Download Image Guided Radiation Therapy: A Refresher

Image-Guided
Image
Guided Radiation Therapy:
A Refresher
D.A. Jaffray, Ph.D.
Radiation Therapy
py Physics
y
Princess Margaret Hospital/Ontario Cancer Institute
Professor
Departments of Radiation Oncology and Medical Biophysics
University of Toronto
Disclosure
Presenter has a financial interest in some of the
imaging technology reported here and
research collaborations with Elekta
Elekta, Philips
Philips,
IMRIS, Modus Medical, and Raysearch.
Results from studies using investigational
devices will be described in this presentation.
Learning Objectives
• Learn the challenges in achieving precision
and accuracy in treatment sites influenced by
organ motion.
• Identifyy the technologies
g available or beingg
developed for image-guided RT.
• Understand the benefits and limitations of
current solutions.
• Be aware of quality and safety issues related
to IGRT practice
Pre- Test Question
Pre
• What type of geometric targeting uncertainty
has the biggest impact on the PTV margin in
fractionated RT?
1. The Random-type Errors
2 The Systematic-type
2.
Systematic type Errors
3. The Residual Errors
4 The Absolute
4.
Absol te Error
5. Not Sure
IGRT: Targeting vs Image-based
M
Management
t
Therapy
Design
Intervention
IGRT
Clinical Objective
Monitoring
Inter- and Intra-fraction Uncertainties
Local Therapy
py and Image-Guidance
g
• Radiation therapy is a proven local therapy.
• Precise radiation therapy offers:
– Reduce severity and risk of therapy-induced complications.
– Increase both quality and probability of success.
• Further potential:
– Broaden application of proven therapies.
– Permit new therapies that are intolerant to geometric
imprecision.
• Addressingg geometric
g
uncertainties mayy expose
p
other
factors determining outcome.
Co-localization of the target and therapeutic
dose distribution within the human body is a
significant technical challenge.
Targeting Uncertainty in RT
• Setup Variation
• Internal Organ
Displacement
• Volume Change and
Deformation
Motion: Respiration-Induced
Normal
Breathingg
Breath-hold
Exhale
FAST,
‘PERIODIC’
Deep
Breathing
Breath-hold
Inhale
Siemens 1.5T (2000)
Motion: Bladder Filling
MODERATE, NOT
REPRODUCIBLE
1 hr cine MR (sagittal, TRUFISP sequence)
Motion: Bowel Effects
“Full” Rectum
“Empty” Rectum
FAST, NOT
PERIODIC
Motion: Bowel
Effects
Measured Prostate and
Rectal Wall Motion
Movie loop derived from 17
volumetric CT scans.
Prostate
P
t t - Red
R d
Rectum - Green
Left Lateral – Treatment Beam Perspective
Cancer
h
off the
Cervix:
Therapyinduced
Changes
Week 1
Week 2
Sagittal
S
i l
Images
Chan, Dinniwell
et al., PMH
Week 3
FAST + SLOW,
Week 4
UNPREDICTABLE
IG Technologies - Generation I
Cyberknife
Ultrasound
kV
Radiographic
Portal
Imaging
Markers
(Active and
Passive)
IG Technologies - Generation II
Siemens
PRIMATOM™
O
TomoTherapy
Hi-Art™
t
kV CT
Approach
MV CT
Approach
Elekta Synergy™
Siemens MVision™
Varian OBI™
Siemens Artiste™
kV and MV Cone-beam CT
Approach
Sample IGRT
Images
kV
CBCT
MV CT
EPID
kV
CBCT
MV
CBCT
Typical On-line Image-Guidance Process
Estimate Error
& Adjust
If Error >
Tolerance
Position Patient
and Acquire
Image
Align to
Reference
g Used in
Images
Planning
Real-time
Tumor-tracking
System for
Gated
Radiotherapy
Highly Integrated System (4 xray tubes,
b 4 Image Intensifiers)
ifi )
Temporal Resolution: 30 fps
Spatial Targeting Precision: 1.5
mm @ 40 mm/s
Shirato H et al., Hokkaido University School of Medicine, Sapporo, Japan.
IGRT and Timelines of Intervention
• Definitely not exclusive
processes
On-line
Real-time
• Efficiency,
Efficiency technology,
technology
and degree of mobility will
drive the relative use of
these scales.
• Need sufficient
information in the on-line
imaging to indicate the
need for off-line
off line rere
planning.
Off-line Imaging,
Off line planning may
Planning/Adaptation • Off-line
require additional and/or
different information.
Comment on IG and Surrogacy
• We very rarely image the target.
• Usually image something that is a
surrogate, Xs, of the target position,
Xt.
• Strength of surrogate needs to be
accommodated in margin design.
design
Xt
Xt
High Quality Surrogate
Poor
Surrogate
xs
xs
Illustration: IGRT Activity at PMH
•
•
•
•
IGRT Database (within Mosaiq)
Period: 2007-2010 (incl.)
# off Patients:
i
4592
4 92
# of Eligible Volume Registrations: 117,301
– # 2nd guesses = 248
– # Longg Decisions (>12
(
hrs)) = 11
– # Registrations with missing patient site: 30,597
• No change in reimbursement over past 10 years
IS3R’11
Princess Margaret Hospital
IS3R’11
IS3R’11
IG Technologies
g - Generation III?
Clarity System
Mitsubishi Unit
US++
Approach
kV-CBCT++
kV
CBCT++
Approach
Edmonton
Solution
Utrecht Solution
Viewray Solution
Adjacent Solutions
MR-Guided RT
T. Pawlicki – Sunday 11:15-12:15 am
Faster imaging, higher CNR, more responsive in delivery.
Ultrasound-based 4D Prostate Tracking
•
•
•
•
•
•
State-of-the-art
St
t f th
t US Image
I
Quality
Q lit
Does not require bladder fill for prostate
imaging
Potential application in prostatectomy and
GYN patients
ti t
Mechanical 3D probe operated remotely
Probe outside of radiation fields
• no effect on dosimetry orcollision
N i
Non-invasive
i and
d non-ionizing
i i i
Exterior view of the system. The
O-ring is skewed in the
counterclockwise direction.
O-ring Structure (d = 3.3 m)
Gimbal Mounted Treatment Head (c MLC)
Two kV x-ray Tubes for Stereo Localization
Two Flat-panel Detectors
(a) Cone beam computed tomography image of the
pelvis for a prostate case. The X-ray parameters
were 120 kVp, 200 mA, 10 ms, and 800 mAs. The
total monitoring dose was 19.4 mGy. (b) The
conventional X-ray computed tomography image of
the same area of the same patient.
Kamino et al. IJORBP, 2006
MRgRT External Beam Workflow
Research Facility - under construction – operational spring 2013
IGRT-guided pre-localization
of MR Imaging FOV
Robotic control of MR, table
and Shielding System
Confirmation of delivery
viability
i bilit
Linear motion of magnet
over patient.
ti t
Reference CBCT for MRguidance
RT present for movement.
Pre-stored MR configuration
f
from
MR-simulation
MR i l ti St
Stage
Critical time specification
(<90s) from end of imaging
to beam-on.
IImage processing
i (di
(distortion
t ti
correction, calibration) and
planning (adaptation).
Generation of couch or
machine adjustment.
*MR can begin to image within 5s of stopping.
MRgRT Pelvis Coil: Volunteer Images
Prostate
ƒ1.5 T, T2 weighted images of two volunteers.
First Images March 2009
March 2009
MR imaging without 6 MV irradiation
MR imaging during 6 MV irradiation of
object imaged (no FF)
Courtesy of G. Fallone, Cross Cancer Institute, Edmonton, Canada
Courtesy of J. Lagendijk, Utrecht, Netherlands
Courtesy of J. Lagendijk, Utrecht, Netherlands
Courtesy of J. Lagendijk, Utrecht, Netherlands
ICRU 50 and the Development of
IG in Radiation Therapy
• International Commission of
Radiation Units and
Measurements (ICRU) Report
#50 & #62
• Formalisms developed to
identify and explicitly
communicate the intentions of
the RT intervention:
– Radiation Dosage
– Geometric Extent (the need to
constrain the ggeometric extent for
the avoidance of normal structures)
– Uncertainty in the intervention
Prescription: Merits of
Embracing the ICRU Formalism
• Cl
Clear communication
i i off the
h therapeutic
h
i
intention to the rest of the technical staff
– Extent of microscopic disease and normal
structure
• Quality and Uniformity of Practice
• Created a fulcrum in the system to
explicitly accommodate the geometric
uncertainties inherent in the process.
process
• Driven the development of “margins”
– Margins to guarantee coverage
– Margins to guarantee avoidance (no fly zone)
The Role of the ICRU Formalism
in Advancing RT Practice.
• Explicit accommodation of the geometric uncertainty
associates it with the unnecessary irradiation of a
structure due to technical
t h i l limitations
li it ti
off the
th practice.
ti
• Creates a clear and distinct association between
technology and toxicity can be of great advantage in
formalizing arguments for (i) advancing the
technological state of the field, and (ii) standardizing
th practice.
the
ti
• With standardization comes opportunity for
demonstration of the improvement associated with
technological advancement.
Intent
‘Actual’
4-field box
CRT
3D-CRT
IG-IMRT
Images courtesy Dr. John Schreiner
Prostate
1
Skin Mark
Correc
ction Metho
od
2
Weekly/Pelvis
3
RL
AP
SI
Daily/Pelvis
4
Daily Ultrasound
5
Daily Radiograph/Fiducial
6
Daily CBCT/Tissue
7
Daily CBCT/Fiducial
0
2
4
6
8
10
Residual Error (mm)
Comparison of residual errors for different image-guided
correction techniques in prostate,
prostate in the left-right
left right (LR),
(LR) anterioranterior
posterior (AP), and superior-inferior (SI) directions.
Mageras GS, Mechalakos J. Semin Radiat Oncol. 2007 Oct;17(4):268-77
IGRT ABC
ABC’s:
s: Margins
• ICRU #50 & #62
– Gross Tumor Volume (GTV)
– Clinical Target Volume (CTV)
– Planning Target Volume (PTV)
• Lexicon for Image-guidance
• PTV is a conceptual ‘device’ created to assure
dosimetric coverage of the CTV
• Therefore,
Therefore must accommodate both geometry and
dosimetry in determination of the PTV margins.
• Fractionation also plays a role in margin
determination
PTV Design with IGRT
• IGRT reduces,
reduces but does not eliminate
eliminate,
geometric uncertainties
• Reduced geometric uncertainties may allow
reduced PTV margins
• Parallel/related
P ll l/ l d processes:
– Image guided radiation therapy
– Quality assurance / uncertainty management
• Need to be aware of other uncertainties (i.e.
(
target definition)
“Off-line Corrections”: Increasing Accuracy and
Measuring Precision for Reduced Margins
Individual Uncertainty
Population Uncertainty
SI
Lat
Requires time, new information,
and effort to estimate the
systematic correction and random
uncertainty for a patient.
Population Margins
Systematic
Correction
Individual Margins
“On-line Corrections”: Increasing Accuracy and
Increasingg Precision for Reduced Margins
g
Individual Uncertainty – Off-line
Reduced Uncertainty – On-line
SI
Lat
Concerns: Systematic
Multiple
Correction
(i) Residual Uncertainties (e.g. intra
intra-fraction
fractionOn
On-line
line
motion, measurement and correction errors)
Corrections
(ii) Strength of IG Surrogates (e.g. markers, bones)
(iii) Stability of Systematic Error (e.g. time trends)
Individual Margins
Reduced Margins
PTV Margin Recipes
• Most popular formulation is 2.5Σ + 0.7σ, where:
Σ is the standard deviation of systematic uncertainty
σ is the standard deviation of random uncertainty
• A
Assumes specific
ifi fractionation,
f i
i
dose
d
gradient
di andd
dose coverage objectives.
E.g: “We have measured the random uncertainty for
our prostate patients to be a standard deviation of
4mm and the systematic uncertainty to be a
standard deviation of 2mm.
Using (2.5 x 2mm) + (0.7 x 4mm), this results in 7mm
PTV margins.”
M Van Herk, Seminars in Radiation Oncology, 14(1) 2004 52-64
Rational Margin
g Design
g vs Misplaced
p
Uncertainty – ‘The PTV Carpet’
PTV
Impact of adopting information that
appears to be
b ‘‘obviously
b i l better’
b
’
IS3R’11
Particularly concerning for systematic changes in target
volume delineation.
Geets et al. 2005
4D IGRT Brings More Variables
• Phase-specific treatment approaches
– Gating, tracking, breath-hold
• Recognize phase and amplitude as positioning
variables.
i bl
• Examine the random and systematic errors in
positioning the target with these variables
variables.
• Stability of these parameters over time will challenge
g
current off-line strategies.
• Deformation….many more patient-specific variables.
Published Global Margin Recipes
Ingredients
Σ = SD systematic error
σ = SD random error
σp = dose gradient
A = peak-to-peak amplitude
M = pre
pre-correction
correction margin
Margins
for
Respiration
M Van Herk, Seminars in Radiation Oncology, 14(1) 2004 52-64
Magnitude
of the
Tracking
advantage
Sonke et al. IJROBP
Lung SRT – Cone-beam CT Guidance
Princess Margaret
g
Hospital,
p
Toronto, Canada
Qualification for RTOG 0236
A Phase II Trial of Stereotactic Body
Radiation Therapy (SBRT) in the
Treatment of Patients with Medically
Inoperable Stage I/II Non-Small Cell
Lung Cancer
3x20 Gy 3-4 days apart
ELEKTA
SYNERGYTM
RESEARCH
GROUP
* Under Research Protocol
On-line Image-Guided SRT for Lung
Princess Margaret
g
Hospital,
p
Toronto, Canada
RTOG 0236
A Phase II Trial of Stereotactic
Body Radiation Therapy
(SBRT) in the Treatment of
Patients with Medically
Inoperable Stage I/II NonSmall Cell Lung Cancer
3x20 Gy 3-4 days apart
Planning CT
CBCT Fx #1
CBCT Fx #2
CBCT Fx #3
GTV
PTV
Soft-tissue (CBCT) vs Bone-based
Alignment
32
30
28
26
24
22
20
18
16
14
12
10
8
6
4
2
89 Fractions
F ti
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
0
28 Patients
Numberr of Localiza
ations or Fractions
On-line Image-Guided
g
SRT for Lungg
3D Target-Bone Discrepancy (mm)
Purdie et al., Red Journal (2006)
Lung
Correc
ction Method
1
Weekly Radiograph/Vertebra
Daily Radiograph/Vertebra
2
RL
AP
SI
3
Hypo-Fx Daily CBCT/Vertebra
4
Hypo Fx Daily CBCT/Tumor
Hypo-Fx
0
2
4
6
Residual Error (mm)
8
10
Comparison of residual errors for different image-guided
correction
ti techniques
t h i
in
i treatment
t t
t off lung
l
tumors.
t
Mageras GS, Mechalakos J. Semin Radiat Oncol. 2007 Oct;17(4):268-77
Straightforward. Right?
Warning: These technologies are
prone to hyperbole.
h
b l
Intra-fraction target position using
repeat CBCT imaging
RTOG 0236 Protocol
Median
M
di time
ti between
b t
imaging: 34 minutes
Residual for lower
half: 2.2 mm
Residual for upper
half: 5.3 mm
3D Dev
viation from Isocentre (mm)
8 patients, 26 repeat
scans
12
10
8
6
4
2
0
0
20
40
60
80
Time post Localization CBCT (minutes)
Purdie et al., Red Journal (2006)
Warning: These methods
(corrections and margins) operate
under assumptions.
assumptions
Trends and Chasing Targets
Individual Uncertainty – Off-line
Reduced Uncertainty – On-line
SI
Lat
Systematic
Correction
Individual Margins
Multiple
On line
On-line
Corrections
Reduced Margins
Systematic Corrections in the
context of Soft-tissue Targeting
• The error distribution is characterized as a
combination of systematic and random
components
• We can correct systematic component under an
assumption that the distribution is stable.
• Soft-tissue imaging of treatment sites with
therapy-induced anatomical change highlight
this assumption.
4D Nature of H&N Targets: ‘Trending’
Planning CT sim
Day 1
Day 14
Day 21
Day 7
Day 35
Courtesy of Head and Neck Site Group - PMH
Variability in Target and Motion in
4D CBCT
Repeat 4D Cone-beam CT – Courtesy M. van Herk, NKI
Slide courtesy of M. van Herk
Hitting the Target and Avoiding
Organs at Risk
• Targets can move within the patient
• Normal tissues can move within the patient
p
• These don’t necessarily move together
• ‘Chasing’ a target with IGRT can lead to
overdosing adjacent normal tissues
tissues.
• Seeing the normal tissues may be as
important as seeing the target.
target
Hitting the Target and Avoiding
Organs at Risk
Heart
High Dose Region
PTV
Planning CT
RTOG 0236 Protocol
CBCT
- Target Localized
- Heart Outside
High Dose Region
Hitting the Target and Avoiding
Organs at Risk
Heart
High Dose Region
PTV
Planning CT
RTOG 0236 Protocol
CBCT
- Target Localized
- Heart Outside
High Dose Region
Hitting the Target and Avoiding
Organs at Risk
Heart
High Dose Region
PTV
Planning CT
RTOG 0236 Protocol
CBCT
- Target Localized
- Heart Inside
High Dose Region
Hitting the Target and Avoiding
Organs at Risk
Patient
Re-Positioned
Planning CT
RTOG 0236 Protocol
CBCT
- Target Localized
- Heart Inside
High Dose Region
CBCT
- Target Re-Localized
- Heart Outside
High Dose Region
Hitting the Target and Avoiding
Organs at Risk
• T4N2 NPC for combined modality therapy. GTV
‘hugging’
hugging brainstem and chiasm
• Clivus and cavernous sinus chosen as region of
interest (ROI) / ’clipbox’
clipbox for matching
Head and Neck Group, PMH
Hitting the Target and Avoiding
Organs at Risk
• Spine curvature not reproducible
• Non-uniform margins are appropriate
Head and Neck Group, PMH
Image guided Radiation Therapy
Image-guided
is Quality Assurance
• Streamlined measurement of patient/anatomy
position within the treatment room.
– Quantitative, accurate scale
– Minimallyy invasive
– Large field-of-view
• Verify consistency of planned and actual
geometry
• Feasible to integrate into current
cost/operational paradigm
Impact of IGRT on Localization Errors
IGRT
Gradual adoption
of on
on-line
line CBCT
since 2005.
15/16 Units now
equipped with kV
cone-beam CT.
The rate of reportable
p
incidents ((i.e. non-near miss)) has
decreased by 50% since introduction of IGRT (2005-2007).
Internal Data - PMH, Toronto
Are we applying IGRT technologies properly?
Are we inadvertently doing harm?
IGRT is currently a solid tool to tackle the problem of radiotherapy accuracy
(reduction in systematic errors).
Other
h errors ((read:
d target delineation)
d li
i ) limits
li i the
h PTV margin
i reduction
d i for
f most
RT treatments.
… facilitate implementation of new RT techniques (eg,
(eg liver and lung SBRT)
and in selected sites reduce toxicity and improve local control.
The whole chain of interventions in the RT process should be prospectively
assessed. This is particularly important because other steps in the RT process
(eg, contouring or valid measurements of toxicity) are at least as important as
high
g ggeometric pprecision.
Unlikely we will see RCT for IGRT technology in isolation.
Bujold et al. Semin Radiat Oncol 22:50-61 (2012)
There are clear technical advantages, but there are also costs
(more than just $$$)…
Bujold et al. Semin Radiat Oncol 22:50-61 (2012)
…the
th following
f ll i variables
i bl were significantly
i ifi tl related
l t d to
t worse FFBF:
FFBF
risk group according to the NCCN (high- to very high risk vs.
intermediate- to low-risk), dose (70 vs. 78 Gy), average crosssectional area (>16 vs. <16 cm2) and, unexpectedly, the use of
implanted markers as opposed to bony structures for patient
positioning. In retrospect, the margins around the clinical target
volume appeared to be inadequate in the cases in which markers were
used.
Int. J. Radiation Oncology Biol. Phys., Vol. 74, No. 2, pp. 388–391, 2009
…arbitrarily chosen non-uniform margins of 3 mm LR and 5 mm (AP;
CC)…. narrow LR margin may lead to an underdosage. Second, …the
planning system is unable to handle CC margins that are not a multiple
); … the real CC margin
g was
of the pplanningg CT slice thickness ((2 mm);
4 mm instead.
Int. J. Radiation Oncology Biol. Phys., Vol. 74, No. 2, pp. 388–391, 2009
SD-IGRT: Metastases
An IGRT
enabled
activity.
(all lesions)
(bone only)
MR Imaging for
IGBT
• Intrinsic Contrasts
– Structural and Functional
• High
g Spatial
p
Resolution
• No Known Toxicities
• Volumetric Image
Acquisition
• Concerns of Distortion
• Access/Devices
MRI Anatomy
Cervix Cancer
The mean D90 for HR CTV was 6 Gy higher when using one plan than when using
individual treatment plans. The D2cc increased 3.5 Gy for the bladder, 4.2 Gy for the
rectum and 5.8 Gy for the sigmoid.
The use off only
Th
l one treatment
t t
t plan
l would
ld h
have resulted
lt d iin 8/14 cases exceeding
di
constraints for bladder, rectum or sigmoid.
MR-Guided Brachytherapy: IGRT Success Story
Are we applying IGRT technologies properly?
Are we inadvertently doing harm?
Published Guidance for IGRT:
Commissioning and Use
IGRT Technology
AAPM Task Group #
142
58
104
148
9
Planar kV
Planar MV
9
kV-CBCT
kV
CBCT
9
MV-CBCT
9
135
154
Ultrasound
Non-radiographic
147
9
9
9
9
9
9
Fan Beam kVCT
Fan Beam MVCT
179
9
9
9
9
ACR/ASTRO Practice Guidelines for IGRT – 2009
An Easy Read!
7 pages of
concise text.
IGRT: Areas of Risk and Risk Abatement
Target and Normal
Tissue Definition
Margin Design and
Treatment Planning
!
!
Delineation of Target
and Normal Structures Peer Review
!
QA Transfer of IGRT
Parameters to Tx Unit
Selection of PTV Margins
Consistent with IGRT
Procedure and Data
!
Imaging, Adjustment and
Delivery
!
Consistent IGRT
Procedure at the Tx Unit
Documentation of IG
Performance Data
!
Review of IG Results to
Confirm
Coverage/Avoidance
! Education and Training
! Quality Assurance, Documentation, Evidence of IG Performance
! Nomenclature and IG Lexicon
Recommendation ((1 thru 5))
Reference
IGRT Infrastructure
1. Establish a multi-professional team responsible for IGRT
activities.
ti iti
(White and Kane 2007)
2. Establish and monitor a program of daily, monthly, and
annual QA for all new or existing IGRT sub-systems.
(Klein, Hanley et al.
2009; Yin, Wong
et al. 2009)
3. Provide device and process-specific training for all staff
operating IGRT systems or responsible for IGRT
delivery.
(Yin, Wong et al. 2009)
4. Perform ‘end-to-end’ testing for all new IGRT
procedures (from simulation to dose delivery) and
document pperformance prior
p
to clinical release.
(Yin, Wong et al. 2009)
5. Establish process-specific documentation and procedures
for IGRT.
(Hendee and Herman ;
Yin, Wong et al.
2009)
Recommendation ((6 thru 10))
Reference
IGRT Infrastructure
6. Clearly identify who is responsible for approval of IGRT
correction
ti decision
d i i andd the
th process whereby
h b this
thi
decision is made and documented.
(Potters, Kavanagh et
al.))
7. Establish and document site-specific planning
procedures,
d
specifically,
ifi ll the
h procedure
d
for
f defining
d fi i PTV
margins. Link these planning procedures to IGRT
procedures.
(ICRU50 1993;
ICRU62 1999;
Keall, Mageras et
al. 2006)
Patient-Specific Procedures
8. Multi-professional peer-review of PTV volumes. Peerreview of GTV/CTV volumes by
y RadOncs.
(Adams, Chang et al.
2009)
9. Verify proper creation and transfer of IGRT reference
data (PTV, OARs, DRRs etc.) to IGRT system.
(Potters, Gaspar et al.)
10 Establish a reporting mechanism for IGRT-related
10.
IGRT related
variances in the radiation treatment process.
(Hendee and Herman ;
CAPCA 2006)
How far should we go in
responding to ‘displacements’
d
detected
d with
i h image-guidance
i
id
systems?
IGRT Continuum
• IGRT informs on-line and off-line
correction strategies.
• Accuracy:
– verify target location wrt iso-centre.
– correct & moderate setupp errors
+
• Precision:
– tailor PTV margins (population or patientspecific)
– reduce PTV margins
+
• Adaptation:
– Detect, mitigate/exploit progressive changes
– Re-planning (“naïve” or explicit)
(without or with dose accumulation)
ASTRO 4DIGRT 2008
+
?
“Adaptive
Adaptive radiotherapy has been introduced as a feedback control
strategy to include patient-specific treatment variation explicitly in the
control of treatment planning and delivering during the treatment
course.”” D.
D Y
Yan
4D IGRT – Changes
Ch
iin T
Targeted
t d Tissues
Ti
NSCLC
Detectable Changes in Volume of
‘Something’ Courtesy of Gerald Lim, PMH
IGRT Detected Changes in Lung
T
Targets
– Guidance/Discussion
G id
/Di
i
• Siker ML et al.
al “Tumor
Tumor volume changes on serial
imaging with megavoltage CT for non-small-cell lung
cancer during
g intensity-modulated
y
radiotherapy:
py how
reliable, consistent, and meaningful is the effect?
– Int J Radiat Oncol Biol Phys. 2006 1;66(1):135-41
• Kupelian PA et al. “Serial megavoltage CT imaging
during external beam radiotherapy for non-small-cell
lung cancer: observations on tumor regression during
treatment.
– Int
I t J Radiat
R di t Oncol
O l Biol
Bi l Phys.
Ph 2005 Nov
N 15;63(4):1024-8
15 63(4) 1024 8
Courtesy of J-J. Sonke, NKI
RT-induced Change and the
Domain of Adaptation
• Major concern regarding the true extent of disease (in
planning and during RT).
• Is there opportunity to reduce target volumes as therapy
progresses?
– Depends on what is changing – normal tissue vs target
volumes
l
• Need to reflect on the definition of GTV and CTV
– State-of-the-art
State of the art IGRT imaging systems are not necessarily
standard of care for use in target definition
– Redefinition of target volumes is not standard of care in RT
Adaptive Approaches – with the exception of ‘systematic
shifts’ are in the domain of clinical research.
IG Technologies Needed for 4D
Autosegmentation
Deformable
R i t ti
Registration
Dose
Tracking
Re-planning
These systems are available in the research setting,
but not mature in commercial systems.
Ca Cervix:
Tumour Shrinkage
& Deformation
During RT
Pre-Tx
8 Gy
What is the actual
dose delivered?
Can we
accommodate these
changes to reduce
normall tissue
i
dose?
20 Gy
28 Gy
38 Gy
48 Gy
SLOW,
UNPREDICTABLE
Methods - Deformation Vector Fields (5 wks)
Week 1
Week 2
Week 3
Planning (pre-treatment)
Week 4
Week 5
Brock, et al., Medical Physics 2005;32:1647-1659.
Adaptive Benefit - Conventional vs On-line
1) IMRT with uniform 3mm PTV margin, no re-planning
IMRT Plan
Optimization Function
Planning
Criteria:
• D98% GTV > 50 Gy
• D98% CTV > 49 Gy
• D98% PTV > 47.5 Gy
• OARs subject to RTOG 0418 protocol
Deliver
25 Fractions
2) Automatic re-plan with pre-treatment optimization function
IMRT Plan
Optimization Function
Planning
Deliver
Automatic Weekly Replan
Orbit Workstation, Raysearch Labs
Stewart, et al., IJORBP, 2009
Research Results – Target Coverage (N=33 Pats)
GTV
CTV
51
50
100%
49
98%
48
95%
47
2
(6%)
46
45
Dose to 9
98% Volume (Gy)
Dose to 9
98% Volume (Gy)
51
50
100%
49
98%
48
95%
47
8
(24%)
46
Pl
Planned
d
N R
No
Replan
l
A
Assess
Weekly
W kl
45
Pl
Planned
d
N R
No
Replan
l
A
Assess
Weekly
W kl
Message: A large fraction of patients would maintain coverage with a 3mm margin!
But, who are they? We can’t tell until the 2nd-3rd week of treatment.
Summary
• IGRT seeks to address geometric uncertainties in
dose placement for target and normal tissues.
tissues
• It has become a routine part of current RT
p
practice.
• Safe application of IGRT technology requires
additional training and careful integration into the
clinical
li i l process.
• Numerous new IGRT devices in development.
• IGRT reveals
l changes
h
in
i anatomy during
d i RT that
h
challenge conventional practices – this is an area
of on-going
on going research
research.
Post- Test Question
Post
• What type of geometric targeting uncertainty
has the biggest impact on the PTV margin in
fractionated RT?
1. The Random-type Errors
2 The Systematic-type
2.
Systematic type Errors
3. The Residual Errors
4 The Absolute
4.
Absol te Error
5. Not Sure