Hst motion inradiotherapy

Motion in Radiotherapy

Martijn Engelsman

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Contents• What is motion ?

• Why is motion important ?

• Motion in practice

• Qualitative impact of motion

• Motion management

• Motion in charged particle therapy

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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

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Radiotherapy treatment process

1) Diagnosis2) Patient immobilization3) Imaging (CT-scan)4) Target delineation5) Treatment plan design6) Treatment delivery (35 fractions)7) Patient follow-up

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Why is motion important ?

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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)

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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

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Example source of motion

www.pi-medical.gr

35 Fractions=

35 times patient setup

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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.

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Subdivision of motion

• Systematic versus Random

• Inter-fractional versus Intra-fractional

• Treatment Preparation versus Treatment Execution– Less commonly used

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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

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x

y

Setup errors for three patients

Beam’s Eye View

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Systematic (x)

Random (y)

Random (x)

Setup errors for a single patient

Systematic (y)

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Inter-fractional versus Intra-fractional

• Inter-fractional– Variation between fractions

• Intra-fractional– Variation within a fraction

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Treatment preparation versus treatment execution

2) Patient immobilization3) CT-scan4) Target delineation5) Treatment plan design6) Treatment delivery (35 fractions)

Treatment preparation

Treatment execution

Always systematic

Systematic and/or random

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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

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Patient setup

x

y

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Target deformation / motion 1/3

TargetBladder

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TargetBladder

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2) Patient immobilization3) CT-scan4) Target delineation5) Treatment plan design6) Treatment delivery (35 fractions)


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Breathing motion



Movie by John Wolfgang

“ ”

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Qualitative impact of motion

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Importance of motion

• Breathing motion / heart beat

• Systematic errors

• Random errors

Raise your hand to vote

Let’s “prove” it

Most

Least

Almost least

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Simulation parameters (1)

GTVCTVPTVHigh Dose

GTVCTV

High Dose

To enhance the visible effect of motion: High dose conformed to CTV

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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 %

Dos

e (%

of p

resc

ribed

dos

e)

distance from beam axis (mm)

CTV

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80 85 90 95 100 1050

5

10

15

20

25

30

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Dose, % of ICRU reference dose

Vol

ume

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


Vol

ume

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


Vol

ume

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)

TCP

DVH reduction into:

• Tumor Control Probability (TCP)• Assumption: homogeneous irradiation of the CTV to 84 Gy results in a

TCP = 50 %

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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

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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…

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Motion management

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2) Patient immobilization3) CT-scanning4) Target delineation5) Treatment plan design6) Treatment delivery

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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

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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”

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Target delineation

• Multi-modality imaging- CT-scan, MRI, PET, etc.

• Physician training and inter-collegial verification

• Improved drawing tools and auto-delineation

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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”

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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

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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?

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Motion management

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Motion management for setup errors

• Portal imaging

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Portal imaging

Obtained from Treatment Planning System

Obtained in treatment room

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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

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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

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Breathing tracesTrace PDF =

ProbabilityDensityFunction

1)

2)

3)

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Margin increase

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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)

Dose

(rel

ativ

e)Only a limited shift in 95% isodose level

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Margin for breathing (conformal)

5 10 15

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Margin for breathing (IMRT)

0 10 20 30 40 50 60 700.0

0.2

0.4

0.6

0.8

1.0IMRT beam


Dose

(rel

ativ

e)

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


Dose

(rel

ativ

e)

HypotheticallySharpDose

Distribution

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Margin for breathing (IMRT)

5 10 15

IMRT

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Breath hold

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Control / stop patient breathing

• Exhale position most reproducible

• Inhale position most beneficial for sparing lung tissue

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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

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Gating

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Gated radiotherapy

• External or internal markers• Usually 20% duty cycle• Some residual motion

Gating window

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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

+

+

+

-

-

-

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Motion in charged particle therapy

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T. Bortfeld

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Range sensitivity

Paralell opposed -photons

Single field -protons

Single field -photons

Spherical tumor in lung

Displayed isodose levels: 50%, 80%, 95% and 100%

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Range sensitivity


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Range sensitivity


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Dose-Volume Histogram (protons)

PTV (static)CTVGTVCTV-GTV

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SOBP Modulation

Aperture

High-DensityStructure

BodySurface

CriticalStructure

TargetVolume

Beam

RangeCompensator

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+ =

Passive scattering system

Aperture Range Compensator

Lateral conformation

Distal conformation

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Smearing the range compensator

Aperture


BodySurface

CriticalStructure

TargetVolume

Beam

RangeCompensator

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Smearing the range compensator

Aperture


BodySurface

CriticalStructure

TargetVolume

Beam

RangeCompensator

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SmearSetupError

A 0 0

B 0 10

C 10 0

D 10 10

A B C D

E F G HC D


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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”

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Thank you for your attention

Hst motion inradiotherapy

Health & Medicine

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