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Image-Guided Radiation Therapy:Image Guided Radiation Therapy: A Refresher

D.A. Jaffray, Ph.D.

Radiation Therapy Physicspy yPrincess Margaret Hospital/Ontario Cancer Institute

ProfessorDepartments of Radiation Oncology and Medical Biophysics

University of Toronto

DisclosureDisclosure

Presenter has a financial interest in some of thePresenter has a financial interest in some of the imaging technology reported here and

research collaborations with Elekta Philipsresearch collaborations with Elekta, 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.

• Identify the technologies available or being y g gdeveloped for image-guided RT.

• Understand the benefits and limitations ofUnderstand the benefits and limitations of current solutions.

• Be aware of quality and safety issues related• Be aware of quality and safety issues related to IGRT practice

Pre- Test QuestionPre Test Question

• What type of geometric targeting uncertaintyWhat type of geometric targeting uncertainty has the biggest impact on the PTV margin in fractionated RT?fractionated RT?1. The Random-type Errors

2 The Systematic type Errors2. The Systematic-type Errors

3. The Residual Errors

4 The Absol te Error4. The Absolute Error

5. Not Sure

IGRT: Targeting vs Image-based M tManagement

Therapy Design

Intervention

IGRT

Clinical ObjectiveMonitoring

Inter- and Intra-fraction Uncertainties

Local Therapy and Image-Guidancepy g• Radiation therapy is a proven local therapy. • Precise radiation therapy offers: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– Permit new therapies that are intolerant to geometric imprecision.

• Addressing geometric uncertainties may expose other g g y pfactors determining outcome.Co-localization of the target and therapeutic dose distribution within the human body is a

significant technical challenge.

Targeting Uncertainty in RTTargeting Uncertainty in RT• Setup Variation

• Internal Organ Displacement

• Volume Change and Deformation

Motion: Respiration-Induced

Normal Breathing

Deep Breathingg Breathing

Breath-hold Exhale

Breath-hold Inhale

Siemens 1.5T (2000)

FAST, ‘PERIODIC’

Motion: Bladder Filling

1 hr cine MR (sagittal, TRUFISP sequence)

MODERATE, NOT REPRODUCIBLE

Motion: Bowel Effects“Full” Rectum “Empty” Rectum

FAST, NOT PERIODIC

Motion: Bowel Effects

Measured Prostate and Rectal Wall Motion

Movie loop derived from 17Movie loop derived from 17 volumetric CT scans.

P t t R dProstate - RedRectum - Green

Left Lateral – Treatment Beam Perspective

Cancer f hof the

Cervix: Therapy-induced Changes Week 1 Week 2

S i lSagittal Images

Week 3 Week 4Chan, Dinniwell et al., PMH

FAST + SLOW, UNPREDICTABLE

IG Technologies - Generation IIG Technologies Generation I

Cyberknife

kV Radiographic

Ultrasound Portal Imaging

Markers (Active and

Passive)

IG Technologies - Generation IIIG Technologies Generation II

Elekta Synergy™ Siemens MVision™TomoTherapy Hi-Art™

Siemens PRIMATOM™ tO

MV CT Approach

kV CT Approach

Varian OBI™ Siemens Artiste™

kV and MV Cone-beam CT Approach

EPIDSample IGRTSample IGRT

ImageskV

CBCTkV

CBCT

MV CT MV CBCT

Typical On-line Image-Guidance Process

Estimate Error & Adjust& Adjust If Error > Tolerance

Position Patient and Acquire

Image

Align to Reference

Images Used in Image gPlanning

Real-time Tumor-tracking

System forSystem for Gated

RadiotherapyRadiotherapyHighly Integrated System (4 x-

b ifi )ray tubes, 4 Image Intensifiers)

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• Definitely not exclusiveprocesses

• Efficiency technology• Efficiency, technology, and degree of mobility will drive the relative use of On-linethese scales.

• Need sufficient Real-time

information in the on-line imaging to indicate the need for off line reneed for off-line re-planning.

• Off line planning mayOff-line Imaging, • Off-line planning may require additional and/or different information.

Planning/Adaptation

Comment on IG and SurrogacyComment on IG and Surrogacy• We very rarely image the target. X• Usually image something that is a

surrogate, Xs, of the target position, X

Xt

Xt.• Strength of surrogate needs to be

accommodated in margin design xaccommodated in margin design. xsXt

High Quality SurrogatePoor

Surrogate

xs

Illustration: IGRT Activity at PMHIllustration: IGRT Activity at PMH

• IGRT Database (within Mosaiq)IGRT Database (within Mosaiq)• Period: 2007-2010 (incl.)

# f i 4 92• # of Patients: 4592• # of Eligible Volume Registrations: 117,301

– # 2nd guesses = 248– # Long Decisions (>12 hrs) = 11g ( )– # Registrations with missing patient site: 30,597

• No change in reimbursement over past 10 years

IS3R’11

No change in reimbursement over past 10 years

Princess Margaret Hospital

IS3R’11

IG Technologies - Generation III?g

Edmonton Solution

Utrecht SolutionMitsubishi Unit

kV CBCT++US++

Clarity System

kV-CBCT++ Approach

US++ Approach

Viewray Solution

MR-Guided RT

Adjacent Solutions

Faster imaging, higher CNR, more responsive in delivery.T. Pawlicki – Sunday 11:15-12:15 am

Ultrasound-based 4D Prostate Tracking

St t f th t US I Q lit• State-of-the-art US Image Quality• Does not require bladder fill for prostate

imaging• Potential application in prostatectomy and

GYN ti tGYN patients• Mechanical 3D probe operated remotely• Probe outside of radiation fields

• no effect on dosimetry orcollisionN i i d i i i• Non-invasive and non-ionizing

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 LocalizationTwo 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 WorkflowResearch Facility - under construction – operational spring 2013

IGRT-guided pre-localization of MR Imaging FOV

Confirmation of delivery i bilit

Robotic control of MR, table and Shielding System

Linear motion of magnet ti t

Critical time specification (<90s) from end of imaging

to beam-on.

I i (di t tiviability

Reference CBCT for MR-guidance

over patient.

RT present for movement.

Pre-stored MR configuration f MR i l ti St

Image processing (distortion correction, calibration) and

planning (adaptation).

Generation of couch orfrom MR-simulation Stage Generation of couch or machine adjustment.

*MR can begin to image within 5s of stopping.

MRgRT Pelvis Coil: Volunteer Images

Prostate

1.5 T, T2 weighted images of two volunteers.

March 2009First Images March 2009

MR imaging without 6 MV irradiation

MR imaging during 6 MV irradiation ofMR 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

ICRU 50 and the Development of IG in Radiation Therapy

• International Commission of Radiation Units and Measurements (ICRU) Report #50 & #62#50 & #62

• Formalisms developed to identify and explicitlyidentify and explicitly communicate the intentions of the RT intervention:– Radiation Dosage– Geometric Extent (the need to

constrain the geometric extent for gthe avoidance of normal structures)

– Uncertainty in the intervention

Prescription: Merits of Embracing the ICRU Formalism

Cl i i f h h i• Clear communication of the therapeutic intention to the rest of the technical staff– Extent of microscopic disease and normalExtent 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 processuncertainties inherent in the process.

• Driven the development of “margins”– Margins to guarantee coverageMargins to guarantee coverage– Margins to guarantee avoidance (no fly zone)

The Role of the ICRU FormalismThe 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 t h i l li it ti f th tistructure due to technical limitations of the practice.

• Creates a clear and distinct association between technology and toxicity can be of great advantage intechnology and toxicity can be of great advantage in formalizing arguments for (i) advancing the technological state of the field, and (ii) standardizing th tithe practice.

• With standardization comes opportunity for demonstration of the improvement associated withdemonstration of the improvement associated with technological advancement.

IntentIntent

‘Actual’

4-field box CRT 3D-CRT IG-IMRT

Images courtesy Dr. John Schreiner

1

Prostate

2

1

Weekly/Pelvis

Skin Mark

od RL

4

3

Daily Ultrasound

Daily/Pelvis

ctio

n M

etho

RL AP SI

6

5

Daily CBCT/Tissue

Daily Radiograph/Fiducial

Cor

rec

7

0 2 4 6 8 10

Daily CBCT/Fiducial

Comparison of residual errors for different image-guided correction techniques in prostate in the left right (LR) anterior

Residual Error (mm)

correction techniques in prostate, in the left-right (LR), anterior-posterior (AP), and superior-inferior (SI) directions.

Mageras GS, Mechalakos J. Semin Radiat Oncol. 2007 Oct;17(4):268-77

IGRT ABC’s: MarginsIGRT ABC s: Margins

• ICRU #50 & #62ICRU #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 must accommodate both geometry and• Therefore, must accommodate both geometry and

dosimetry in determination of the PTV margins.• Fractionation also plays a role in marginFractionation also plays a role in margin

determination

PTV Design with IGRTPTV Design with IGRT

• IGRT reduces but does not eliminateIGRT reduces, but does not eliminate, geometric uncertainties

• Reduced geometric uncertainties may allow• Reduced geometric uncertainties may allow reduced PTV marginsP ll l/ l d• Parallel/related 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 UncertaintyPopulation UncertaintySI

Lat

SystematicCorrection

Requires time, new information, and effort to estimate the

systematic correction and random uncertainty for a patient.

Population Margins Individual Margins

“On-line Corrections”: Increasing Accuracy and Increasing Precision for Reduced Margins

Individual Uncertainty – Off-lineg g

Reduced Uncertainty – On-lineSI

Lat

SystematicCorrection Multiple

On-line

Concerns:(i) Residual Uncertainties (e.g. intra-fractionOn line

Corrections(i) Residual Uncertainties (e.g. intra fraction

motion, measurement and correction errors)(ii) Strength of IG Surrogates (e.g. markers, bones)

Reduced MarginsIndividual Margins(iii) Stability of Systematic Error (e.g. time trends)

PTV Margin Recipes• Most popular formulation is 2.5Σ + 0.7σ, where:

Σ is the standard deviation of systematic uncertaintyΣ is the standard deviation of systematic uncertaintyσ is the standard deviation of random uncertainty

A ifi f i i d di d• Assumes specific fractionation, dose gradient and 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 a4mm and the systematic uncertainty to be a standard deviation of 2mm.Using (2.5 x 2mm) + (0.7 x 4mm), this results in 7mm

M Van Herk, Seminars in Radiation Oncology, 14(1) 2004 52-64

Using (2.5 x 2mm) + (0.7 x 4mm), this results in 7mm PTV margins.”

Rational Margin Design vs Misplaced g g pUncertainty – ‘The PTV Carpet’

PTV

Impact of adopting information that b ‘ b i l b ’appears to be ‘obviously better’

IS3R’11 Geets et al. 2005Particularly concerning for systematic changes in target

volume delineation.

4D IGRT Brings More Variables4D IGRT Brings More Variables• Phase-specific treatment approaches

– Gating, tracking, breath-hold• Recognize phase and amplitude as positioning

i blvariables.• Examine the random and systematic errors in

positioning the target with these variablespositioning the target with these variables.• Stability of these parameters over time will challenge

current off-line strategies.g• Deformation….many more patient-specific variables.

Published Global Margin RecipesIngredients

Σ = SD systematic errorσ = SD random errorσp = dose gradientA = peak-to-peak amplitudeM = pre-correction marginM pre correction margin

Margins forfor

Respiration

M Van Herk, Seminars in Radiation Oncology, 14(1) 2004 52-64

MagnitudeMagnitude of the

Tracking advantage

Sonke et al. IJROBP

Lung SRT – Cone-beam CT Guidance

Princess Margaret Hospital, Toronto, Canadag p

Qualification for RTOG 0236A 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

ELEKTAELEKTA SYNERGYTM

RESEARCH GROUP

* Under Research Protocol

On-line Image-Guided SRT for LungPrincess Margaret Hospital, Toronto, Canadag p

RTOG 0236A Phase II Trial of Stereotactic

Body Radiation Therapy 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

CBCT Fx #1CBCT Fx #1


Planning CTPlanning CT


GTVGTVPTVPTV

Soft-tissue (CBCT) vs Bone-based Alignment

On-line Image-Guided SRT for Lung

14151617

actio

ns28 Patients

89 F ti

g g

91011121314

atio

ns o

r Fr89 Fractions

345678

r of L

ocal

iza

0123

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32

Num

ber

3D Target-Bone Discrepancy (mm)

Purdie et al., Red Journal (2006)

Lung

1

Daily Radiograph/Vertebra

Weekly Radiograph/Vertebra

od

3

2 Daily Radiograph/Vertebract

ion

Met

h RL APSI

4

3

Hypo Fx Daily CBCT/Tumor

Hypo-Fx Daily CBCT/VertebraCor

rec

4

0 2 4 6 8 10

Hypo-Fx Daily CBCT/Tumor

Residual Error (mm)

Comparison of residual errors for different image-guided ti t h i i t t t f l t

Residual Error (mm)

correction techniques in treatment of lung tumors.

Mageras GS, Mechalakos J. Semin Radiat Oncol. 2007 Oct;17(4):268-77

Straightforward. Right?

Warning: These technologies are h b lprone to hyperbole.

Intra-fraction target position using repeat CBCT imaging

10

12

mm

)

RTOG 0236 Protocol

8 patients, 26 repeat

8

10

Isoc

entr

e (8 patients, 26 repeat

scans

M di ti b t

4

6

viat

ion

from

Median time between imaging: 34 minutes

Residual for lower

0

2

0 20 40 60 80

3D D

evResidual for lower half: 2.2 mm

Residual for upper 0 20 40 60 80Time post Localization CBCT (minutes)

Residual for upper half: 5.3 mm

Purdie et al., Red Journal (2006)

Warning: These methods (corrections and margins) operate

under assumptionsunder assumptions.

Trends and Chasing TargetsIndividual Uncertainty – Off-line Reduced Uncertainty – On-line

SI

Lat

SystematicCorrection Multiple

On-lineOn lineCorrections

Reduced MarginsIndividual Margins

Systematic Corrections in theSystematic Corrections in the context of Soft-tissue Targeting

• The error distribution is characterized as a combination of systematic and randomcomponents

• 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 7

Courtesy of Head and Neck Site Group - PMHDay 14 Day 21 Day 35

Variability in Target and Motion in 4D CBCT4D 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 patientp• These don’t necessarily move together

• ‘Chasing’ a target with IGRT can lead to overdosing adjacent normal tissuesoverdosing adjacent normal tissues.

• Seeing the normal tissues may be as important as seeing the targetimportant as seeing the target.


Heart

Organs at Risk

High Dose Region

PTVPTV

Planning CT CBCT - Target Localized - Heart Outside

High Dose RegionHigh Dose Region

RTOG 0236 Protocol


Heart

Organs at Risk

High Dose Region

PTVPTV

Planning CT CBCT - Target Localized - Heart Inside

High Dose RegionHigh Dose Region

RTOG 0236 Protocol


Patient Re-Positioned

Organs at Risk

Planning CT CBCT - Target Localized - Heart Inside

High Dose Region

CBCT - Target Re-Localized - Heart Outside

High Dose RegionHigh Dose Region High Dose Region

RTOG 0236 Protocol


• T4N2 NPC for combined modality therapy. GTV ‘hugging’ brainstem and chiasm

Organs at Risk

hugging brainstem and chiasm• Clivus and cavernous sinus chosen as region of

interest (ROI) / ’clipbox’ for matchinginterest (ROI) / clipbox for matching

Head and Neck Group, PMH


• Spine curvature not reproducible

Organs at Risk

• Non-uniform margins are appropriate

Head and Neck Group, PMH

Image-guided Radiation TherapyImage guided Radiation Therapy is Quality Assurance

• Streamlined measurement of patient/anatomy position within the treatment room.– Quantitative, accurate scale– Minimally invasivey– Large field-of-view

• Verify consistency of planned and actualVerify consistency of planned and actual geometry

• Feasible to integrate into current• Feasible to integrate into current cost/operational paradigm

Impact of IGRT on Localization ErrorsImpact of IGRT on Localization ErrorsGradual adoption of on line CBCT

IGRTof on-line CBCT

since 2005.

15/16 Units now equipped with kV

cone-beam CT.

The rate of reportable incidents (i.e. non-near miss) has p ( )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).

h ( d d li i ) li i h i d i fOther errors (read: target delineation) limits the PTV margin reduction for most RT treatments.

facilitate implementation of new RT techniques (eg liver and lung SBRT)… facilitate implementation of new RT techniques (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 prospectivelyThe 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 geometric precision.

Bujold et al. Semin Radiat Oncol 22:50-61 (2012)

g g p

Unlikely we will see RCT for IGRT technology in isolation.

There are clear technical advantages, but there are also costs (more than just $$$)…

Bujold et al. Semin Radiat Oncol 22:50-61 (2012)

th f ll i i bl i ifi tl l t d t FFBF…the following variables were significantly related to worse FFBF: risk group according to the NCCN (high- to very high risk vs. intermediate- to low-risk), dose (70 vs. 78 Gy), average cross-sectional 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

Int. J. Radiation Oncology Biol. Phys., Vol. 74, No. 2, pp. 388–391, 2009

positioning. In retrospect, the margins around the clinical target volume appeared to be inadequate in the cases in which markers were used.

…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 of the planning CT slice thickness (2 mm); … the real CC margin was

Int. J. Radiation Oncology Biol. Phys., Vol. 74, No. 2, pp. 388–391, 2009

p g ( ); g4 mm instead.

SD-IGRT: MetastasesAn IGRT enabled activity.

(all lesions) (bone only)

MR Imaging for IGBTIGBT

• Intrinsic ContrastsIntrinsic Contrasts– Structural and Functional

• High Spatial Resolutiong p• No Known Toxicities• Volumetric Image

Acquisition• Concerns of Distortion• Access/Devices

MRI AnatomyMRI Anatomy -

Cervix CancerCervix 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.

Th f l t t t l ld h lt d i 8/14 diThe use of only one treatment plan would have resulted in 8/14 cases exceeding 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 58 104 148 135 154 179 147Planar kV Planar MVkV-CBCTkV CBCTMV-CBCT Fan Beam kVCTFan Beam MVCTUltrasoundNon-radiographicNon-radiographic

ACR/ASTRO Practice Guidelines for IGRT – 2009

An Easy Read!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

Imaging, Adjustment and DeliveryTissue Definition Treatment Planning Delivery

QA Transfer of IGRT Parameters to Tx Unit !

Selection of PTV Margins Consistent with IGRT Procedure and Data

Consistent IGRT Procedure at the Tx Unit

Delineation of Target and Normal Structures -

Peer Review!!!

Review of IG Results to

! Documentation of IG Performance Data

! 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

ti iti(White and Kane 2007)

activities.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 performance prior to clinical release.

(Yin, Wong et al. 2009)

p p5. 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

ti d i i d th h b thi(Potters, Kavanagh et

al.)correction decision and the process whereby this decision is made and documented.

)

7. Establish and document site-specific planning d ifi ll h d f d fi i

(ICRU50 1993; ICRU62 1999;procedures, specifically, the procedure for defining PTV

margins. Link these planning procedures to IGRT procedures.

ICRU62 1999; Keall, Mageras et al. 2006)

Patient-Specific Procedures8. Multi-professional peer-review of PTV volumes. Peer-

review of GTV/CTV volumes by RadOncs.(Adams, Chang et al.

2009)y9. 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 (Hendee and Herman ;10. Establish a reporting mechanism for IGRT-related variances in the radiation treatment process.

(Hendee and Herman ; CAPCA 2006)

How far should we go inHow far should we go in responding to ‘displacements’ d d i h i iddetected with image-guidance

systems?systems?

IGRT Continuum• IGRT informs on-line and off-line

correction strategies.• Accuracy:• Accuracy:

– verify target location wrt iso-centre.– correct & moderate setup errors

+p

• Precision: – tailor PTV margins (population or patient-

specific)– reduce PTV margins

• Adaptation:

+

• Adaptation:– Detect, mitigate/exploit progressive changes – Re-planning (“naïve” or explicit) +

?

ASTRO 4DIGRT 2008

(without or with dose accumulation)

“Adaptive radiotherapy has been introduced as a feedback controlAdaptive 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

” D Ycourse.” D. Yan

4D IGRT Ch i T t d Ti4D IGRT – Changes in Targeted Tissues

Detectable Changes in Volume of ‘Something’ Courtesy of Gerald Lim, PMHNSCLC

IGRT Detected Changes in Lung T G id /Di iTargets – Guidance/Discussion

• Siker ML et al “Tumor volume changes on serial• Siker ML et al. Tumor volume changes on serial imaging with megavoltage CT for non-small-cell lung cancer during intensity-modulated radiotherapy: how g y pyreliable, 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.

I t J R di t O l Bi l Ph 2005 N 15 63(4) 1024 8– Int J Radiat Oncol Biol Phys. 2005 Nov 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• Major concern regarding the true extent of disease (in planning and during RT).

• Is there opportunity to reduce target volumes as therapyIs there opportunity to reduce target volumes as therapy progresses?– Depends on what is changing – normal tissue vs target

lvolumes• Need to reflect on the definition of GTV and CTV

– State-of-the-art IGRT imaging systems are not necessarilyState 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 RTAdaptive Approaches – with the exception of ‘systematic

shifts’ are in the domain of clinical research.

IG Technologies Needed for 4D

Deformable R i t ti

Auto-Registrationsegmentation

Dose Tracking

Re-planningTracking

These systems are available in the research setting, but not mature in commercial systems.

8 GyPre-TxCa Cervix: Tumour Shrinkage

& Deformation

20 Gy 28 GyDuring RT

What is the actual dose delivered?

Can we

38 Gy 48 Gy

accommodate these changes to reduce

l inormal tissue dose?

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

Planning Deliver

Criteria:• D98% GTV > 50 Gy

IMRT Plan Optimization Function

• D98% GTV > 50 Gy• D98% CTV > 49 Gy• D98% PTV > 47.5 Gy• OARs subject to RTOG 0418 protocol

25 Fractions

2) Automatic re-plan with pre-treatment optimization function

Planning DeliverIMRT Plan Optimization Function

Automatic Weekly Replan

Stewart, et al., IJORBP, 2009Orbit Workstation, Raysearch Labs

Research Results – Target Coverage (N=33 Pats)GTV CTV

5151GTV CTV

49

50

Gy)

100%

98%49

50

Gy)

100%

98%

48

98%

Vol

ume

(

95%

48

98%

Vol

ume

(

95%

47

Dos

e to

9 95%

47

Dos

e to

9 95%

8 (24%)

2(6%)

Pl d N R l A W kl45

46

Pl d N R l A W kl45

46(24%)

Planned No Replan Assess WeeklyPlanned No Replan Assess Weekly

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 tissuesdose placement for target and normal tissues.• It has become a routine part of current RT

practice.p• Safe application of IGRT technology requires

additional training and careful integration into the li i lclinical process.

• Numerous new IGRT devices in development.IGRT l h i d i RT h• IGRT reveals changes in anatomy during RT that challenge conventional practices – this is an area of on-going researchof on going research.

Post- Test QuestionPost Test Question

• What type of geometric targeting uncertaintyWhat type of geometric targeting uncertainty has the biggest impact on the PTV margin in fractionated RT?fractionated RT?1. The Random-type Errors

2 The Systematic type Errors2. The Systematic-type Errors

3. The Residual Errors

4 The Absol te Error4. The Absolute Error

5. Not Sure

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