SBRT in lung cancer

IGRT IN LUNG CANCER
(PART-I)
Bharti Devnani
Moderator- Dr Shaleen Kumar

ROADMAP
1. Indications of RT in lung cancers
2. Role of IGRT in lung cancer
3. IGRT (motion management) strategies
 Free breathing
 Breath hold methods
4. Technological aspects
 Acquiring CT
 Appreciation of tumor motion
5. Segmentation
 Tumor
 Normal tissues

6. Objectives
 Hypofractionation schedules
 BED calculations
 Constrains
7. Outcomes and patterns of failure
8. Toxicities and challenges
9. Comparison with other competing modalities
10. Follow-up
11. Conclusions and future directions

INDICATIONS OF RT IN LUNG
CANCERS

INDICATIONS OF RT IN NSCLC
Early stage (I) tumors
 SBRT (T1, T2a inoperable)
 PORT for margin + / upstage to N2
Locally advanced stage (II/III)
Inoperable disease
 Concurrent CTRT
 Sequential ChemoRT/ RT alone in frail patients
 Accelarated RT

Locally advanced stage (II/III)
Operable disease
 NACT+RT
 NACT-Sx-Post op RT
 PORT
Advanced /Metastatic disease
 For palliation pain/ bleeding/obstruction

Lobectomy
 FEV1 >75% of predicted volume or >1 liter
 DLCO >60% of predicted capacity.
 For ambiguous cases that are near these
thresholds, a Xenon study is obtained to predict
postoperative pulmonary function.
 Predicted postop.FEV1 <35% there is an increased
risk of death.
 Predicted postop. DLCO <40% is associated with
an increased surgical complication rate.

INDICATIONS FOR SBRT
Indiana University Criteria (Pulmonary)
- Baseline FEV1 < 40%
- Likely post-op FEV1 < 30% predicted
- DLCO < 40% predicted
- Hypoxemia (pO2 < 70mm Hg)
- Hypercapnea (pCO2 > 50 mm Hg)
- Exercise oxygen consumption < 50% predicted
Other Potential Factors
- Cardiac (IHD, LVF, PAH)
- Anesthesia
- Post-operative recovery
Timmerman, Nov 2003 Chest 124(5):1946-55

WHY IGRT
“Normal” Treatment plan

 Cranio-caudal movement 0-12 mm +3 mm
 Medio-lateral 2-3 mm+2 mm
 Dorso-ventral 2-3 mm+2 mm
 50% of tumors move > 5 mm and >11% move >1
cm (up to 4 cm), particularly those close to
diaphagram
Ekberg L et al Radiother Oncol 1998 Jul;48(1):71-7
Bissonette JP.IJROBP 2009;75:688-695

MOTION MANAGEMENT SOLUTIONS
Breath hold methods
 Organ motion dampening – Abdominal
compression
 Automated breath coordinator (ABC)
Free breathing methods
 ITV based treatment
 Respiratory gating
Real time position managment(RPM)
 Tumor tracking (Exac trac/ Cyberknife/VERO)

ABDOMINAL COMPRESSION
Abdominal compression reduces diaphragmatic excursion with
inspiration.
Dampens tumor motion throughout the respiratory cycle.

PNEUMATIC COMPRESSION BELT
 Air inflation bulb
 Pressure gauge
 Non-Rigid
 Recording of the pressure
 Easy to use!
 Less comfortable for patients
 more compression compared to the paddle

Advantages
 Abdominal compression reduces diaphragmatic excursion
with inspiration.
 Dampens tumor motion throughout the respiratory cycle.
 Lower lobe tumors near diaphragm
Disadvantage
 Patient discomfort
 Poor pulmonary function
 Med. comorbidities precluding the use of abdominal
compression
 Placement of a percutaneous gastrostomy tube
 large abdominal aortic aneurysm
 significant abdominal pathology.

AUTOMATED BREATH COORDINATOR (ABC)
Components
Nose clip
Mouth piece
Spirometer to
measure respiratory
trace
Balloon valve

 A baseline PFT is done to know the patient’s
inspiratory capacity
 Coaching of breath hold to achieve a steady
breathing pattern
 The mouth piece and the nasal clips are placed and
patient is asked to breath normally.
 Once the patient achieves normal respiration, three
measurements of inspiratory capacity are made

 The threshold is then fixed at 75 % of the average
inspiratory capacity and value is documented.
 When the operator activates the system, the
balloon valve closes.
 The patient is then instructed to reach the specified
lung volume. The breath hold starts.

Advantage
 V20 and the mean lung dose decreases with an
increase in lung volume
 Increases the distance between the tumor and
critical structures
Disadvantage
 Increase t/t time
 Poor pulmonary reserve

ITV BASED TREATMENT
Generates a composite target
volume for lung tumors, taking into
account the different shape, size
and position of the tumor in each
phase of respiration

THE PRINCIPLE OF GATING
Beam delivery is coupled with the phase of
respiration
Treatment delivery is done in the phase of respiration
where the tumor motion & resulting tumor treatment
volume is minimum, by coupling the beam delivery
with the phase of respiration

RPM
Real time Position Management (RPM)
1. CCD camera with attached illuminator
2.Camera interfaced with PC
3. Infrared reflective markers that are rigidly
embedded in a lightweight plastic block

EXT. FIDUCIAL SYSTEM (IR REFLECTORS)

Plastic block is placed on the chest of the patient.
 The system tracks the upper marker as the
indicator of the breathing motion .The user selects
the portion of the breathing cycle for the gate.

THE PRINCIPLE OF “TRACKING”

SYNCHRONY
Synchrony camera
Synchrony tracking markers
Fiber optic sensing technology
Tracks patient’s respiratory motion

IMAGE ACQUISITION
Motion artifacts in free breathing 3 D scan
 Severe geometrical distortion
 Center of the imaged target can be displaced by as
much as the amplitude of the motion

SOLUTIONS
 Breath-hold CT scan
Voluntary breath hold
Active breathing control
Combine inhale and exhale GTVs to get ITV
 Slow CT san
4 seconds per slice in axial mode
 Gated CT scan
Images at only 1 phase, acquisition times 4-5x
longer
 4D CT scan
3D scans at multiple phases

SLOW CT
Patient breathes normally
Rotation time >> breathing period
CT images are an average over all
breathing phases
Borders of organs tumor volumes can
become diffuse
Observe target movement under
fluoroscopy

3 D CT SCAN
3
2
14
5
6
7
8 9
10

A large amount of
data is generated!
(>800 slices)

X-ray on
Exhalation
Inhalation
1st couch
position
2nd couch
position
3rd couch
position
“Image acquired”
signal to RPM
system
(Ford 2003, Vedam 2003)
Retrospective 4D CT Image
Acquisition

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
Prospective CT Image Acquisition

SEGMENTATION OF TUMOR
GTV
 Contrast if tumor located near great vessels or
close bronchial tree
 CT pulmonary windows for target segmentation
 Soft tissue windows with contrast may be used to
avoid inclusion of adjacent vessels, atelectasis, or
mediastinal or chest wall structures within the GTV.

Role of PET-CT
 To differentiate tumor from atelectasis
 To differentiate chest wall
musculature from tumor
 Accurate target Delineation
and Volume reduction

Generation of iGTV
 Combining the entire GTV from all resp phases
 Combining the GTV contours from two extreme
respiratory phases (0% and 50%)
 Defining the GTV contour as the maximum intensity
projection (MIP) at each voxel during an entire
respiratory cycle
 Using MIP technique, modifying the contours as
needed with visual verification in each individual
respiratory phase

CTV- controversy
 No CTV in RTOG trials
 CTV=GTV
 Some centres CTV=5-8 mm expansion of GTV
PTV
 Appropriate PTV margin(See set up, motion =
5mm)
 1 cm craniocaudally and 5 mm axially in RTOG
trials

Size of movement dependent on:
-tumour location in the lung
-fixation to adjacent structures
-lung capacity and oxygenation
-patient fixation and anxiety
Average movement in normal breathing:
-Upper lobe 0 -0.5cm
-Lower lobe 1.5 -4.0cm
-Middle lobe 0.5 -2.5cm
-Hilum1.0 -1.5cm

PTV Plus 2 cm
 As part of the QA requirements for “intermediate
dose spillage” a maximum dose to any point 2 cm
away in any direction is to be determined.
 An artificial structure 2 cm larger in all directions
from the PTV is contoured with automatic
contouring .

ORGANS AT RISK
Lung
Spinal cord
Esophagus
Trachea
bronchus
Brachial plexus

Serial –parallel
Heart
Chest wall??

SEGMENTATION OF OARS
Average intensity projection when using 4D CT data
Spinal cord
Based on the bony limits of the spinal canal. It
should be contoured starting at least 10 cm above
the superior extent of the PTV & continuing on
every CT slice to at least 10 below the inferior
extent of the PTV.
Esophagus
Mediastinal window on CT to correspond to the
mucosal, submucosa, and all muscular layers out to
the fatty adventitia. 10cm above and below

Heart
Contoured along with the pericardial sac. Superiorly
from the level of the inferior aspect of the aortic
arch (aorto-pulmonary window) to extend inferiorly
to the apex of the heart.
Whole lung
 Both the right and left lungs should be contoured as
one structure. (common lung)
 Pulmonary windows.
 All inflated and collapsed lung should be contoured;
 GTV & trachea/ipsilateral bronchus should be
subtracted.

Brachial Plexus
RTOG guidelines
Great vessels
Rt sided tumors- IVC
Lt sided –Aorta
All musculer layer out of fatty adventitia
10cm above below PTV

Trachea
 Proximal-10 cm sup to PTV or 5 cm proximal to
carina till 2 cm proximal to carina
 Distal 2 cm trachea-included in proximal broncial
tree
Proximal bronchial tree
2 cm above carina up till segmental bifurcation
Proximal broncial tree+ 2 cm margin

D
Dose/toxicity
concerns for
•Bronchus/trachea
•Esophagus
•Great vessels

Skin
It is contoured as rind of uniform thickness (0.5 cm)
which envelopes the entire body in the axial planes.
Rib
 Ribs within 5 cm of the PTV should be contoured by
outlining the bone and marrow.
 Several portions of adjacent ribs can be contoured
as one structure but not in a contiguous fashion
(avoid ICS)

RADIOBIOLOGICAL CONSIDERATIONS IN SBRT
SCHEDULES
 Endothelial cell damage
 Lethal cell damage
 Immunological effects?

LQ MODEL: HYPO FRACTIONATED
TREATMENTS
 In vitro studies: LQ Model fits well between 0-16 Gy
*Garcia LM et al Phys Med Biol 2006;51:2813–2823
 In Vivo studies :Also shows that LQ model reliably predicts
dose response between 2-20 Gy
Barendsen GW et al. Int J Radiat Oncol Biol Phys
1982;8:1981–1997
Van der Kogel AJ. Radiat Res Suppl 1985;8:S208–S216
Peck JW, Gibbs FA. Radiat Res 1994;138:272–281

WHAT HAPPENS WHEN LQ EQUATION IS USED TO
CALCULATE DOSE EQUIVALENCE AT HIGH DOSE PER
FRACTION

Range BED (Gy) 3yr OS T1 3 Yr OS T2 Gr III –V
toxicity
Low <83.2 0.554 0.170 0.053
Medium 83.2-106 0.863 0.544 0.073
Medium to
high
106-146 0.750 0.580 0.078
High >146 0.55 0.35 0.093
The OS for the medium or medium to high BED (range, 83.2–146 Gy)
was higher than those for the low or high BED group
Zhang,vol 81,305-16 IJROBP 2011

LC and OS rates in 5 years with a BED of 100 Gy or more were
superior
BED <180 Gy -safe for stage I NSCLC
J Thorac Oncol. 2007;2: Suppl 3, S94–S100)

location #
Away from
chest wall
20X3
Close to chest
wall
12X 4
Central lesion 8x6
Avoid hot spots in hilum, chest wall,
mediastinum

Structure RTOG 0915 RTOG 0236 RTOG 915 RTOG 813
34X1 20x3 12x4 10-12x5
Cord 14Gy 18(6) Gy 26Gy 30(6) Gy
Esophagus 15.4Gy 27(9) Gy 30Gy 105% PP
I/L brachial
plexus
17.5Gy 24(8) Gy 27.2Gy 32(6.4) Gy
Heart 22Gy 30(10) Gy 34Gy 105% PP
Trachea ,
brochus
20.2Gy 30(10) Gy 34.8Gy 105% PP
Skin 26Gy - 36Gy 32(6.4) Gy
Ribs 30Gy - 40Gy -
Great
vessels
37Gy - 49Gy 105% PP

Critical volume
lung
Critical volume
Dmax lung
End point
RTOG-0813 1000cc 13.5 Gy pnemonitis
RTOG-0915 1000cc 7.4 Gy
(single #)
12.4 Gy (4#)
pnemonitis

Trial Dose # Min gap Total time note
RTOG-0236 20x3 40 hrs
Max-8 days
1.5 wks Not more
than 2# a wk
allowed
RTOG-0813 10-12x5
(Central)
40hrs 1.5-2 wks Upto 3 #/wk
RTOG-0915 12x4
34x1
18hrs 4 days 4
consecutive
days

PLANNING
Multiple , non opposing, non coplanar beams
Prescription isodose:
The prescription isodose surface must be ≥ 60% and
< 90% of the maximum dose
 The prescription isodose surface should be chosen
that 95% PTV is conformally covered by the
prescription isodose surface & 99% of PTV
receives a min. of 90% of the prescription dose
?

High Dose Spillage
The cumulative volume of all tissue outside the
PTV receiving a dose > 105% of prescription dose
should be no more than 15% of the PTV volume.
Intermediate Dose Spillage
 To evaluate the falloff gradient beyond the PTV
extending into normal tissue structures

SBRT in lung cancer

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