Respiration motion management

1. Management of respiration motion
Dr Kiran Kumar BR

2. PROBLEMS OF RESPIRATORY MOTION DURING
RADIOTHERAPY
Image acquisition Radiation delivery
Treatment planning

3. Image Acquisition Limitations
• If respiratory motion is not accounted for, imaging thoracic and
abdominal sites, it causes artifacts during image acquisition (motion
artifacts)
• These artifacts cause distortion of the target volume and incorrect
positional and volumetric information.
• These motion artifacts occur because different parts of the object
move in and out during image acquisition.
• Artifacts from scans manifest themselves not only as target/normal
tissue delineation, but also negatively affect dose calculation
accuracy.

5. Treatment Planning Limitations
• During treatment planning, margins need to be large enough
to ensure coverage of the target for most of the treatment
delivery.
• International Commission on Radiation Units and
Measurements (ICRU) report 62 recommends to add ITM to
the CTV involves to account for intrafraction motion (due to
respiration).
• this increases the radiation field size and consequently the
volume of healthy tissues exposed to high doses.

6. Radiation Delivery Limitations
• Radiation delivery in the presence of intrafraction
organ motion causes an averaging or blurring of the
dose distribution over the path of the motion.
• This displacement results in a deviation between the
intended and delivered dose distributions.

7. METHODS TO ACCOUNT FOR RESPIRATORY MOTION
MOTION ENCOMPASSING
METHODS
FORCED SHALLOW BREATHING
TECHNIQUES
BREATH HOLD TECHNIQUES
RESPIRATORY GATING
TECHNIQUES
Respiration synchronized technique
Real time tumor tracking
TECHNIQUES

8. Motion Encompassing Methods
• The three techniques possible for CT imaging
that can include the entire range of tumor
motion for respiration
– slow CT
– inhale and exhale breath-hold CT
– four dimensional (4-D) or respiration-correlated
CT

9. Slow CT
• In the slow-scanning method, the CT scanner is
operated very slowly, and/or multiple CT scans are
averaged such that multiple respiration phases are
recorded per slice.
• For slow CT scanning, one CT scan is obtained, so the
overall treatment process does not increase in
complexity over that of a free-breathing CT scan.

10. • Advantages:
– Slow CT scanning is available on most CT scanners;
therefore, is generally the method most available.
– the dose calculation is performed on a geometry that is
more representative of that during the entire respiratory
cycle, as occurs during treatment.
• Disadvantages:
– loss of resolution due to motion blurring, which
potentially leads to larger observer errors in tumor and
normal organ delineation.

11. Inhale and Exhale breath-hold CT
• Taking both inhale and exhale CT scans will more than double the CT
scanning time and relies on the patient’s ability to hold his or her
breath reproducibly.
• Two scans will be obtained; thus, image fusion and extra contouring
are required.
• The exhale scan will tend to underestimate the lung volumes and,
hence, overestimate the percentage of lung volume receiving a
specific dose.
• To save time, a free-breathing CT could be used for the entire scan
region with either breath-hold or gated CT scans at inhale and exhale
of a scan length sufficient to cover the tumor volume to determine
range of motion of the GTV.

12. 4D or Respiration correlated CT
Four dimensional data can be analysed to
determine the mean tumor position, tumor
range of motion for treatment planning and the
relation of tumor trajectory to other organs and
to a respiration monitor

14. • A 4-D CT scan can be obtained in approximately 1
minute of scanning time with a 16-slice CT
scanner.
• Generally 8 to 25 complete CT datasets are
reconstructed, the optimal use of which has yet
to be determined.
• Four-dimensional CT can be used to reconstruct
inhale, exhale, and slow CT scans.

15. Respiratory Gating Methods
Respiratory gating involves the administration of
radiation (during both imaging and treatment
delivery) within a particular portion of the patient’s
breathing cycle, commonly referred to as the “gate.”

16. The position and width of the gate within a
respiratory cycle are determined by monitoring the
patient’s respiratory motion, using either an external
respiration signal or internal fiducial markers.

17. • Respiratory motion can be characterized by two
variables that are recorded as part of the
respiration signal or the motion of the internal
anatomy.
• These variables are
– Displacement
– Phase
• Accordingly, the method of gating is referred to as
either displacement gating or phase gating.

18. • The displacement of the respiration signal
measures its relative position between two
extremes of breathing motion, namely, inhale
and exhale.
• In displacement-based gating, the radiation
beam is activated whenever the respiration
signal is within a pre-set window of relative
positions

19. • In phase-based gating, the radiation beam is
activated when the phase of the respiration
signal is within a pre-set phase window.
• complete breathing cycle corresponds with a
phase interval from 0 to 2π (for fully periodic
motion, 0 is at the inhale level of the
respiration trace).

20. Typically, a gate extends over a region of the
breathing cycle where the motion of the tumor
is estimated to be less, compared with the rest
of the respiratory cycle (such as at exhale), or
where the lung volume is maximal (such as at
inhale)

21. • Some tumor motion still occurs within the gate and is
referred to as “residual motion.”
• The choice of gate width is a trade-off between the
amount of residual motion and duty cycle.
– The fraction of time a radiation beam is active during the
delivery of a respiratory-gated treatment field is referred to
as the duty cycle and is a measure of the efficiency of the
method.
• The thresholds for the gate are manually determined
based on the motion learned by the system.

22. GATING
INTERNAL MARKER
External marker

23. Gating Using External Markers
• Currently, the commercially available
respiratory gating system using an external
respiration signal are
– Varian Real-time Position Management (RPM)
system

24. RPM
• RPM Respiratory Gating technology enables
correlation of the tumor position with the patient’s
respiratory cycle.
• Using an infrared tracking camera and a reflective
marker placed on the patient, the system measures
the patient’s respiratory pattern and range of motion
and displays them as a waveform.

25. • Once it is determined how the tumor moves in
relation to the waveform, gating thresholds can be
set along the waveform to mark when the tumor is
in the desired portion of the respiratory cycle.
• These thresholds determine when the automatic
gating system turns the treatment beam on and off.

26. Major Components of RPM
• Infrared Tracking Camera
• Marker block
• CT Scanner
• GE 4D Software
• RPM Switchbox
• RPM Workstation
• Predictive Filter

27. • Infrared Tracking Camera
– The infrared tracking camera is a video camera equipped
with an array of LEDs that emit infrared light in the direction
in which the camera is pointing.
– Dots on the marker block reflect the infrared light back to
the camera, which captures the signal.
– The software then uses this signal to track and analyze the
motion of the dots, which corresponds to motion of the
chest or abdomen.

28. • Marker block
– The marker block is a lightweight plastic box available with
either two or six reflective dots on one side.
– The marker block is placed on the patient within view of
the tracking camera, usually between the umbilicus and
the xiphoid.
– It should be placed at the same location during imaging for
planning and simulation, and throughout the treatment
course.
– The six-dot version of the marker block is required for 3D
real-time patient position monitoring.

29. • RPM workstation
– The 4D workstation uses the patient’s s respiratory file to
sort the series images into one of ten segments of the
breathing cycle

30. – Once the images are sorted, the position of the
tumor is noted in each of the ten phases, and those
phases that exhibit minimal motion are chosen for
treatment planning

31. – new CT series is created based on these phases and is
exported to the treatment planning system
– To confirm the proper choice of phases for gating, a movie
mode is available in the 4D software for observing tumor
motion

32. • Predictive filter
– The patented Predictive Filter, a crucial part of the RPM
software, monitors and predicts the patient’s breathing pattern.
– Once the pattern has been established, the Predictive Filter
continuously verifies that this pattern is being followed.
– If the patient coughs or otherwise interrupts the predicted
breathing pattern, the Predictive Filter detects the interruption
and RPM instantly gates the beam off.

34. • CT Simulation:
– an infrared reflective plastic box serving as the
external fiducial marker is placed on the patient’s
anterior abdominal surface, typically midway
between the xyphoid process and the umbilicus.
– The exact position is chosen to maximize the AP
respiratory-induced motion.
– The marker box should be placed nearly
horizontally to permit the in room camera to
accurately detect the reflective markers.

35. • Prospective gated imaging:
– In prospectively gated imaging, the CT scanner uses
the RPM trigger signal to synchronize image
acquisition with respirations.
– The therapist determines the gating thresholds
before the scan, and the scanner acquires images
when the marker block (tumor) is within the defined
thresholds.
– The result is a single gated volumetric data set.

36. • Retrospective gated imaging:
– In retrospective image acquisition, the CT scanner acquires
images continuously, and the scan is acquired through at
least one respiratory cycle at each couch position.
– Following image acquisition, the CT image set is
synchronized with the RPM reference motion file.
– The images are sorted into the corresponding phase bins
of the respiration cycle, and are then evaluated to
determine the optimum phase for treatment.
– The selected phase bin of images is sent on to treatment
planning.

37. • Treatment:
– Following patient setup, the marker box is positioned
as in simulation, and the patient is instructed to relax
and breathe normally, or to follow audio and/or visual
prompting if it was used during simulation.
– Once a stable respiration trace has been established
and gating thresholds are verified, gated radiation
delivery is initiated.
– The position of the patient’s internal anatomy is
verified using gated radiographs or portal images and
comparing them with digitally reconstructed
radiographs (DRRs) from the gated planning CT.

38. – Although the commercial system enables the radiation
beam automatically, the therapist should be alert to
the graphic cues on the system monitor and be
prepared to intervene if the patient’s breathing is very
irregular or different from simulation.
– Portal images that show the tumor, if possible, or an
internal anatomic surrogate (often the diaphragm) are
helpful in assessing the performance of the gating
system over the course of treatment.

40. • Pre-treatment verification:
– The system allows efficient pre-treatment verification
of gating thresholds and anticipated gated delivery
before setting up the patient on the accelerator for
treatment.
– If adjustments to the gating parameters are required,
they can be made in advance of treatment delivery.
– Acuity supports both 2D and 3D position verification,
as well as fluoroscopic evaluation of gating thresholds

41. Gating using Internal markers
• Most commercially available tracking systems use
fluoroscopy to detect metal fiducials implanted
into the tumor.
• Fiducials are continually imaged during
irradiation and the treatment beam is turned on
or off depending on whether the detected image
of the fiducial is within or outside the predefined
gating window.

42. • Hokkaido University Fluoroscopic System:
– The imaging system consists of two diagnostic x-
ray tubes that can rotate on a circular track
embedded in the floor.
– The opposing x-ray detector for each tube rotates
synchronously on a track mounted in the ceiling.
– During irradiation, the two imaging systems
continuously track radio-opaque fiducials
implanted in the tumor.

43. – The image data from the two fluoroscopic views
are combined to construct trajectories of tumor
motion in three dimensions.
– Pre-treatment imaging is used to define a gating
window.
– During irradiation, the beam is turned on when
the image of the fiducial is within the window and
turned off when it is outside the window.

46. ExacTrac Gating/Novalis Gating
• It is a room-mounted system that provides IGRT
capabilities for the delivery of stereotactic
radiosurgery or stereotactic radiotherapy.
• Two real-time imaging systems are used:
– optical based
– fluoroscopy based.

47. • In the optical system, IR reflecting markers are placed on
marked spots on the patient's surface or on the
immobilization device.
• Two IR cameras mounted in the ceiling detect the position
of the IR markers.
• Based on the location of the markers, in comparison with
the stored reference information, the system automatically
steers the treatment couch to match the planned
treatment isocenter with the linac isocenter.
• An additional visual feedback of the patient's position is
provided by a video camera.

48. • Internal target localization and alignment are
provided by a stereoscopic x-ray imaging device.
• This device consists of two x-ray tubes placed in holes
in the floor and two opposing a-Si detectors mounted
in the ceiling.
• The system is configured so that the beam axes of
both tubes meet at the linac isocenter.

49. • The x-ray imaging system is fully integrated into
the IR tracking system so that the two systems can
work together in monitoring target position.
• Target alignment is based on implanted fiducials or
internal bony landmarks.
• The ExacTrac system is capable of providing
adaptive gating of the treatment beam using a six-
dimensional (6-D) robotic couch.

50. Quality Assurance
• The coordinate systems of the fluoroscopy unit and
linear accelerator must be properly aligned.
• The coordinate system alignment should be checked
regularly, particularly if substantial drifts are seen,
since there is a potential for drift with both systems.
• The magnitude of marker motion detected by the
system needs to be verified, and it must also be
assured that the automated tracking of the internal
fiducial markers is robust.

51. Breath Hold Techniques
Deep inspiration Breath hold
Self held breath hold
Active breathing control
With monitoring
Without monitoring

52. Deep Inspiration Breath Hold
A reproducible state of maximum breath-hold
(deep-inspiration breath-hold [DIBH]) is
advantageous for treating thoracic tumors,
because it significantly reduces respiratory
tumor motion and changes internal anatomy in
a way that often protects critical normal tissues.

53. DIBH
SPIROMETRY MONITORED
BREATH HOLD
FREE BREATHING
BREATH HOLD

55. • The spirometer is a differential pressure transducer that
measures air flow; a computer program integrates the
signal to obtain the volume of air breathed in and out,
which is displayed and recorded as a function of time.
• While watching the display, the therapist coaches the
patient through a modified version of the slow vital
capacity moment, consisting of a deep inhale, deep exhale,
second deep inhale, and breathhold.
• At each stage of the moment, the therapist waits for the
breathing trace to plateau before coaching the patient to
the next stage.

57. • Treatment
– During treatment, the therapists are instructed to turn
on the beam only when the target breath-hold level has
been achieved and to stop treatment if the level has
fallen below a pre-set tolerance.
– For static conformal treatments at 2 Gy/fraction on
linear accelerators operated at 500 to 600 MU/min, a
single breath-hold is usually sufficient for each field.
– Treatment sessions usually take 5 to 10 minutes longer
than a similar beam arrangement for an Free Breathing
patient.

58. Active Breathing Control
Active-breathing control (ABC) is a method to
facilitate reproducible breath hold.
Active Breathing Coordinator (ABC) is a
noninvasive, advanced technology that
helps patients hold their breath while they
receive radiation therapy

59. • The major components are
– Spirometer
– Bacterial Filter
– Nose clip
– Balloon Valve
– Patient control switch

60. • Spirometer
– It is used to measure the relative airflow and
displays a visual representation of the
respiratory curve on a laptop computer.

61. • Bacterial Filter and Nose Clip
– The patient is connected to the system via a
length of tubing and a bacterial filter, with a nose
clip to prevent leakage and increase accuracy of
the spirometry measurement.

62. • Balloon Valve:
– After a predefined volume of air (threshold
volume) has passed through the spirometer, a
small balloon valve will inflate and occlude the
tube, applying an assisted Breath Hold (BH).

63. • Control Switch
– At all times the patient is in control of the Breath
Hold, via a patient control switch. This switch
must be depressed to initiate an ABC procedure
and if released will automatically open the balloon
valve and allow the patient to breathe freely.

64. • Treatment
– The documented breath-hold state and duration should
be used as guidelines for assisted breath-hold.
– If possible, each beam angle should be delivered in a
single breath-hold.
– If a single breath-hold is too long, then one can “break
up” the single breath-hold into two or more smaller
breath-holds.
– Each beam needs to be delivered before the patient is
released from breath-hold.

65. Self Held Breath Hold Without
Monitoring
• As the name “self-held breath-hold
techniques” implies, the patient voluntarily
holds his/her breath at some point in the
breathing cycle.
• During a breath-hold, the beam is turned on,
and the dose is delivered to the tumor.

66. As part of the implementation of the self-held
breath-hold technique, a control system has
been developed for the Varian C Series
accelerators, which make use of the “Customer
Minor (CMNR)” interlock

67. • The patient is given a hand-held switch that is connected to
the CMNR interlock circuit.
• When the switch is depressed, the CMNR interlock is
cleared at the console, allowing the therapist to activate
the beam.
• When the switch is released, the CMNR interlock is active,
turning the beam off and disabling any further delivery
until the switch is depressed again.
• Since this makes use of the existing interlock circuitry, there
are no modifications to the beam-delivery system or any of
the safety features of the accelerator.
• The self-held breath-hold system is not commercially
available.

68. QA
• There is minimal QA required for the
equipment itself.
• Every time it is used, there is visual
confirmation on the treatment console that
the CMNR interlock is operational.
• Since a standard accelerator interlock is used,
it should be sufficient to test annually that
interrupting the beam does not cause a
change in output.

69. Self Held Breath Hold with Monitoring
• This technique uses a commercially available device
(Varian RPM), to monitor patient respiration and to
control dose delivery, but requires patients to
voluntarily hold their breaths during a specific part of
the respiratory cycle.
• One advantage of this technique is that the
simulation and treatments can be delivered more
efficiently than with FB respiratory-gated techniques,
because the radiation is delivered continuously
during the breath-hold

70. • Simulation:
– Programmed audio instructions such as “breathe in, breathe out,
hold your breath” are used to synchronize the CT scan with
breath-hold.
– The patient holds his/her breath at exhale for periods of 7 to 15
seconds, depending on ability.
– CT images are acquired using a helical scan mode.
– At the end of a scan segment, the CT scanner is programmed to
issue a “breathe” command followed by a 20-second break.
– The sequence may be automatically repeated until the entire
region of interest has been scanned; typically, multiple breath-
holds are required to scan the thorax.

71. Forced Shallow Breathing Technique
• Forced shallow breathing (FSB) was originally
developed for stereotactic irradiation of small
lung and liver lesions.
• The technique employs a stereotactic body
frame with an attached plate that is pressed
against the abdomen.
• The applied pressure to the abdomen reduces
diaphragmatic excursions, while still
permitting limited normal respiration.

72. • The patient is immobilized and positioned using the stereotactic
body frame (SBF), consisting of a rigid frame with an attached
“vacuum pillow” that is custom fitted to each patient.
• At simulation, laser markers are attached to the rigid frame;
they later aid in the initial positioning for treatment.
• Marks are also placed on the anterior surface of the patient, to
help realign the patient in the SBF as well as to reposition the
SBF in the treatment room.
• Tumor motion in the cranial–caudal direction is assessed using a
fluoroscopic simulator.

73. • If the motion exceeds 5 mm, a small pressure plate
is applied to the abdomen such that the two
superior, angled sides of the plate are positioned 2
to 3 cm below the triangular rib cage.
• The position of the bar that is attached to the SBF
and supports the plate is read from a scale on the
side of the frame and is reproduced at each
treatment setup.

74. • The position of the plate is controlled by a
screw mechanism and is measured on a scale
marked on the screw in order to reproduce
the amount of compression at each
treatment.
• Measurements of diaphragm motion (under
fluoroscopy) on different days can be made to
verify reproducibility.

75. Real Time Tumor Tracking Methods
ELECTRO MAGNETIC FIELD
TRACKING
Fluoroscopy based system
CYBERKNIFE
Exactrac/ novalis body system
HOKKAIDO UNIVERSITY FLUROSCOPIC system

76. Cyber Knife
• The CyberKnife is an image-
guided frameless stereotactic
radiosurgery system for treating cranial or
extracranial lesions.
• It is used for either single-fraction
radiosurgery or hypofractionated radiotherapy
(two to five fractions).

78. • The system consists of an orthogonal pair of x-
ray cameras coupled to a small X-band2 linear
accelerator mounted on a robotic arm.
• Using a higher microwave frequency in the X-
band for accelerating electrons reduces the
size and weight of the accelerator
substantially

79. • The imaging system in CyberKnife consists of two
diagnostic x-ray tubes mounted orthogonally (90
degrees offset) in the ceiling and two opposing a-Si
flat-panel detectors.
• The system is capable of acquiring and processing
multiple images for patient setup as well as for
tracking target motion during treatment.
• The target location is confirmed in relationship to
skeletal structure by comparing real-time
radiographic images with the reference treatment-
planning CT images.

80. • The robotic arm has six degrees of freedom
and is capable of maneuvering and pointing
the linac beam almost anywhere in space.
• After sensing any target motion, the robotic
arm moves the beam to the newly detected
target position for alignment.

81. QA
• For the CyberKnife system, the geometrical
relationship between the tracking system and the
beam-delivery system is monitored and verified via
an end-to-end dose-delivery test utilizing a
specifically designed composite imaging/dosimetry
phantom.
• The phantom is localized within the CyberKnife
dose-delivery system using the imaging/tracking
system and irradiated with the planned dose.

82. • The position of the delivered dose, relative to
the plan, reveals any systematic co-alignment
error of the tracking and delivery systems.
• If this alignment is compromised, the
delivered dose will be shifted from its
intended location in the phantom.
• This test takes approximately 1.5 hours and
should be performed monthly.

83. THANK YOU