2. 2
Contents
• What is motion ?
• Why is motion important ?
• Motion in practice
• Qualitative impact of motion
• Motion management
• Motion in charged particle therapy
4. 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
7. 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. 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
GTV
CTV
PTV
High Dose
9. 9
Example source of motion
www.pi-medical.gr
35 Fractions
=
35 times patient setup
11. 11
Subdivision of motion
• Systematic versus Random
• Inter-fractional versus Intra-fractional
• Treatment Preparation versus Treatment Execution
– Less commonly used
12. 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
25. 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
33. 33
Importance of motion
• Breathing motion / heart beat
• Systematic errors
• Random errors
Therefore …
Most
Least
Almost least
34. 34
Why are systematic errors worse ?
dose
CTV
Random errors / breathing blurs the cumulative dose distribution
Systematic errors shift the cumulative dose distribution
Slide by
M. van Herk
35. 35
• 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…
41. 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”
45. 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”
47. 47
Magnitude of motion in treatment delivery
• Systematic setup error
– Laser: Σ = 3 mm
– Bony anatomy: Σ = 2 mm
– Cone-beam CT: Σ = 1 mm
• Random setup errors
– σ = 3 mm
• Breathing motion
– Up to 30 mm peak-to-peak
– Typically 10 mm peak-to-peak
• Tumor delineation
– See next slide
52. 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. 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
61. 61
Control / stop patient breathing
• Exhale position most reproducible
• Inhale position most beneficial for sparing
lung tissue
62. 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
65. 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
+
+
+
-
-
-
68. 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. 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. 70
Paralell opposed -
photons
Single field -
protons
Single field -
photons
Spherical tumor in lung
Range sensitivity
Displayed isodose levels: 50%, 80%, 95% and 100%
73. 73
+ =
Passive scattering system
Aperture Range Compensator
Lateral
conformation
Distal
conformation
74. 74
Smearing the range compensator
Aperture
High-Density
Structure
Body
Surface
Critical
Structure
Target
Volume
Beam
Range
Compensator
75. 75
Smearing the range compensator
Aperture
High-Density
Structure
Body
Surface
Critical
Structure
Target
Volume
Beam
Range
Compensator
76. 76
Smear
Setup
Error
A 0 0
B 0 10
C 10 0
D 10 10
A B C
E F GC D
Displayed isodose levels: 50%, 80%, 95% and 100%
77. 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”
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.
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
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
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.
Relatively known means neither type. Breathing can furthermore be both systematic and random
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.
Whenever there is random, there is also systematic.
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
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
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
Patient spends 10-60 minutes on a not too comfortable treatment couch
Large section on motion management in treatment delivery
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.
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
Digitally Reconstructed Radiograph
Daily imaging is the standard here at the proton center. Usually weekly imaging is performed with lasers used for
This is for a photon profile in lung. The shift would be larger for a steeper profile (e.g. due to IMRT)
Usually, lung cancer patients have an impaired lung function and can not really hold there breath that easily.