1. Motion in Radiotherapy
Martijn Engelsman
May as well have been called “Radiotherapy in motion” because motion-management has been, and still is, a rapidly evolving important part of Radiotherapy
My feeling is that at least some of the previous presentations have gone pretty fast. Out of my own experience it is easy to assume basic understanding.
Anecdote about treatment planning.
I’ll try to be thorough and apologize to non-students and possibly even to students.

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
Diagnosis
Patient immobilization
Imaging (CT-scan)
Target delineation
Treatment plan design
Treatment delivery (35 fractions)
Patient follow-up

6. Why is motion important ?

7. PTV concept (1) (ICRU 50 and 62)
High dose region
PTV (Planning Target Volume):  = 8 cm, V = 268 cm3
CTV (Clinical Target Volume):  = 6 cm, V = 113 cm3
GTV (Gross Tumor Volume):  = 5 cm, V = 65 cm3
Simplified (hej, patients are not square with round tumors, but as a physicist I’m allowed to shape reality into a comprehensive model), but the basis of radiotherapy treatment for the vast majority of patients

8. PTV concept (2) Margin from GTV to CTV Margin from CTV to PTV
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
Motion management
Smart treatment planning
GTV
CTV
PTV
High Dose

9. Example source of motion
35 Fractions =
35 times patient setup
For the vast majority of radiations are isocentric meaning that for each fraction the patient is positioned with respect to the treatment machine isocenter and then the treatment is delivered as a whole.
During a treatment fraction, the patient will be irriated from several, static, angles.
Many patients set-up to lasers only.
Many exceptions and more sophisticated approaches, but for explaining types of motion lasers will visualize nicely.
35 fractions; never the same alignment twice.
Patient skin is “loose” so markers can move. Patient can gain or loose weight resulting in “motion”
The lasers have an inherent width
The lasers may be half a mm displaced with respect to the iso-center of the linear accelerator. THAT’S WHY WE DO REGULAR QUALITY ASSURANCE

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.
I’ll discuss all of these in more detail within a few slides, this is just to give an idea.
Patient setup: just imagine lining up to the lasers every fraction
Target delineation: The physician uses the CT-scan to draw where he thinks is target. Inherently flawed approach
Target deformation: Filled bladder / empty bladder. Gas in rectum, 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
Same error for all fractions (possibly even all patients).
Random
Unpredictable. Day to day variations around a mean.
Known but neither
Breathing, heartbeat
Relatively known means neither type.
Breathing can furthermore be both systematic and random

13. Setup errors for three patientsy
Beam’s Eye View x
Imagine I’m looking at the patient in the direction of the treatment beam.
Center of patient tumor is supposed to be aligned with the axis origin.

14. Setup errors for a single patient
Random (x)
Random (y)
Systematic (y)
Systematic (x)
Whenever there is random, there is also systematic.

15. Inter-fractional versus Intra-fractional
Variation between fractions
Intra-fractional
Variation within a fraction
Treatment preparation errors affect the whole treatment -> hence: systematic
Treatment execution errors

16. Treatment preparation versus treatment execution
Patient immobilization
CT-scan
Target delineation
Treatment plan design
Treatment delivery (35 fractions)
Always systematic
Systematic and/or random
Treatment
preparation
Treatment
execution

17. Motion in practice

18. Treatment preparation
Target delineation
Steenbakkers et al.
Radiother Oncol. 2005; 77:182-90
Systematic
Inter-fractional
Treatment preparation
Random
Intra-fractional
Treatment execution

19. Treatment preparation
Patient setup x y
Systematic
Inter-fractional
Treatment preparation
Random
Intra-fractional
Treatment execution

20. Treatment preparation
Target deformation / motion 1/3
Bladder
Target
Notice: variation in bladder shape due to bladder filling, may be different from day to day
Bladder extends more downward in second scan
Variation in rectum filling as well (both gasseous filling and non-gasseous filling)
Note: overlap between bladder and target because of automatic expansion of the tumor volume
Systematic
Inter-fractional
Treatment preparation
Random
Intra-fractional
Treatment execution

21. Treatment preparation
Target deformation / motion 2/3
Bladder
Target
Systematic
Inter-fractional
Treatment preparation
Random
Intra-fractional
Treatment execution

22. Target deformation / motion 3/3
Patient immobilization
CT-scan
Target delineation
Treatment plan design
Treatment delivery (35 fractions)

23. Treatment preparation
Breathing motion
Movie by
John Wolfgang
Systematic
Inter-fractional
Treatment preparation
Random
Intra-fractional
Treatment execution “ ”

24. Qualitative impact of motion

25. Importance of motion Breathing motion / heart beat Systematic errors
Raise your hand to vote
Breathing motion / heart beat
Systematic errors
Random errors
Let’s “prove” it
Most
Least
Almost least
Of course, it depends on the magnitude of motion you can typically expect. But, without telling you magnitudes what do you think?
I’ll give you magnitudes later

26. Simulation parameters (1)
To enhance the visible effect of motion:
High dose conformed to CTV
GTV
CTV
PTV
High Dose
GTV
CTV
High Dose

27. Dose (% of prescribed dose) distance from beam axis (mm)
Simulation parameters (2)
-60
-50
-40
-30
-20
-10 10 20 30 40 50 60 70 80 90
100
95 %
Dose (% of prescribed dose)
distance from beam axis (mm)
CTV
Parallel opposed beams
GTV
CTV
High Dose
Direction of motion

31. 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)
Systematic setup error
TCP
(%)
47.3 5 -
47.0 10
46.3 15
44.3
46.8
43.5
36.9
45.5
40.1
6.0
Typical motion:

33. Importance of motion Breathing motion / heart beat Systematic errors
Therefore …
Breathing motion / heart beat
Systematic errors
Random errors
Most
Least
Almost least
Of course, it depends on the magnitude of motion you can typically expect. But, without telling you magnitudes what do you think?
I’ll give you magnitudes later

34. 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

35. 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

36. Motion management

37. Radiotherapy treatment process
Patient immobilization
CT-scanning
Target delineation
Treatment plan design
Treatment delivery

38. Patient immobilization
Leg pillow
Intra-cranial mask
GTC frame
Breast board

39. Benefits of immobilization
Reproducible patient setup
Limits intra-fraction motion
Patient spends minutes on a not too comfortable treatment couch

40. Radiotherapy treatment process
Patient immobilization
CT-scanning
Target delineation
Treatment plan design
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
Patient immobilization
CT-scanning
Target delineation
Treatment plan design
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
Patient immobilization
CT-scanning
Target delineation
Treatment plan design
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
Patient immobilization
CT-scanning
Target delineation
Treatment plan design
Treatment delivery
Large section on motion management in treatment delivery

47. 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
Numbers express order of magnitude and are a little bit fuzzy because they sometimes express setup error of bony anatomy, sometimes of actual tumor location.

48. Tumor delineation 5? 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 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
Perhaps it is 5 mm for any given point on other targets. But then we are talking about the GTV.
Delineation of the CTV may be more error-prone because it is by nature non-visible.
Naturally, better imaging helps a lot, e.g. PET 5?
Steenbakkers et al.
Radiother Oncol. 2005; 77:182-90

49. Motion management

50. Motion management for setup errors
Portal imaging

51. Obtained from Treatment Planning System
Portal imaging
Obtained from Treatment Planning System
Obtained in
treatment room
Digitally Reconstructed Radiograph

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
Daily imaging is the standard here at the proton center.
Usually weekly imaging is performed with lasers used for
de Boer HC, Heijmen BJ.
Int J Radiat Oncol Biol Phys.
2001;50(5):
Lasers only

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
Probability
Density
Function
PDF = 1) 2) 3)

55. Margin increase

56. Effect of blurring on dose profile (conformal)
Only a limited shift
in 95% isodose level
This is for a photon profile in lung.
The shift would be larger for a steeper profile (e.g. due to IMRT)

57. Margin for breathing (conformal)5 10 15

58. Margin for breathing (IMRT)
Hypothetically
Sharp
Dose
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
Usually, lung cancer patients have an impaired lung function and can not really hold there breath that easily.

63. Gating

64. Gated radiotherapy Gating window External or internal markers
Usually 20% duty cycle
Some residual motion

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 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. Range sensitivity Spherical tumor in lung Paralell opposed - photons
Single field -
photons
Single field -
protons
Displayed isodose levels: 50%, 80%, 95% and 100%

71. Dose-Volume Histogram (protons)
PTV (static)
CTV
GTV
CTV-GTV

72. SOBP Modulation Beam High-Density Structure Target Volume Critical
Range
Compensator
Body
Surface

73. Passive scattering system
Aperture
Range Compensator + =
Lateral
conformation
Distal
conformation

74. Smearing the range compensator
High-Density
Structure
Target
Volume
Beam
Critical
Structure
Range
Compensator
Body
Surface

75. Smearing the range compensator
High-Density
Structure
Target
Volume
Beam
Critical
Structure
Range
Compensator
Body
Surface

76. C D Smear Setup Error A B 10 C DB 10 C 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