Presentation is loading. Please wait.

Presentation is loading. Please wait.

Motion in Radiotherapy Martijn Engelsman. 2 Contents What is motion ? Why is motion important ? Motion in practice Qualitative impact of motion Motion.

Similar presentations


Presentation on theme: "Motion in Radiotherapy Martijn Engelsman. 2 Contents What is motion ? Why is motion important ? Motion in practice Qualitative impact of motion Motion."— Presentation 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 cm 3 CTV (Clinical Target Volume): = 6 cm, V = 113 cm 3 PTV (Planning Target Volume): = 8 cm, V = 268 cm 3 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 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 Beams 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 SystematicInter-fractionalTreatment preparation RandomIntra-fractionalTreatment execution Target delineation Steenbakkers et al. Radiother Oncol. 2005; 77:182-90

19 19 SystematicInter-fractionalTreatment preparation RandomIntra-fractionalTreatment execution Patient setup x y

20 20 SystematicInter-fractionalTreatment preparation RandomIntra-fractionalTreatment execution Target deformation / motion1/3 Target Bladder

21 21 SystematicInter-fractionalTreatment preparation RandomIntra-fractionalTreatment execution Target deformation / motion2/3 Target Bladder

22 22 2)Patient immobilization 3)CT-scan 4)Target delineation 5)Treatment plan design 6)Treatment delivery (35 fractions) Target deformation / motion3/3

23 23 Breathing motion SystematicInter-fractionalTreatment preparation RandomIntra-fractionalTreatment 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 Lets 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) % Dose (% of prescribed dose) distance from beam axis (mm) CTV

28 28

29 29

30 30

31 31 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 (%) 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 dont 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 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: = 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 48 Tumor delineation 22 Patients with lung cancer 11 Radiation oncologists from 5 institutions Comparison to median target surface Rad. Onc. #Mean volume (cm 3 ) Mean distance (mm) Overall SD (mm) All69 ( 25) Steenbakkers et al. Radiother Oncol. 2005; 77: ?

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 N m 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):

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) Only a limited shift in 95% isodose level

57 57 Margin for breathing (conformal)

58 58 Margin for breathing (IMRT) Hypothetically Sharp Dose Distribution

59 59 Margin for breathing (IMRT) 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 High-Density Structure Body Surface Critical Structure Target Volume Beam Range Compensator

73 73 + = Passive scattering system ApertureRange Compensator Lateral conformation Distal conformation

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

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

76 76 Smear Setup Error A00 B010 C 0 D C 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


Download ppt "Motion in Radiotherapy Martijn Engelsman. 2 Contents What is motion ? Why is motion important ? Motion in practice Qualitative impact of motion Motion."

Similar presentations


Ads by Google