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Pitch = Table travel per rotation/Beam width Helical Approach – Philips approach - Combine image data at same phase from several respiratory cycles Cine approach – GE - Acquire limited thickness image data at specific phases in respiratory cycle
The registration is made based on the nearest neighbor criterion, where at each slice location the image is selected so that its phase is closest to each phase bin.
Even if a 4DCT scan is of a very high quality with few artifacts, the motion of a structure exhibited in a 4DCT scan is still only representative of the motion taking place in the few breathing cycles during which the patient passes through the CT-scanner. It is a movie ‘snapshot’ of the motion.
Mean IP represents time-weighted location of the tumor
In contrast to prior RTOG lung studies of contouring the major trunks of the brachial plexus with inclusion of subclavian and axillary vessels, this trial requests contouring the nerves according to the CT anatomy on every other CT slice.
Evaluation and imaging for lung SBRT
Pre SBRT workup, Imaging
Dr. Naveen Mummudi,
Dr. J P Agarwal
IAEA-RTC meet – May 2017
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
MDT / clinical forum
• Patient preference
• Clinical trial setting
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
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
• 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).
• Cardiopulmonary Exercise Testing
• 6 minute walk test / Incremental shuttle walk test
• Split function test
• Ventilation/perfusion scinitigraphy
• Cardiac evaluation
• 2D ECHO
Algorithm for cardiac assessment
ERS/ESTS task force 2009
• 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
• 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
Abdominal compression belt
• Plastic board with two long slits on
• 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
• Marking of the patient skin &
• Recording of the pressure
• Careful positioning in the immobilization device, supporting the hands and
• 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
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
The Management of Respiratory Motion in Radiation
Oncology; Report of AAPM Task Group 76 July 2006 by
American Association of Physicists in Medicine
Recommended Clinical Process for patients with
whom respiratory motion during RT is a concern
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
Motion Management Strategies
Incorporate all movements 4DCT or Slow CT
Freeze movement Breath hold
Intercept movement Gated Radiotherapy
Track or Chase the tumor Implanted markers and specialized
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.
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.
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.
• 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.
Different ways to acquire respiratory trace
• VARIAN : Real-Time Position Management System (RPM)
• ELEKTA : Active Breath Coordinator (ABC)
• SIEMENS : ANZAI
• 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
• A infrared camera records the abdominal surface
• RPM software tracks the marker trajectory in real time
and calculates the respiratory phase on the basis of
• CT scanner and RPM system communicate during data
acquisition to indicate when beam is turned on or off.
RPM system can detect the motion of the marker block in vertical,
lateral and longitudinal dimensions.
• 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
• 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.
• 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 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.
Rietzel E, Pan TS, C hen GTY. 4D CT: Image formation
and clinical protocol. Med Phys. 2005;32(4):874-889
• 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.
• 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
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
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
• 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.
4-D CT: Generating Target Volumes
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
Maximal Intensity Projection (MIP)
• When a significant density difference exists between the tumor and
surrounding tissue, it may be exploited to decrease the contouring
• 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
• For a lung tumor, this results in identification and localization of high-
density tumor voxels compared with lower density lung tissue voxels.
Failure of MIP technique
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
For Parenchymal disease: W=1600 L= -600
For Mediastinal disease: W=400 L=20
These correlate best with pathological tumor sizes
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
• In certain circumstances, for example OAR proximity, this may be individualized
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
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
• 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
• Hilar region and trachea/main bronchus should not be included in this
• 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.
• 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.
• 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.
Begin one slice above the top of aortic arch
• Contoured separately from the heart, using mediastinal windowing to
correspond to the vascular wall and all muscular layers out to the fatty
• 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.
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.
Proximal Bronchus Tree Ends
at the level of lobar bronchus bifurcating
into segmental bronchus
• Required for patients with tumors
of upper lobes.
• Only the ipsilateral brachial plexus
• Includes the spinal nerves exiting
the neuroforamine from top of C5
to top of T2.
• Should extend at least 3 cm above
Identify anterior and middle scalene muscles from
C5 to insertion onto the first rib.
Start at the neural foramina from
C5 to T1
Extend from the lateral aspect of the spinal canal to the
small space between the anterior and middle scalene
Contour the trunks of the brachial plexus between the
anterior and middle scalene muscles.
Where no neural foramen is present, contour only
the space between the anterior and middle scalene muscles
Contour the trunks of the brachial plexus between the
anterior and middle scalene muscles.
Eventually the middle scalene will end in the
region of the subclavian neurovascular bundle.
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.
IV contrast greatly facilitates contouring
The first and second ribs serve as the medial limit
• 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
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.