1.Aim of Radiotherapy The goal of radiotherapy is to deliver a prescribed dose of radiation to the Target while sparing surrounding Healthy tissues to the largest extent possible 2.Organ Motion Intra-fraction motion during the fraction Heartbeat Swallowing Coughing Eye movement Inter-fraction motion - in between the fractions   Tumour change Weight gain/loss Positioning deviation Breathing Bowel and rectal filling Bladder filling Muscle relaxation/tension 3. Respiratory motion affects: Respiratory motion affects all tumour sites in the thorax, abdomen and Pelvis. Tumours in the Lung, Liver, Pancreas, Oesophagus, Breast, Kidneys, prostate Tumour displacement varies depending on the site and organ Location Lung tumours can move several cm in any direction during irradiation It is most prevalent and prominent in Lung cancers 4. Problems associated with respiratory motion during RT Image acquisition limitations Treatment planning limitations Radiation delivery limitations 5. Methods to Account for Respiratory Motion 1. Motion encompassing methods 2. Respiratory gating methods 3. Breath hold methods 4. Forced shallow breathing with abdominal compression 5. Real-time tumor tracking methods Summary: The management of respiratory motion in radiation oncology is an evolving field IGRT provides a solution for combating organ motion in radiotherapy Delivering higher dose to tumor and less dose to normal tissue. Limited clinical studies, needs to be studied further IGRT – the future of radiotherapy

2. The goal of
radiotherapy is to
deliver a prescribed
dose of radiation to
the Target while
sparing surrounding
Healthy tissues to
the largest extent
possible
Aim of Radiotherapy

3. How to achieve
 Correct tumour delineation
 Accurate planning
 Proper Delivery

4. Tumor Volume Delineation
International Commission on Radiation Units and Measurements

5. ICRU 62: IM and ITV
• Internal Margin (IM)
 Compensates for expected physiologic movements and variations in
size, shape and position of the CTV in relation to an Internal Reference
Point
 Commonly asymmetric
 May result from Respiration(Motion), different filling of
Rectum/Bladder, Swallowing, Heart beat
 These variations cannot be easily controlled
 Internal Target Volume (ITV) = CTV + IM
PTV = ITV + SM

6. Organ Motion
Intra-fraction motion
– during the fraction
 Heartbeat
 Swallowing
 Coughing
 Eye movement
Inter-fraction motion
- in between the fractions
 Tumour change
 Weight gain/loss
 Positioning deviation
Breathing
Bowel and rectal filling
Bladder filling
Muscle
relaxation/tension

7. • All tumor motion is complex
Tumor
Cross-sectional View
of Patient’s Chest
Tumor
Some motion is mostly
Anterior / Posterior
Some motion is mostly
Superior / Inferior
All tumor motion is
Complex
Organ motion during Respiration
Ant
Post

8. Reducing the CTV to PTV margin
GTV
CTV
ITV
PTV
• Conventional: Increases dose to normal tissues, limiting factor for dose
escalation
• Accounting motion: CTV – PTV margin reduced

9. 4D Radiotherapy 9
Tumorshrinkage
Tumor spread
Weight loss
Cardiac motion
Hormone response
Diet
Intra-observer
differences
Respiratory motion

10. Respiratory motion affects:
 Respiratory motion affects all tumour sites in the thorax,
abdomen and Pelvis. Tumours in the Lung, Liver, Pancreas,
Oesophagus, Breast, Kidneys, prostate
 Tumour displacement varies depending on the site and organ
Location
 Lung tumours can move several cm in any direction during
irradiation
 It is most prevalent and prominent in Lung cancers

11. Problems associated with respiratory
motion during RT
 Image acquisition limitations
 Treatment planning limitations
 Radiation delivery limitations

12. Image Acquisition Limitations
 Motion artifacts result if respiratory motion not accounted for
 This can result in target/normal tissue delineation errors
 Distorted images, incorrect anatomical positions, volumes or shapes
Conventional With gated imaging
Tumor

13. Treatment Planning Limitations
Larger margins have to be used when creating PTV from
CTV
Increased margins mean greater volumes of healthy tissue
treated
CTV
CTV
PTV
PTV
Motion taken into accountConventional

14. Radiation Delivery Limitations
Intrafraction motion produces averaging/blurring of dose
distribution over path of motion Interfraction motion
produces shift of dose distribution
Overall effect is blurring of the dose distribution near the
beam edges

15. • Respiratory motion management
 If target motion >5 mm – RMM technology is appropriate
 also appropriate when the procedure will increase normal tissue sparing
A clinical process guide for managing respiratory motion

16. Various Types of
Tracking Respiration
R
P
M
C
A
L
Y
P
S
O
A
N
Z
A
I
S
P
I
R
O
M
E
T
E
R
ABC

17. Tracking Respiration – VARiAN
RPM
• External Marker
 RPM (Real time Position
Management ) by Varian
 Reflective markers “learn” the
patient’s breathing pattern
Camera system
Sends signal
Reflected off markers
Respiratory waveform created
Shape represents tumor
movement

18. Tracking Respiration
 Internal Markers
– Implanted gold
seeds
– Use flouroscopy
to locate

19. Respiratory Waveform
Expiration
Inspiration
One breathing cycle

20. Methods to Account for Respiratory Motion
 1. Motion encompassing methods
 2. Respiratory gating methods
 3. Breath hold methods
 4. Forced shallow breathing with abdominal compression
 5. Real-time tumor tracking methods

21. 1. Motion encompassing methods
Technique that include entire range of tumor motion
 Slow CT
 Inhalation and exhalation breath-hold CT
 Four-dimensional 4D or respiration-correlated CT

22. Slow CT scanning
 Acquire CT images at single couch position during a respiratory
cycle (slightly longer)
-Record amplitude and phase for each slice
 Move the couch the distance of the detector width and obtain CT
images for respiratory cycle
 Fuse images based on phase of respiratory cycle
 Generate 4D images
 Disadvantage
– Loss of resolution due to motion blurring (larger errors in tumor
and normal tissue delineation)

23. Motion encompassing methods: 4DCT

24. Inhalation and exhalation breath - hold CT
• Acquire both inhalation and exhalation gated or breath-hold CT
scans
• Relies on the patient’s ability to hold his or her breath reproducibly.
• Require image fusion and extra contouring.
• For lung tumors, Maximum Intensity Projection (MIP) tool can be
used to obtain the tumor-motion encompassing volume,
• Advantage over slow scanning method
– Blurring caused by the motion present during Free Breathing is
significantly reduced

25. 5 different phases
MIP =

26. 4D-CT / Respiration-correlated CT
• Determines the mean tumor position, tumor range of motion for
treatment planning
• Can be used to reconstruct inhalation, exhalation, and slow CT
Scans
• The MIP tool can be used for obtaining the tumor-motion-
encompassing target volume
• Another motion-encompassing method is to derive a single set out
of the 4D CT scan where the tumor is close to its time-averaged
position. In that case, the expected dose blurring effect of respiration
can be accounted for in the CTV-PTV margin

27. 2. Respiratory Gating Methods
Displacement gating
(Amplitude) Phase gating

28. Respiratory gating methods
 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”
 Displacement Gating (Amplitude)
– relative position between two extremes of breathing motion,
namely, inhalation and exhalation.
– the radiation beam is activated whenever the respiration signal is
within a pre-set window of relative positions.
 Phase Gating
– respiration signal that must satisfy periodicity criteria
– the radiation beam is activated when the phase of the respiration
signal is within a pre-set phase window.

29. Breathe
Out
Breathe
In
Amplitude Gating Example
Beam On!
Beam Hold! Beam Hold!
Beam On! Beam On!
Upper threshold
Lower threshold
Full Expiration
Full Inspiration

30. Breathe
Out
Breathe
In
Phase Gating Example
Beam On!
Beam Hold! Beam Hold!
Beam On! Beam On!
On Off On Off On Off

31. Respiratory gating methods
4D CT Data Acquisition
RetrospectiveProspective

32. Breathing Cycle
Full Inspiration
0%
50%
Full expiration
25%75%

33. 4D CT Data Acquisition - Prospective
CT Scan
Axial scan trigger,
1st couch position
Axial scan trigger,
2nd couch position
Exhalation
Inhalation
Scan Scan Scan
Axial scan trigger,
3rd couch position
Images are acquired only during a portion of the respiration cycle

34. 4D CT Data Acquisition -Retrospective
Images are acquired during the entire respiration cycle and sorted later
X-ray on
Exhalation
Inhalation
1st couch
position
2nd couch
position
3rd couch
position
“Image acquired”
signal to RPM
system
(Ford 2003, Vedam 2003)

35. • Deep - Inspiration Breath Hold (DIBH)
• Active-breathing control (ABC)
• Self-held breath hold without respiratory monitoring
3. Breath-hold methods

36. Deep-Inspiration Breath Hold
 Patient is trained to reproduce a deep inhalation breath hold during
simulation and treatment
 Volume of air inhaled by patient monitored by spirometer
 Highly reproducible results possible

37. Active-Breathing Control
 Technique for suspending breathing at any predetermined position
(usually moderate or deep inhalation)
 Monitoring apparatus consists of Spirometer connected to balloon
valve
 After a pre-defined volume of air (threshold volume) has passed
through the spirometer
 spirometer, a small balloon valve, inflates and occludes the tube,
applying an assisted breath hold for a predefined period of time

38. Active Breathing Co-ordinator
Spirometer
Breath Hold Pattern

39. • Originally developed for stereotactic irradiation of small lung and
liver lesions
• 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.
4. Forced shallow breathing with abdominal compression

40. 5. Real-time tracking methods
Fluoroscopy based tracking
Systems
Fiducial Markers Implanted
Systems (Gold Seeds)
Electromagnetic Field
Tracking Systems

41. Real-time tumor-tracking methods - Fluoroscopy
based tracking Systems
• To detect respiratory motion using radiation beam follow the
tumours changing position
• Difficulty of detecting the tumour itself, Surrogate markers are used
in most cases

42. Real-time tumor-tracking methods - Fiducial
Markers Implanted Systems
 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
+
-
-
+

43. Real-time tumor-tracking methods -
Electromagnetic Field Tracking Systems
• Calypso® Extracranial Tracking
Step 1 Step 2
Electromagnetic Locate and Track Continuously
Electromagnetic array sends pulses
of electromagnetic energy to beacons
Beacons return electromagnetic
signal to the array

45. Quality Assurance (During Commissioning)
 RPM mini-phantom in conjunction with the marker block is used to
test the RPM system’s tracking ability in both the CT room and the
treatment room prior to any respiratory gating procedure
Breathing Mini-Phantom
Six dot marker block
Breathing Pattern

46. CIRS – Dynamic Phantom
Point Dose Measurement

47. 4D Radiotherapy
4D CT Imaging
4D Treatment Planning
4D Treatment Delivery
Acquisition of a sequence of CT
image sets over consecutive
phases of a breathing cycle
The explicit inclusion of
the temporal changes in
anatomy during the
imaging, planning and
delivery of radiotherapy
Designing treatment plans on CT
image sets obtained for each
phase of the breathing cycle
Continuous delivery of the 4D
treatment plans throughout the
breathing cycle
The 4D radiotherapy process

48. Recommended clinical process for respiratory motion
during the radiotherapy
• Recommended 5 mm motion-limit
criterion value may be reduced for
special procedures, such as SBRT
• May be reduced in the future as other
errors in radiotherapy, such as target
delineation and setup error, are
reduced, with respiratory motion
thereby becoming the accuracy limiting
factor.
• Exhale position most reproducible
• Inhale position most beneficial for
sparing lung tissue
AAPM Task Group 76

49. Conclusion
 The management of respiratory motion in radiation oncology is an
evolving field
 IGRT provides a solution for combating organ motion in
radiotherapy
 Delivering higher dose to tumor and less dose to normal tissue.
 Limited clinical studies, needs to be studied further
 IGRT – the future of radiotherapy