Thailand/Indra/2011 IMRT: Impact of ICRU-83 Indra J. Das, PhD, FACR Department of Radiation Oncology Indiana University School of Medicine Indianapolis, USA Thailand/Indra/2011 ICRU:International Commission on Radiation Units and Measurements 1978, ICRU-29; Dose specification for reporting external beam therapy with photon and electron beams. 1993, ICRU-50; Prescribing, recording and reporting photon beam therapy. 1999, ICRU-62; Prescribing, recording and reporting photon beam therapy (Supplement to ICRU 50). Thailand/Indra/2011 Nomenclature GTV Gross Tumor Volume CTV Clinical Target Volume IM Internal Margin ITV Internal Target Volume SM Set Up Margin PTV Planning Target Volume OR Organ at Risk PRV Planning organ at Risk Volume TV Treated Volume IR Irradiated volume Thailand/Indra/2011 Tumor Cell Density Distance Tumor Vessel Lymph node GTV CTV I CTV II high Low?, Zero? ? ? ? Thailand/Indra/2011 GTV CTV ITV PTV Irradiated Volume (IV) Treated Volume (TV) IR=TV + penumbra Thailand/Indra/2011 SM = Setup margin is uncertainties in patients positioning, and alignment during treatment. It is physical parameter associated with geometry and technical factors. SM is easy to control by immobilization devices and maintenance of accuracy and stability of machine. PTV = ITV + SM
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Thailand/Indra/2011
IMRT: Impact of ICRU-83
Indra J. Das, PhD, FACRDepartment of Radiation Oncology
Indiana University School of MedicineIndianapolis, USA Thailand/Indra/2011
ICRU:International Commission on Radiation Units and Measurements
1978, ICRU-29; Dose specification for reporting external beam therapy with photon and electron beams.
1993, ICRU-50; Prescribing, recording and reporting photon beam therapy.
1999, ICRU-62; Prescribing, recording and reporting photon beam therapy (Supplement to ICRU 50).
Thailand/Indra/2011
Nomenclature
GTV Gross Tumor Volume
CTV Clinical Target Volume
IM Internal Margin
ITV Internal Target Volume
SM Set Up Margin
PTV Planning Target Volume
OR Organ at Risk
PRV Planning organ at Risk Volume
TV Treated Volume
IR Irradiated volume
Thailand/Indra/2011
Tu
mor
Cel
l D
ensi
ty
Distance
Tumor
Vessel
Lymph node
GTV
CTV I CTV II
high
Low?, Zero?
? ?
?
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GTV
CTV
ITV
PTV
Irradiated Volume
(IV)
Treated Volume
(TV)
IR=TV + penumbra
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SM = Setup margin is uncertainties in patients
positioning, and alignment during treatment.
It is physical parameter associated with
geometry and technical factors.
SM is easy to control by immobilization devices
and maintenance of accuracy and stability of
machine.
PTV = ITV + SM
Thailand/Indra/2011
GTV
Subclinical disease
CTV
IM
ITV= CTV+IM
SM
PTV= CTV+SM
OR
Set up margin
Internal margin
PRV, Planning organ
at Risk Volume
PTV & PRV
Schema
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Radical vs Palliation
ICRU defines that if adequate dose
cannot be delivered to the GTV, the
whole aim of therapy should be
termed as palliative.
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Conformity Index; ICRU-50
CIiso=TV covered by % Isodose
Planning Target Volume
CI = > optimized closed to 1.0
Conformity index (CI) =TV/PTV
TV= treated volume is the tissue volume that
receives at least the dose selected and specified
by radiation oncologist.
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Dose Reporting
Dose must be reported to the ICRU reference point
ICRU Reference point is usually isocenter
It could be a point in the center of the PTV
Maximum and minimum Dose must be reported in PTV
Whenever possible Dose should be reported to PRV
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Digital Dose Era
IMRT is a digital dose
distribution
3D is an analogue dose
distribution
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Thailand/Indra/2011
Traditional Treatment
3D-CRT Treatment
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IMRT Plan
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IMRT Plan of head and neck nodes
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Difference between 3DCRT and IMRT
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Paradigm Shift
In 3D conformal therapy, ICRU-50 recommended Uniform dose to PTV (-5% to +7%)
Report dose @ isocenter
IMRT represents ≈40% of the radiation treatment with a paradigm shift Non uniform dose (dose painting)
Large dosimetric variations
Isocenter dose is meaningless
Radiobiological consequence of large heterogeneous dose is uncertain (ie 180cGy/day versus 250cGy/day)
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3D-CRT vs IMRT
Simple
No need of volume and OAR
Forward calculation
Give what you wish to target volume
Uniform fluence
Exact solution
Uniform dose
Low MU
Analogue dose
Dose defined to volume but specified at isocenter
Complex
Target and OAR must be present
Inverse calculation
Requires dose-volume constraints and cost function
Non-uniform
Approximate solution
High gradient dose
High MU
Digital dose
Isocenter dose undefined and meaningless
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Software
Inverse planning
(simulated
annealing)
Optimization
Gradient search
Global minimum
Cost functions
Hardware
Mimic (binary
MLC by NOMOS)
MLC
Tomotherapy
Compensator
Based
IMRT APPROACHES
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IMRT Terminology Number of Fields
Non opposing, odd/even numbers
Coplanar/noncoplanar
Beam divided into:
Beamlet (5, 10, 15, 30 etc)
Segments (no longer rectangular field)
Beamlet =segments
Bixels (resolution of the MLC)
Level (dose painting in a Bixel)
Intensity level
Integer number (5, 7, 10, 15, 20 etc)
Beamlet, single level
1
2 3
4
7
5
Multi level, beamlet
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IMRT Segments
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IMRT Field
Subfields (beamlets)
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0 1 1 1 0
0 1 1 1 0
0 0 1 1 0
0 1 1 1 0
0 1 0 1 0
0 1 1 1 0
0 1 1 1 0
0 0 1 1 0
0 1 1 1 0
0 1 0 1 0
0 1 1 1 0
0 1 1 1 0
0 0 1 1 0
0 1 1 1 0
0 1 0 1 0
0 1 1 1 0
0 1 1 1 0
0 0 1 1 0
0 1 1 1 0
0 1 0 1 0
0 4 4 4 0
0 4 4 4 0
0 0 4 4 0
0 4 4 4 0
0 4 0 4 0
Digital Dose Matrix
& Understanding
Intensity Level=
Layer of dose level
Level 1
Level 4
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Segmentation
Beam’s Eye View , BEV
Selection of grid size (mm)
Split fields in small building
block, beamlets, bixels
Segment = Collection of
beamlets with same
intensity level
PTV
Map (Fluence) =
Collection of segments
with different intensity
level
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Calculation of beamlet/ segmentation
Rx with 5 fields of 10x10 cm2 and 5 levels
10x10 mm =>100x5 = 500
5x5 mm =>20x20x5 = 2000
4x4 mm =>25x25x5 = 3125
3x3 mm =>33x33x5 = 5445
2x2 mm =>50x50x5 = 12500
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S S S wijk(Dopt-Dcal)2 = minimum
i,j,k
wijk= weight for constraint of an organ
Optimization & Cost Function
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Imaging
Target volume
DVHConstraints Inverse
planning
Transfer& sequencing
Beamletsequencing
Phantom Plan
Dose MeasurementsFilm dosimetry
Treatment
Record &Verification
PortalImaging
IMRT
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Inverse Planning Systems Corvous; NOMOS Corp, Pennsylvania, USA