Evaluation and imaging for lung SBRT

1. Pre SBRT workup, Imaging
and Contouring
Dr. Naveen Mummudi,
Dr. J P Agarwal
IAEA-RTC meet – May 2017

2. MDT
discussion
Pre-SBRT
work up
Simulation
Tumour
and OAR
contouring
Treatment
planning
and plan
evaluation
Treatment
delivery
Follow up
for toxicity

3. MDT / clinical forum

4. MDT / clinical forum
• Patients with stage I lung cancer are candidates for curative treatment
and can be divided into three major groups:
• Low-risk surgical patients - usually treated by lobectomy;
• High-risk surgical patients - treated with sublobar (segmental or wedge)
resection or SBRT; and
• Medically inoperable patients - treated with EBRT or SBRT

5. MDT / clinical forum
• Inoperable
• Majority
• Operable
• Patient preference
• Clinical trial setting
 Medical inoperability
 Defined as “the presence of co-morbid illnesses that
renders the patient at higher than acceptable risk of
surgical morbidity and mortality.”
 Competing risk scenario - where risk of death from
medical illnesses is balanced by the risk of death
from lung cancer.
Colice, Shafazand et al. 2007

6. Pre SBRT work up
• Metastatic workup
• Diagnosis – Pathological / Radiological
• Imaging – CT / PET CT / MR Brain
• Medical condition assessment
• Pulmonary reserve
• Cardiology status
• Other comorbid conditions
• Tumour characteristics
• Location – Peripheral / central / ultra central

7. Oncological assessment
• Imaging
• PET CT whole body / CECT Thorax
• MRI brain
• EUS-TBNA: ?role
• 2 prospective trials evaluating PET+/- EUS-TBNA
• Confirmation of diagnosis
• Pathological – CT guided/trans-bronchial
• Radiological – imaging characteristics

8. Oncological assessment

9. Oncological assessment
…developed a model that demonstrates that treating an SPN
without pathology is justified when the likelihood of
malignancy is 85%
Louie 2014

10. Medical assessment
• Pulmonary function
• GOLD – COPD
• ACCP recommendations
• Cardiac evaluation
• Charlson comorbidity index

11. Lung volumes - Spirometry

12. Spirometry
• Patients with advanced lung disease have decreased survival defined
by the severity of their disease.
• In patients with COPD, FEV 1 < 35%
predicts approximately 10% mortality
per year (50% 5-year survival).

13. Medical evaluation
• DLCO
• Cardiopulmonary Exercise Testing
• 6 minute walk test / Incremental shuttle walk test
• Split function test
• Ventilation/perfusion scinitigraphy
• Cardiac evaluation
• 2D ECHO

14. Algorithm for cardiac assessment
ERS/ESTS task force 2009

15. ERS/ESTS task force 2009

16. Charlson comorbidity index

17. Tumour characteristics
• Size
• Location of tumour
• Severe toxicity rates of 17% and
46% at 3 years for peripheral
and central lesions
Timmerman, 2003, Chest
McGarry, 2005, IJROBP
Glide-Hurst, 2014, J thorac dis

18. Tumour characteristics
Roesch, RO, 2016

19. Tumour characteristics

20. Tumour characteristics

22. Immobilization
• Accurately re-position patient
• Reduce/Minimize patient voluntary and involuntary motion
• Reduce/Minimize organ/target motion
• Abdominal compression
• Comfortable for long treatment
• Compatible with IGRT
• Not interfere with treatment beam
Body Pro-Lok TM frame Body Fix Abdominal Compression
Thermoplastic Long mask

23. Commercial devices
Abdominal compression belt
• Plastic board with two long slits on
the sides
• Blood pressure cuff, Velcro® mounted
under the board
• Adjustable, Velcro® covered belt
• Sewn-on ruler for consistent setup
Pneumatic Compression Belt
• Air inflation bulb
• Pressure gauge
• Non-Rigid
• Marking of the patient skin &
immobilization device
• Recording of the pressure

24. Immobilization/Simulation
• Careful positioning in the immobilization device, supporting the hands and
shoulders
• premedication with analgesia (e.g., to prevent shoulder pain)
• anxiolytic may be needed
• Scanning in TX Position
• CT, MR, PET-CT
• CT scan with ≤ 3 mm slice thickness
• Motion Management
• Abdominal Compression Plate
• Pressure Belt
• Body Immobilization

25. Respiratory motion
Causes artifacts during imaging acquisitions
Radiation delivery limitations
Limiting treatment planning
Treatment planning difficulty

26. When to manage respiratory motion?
AAPM Task Group 76: respiratory management techniques should be
considered if either of the following conditions occur –
• > 5 mm range of motion is observed in any direction
• Significant normal tissue sparing can be gained using respiration
management
26
The Management of Respiratory Motion in Radiation
Oncology; Report of AAPM Task Group 76 July 2006 by
American Association of Physicists in Medicine

27. Recommended Clinical Process for patients with
whom respiratory motion during RT is a concern
27

28. Methods to Account for Motion
• Motion-encompassing methods
• Respiratory gating methods
• Breath-hold methods
• Forced shallow breathing with abdominal compression
• Real-time tumor-tracking methods

29. CT Simulation
• Suppressed respiratory motion techniques
• Compression Paddle, Pressure Belt
• Free Breathing (FB) & Slow CT-Scanners
• Free Breathing & Fast CT-Scanners
• Breath-Hold (BH) CT-Scans
• Respiratory Correlated CT (4D-CT)

30. Motion Management Strategies
Method Technique
Incorporate all movements 4DCT or Slow CT
Freeze movement Breath hold
Intercept movement Gated Radiotherapy
Track or Chase the tumor Implanted markers and specialized
treatment delivery
30

31. Slow CT scanning
• Scanner operates at a particular couch position for longer than the respiratory cycle so that the
image of the tumor would show the full extent of respiratory motion.
• Yields a tumor-encompassing volume
• Limitation: respiratory motion will change between imaging and treatment;
• additional margins are required to account for these variations.
• One CT scan is obtained
• overall treatment process does not increase in complexity over that of a free-breathing CT scan
• Loss of resolution due to motion blurring, which potentially leads to larger observer errors in
tumor and OAR delineation.
• only recommended for lung tumors that are not involved with either the mediastinum or the chest wall.
• Increased dose of radiation from slow CT scanning compared with conventional CT scanning.
31

32. Inhale and exhale breath-hold CT
• Advantage: blurring caused by motion present during free breathing is
significantly reduced during breath-hold.
• But taking both inhale and exhale CT scans will increase scanning time and relies
on the patient’s ability to hold breath reproducibly.
• Two scans will be obtained; thus, image fusion and extra contouring are required.
• Dose calculation should be performed on the CT data set that is most appropriate
for the particular patient, e.g., exhale CT for patients generally spending more
time at exhale than inhale.
• The exhale scan will tend to underestimate the lung volumes and, hence,
overestimate the percentage of lung volume receiving a specific dose.
32

33. Respiratory-triggered CT scan
• Slice acquisition is triggered by a respiratory signal, such that slices are
only acquired in a pre-set phase of respiratory cycle.
• The result is a 3D image in which all the slices are acquired in the same
phase of breathing.
• A scan is acquired with the imaging beam on during the entire breathing
cycle and this is performed at all couch positions. Subsequently CT slices
are reconstructed at consecutive points of the breathing cycle.
33
4-D CT

34. Patient Training
• The ability to achieve reproducible breathing or breath-hold patterns is a
requirement for allowing the patient to proceed to simulation and treatment.
• Prior to the start of simulation, the patient should be made familiar with the
equipment and its purpose.
• A physicist or trained designee should perform the coaching and evaluation, at
least in the initial clinical implementation.
34

35. Different ways to acquire respiratory trace
• VARIAN : Real-Time Position Management System (RPM)
35
• ELEKTA : Active Breath Coordinator (ABC)
• SIEMENS : ANZAI
belt

36. RPM system
• Consists of a plastic marker block with six metallic
reflectors (3 cm apart for calibrating amplitude) which
is placed on patient’s abdomen between the xiphoid
and umbilicus.
• A infrared camera records the abdominal surface
motion.
• RPM software tracks the marker trajectory in real time
and calculates the respiratory phase on the basis of
observed amplitude.
• CT scanner and RPM system communicate during data
acquisition to indicate when beam is turned on or off.
36

37. Marker Block
RPM system can detect the motion of the marker block in vertical,
lateral and longitudinal dimensions.
37

38. 4DCT
• 4DCT scans can be performed both in sequential and in helical
scanning modes —
• In sequential mode, beam is kept on during a breathing cycle at each
couch position
• In helical mode, beam is kept on during the entire scan, while the
pitch is very low.
• In both cases, this in effect provides a densely oversampled scan.
38

39. 39

40. 40

41. 4DCT
• Typically, a total of 1000 –1500 images are acquired during a 4D-CT study.
Approximately 20 –25 images are reconstructed per slice, evenly distributed
throughout the respiratory period.
• Each reconstructed axial image represents the anatomy at a different instant
during the patient’s respiratory cycle.
• On the basis of the temporal correlation between the surface motion and image
data acquisition, a specific respiratory phase is assigned to each image.
• An axial image at a given couch position is binned on the basis of its respiratory
phase. 41

42. 42

43. Phase vs. Amplitude sorting
• Majority of the published 4D-C T techniques have used a time-based phase
sorting method for retrospectively gating image data.
• This is subject to misalignment due to varying inhale and exhale slopes,
periods, and amplitudes in the respiration trace.
• Rietzel et al. proposed an amplitude sorting method -- a constant amplitude on
the respiratory curve is chosen to designate the phase position.
• Although this method eliminates the possibility of misalignment, it increases the
potential for missing phase sets. If a certain amplitude is not reached in all cycles
of the recorded respiration trace, then that phase set cannot be created without
a gap in the volume.
43
Rietzel E, Pan TS, C hen GTY. 4D CT: Image formation
and clinical protocol. Med Phys. 2005;32(4):874-889

44. 4DCT
• 4D CT scan not only reduces motion artifacts, but also gives the
tumor/organ motion information.
• There may still be blurring artifacts in each slice caused by the
residual motion within the slice acquisition time, but shorter the slice
acquisition time, smaller the artifacts.
• 4D CT scan is NOT really 4D
Temporal information is mapped onto one breathing cycle.
Irregular respiration will cause artifacts in 4D CT images.
Breath coaching is always needed.
44

45. 4DCT
• 4DCT scanning procedure of the entire thorax takes about 90 s.
• Radiation exposure from 4DCT acquisition is approximately six times
the dose of a single conventional helical CT scan (range 0.02 - 0.09 Gy)
• Generation of individualized and usually smaller target volumes
derived from 4DCT scans in comparison to standard PTVs justifies this
additional radiation exposure
45

46. 46

47. H. Hof et al. / Radiotherapy and Oncology 93 (2009) 419–423
Conventional vs. 4D based target definition
PTV4D is not only smaller in most parts but also extends to areas
not covered by PTVconv 47

48. Using 4DCT data to draw Target
• A composite target volume is the union of individual target volumes at different
instants in time.
• The standard approach would include contouring GTVs on all binned data sets
(usually 10).
• Alternatively, contour GTV on the volumes at end-inhale and end-exhale and fuse
them. The composite contours from these extreme data sets are then overlaid
onto each breathing phase and visually verify whether the composite volume
includes all instances of GTVs at other respiratory phases.
• Strategy of contouring extreme tumor positions will fail whenever the size of the
tumor is smaller than its motion amplitude.
48

49. 4-D CT: Generating Target Volumes
49
Different Target Volumes derived from GTV
Target definition according to the
recommendations in ICRU Report 62
ICRU Report 62 recommends use of an internal target volume (ITV)
to account for variations in size, shape, and position of the CTV
International Commission on Radiation Units and Measurements.
ICRU report 62: Prescribing, recording, and reporting photon beam
therapy (Supplement to ICRU report 50). Bethesda, MD: ICRU 1999

50. Maximal Intensity Projection (MIP)
• When a significant density difference exists between the tumor and
surrounding tissue, it may be exploited to decrease the contouring
workload.
• A Maximal Intensity Projection (MIP) is automatically generated from
the entire 4D-CT by assigning each voxel the greatest Hounsfield unit
value from all corresponding voxels over the multiple respiratory phase
image data.
• For a lung tumor, this results in identification and localization of high-
density tumor voxels compared with lower density lung tissue voxels.
50

51. Failure of MIP technique
51
Rietzel et al. Maximum-intensity volumes for fast contouring of lung tumors
Including respiratory motion in 4dct planning; Int. J. Radiation Oncology Biol.
Phys., Vol. 71, No. 4, pp. 1245–1252, 2008
While contouring using MIP technique one needs to be
careful for nodal volumes within the hilum or
mediastinum, tumors located near the diaphragm, and
tumors surrounded by atelectasis

52. Window effect
For Parenchymal disease: W=1600 L= -600
For Mediastinal disease: W=400 L=20
These correlate best with pathological tumor sizes

53. Tumor and OAR Delineation
• If 4DCT unavailable or unsuitable free-breathing helical images can be
used for treatment planning
• In selected patients intravenous CT contrast may help to identify the GTV
• When PET imaging is available (either in the diagnostic or preferably, the
treatment position) it is fused to the exhale CT and may be used to inform
the contouring process, especially in instances where there is a
neighbouring region of atelectasis
Planning Target Volume (PTV)
• For the remaining uncertainty a setup margin is required
• A uniform expansion of 5 mm is typically applied to the 4DCT based ITV to generate
the PTV
• In certain circumstances, for example OAR proximity, this may be individualized

54. OAR delineation

55. Atlas of lung, esophagus, and spinal cord
Int J Radiat Oncol Biol Phys. 2011 81(5):1442-57
Recommendation based on Timmerman et al for RTOG 0236 and RTOG 0618,
Bezjak et al for RTOG 0813

56. Atlases for Organs at Risk (OARs) in
Thoracic Radiation Therapy
• Feng-Ming (Spring) Kong MD PhD
• Leslie Quint MD
• Mitchell Machtay MD
• Jeffrey Bradley MD

57. Lungs
• Both lungs should be contoured using pulmonary windows.
• The right and left lungs can be contoured separately
• Total lung for dosimetry
• All inflated and collapsed, fibrotic and emphysematic lungs should be
contoured.
• Hilar region and trachea/main bronchus should not be included in this
structure

58. Esophagus
• Begin at the level just below the cricoid to its entrance to the stomach
at GE junction.
• Contoured using mediastinal window/level on CT to correspond to the
mucosal, submucosa, and all muscular layers out to the fatty adventitia.
• Barium swallow for better delineation.

59. Spinal cord
• Bony limits of the spinal canal.
• Start at the level just below cricoid to the bottom of L2
• base of skull for apex tumors and continuing
• Neuroformanines should not be included.

60. Begin below the level of post-cricoid region

61. Include the entire spinal canal

62. Barium swallow allows better delineation of esophagus

63. Barium swallow

65. Inferiorly till the GE junction

66. Pericardium
• Includes pericardial fatty tissue, part of great vessels, normal recesses,
pericardial effusion (if present) and heart chambers.
• Starts at one slice above the top of aortic arch, ends at the last slice of
heart apex at diaphragm.
• Pericardium includes the heart.

67. PericardiumSVC
Begin one slice above the top of aortic arch

69. PericardiumArch of aorta

70. PericardiumAscending aorta
Pulmonary A

71. Pulmonary V

72. Descending aorta

76. Great vessels
• Contoured separately from the heart, using mediastinal windowing to
correspond to the vascular wall and all muscular layers out to the fatty
adventitia.
• Start at least 3 cm above the superior extent of the PTV and up to at
least 3 cm below the inferior extent of the PTV.
• For right sided tumors, SVC will be contoured, and
• For left sided tumors, the aorta will be contoured.
• The ipsilateral PA will be delineated for tumor of either side.

77. Pulmonary AAscending aorta
Descending Aorta
SVC

78. IVC

79. Heart
• Contoured along with the pericardial sac.
• Superiorly begin at the level of the inferior aspect of the pulmonary
artery passing the midline and extend inferiorly to the apex of the heart.

80. Start at the level of the inferior aspect of
the pulmonary artery passing the midline

83. Heart and pericardium are to be overlapped

84. Proximal bronchial tree
• Includes the
• distal 2 cm of the trachea,
• the carina,
• the right and left mainstem bronchi,
• the right and left upper lobe bronchi,
• the intermedius bronchus,
• the right middle lobe bronchus,
• the lingular bronchus, and
• the right and left lower lobe bronchi.

89. Proximal Bronchus Tree Ends
at the level of lobar bronchus bifurcating
into segmental bronchus

90. Brachial plexus
• Required for patients with tumors
of upper lobes.
• Only the ipsilateral brachial plexus
is contoured.
• Includes the spinal nerves exiting
the neuroforamine from top of C5
to top of T2.
• Should extend at least 3 cm above
the PTV.

91. Identify anterior and middle scalene muscles from
C5 to insertion onto the first rib.
Start at the neural foramina from
C5 to T1

92. Extend from the lateral aspect of the spinal canal to the
small space between the anterior and middle scalene
muscles.

93. Contour the trunks of the brachial plexus between the
anterior and middle scalene muscles.

95. Where no neural foramen is present, contour only
the space between the anterior and middle scalene muscles

96. Contour the trunks of the brachial plexus between the
anterior and middle scalene muscles.

97. Eventually the middle scalene will end in the
region of the subclavian neurovascular bundle.

98. Vein, artery, and nerve (VAN, anterior to posterior) will go
over the 1st rib and under the clavicle
Contour the brachial plexus as the posterior aspect of
the neurovascular bundle.

99. IV contrast greatly facilitates contouring
The first and second ribs serve as the medial limit

102. Chest wall
• Autosegmented from the ipsilateral lung with a 2-cm expansion in the
lateral, anterior, and posterior directions.
• Anteriorly and medially, it ends at the edge of the sternum.
• Posteriorly and medially, it stops at the edge of the vertebral body with inclusion
of the spinal nerve root exit site.
• Includes intercostal muscles, nerves exclude vertebrate bodies, sternum
and skin.
This recommendation was based on
1. Kong et al, Int J Radiat Oncol Biol Phys. 2010 Oct 7.
2. “CW2cm consistently enabled better prediction of CW toxicity than CW3cm” in Mutter
et al, Int J Radiat Oncol Biol Phys. 2011 Aug 23.