherapy treatment process
2) Patient immobilization
3) CT-scanning
4) Target delineation
5) Treatment plan design
6) Treatment delivery
47
Magnitude of motion in treatment delivery
• Systematic setup error– Laser: = 3 mm
– Bony anatomy: = 2 mm
– Cone-beam CT: = 1 mm
• Random setup errors– = 3 mm
• Breathing motion– Up to 30 mm peak-to-peak
– Typically 10 mm peak-to-peak
• Tumor delineation– See next slide
48
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
Steenbakkers et al.
Radiother Oncol. 2005; 77:182-90
5?
49
Motion management
50
Motion management for setup errors
• Portal imaging
51
Portal imaging
Obtained from Treatment Planning System
Obtained in treatment room
52
Setup protocol
• NAL-protocol (No Action Level)– Portal imaging for first Nm fractions
– Calculate a single correction vector compared to markers for laser setup
Lasers only
de Boer HC, Heijmen BJ.
Int J Radiat Oncol Biol Phys.
2001;50(5):1350-65
53
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
54
Breathing traces
Trace PDF =ProbabilityDensityFunction
1)
2)
3)
55
Margin increase
56
Effect of blurring on dose profile (conformal)
0 10 20 30 40 50 60 700.0
0.2
0.4
0.6
0.8
1.0Conformal beam
Unblurred Breathing Random setup errors Both
distance (from central axis, mm)
Do
se (
rela
tive
)Only a limited shift in 95% isodose level
57
Margin for breathing (conformal)
5 10 15
58
Margin for breathing (IMRT)
0 10 20 30 40 50 60 700.0
0.2
0.4
0.6
0.8
1.0
IMRT beam
distance (from central axis, mm)
Do
se (
rela
tive
)
0 10 20 30 40 50 60 700.0
0.2
0.4
0.6
0.8
1.0Conformal beam
Unblurred Breathing Random setup errors Both
distance (from central axis, mm)
Do
se (
rela
tive
)
HypotheticallySharpDose
Distribution
59
Margin for breathing (IMRT)
5 10 15
IMRT
60
Breath hold
61
Control / stop patient breathing
• Exhale position most reproducible
• Inhale position most beneficial for sparing lung tissue
62
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
63
Gating
64
Gated radiotherapy
• External or internal markers• Usually 20% duty cycle• Some residual motion
Gating window
65
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
+
+
+
-
-
-
66
Motion in charged particle therapy
67
T. Bortfeld
68
Range sensitivity
Paralell opposed -photons
Single field -protons
Single field -photons
Spherical tumor in lung
Displayed isodose levels: 50%, 80%, 95% and 100%
69
Paralell opposed -photons
Single field -protons
Single field -photons
Spherical tumor in lung
Range sensitivity
Displayed isodose levels: 50%, 80%, 95% and 100%
70
Paralell opposed -photons
Single field -protons
Single field -photons
Spherical tumor in lung
Range sensitivity
Displayed isodose levels: 50%, 80%, 95% and 100%
71
Dose-Volume Histogram (protons)
PTV (static)CTVGTVCTV-GTV
72
SOBP Modulation
Aperture
High-DensityStructure
BodySurface
CriticalStructure
TargetVolume
Beam
RangeCompensator
73
+ =
Passive scattering system
Aperture Range Compensator
Lateral conformation
Distal conformation
74
Smearing the range compensator
Aperture
High-DensityStructure
BodySurface
CriticalStructure
TargetVolume
Beam
RangeCompensator
75
Smearing the range compensator
Aperture
High-DensityStructure
BodySurface
CriticalStructure
TargetVolume
Beam
RangeCompensator
76
Smear
Setup
Error
A 0 0
B 0 10
C 10 0
D 10 10
A B C D
E F G HC D
Displayed isodose levels: 50%, 80%, 95% and 100%
77
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”
78
Thank you for your attention