Samir Laoui, Ph.D. UC, Irvine

Introduction

o Respiratory, cardiac and gastrointestinal

systems cause Intrafractional motion

o Respiratory motion management can improve

the treatment results of non-small-cell lung

cancer

Respiratory motion is both intra- and

inter-fraction motion

Inter-fraction motion

Intra-fraction motion

Scope

o The magnitude of respiratory motion

o Problems caused by respiratory motion

o Methods that have been used to mitigate

respiratory motion during RT

Problems associated with respiratory

motion during RT

o Image acquisition issues

Motion Induced Artifacts

o Respiratory organ motion can cause severe geometrical distortion in free breathing CT scanning

o Distortions along the axis of motion could either lengthen or shorten the target, kind of random

o In addition to shape distortion, the center of the imaged target can be displaced by as much as the amplitude of the motion

Problems associated with respiratory

motion during RT

o Image acquisition issues

George TY Chen, MGH

Problems associated with respiratory

motion during RT

o Issues during treatment planning

o Extended margins to account for motion

o Radiation delivery limitations

o Blurring of the static dose distribution over the

path of the motion

oWorse in IMRT delivery

Magnitude and measurement of

respiratory motion

o The lungs, esophagus, liver, pancreas, breast,

prostate, and kidneys, among other organs, are

known to move with breathing

Breathing pattern is never

reproducible which makes it

difficult to predict

Magnitude and measurement of

respiratory motion

Magnitude and measurement of

respiratory motion

Common issues for respiratory motion

management- Planning

o Motion artifact in the CT scan

o Daily variation of respiratory motion

o Organ volume changes

o Tumor growth and shrinkage

o Lung volume changes

Common issues for respiratory motion

management- QA

o When using gated or breath hold treatments,

the monitors have to be accurate and calibrated

o Instrument has to be calibrated routinely

o Patient training- Reproducible breath patterns

o Patient needs to be coached prior to simulation

IMRT

o Respiratory motion presents considerable

issues for IMRT delivery

o Up to 100% variation can be caused by

respiratory motion (Yu el al)

o Variation tends to average out with

fractionation

o Caution during SBRT

Methods used in the management of

respiratory motion

I. Motion-encompassing methods

II. Respiratory gated techniques

III. Breath-hold techniques

IV.Forced shallow-breathing methods

V. Real-time tumor-tracking methods

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I. Motion encompassing methods

o During imaging, respiratory motion can be

accounted for by:

o Slow CT

o Inhale-Exhale breath-hold CT

o 4D CT

o It should be noted that extra dose comes with

the use of the above techniques

I. Motion encompassing methods: Slow

CT scanning

o The CT scanner is operated very slowly, and/or

multiple CT scans are averaged such that

multiple respiration phases are recorded per

slice

o Most available

o Loss of resolution due to motion blurring

o Increased dose

I. Motion encompassing methods:

Inhale and exhale breath-hold CT

o Acquire both inhale and exhale gated or

breath-hold CT scans

o Relies on the patient’s ability to hold his/her

breath reproducibly

o Maximum intensity projection (MIP) is

generated from the 2 individual scans for

planning purposes

I. Motion encompassing methods:

4DCT

o acquisition of a sequence of CT image sets over consecutive segments of breathing cycle

o Concept:

oAcquire CT images at all phases in a series of respiratory cycles

o Each image is tagged with breathing signal(time stamp)

owhen the scan is done, all the images of the selected phase are retrospectively organized to form 4D video images(3D+time).

I. Motion-encompassing methods:

4DCT

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II. Respiratory gating methods

o Administration of radiation within a portion of

the patient’s breathing cycle “gate”

o The position and width of the “gate” is

determined using external respiration signal or

internal fiducial markers

o Can result in a decrease of margins

o There are 2 types: displacement and phase

gating

II. Respiratory gating methods

o Most widely used solution developed by

Varian is the RPM (real time position

management) system.

o An infrared reflective plastic box is placed on

the patient’s anterior abdominal surface,

typically midway between the xyphoid process

and the umbilicus.

II. Gating using an external respiration signal

o Patient related quality assurance o Time-dependent internal target position will not match the

respiration monitoring.

Comparison of external marker block motion with internal motion of the clinical target

volume (CTV) for a patient with (a) no phase shift and (b) a patient with significant

phase shift. The respiratory gating thresholds are set using the external marker block

motion. The beam-on pulses are highlighted in red over the internal CTV position. 24

II. Gating using internal fiducial

markers

o Invasive

o Implanted fiducial markers in or near the

tumor for real time tracking

o Fiducial position is tracked in all 3D several

times a second using a pair of stereotactic KV

–x-rays

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II. Gating using internal fiducial

markers

III. Breath hold methods

o Used primarily for lung treatment

o Breath hold techniques

oDeep-inspiration breath hold

oActive breathing control

o Self-held breath hold without monitoring

o Self-held breath hold with monitoring

III. Breath hold methods: Deep-Inspiration

Breath-Hold (DIBH)

o For thoracic tumors, DIBH helps in

reproducing a state of maximum breath hold

oMinimize dose to OAR

o Involves spirometer

oWas developed by MSKCC in late 90’s

o Limited by patient compliance

III. Breath hold methods: Active Breathing

Control (ABC)

o The ABC apparatus can suspend patient’s

breathing at any predetermined position

III. Breath hold methods: Active

Breathing Control (ABC)

o Moderate deep inspiration breath-hold (DIBH)

at 75% to 80% of maximum inspiration

capacity to displace of thoracic contents and

avoid tiring the patient

o Patient selection; long breath-hold (>15 sec) is

desirable

o Therapists involve in verbal coaching

III. Breath hold methods: Self-held breath

hold without external monitoring

o Although only the therapist is allowed to turn

the beam on, the patient is given the ability to

release a treatment interlock

o Depends highly on patient compliance

III. Breath hold methods: Self-held breath

hold with external respiratory monitoring

o It is RPM based technique

o Patient is coached to hold breath at a specified

part of the respiratory cycle

o Depends highly on patient compliance

IV. Forced shallow breathing with

abdominal compression (FSB)

o Frame for abdomen compression

o FSB has predominantly been applied to early

stage lung and liver tumors without

mediastinal involvement or nodal disease.

V. Real time tracking methods

o Reposition the radiation beam dynamically so

as to follow the tumor’s changing position

o Identify tumor position in real time

oAnticipate tumor motion

o Reposition the beam

oAccount for lung volume changes and OAR

location

V. Real time tracking methods

o Tumor position

o Real time imaging of tumor itself (Fluoroscopy)

o Fiducials (High Z)

o Surrogate breathing signal

oNon-radiographic tumor tracking (Calypso)

Clinical process recommendation

Treatment planning recommendation

oWhen deriving CTV/PTV:

oAccount for image distortion due to respiratory motion

o If a structure is used as a surrogate, the displacement

and phase relationship between structure and tumor can

have uncertainties which have to be accounted for

o Irregularities in breathing cycles have to be accounted

for

oMargins have to be increased in the absence of a

respiratory motion device

Other recommendations

oWhen a respiratory management device is used, a

qualified medical physicist has to be present

o Strict QA procedures for the imaging, planning,

and delivery of radiotherapy using respiratory

management devices are required to ensure the

safe and effective use of these devices

The end