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Hst motion inradiotherapy

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  • 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.
  • Treatment preparation errors affect the whole treatment -> hence: systematic Treatment execution errors
  • 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.
  • Transcript

    • 1. Motion in Radiotherapy Martijn Engelsman
    • 2. 2 Contents • What is motion ? • Why is motion important ? • Motion in practice • Qualitative impact of motion • Motion management • Motion in charged particle therapy
    • 3. 3 What is motion ?
    • 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
    • 5. 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. 6 Why is motion important ?
    • 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
    • 10. 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. 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
    • 13. 13 x y Setup errors for three patients Beam’s Eye View
    • 14. 14 Systematic (x) Random (y) Random (x) Setup errors for a single patient Systematic (y)
    • 15. 15 Inter-fractional versus Intra-fractional • Inter-fractional – Variation between fractions • Intra-fractional – Variation within a fraction
    • 16. 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. 17 Motion in practice
    • 18. 18 Systematic Inter-fractional Treatment preparation Random Intra-fractional Treatment execution Target delineation Steenbakkers et al. Radiother Oncol. 2005; 77:182-90
    • 19. 19 Systematic Inter-fractional Treatment preparation Random Intra-fractional Treatment execution Patient setup x y
    • 20. 20 Systematic Inter-fractional Treatment preparation Random Intra-fractional Treatment execution Target deformation / motion 1/3 Target Bladder
    • 21. 21 Systematic Inter-fractional Treatment preparation Random Intra-fractional Treatment execution Target deformation / motion 2/3 Target Bladder
    • 22. 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. 23 Breathing motion Systematic Inter-fractional Treatment preparation Random Intra-fractional Treatment execution Movie by John Wolfgang “ ”
    • 24. 24 Qualitative impact of motion
    • 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
    • 26. 26 Simulation parameters (1) GTV CTV PTV High Dose GTV CTV High Dose To enhance the visible effect of motion: High dose conformed to CTV
    • 27. 27 GTV CTV High Dose Parallel opposed beams Direction of motion Simulation parameters (2) -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 50 60 70 80 90 100 95 % Dose(%ofprescribeddose) distance from beam axis (mm) CTV
    • 28. 28 80 85 90 95 100 105 0 5 10 15 20 25 30 35 Dose, % of ICRU reference dose Volumea.u. Amplitude of breathing motion: 0 mm 5 mm 10 mm
    • 29. 29 80 85 90 95 100 105 0 5 10 15 20 25 30 35 Dose, % of ICRU reference dose Volumea.u. Standard deviation of random errors: 0 mm 5 mm 10 mm
    • 30. 30 80 85 90 95 100 105 0 5 10 15 20 25 30 35 Dose, % of ICRU reference dose Volumea.u. Systematic error: 0 mm 5 mm 10 mm
    • 31. 31 0 20 40 60 80 100 120 0.0 0.2 0.4 0.6 0.8 1.0 Dose (Gy) TCP DVH reduction into: • Tumor Control Probability (TCP) • Assumption: homogeneous irradiation of the CTV to 84 Gy results in a TCP = 50 %
    • 32. 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:
    • 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…
    • 36. 36 Motion management
    • 37. 37 Radiotherapy treatment process 2) Patient immobilization 3) CT-scanning 4) Target delineation 5) Treatment plan design 6) Treatment delivery
    • 38. 38 Patient immobilization Breast board Intra-cranial mask GTC frame www.massgeneral.og www.sinmed.com www.sinmed.com Leg pillow
    • 39. 39 Benefits of immobilization • Reproducible patient setup • Limits intra-fraction motion
    • 40. 40 Radiotherapy treatment process 2) Patient immobilization 3) CT-scanning 4) Target delineation 5) Treatment plan design 6) Treatment delivery
    • 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”
    • 42. 42 Radiotherapy treatment process 2) Patient immobilization 3) CT-scanning 4) Target delineation 5) Treatment plan design 6) Treatment delivery
    • 43. 43 Target delineation • Multi-modality imaging - CT-scan, MRI, PET, etc. • Physician training and inter-collegial verification • Improved drawing tools and auto-delineation
    • 44. 44 Radiotherapy treatment process 2) Patient immobilization 3) CT-scanning 4) Target delineation 5) Treatment plan design 6) Treatment delivery
    • 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”
    • 46. 46 Radiotherapy treatment process 2) Patient immobilization 3) CT-scanning 4) Target delineation 5) Treatment plan design 6) Treatment delivery
    • 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
    • 48. 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. 49 Motion management
    • 50. 50 Motion management for setup errors • Portal imaging
    • 51. 51 Portal imaging Obtained from Treatment Planning System Obtained in treatment room
    • 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
    • 54. 54 Breathing traces Trace PDF = Probability Density Function 1) 2) 3)
    • 55. 55 Margin increase
    • 56. 56 Effect of blurring on dose profile (conformal) 0 10 20 30 40 50 60 70 0.0 0.2 0.4 0.6 0.8 1.0 Conformal beam Unblurred Breathing Random setup errors Both distance (from central axis, mm) Dose(relative) Only a limited shift in 95% isodose level
    • 57. 57 Margin for breathing (conformal) 5 10 15
    • 58. 58 Margin for breathing (IMRT) 0 10 20 30 40 50 60 70 0.0 0.2 0.4 0.6 0.8 1.0 IMRT beam distance (from central axis, mm) Dose(relative) 0 10 20 30 40 50 60 70 0.0 0.2 0.4 0.6 0.8 1.0 Conformal beam Unblurred Breathing Random setup errors Both distance (from central axis, mm) Dose(relative) Hypothetically Sharp Dose Distribution
    • 59. 59 Margin for breathing (IMRT) 5 10 15 IMRT
    • 60. 60 Breath hold
    • 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
    • 63. 63 Gating
    • 64. 64 Gated radiotherapy • External or internal markers • Usually 20% duty cycle • Some residual motion Gating window
    • 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 + + + - - -
    • 66. 66 Motion in charged particle therapy
    • 67. 67 T. Bortfeld
    • 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%
    • 71. 71 Dose-Volume Histogram (protons) PTV (static) CTV GTV CTV-GTV
    • 72. 72 SOBP Modulation Aperture High-Density Structure Body Surface Critical Structure Target Volume Beam Range Compensator
    • 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”
    • 78. 78 Thank you for your attention