Recomendaciones ICRU Márgenes Tratamiento

7/26/2019 Recomendaciones ICRU Mrgenes Tratamiento

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ICRU report 62, 199

Gross Tumor Vo

lume:GTV

Clinical Target Volume:CTV

Internal Target Volume:ITV

Planning Target

Volume: PTV Organ at Risk: OAR

Planning Organ at RiskVolume: PRV

Target Volumes in Radiation Oncology:

ICRU 50 and 62:


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The Need for an New ICRU Report on IMRT

Biological Target Volume (BTV): C. Ling, IJROBP2000,

Hypoxic TV (HTV), Proliferation TV (PTV), :ESTRO physics meeting, 2003,

working PTV (wPTV): Ciernik IF, IJROBP, 2005, AAPM 2005: with the use of IMRT, ICRU

recommendations will not be needed

anymore.

It was published and/ormentioned


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Issues for 3D-CRT and IMRT

Multiple GTV, e.g. anatomic vs functional

imaging; before and during treatment, , GTV to CTV margins: clinical probability,

CTV to PTV margins: geometric probability;overlapping volumes,

ITV ???

OAR: open vs closed volume? Remaining normaltissues?

PRV: planning organ at risk volume - serial vs

parallel OAR.


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Before Rx-CH

46 Gy (Rx-CH

CT MRI T2 FS FDG-PET

Right piriform sinus(ICDO-10: C12.9)SCC grade 2

TNM 6 th ed: T4N0M0

Fiberoptic examination


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Two Types of MarginsGTV 1

CTV 1

PTV 1

CTV 2

PTV 2

CTV 3

PTV 3

Microscopic

Extension

RegionalInvolvement


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PTV 1: dose 1

CTV 1

PTV 2: dose 2

GTV 1 (pre-RxTh CT+ ivcontrast)

Example 1

CTV 2 = GTV 1


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PTV 1: dose 1

CTV 1

GTV 1 (pre-RxTh CT+ ivcontrast)

Example 2

CTV 2 = GTV 2

PTV 2: dose 2

GTV 2 (FDG-PET @ 46 Gy)


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The Clinical Target Volume (CTV) isa volume of tissue that contains ademonstrable GTV and/or subclinicalmalignant disease at a certainprobability considered relevant for therapy,

The CTV is thus an anatomical-clinical concept.

Clinical Target Volume (CTV)


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Sometimes the largest componentof the margin between the GTV andCTV will be the delineation error indrawing the GTV,

Consideration should be made for this in the clinical margin.



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Target volumes in Radiation Oncology


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The Planning Target Volume is ageometrical concept, introduced for treatment planning and evaluation. It

is the recommended tool to shapedose distributions that ensure with aclinically acceptable probability that

an adequate dose will actually bedelivered to all parts of the CTV

Planning Target Volume (PTV)


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Planning Target Volume (PTV) Include both internal and external variations

of the CTV,

Separate delineation of the ITV is not necessarybut motion should be included in the PTV,

Expansion of the CTV using rolling ball

algorithms, CTV to PTV margin recipe based on random and

systematic errors, and beam penumbra,

Priority rules when overlapping PTVs or PTV-PRV,

Dose is prescribed and reported on the PTV.

IMRT can result in hot and cold spots within thePTV.


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Cheating on the PTV Margins The practice of shrinking the CTV to PTV

margin to accommodate an OAR is

discouraged as it results in a deceptivelybetter PTV homogeneity,

In IMRT the trade-off can be accomplishedby changing the planning aims in theoptimizer,

In 3-D CRT, the trade-off can beaccomplished with a separate targetdelineation used to draw the beamboundary.


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PTV

PRV

PTV SV-1 PTV SV-2

PTV SV-1PTV SV-2

Absorbed Dose

Volume

PTV

Absorbed Dose

Volume

PTV = PTV SV-1 + PTV SV-2

Can Use Sub-Volumes to Guide Optimization


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CTV to PTV Margin RecipeAuthor Application Recipe AssumptionsBel et al 1996b Target 0.7 s Random errors only (linear approximation)

Monte Carlo

Antolak and Rosen 1999 Target 1.65 s Random errors only, block margin?

Stroom et al 1999 Target 2 S + 0.7 s 95% dose to on average 99% of CTV testedin realistic plans

Van Herk et al 2000 Target 2.5 S + 0.7 sor (more correct):2.5 S + 1.64 (s - s p)

Minimum dose to CTV is 95% for 90% of patients. Analytical solution for perfectconformation

McKenzie et al 2000a Target 2.5 S + b (s - s p) Extension of van Herk et al for fringe dose todue to limited number of beams

Parker et al 2002 Target S + (s2 + S2) 95% minimum dose and 100% dose for 95%

of volume. Probability levels not specifiedVan Herk et al 2002 Target 2.5 S + 0.7 s - 3 mm

or (more correct):mm8.26.17.2 2222

Symbols: S = SD of systematic errors; s = SD of random errors; s p = describes width of beam penumbra fitted to aGauss function; A = Peak-peak amplitude of respiration.

Van Herk,2003


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Distinction between serial-like (e.g.spinal cord) and parallel-like organs(e.g. parotid gland),

For tubed organs (e.g. rectum) walldelineation,

Remaining Volume at Risk (RVR): aidsoptimization and may assist inevaluating very late effects (e.g.

carcinogenesis).

Organ At Risk (OAR) andRemaining Volume at Risk (RVR)


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Organ At Risk (OAR)

PTV

Rectal wallRectum

ProstateRectum With Contents

Rectal Wall

Contents of tubed

organs should not beincluded


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PRV is a geometrical concept (tool) introduced

to ensure that adequate sparing of OAR willactually be achieved with a reasonableprobability ,

A positive OAR to PRV margin for serial organ. Dose-volume constraints on OAR are with

respect to the PRV,

Priority rules when overlapping PTVs or PTV-PRV(OAR),

Dose metrics are reported to the PRV.

Planning Organ at Risk Volume(PRV)


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Absorbed Dose in Radiation Oncology:ICRU 50 and 62:

Dose prescription: Responsibility of the treating

physician.

Dose reporting: ICRU reference point, Three-levels of dose reporting,

Point-doses: D ICRU point , D min ,Dmax ,

Dose recording.


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Issues for IMRT

Discrepancy between dose-volume constraintprescription and dose delivery,

Single point dose prescription,

Single point dose reporting, Biological metrics (e.g. EUD, TCP, NTCP, ),

Uncertainties in dose prescription andreporting,

More quality assurance required.


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PRE-RADIOTHERAPY WORKUP

Diagnosis3-D Imaging and

Staging

Multi-Disciplinary

Tumor Board

RADIOTHERAPY PREPARATION

Immobilization3-D Planning

Images

Delineation of Volumes ofInterest (VOIs), E.g. GTV,

CTV, OAR

PLANNING

Planning Aims OptimizedTreatment Plan

Modification of Aimsand Creation of TV or

Avoidance Structures

DELIVERY

Setup Patientwith

Immobilization

ImageVerification

AdjustSetup

Treat

PLAN ADAPTATION (if necessary)

Optimizer

Prescriptionand

TechnicalData

AcceptedTreatment Plan

PatientHistory


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RADIOTHERAPY PREPARATION

Immobilization3-D Planning

Images

Delineation of Volumes ofInterest (VOIs), E.g. GTV,

CTV, OAR

PLANNING

Planning Aims OptimizedTreatment Plan

Modification of Aimsand Creation of TV or

Avoidance Structures

DELIVERY

Setup Patientwith

Immobilization

ImageVerification

AdjustSetup

Treat

PLAN ADAPTATION (if necessary)

EvaluateDose

Delivered

EvaluateImages andCreate New

VOIs

RECORD AND REPORT

Record Level 2 or 3Reporting

Optimizer

Prescriptionand

Technical

Data

AcceptedTreatment Plan


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Planning aims:- PTV 1: dose x, D-V constraints, ,

- Spinal cord: D max = x Gy, ,- Prescription:

- Physicians responsibility,- Acceptance of doses, fraction #, OTT, D-Vconstraints, beam number, beam orientation,

Technical data for treatment delivery:- Instruction file sent to the linac and/or RVS.

Dose Prescription in IMRT


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Level 1: not adequate for IMRT,

Level 2: standard level for dosereporting,

Level 3: homogeneity, conformity andbiological metrics (TCP, NTCP, EUD, )and confidence intervals.

ICRU Levels of Reporting


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ICRU Reference Point NotA Typical Point for IMRT

Segment 1 Segment 2

Segment 3 Segment 8

Segments 4-7, 9-13

13 segment IM Field

From Jatinder Palta, University of Florida


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Reliability of Planning Metrics

From Indra DasMedian dose is most reliable


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Absorbed dose in Radiation Oncology:

Dose-volume reporting ( ie., Dv)- D

50%(D

median), prescription value,

e.g., D 95%- Dmean- Near Minimum dose: D 98%- Near Maximum dose: D 2%

State the make, model and version

number of the treatment planningand delivery software used toproduce the plans and deliver the

treatment.

Metrics for Level 2 Reporting of PTV


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01020

304050607080

90100

0 5 10 15 20 25 30 35 40 45 50 55 60 65Absorbed Dose (Gy)

Dif

f er

en

ti

alCum

ulat

ive

D 95

D98

D 50 %

D 2 %

Percent Volume

)

D mean

PTV Diff.PTV

Cum. PRV Diff. PRV

Cum.

%

%

Dose-Volume Reporting

Doses at a point are not as reliable as DVH near-min and near-max PTV median dose is the typical dose to the PTV PTV mean dose and PTV median dose are nearly identical

PRV mean dose and PRV median dose are not necessarily similar


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Dose-Volume Reporting

D95

D2

Dose-Volume Histogram

0

1020

30

4050

60

70

8090

100

50 55 60 65 70

Dose (Gy)

P e r c e n t V o l u m e

D98=60Gy

D50=60Gy

Dv with v 50 may require a change in prescription value

D98%D50% is closeto ICRU ReferenceDose at a Point


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Serial-like organs:- Dnear-max = D 98 .

Parallel-like organs:- Dmean (e.g. parotid) ,

- Vd where d refers to dose in Gy(e.g. V 20 Gy for lung).

Metrics for Level 2Reporting of PRV


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Homogeneity and Conformity

Vol

Dose

Vol

Dose

Vol

Dose

Vol

Dose

Low Homogenenity High Conformity

High Homogeneity Low Conformity

High Homogeneity HighConformity

Low Homogeneity LowConformity

Dose Dose

DoseDose

V o l

V o l

V o l

V o l

Dose

DoseDose

V o l

V o l

V o l


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Homogeneity:- Standard deviation in dose to the PTV.

Conformity:- Conformity Index: CI = TVpresc/PTV,- Dice Similarity Coefficient (DSC):

DSC = 2(TVpresc PTV)/(TVpresc +PTV)

Examples of Metrics for Level 3Reporting of PTV


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Recording in IMRT

Electronic archiving for at least the lifeof patient or 5 years whatever islonger,

Complete reconstruction of thetreatment technical data, plan and

delivery record, For clinical trials, longer archiving if

scientifically justified.


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Use Doses Corrected for Tissue

Heterogeneities A=Adipose, M=Muscle, B=Bone, L=Lung 4 MV, Parallel Beam

Ahnesjo and Asparadakis, 1999 Phys Med Biol 44:R99-R155


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Report Dose to Water While the dose is corrected for tissue

heterogeneities, the dose to a smallmass of water in tissue is reported.

Consistent with the older methods aswell as convolution/superpositionmethods.

Monte Carlo dose computation willhave to be corrected to dose to a smallmass of water in tissue


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Monitor Units Calculations forModel-Based Dose Calculation

D D A r A r A r b A

MU MU 10

0( , ) ( , ) ( , ) (1 ( ))

ComputedDirectly

BeamOutput

Correction to Account for Backscatter Into Monitor Chamber P

d A


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Monitor Units Calculations forModel-Based Dose Calculation

cal cal

Measured

cal

cal cal

Calculated

D A d

M b A

MU D A d

0

0

( , )(1 ( ))

( , )Ref

d cal A

Not including the effect of backscatter into themonitor chamber will result in about a 2% error at

worst.

B k i M i Ch b


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Backscatter into Monitor Chamber

Varian 2100 10 MV. Resultswith other jaw completely open

The effect is due to backscattered photonsentering the monitor and resulting in feedbackto the linac to lower its output

Liu et al.,Med. Phys 2000;27:737-744


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Monitor Backscatter for Square

On-Axis Fields Varian 2100 10 MV

Liu et al., Med. Phys 2000;27:737-744

f


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QA for IMRT Appropriate QA of TPS and delivery

equipment

Patient-specific QA: Delivery of individual fields into a

dosimeter

Delivery of all of the fields into a phantom

Independent dose calculation algorithms

with similar of better dose calculationaccuracy

In-vivo dosimetry not limited to a singlepoint.

G E i F d t l f


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Gap error Dose error

0.0

5.0

10.0

15.0

20.0

0 1 2 3 4 5

Nominal gap (cm)

% D

o s e

e r r o r

Range of gap width

2.01.0

0.5

0.2

Gap error (mm)

From Tom Losasso, Memorial Sloan Kettering

Gap Error is Fundamental fo

Conventional MLCs

Leaf Latenc is F ndamental


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TomoTherapy useslinear fit ofmeasured data tomodel leaf latency

Plans with small

opening times leadto uncertainty indelivery alsoleads to deliveryinefficiencies

Leaf Latency is Fundamental

fo Binary MLCs


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QA of Individual FieldsExternal diode/ion-chamber arrays

MapCheck PTW Octavius phantom IBA Matrix

Integrated detector systems EPID portal dosimetry

E d E d QA


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End-to-End QA


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QA Measurements

CheesePhantomused for QAmeasurements

Measureplane andpoint doseat the sametime

Film PlanePhantom can be rotated

or turned to acquire anyorthogonal plane


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Delivered Dose: 2.5cm Treatment Beam

0.0

0.5

1.0

1.5

2.0

2.5

-20 -15 -10 -5 0 5 10 15 20

Distance (cm)

D o s e

( G y )

On-Axis Tumor Off-Axis Tumor

On and Off-Axis ResultsFilm and Ion Chamber Absolute Dose

Tomotherapy Example


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QA for Allof the

FieldsTomotherapyExample

li QA l


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Delivery QA Panel

D li QA P l


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Delivery QA Panel

Comparison of Phantom Plan and Verification Film


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Comparison of Phantom Plan and Verification Film

Film

Plan

Film

Plan

Note theHighGradients

From Chet Ramsey, Thompson Cancer Survival Center

Independent Calculation


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p


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Gortec IMRT Test Phantom

Point 1: Isocenter

Point 2: Spinal cord isocenter

Point 3: Spinal cord cranial

Point 4: PTV T R

Point 5: PTV T R cranial

Point 6: PTV N L

Point 7: PTV N L caudalCourtesy M. Tomsej,

Brussels

TLDs are placed at seven locations.


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Dm /Dc=f(CENTER) per meas. pt

0.8

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

CENTER

D m

/ D c

isocenter

spinal cord iso

spinal cord cranial

PTV T D

PTV T D cranial

PTV N G

PTV N G caudal

Audit Results

Sample Result

Inter-Institution Dose Accuracy


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Inter-Institution Dose AccuracyAccuracy Distribution

0

100

200

300400

500

600

0.885 0.905 0.925 0.945 0.965 0.985 1.005 1.025 1.045 1.065 1.085 1.105 1.125

Measured Dose/Computed Dose

F r e q u e n c y

Number of Measurements = 2679Mean = 0.995Standard Deviation = 0.025

(Updated from Zefkili et al 2004)

Intra-Institution Dose Accuracy


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Accuracy Distribution

050

100

150

200

250

300

350

-10 -8 -6 -4 -2 0 2 4 6 8 10

Relative Difference Between Measured and Calculated Dose (% )

F r e q u

e n c y

Number of Measurements = 1591Mean = 0.45%Standard Deviation = 2.5%

Intra Institution Dose Accuracy

(Updated from Dong et al 2003)

IMRT Evaluation using


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Molineu et al IJROBP 2005Ibott et al Tech in Ca RT 2006Followill et al Med Phys 2007

Courtesy Ibott, RPC

Anthropomorphic Phantoms

For H&N, using a criteria of 5% or 4mm, thepassing rate drops from 75% to 58%

QA A f IMRT


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QA Accuracy for IMRT

Previous ICRU 5% point-dose accuracyspecification replaced by a volumetricdose accuracy specification.

Proposed new ICRU volumetric dose

accuracy specification:- High gradient ( 20%/cm): 85% of points

within 5 mm (3.5 mm SD),

- Low gradient (< 20%/cm): 85% of pointswithin 5% of predicted dose normalizedto the prescribed dose (3.5% SD).


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G F i


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m c r r r( , )

m c r r( , )

M D

M d

Pass

Dose accuracy axis

Distance toagreementaxis

Gamma Function 2 2 1 2

m c m c M m c M r r r r D r r r d / ( , ) {[ ( , ) / ] [ ( , ) / ] }

G F ti


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Gamma Function

m c r r r( , )

2 2 1 2

m c m c M m c M r r r r D r r r d / ( , ) {[ ( , ) / ] [ ( , ) / ] }

m c r r( , )

M D

M d

Fail

Dose accuracy axis

Distance toagreementaxis

Summary of Changes Between ICRU


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Summary of Changes Between ICRU50 & 62 and IMRT ICRU (83)

More emphasis on statistics.

Prescription and reporting with dose-volumespecifications.

No longer use ICRU-Reference Point. Want median dose D 50 reported.

Use model-based dose calculations.

Include the effect of tissue heterogeneities.

Report dose to small mass of water, not doseto tissue.

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