ICRU Recommended Dose and Volume
Specification for Reporting Interstitial
Brachytherapy
Ali S. Meigooni, Ph.D.
University of Kentucky Medical Center,
Department of Radiation Medicine
Lexington, KY
Table of Contents
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Introduction
Definitions of Terms and Concepts
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Temporary and Permanent Implants
Source Specification
Description of Source Patterns
Total Reference Air Kerma
Volume and Planes
Description of Dose Distribution
Time Dose Factors
Definition of Quantities
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Absorbed dose
The Kerma (Kinetic Energy Released in Matter
The activity
The air kerma-rate constant, Γδδ
Relationship Between the Quantities
Reference Air Kerma Rate
Table of Contents (continue)
¾ Recommendations For Recording and
Reporting
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Parameters Required for Recording and
Reporting
Priority
Practical Applications of the
Recommendations
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Temporary Implants
Permanent Implant
Single Stationary Source Line
Moving Sources
Surface Applicators
Introduction
With the introduction of miniaturized
brachytherapy sources, the sophisticated
3-D source localization methods have
been introduced, which can be linked to
computerized
methods
for
dose
calculation.
Therefore,
a
common
language is valuable to provide a method
of dose specification and reporting which
can be used for implants of all types of
interstitial brachytherapy procedures.
¾
Introduction (continue)
1985: ICRU Report 38,
Was written regarding
volume specification
reporting intracavitary
in GYN.
¾
the Dose and
as well as
Brachytherapy
1997: ICRU Report 58,
Was written to generate a guideline
about the dose specification and
reporting for interstitial Brachytherapy
Introduction (continue)
¾
¾
The aim of the report 58
develop a common language
based on the presently
concepts.
was to
that was
existing
In this presentation, the ICRU-58
recommended
concepts
and
procedures for dose specifications
and reporting of the interstitial
brachytherapy
implants
will
be
reviewed.
G L ( r ,θ )
⋅ g L (r ) ⋅ F (r ,θ ),
D& (r ,θ ) = S K ⋅ Λ ⋅
G L (r0 , π / 2)
Definitions of Terms and Concepts
¾ Temporary
The radioactive sources are
removed from the tissue after the
treatment is completed
¾ Permanent Implants
The brachytherapy sources
remain in the patient, and they will
not be removed.
G L ( r ,θ )
⋅ g L (r ) ⋅ F (r ,θ ),
D& (r ,θ ) = S K ⋅ Λ ⋅
G L (r0 , π / 2)
Definitions of Terms and Concepts
(Continue)
¾ Traditionally,
the
temporary
implants were performed with the
linear (wires) radioactive sources
or seeds arranged in a linear
fashion
(i.e.
ribbons,
etc.).
However,
in
a
permanent
implants, multiple loose sources
were distributed in random
orientations.
G L ( r ,θ )
⋅ g L (r ) ⋅ F (r ,θ ),
D& (r ,θ ) = S K ⋅ Λ ⋅
G L (r0 , π / 2)
Definitions of Terms and Concepts
(Continue)
¾ With the design of the low energy
radioactive sources in the form of
stranded seeds or radioactive wires,
now the permanent implant can also
be performed with linear or prearranged ribbons.
¾ The loose seed implants are
considered separately in this report.
G L ( r ,θ )
⋅ g L (r ) ⋅ F (r ,θ ),
D& (r ,θ ) = S K ⋅ Λ ⋅
G L (r0 , π / 2)
Definitions of Terms and Concepts
(Continue)
¾
Planning temporary implants,
The total time of implantation depends on
a. Number of sources,
b. Strengths and source
c. Pattern of distribution of sources
G L ( r ,θ )
⋅ g L (r ) ⋅ F (r ,θ ),
D& (r ,θ ) = S K ⋅ Λ ⋅
G L (r0 , π / 2)
Definitions of Terms and Concepts
(Continue)
¾
Planning permanent implants,
The number of sources depends on
a. Their initial strength,
b. Type of the radioisotope.
G L ( r ,θ )
⋅ g L (r ) ⋅ F (r ,θ ),
D& (r ,θ ) = S K ⋅ Λ ⋅
G L (r0 , π / 2)
Definitions of Terms and Concepts
(Continue)
¾
Planning Boost permanent and
temporary implants,
The number of seeds and the initial
activity of the seeds are adjusted
upon the external beam radiation
dose.
Definition of Quantities
¾ Absorbed dose
The mean energy imparted by the radiation to a unit
mass of medium
dε
D=
dm
1Gy = 1J/Kg
¾The Kerma (Kinetic Energy Released in Matter
The sum of the initial kinetic energies of all the ionizing
charged particles liberated by uncharged ionizing
particles.
K=
dE tr
dm
1Gy = 1J/Kg
Definition of Quantities (continue)
¾ The activity
Number of disintegration of a radioactive nucleus per
second (dps).
dΝ
A=
dt
The SI unit : s-1
¾The air kerma-rate constant, Γδδ,
&
Γδ = l K δ
A
2
&
Kδ
The SI unit : J.kg-1m2
Where is the air kerma rate due to photons of energy greater than
δ, at a distance, l , from a point source, with activity of A.
Definition of Quantities (continue)
¾ Relationship Between the Quantities
Where:
⎡ μtr ⎤ m
D = K ⎢
(1 − g )
⎥
m
air⎣ ρ ⎦
air
g = part of the kerma that is lost to bremsstrahlung in medium.
(μtrtr) = energy transfer coefficient for the medium
¾Reference Air Kerma Rate
Reference Air Kerma Rate = Air Kerma Rate at a reference point of 1
cm or 1 m
1U = 1 μGy m22 h-1-1 = 1 cGy cm22 h-1-1
G L ( r ,θ )
⋅ g L (r ) ⋅ F (r ,θ ),
D& (r ,θ ) = S K ⋅ Λ ⋅
G L (r0 , π / 2)
Source Strength Specification
¾ Pre-1995
a. App. mCi (Aapp)
b. mgRaEq.
¾ Post-1995 (TG-43 recommendation)
a. air kerma strength μGy . h-1. m-1 or
cGy . h-1. cm-1 (U)
Total Reference Air Kerma
(TRAK)
TRAK = ∑ t . S
i
i
Where;
Si = Reference air kerma rate for
each source
ti = Irradiation time for each source
This quantity is analogous to mg.h
G L ( r ,θ )
⋅ g L (r ) ⋅ F (r ,θ ),
D& (r ,θ ) = S K ⋅ Λ ⋅
G L (r0 , π / 2)
Description of Source Patterns
¾ single plane: implant is defined as an
implant containing two or more
sources, which lie in the same plane
¾ two-plane (double-plane): implant
contains two planes, which are generally
parallel to each other
¾ Multi-plane: implant, contains three or
more planes
¾ non-planer: sphere or cylinder
Volume and Planes (ICRU 50)
GTV
CTV
PTV
TV
IV
Volume and Planes
¾ Gross Tumor Volume (GTV)
The palpable or visible/demonstrable extent
and location of the malignant growth.
¾ Clinical Volume (CTV)
The volume of the tissue that contains a
gross tumor volume and/or subclinical
microscopic malignant disease which has to
be eliminated.
Volume and Planes (continue)
¾ Planning Target Volume (PTV)
The volume of tissue receiving the
prescribed irradiation.
For an interstitial brachytherapy, the PTV is,
in general, identical to the CTV.
¾ Treatment Volume (TV)
The volume of tissue, which is encompassed
by an isodose surface that has been
specified by the radiation oncologist.
The dose value at this isodose surface is the
minimum target dose
CTV
The maximum diameters measured in three
orthogonal directions must be reported
Central Plane
¾ The plane that is perpendicular to the main
direction of the linear sources and passing
through the estimated center of the implant.
Central Plane (continue)
¾ The plane that is perpendicular to the main
direction of the linear sources and passing
through the estimated center of the implant.
¾
Description of Dose Distribution
Interstitial Brachytherapy Implants:
ƒ Non Homogeneous dose
distribution
ƒ High Regions around
the sources
ƒ Regions of plateau dose
or local minimum doses
Dose Distribution in One or More
Planes Through the Implant
¾
The minimum information needed for
the dose distribution of an implant is,
The isodose curves in at least one plane
either in tabular form or by graphical
presentation
¾ The central plane of the implant should
be used, If only one plane is chosen.
Prescription Dose
The prescribed dose is defined as the dose,
which the physician intends to give, and
enters in the patient’s treatment chart.
¾ Minimum Target Dose (MTD):
The minimum dose at the periphery of the CTV =
Minimum dose decided upon by the clinician as
adequate to treat the CTV (minimum peripheral dose).
MTD ≅ 90% of the prescribed dose in the
Manchester system for interstitial therapy
Prescription Dose (continue)
¾ Mean Central Dose (MCD) : Dm
The minimum dose at the periphery of the CTV
= Arithmetic mean of the local minimum doses
between sources, in the central planes.
Prescription Dose (continue)
Mean Central Dose (MCD) : Dm
Prescription Dose (continue)
¾ High Dose Volume
The volume of tissue that is encompassed that will
receive more than 150% of the mean central dose be
reported.
¾Low Dose Volume
A low dose volume should be defined as a volume within
the clinical target volume, encompassed by an isodose
corresponding to 90% of the prescribed dose. The
maximum dimension of the low dose volume in any
plane calculated should be reported.
Prescription Dose (continue)
¾
Dose Uniformity Parameters
ICRU defines the following two methods for the dose uniformity
i.
The spread of the individual minimum doses
used to calculate the mean central dose in the
central plane (expressed as a percentage of the
mean central dose).
ii.
The dose homogeneity index; defined as the
ratio of minimum target dose to the mean
central dose.
Time Dose Factors
¾
Time and Dose Rates for Temporary Implants
Time = Prescribed dose/initial dose rate
¾
Time Dose Pattern for Temporary Implants
a.
b.
c.
Continuous irradiation
Non-continuous irradiation
Pulsed irradiation
Recommendations for Recording
and Reporting
Parameters Required for Recording and Reporting
ƒ Description of Volumes : GTV, PTV, ….
ƒ Description of Sources :
9 Radioisotope and filtration
9 Pattern of source distribution
ƒ Description of Technique and Source pattern
Practical Applications of the
Recommendations
¾ Temporary Implants : Table 1.
¾ Permanent Implant: Table 2
¾ Single Stationary Source Line: Table 3
¾ Moving Sources: Table 4
¾ Surface Applicators : Table 5
Table 1: Levels of priority for reporting
temporary interstitial implants
Prioritya
Levelb of
computation
1
1
1
1
1
3
1
1
Description of Time Pattern (3.A.iv)
1
1
Total Reference Air Kerma (3.A.v)
1
1
Parameters for reporting
temporary interstitial implants
Description of Volume (3.A.i):
Gross Tumor Volume
Clinical Target Volume
Treated Volume (2.6.4)
Description of Source and Technique
(3.A.ii, 3.A.iii)
Radionuclide, type of sourc
Source size and shape, source pattern
Reference air Kerma rate
Inactivity vector (applicator), if any
Table 1: Levels of priority for reporting
temporary interstitial implants (Cont.)
Prioritya
Levelb of
computation
a. Prescribed dose including point or surface
1
1
of prescriptionc.
Reference Dose in Central Plane
a. Mean Central Dose
b. Minimum Target Dos
1
1
2
2
Description of High and Low Dose
volume (2.F.vi,2.F.vii)
2
3
Uniformity Parameters (2.6.8)
3
3
Alternative Representation of Dose
Distribution (2.F.ix)
3
3
Dose Rates at point or surface of
prescription (2.G.ii, 2.G.iii)
3
3
Parameters for reporting
temporary interstitial implants
Description of Dose (3.A.vi):
a.
1
2
3
Priority
Concerned with doses in the central plan
Required calculations outside the central plan. If this is
not available, then a more detailed description of source
pattern under priority 1 is required.
Additional information mostly of clinical research interest
b.
Level of computation
1.
2.
No computer needed
Hand calculation and/or computer calculation in central
plane.
3-D computation needed
3.
c.
Essential to establish consistent reporting and related to
past experience, necessary for comparison of
brachytherapy data and for relating outcome to treatment.
If a classical system is used, the system should be
identified.
Table 2: Levels of priority for reporting permanent interstitial implants.
Prioritya
Levelb of
computation
1
1
1
1
1
3
Description of Source and Technique (3.A.ii, 3.A.iii)
Radionuclide, type of source
Source size and shape, source pattern
Reference air Kerma rate
Inactivity vector (applicator), if any
1
1
Total Reference Air Kermac (3.A.v)
1
1
1
1
1
1
2
2
Description of High and Low Dose volume (2.F.vi,2.F.vii)
2
3
Uniformity Parameters (2.F.viii)
3
3
Alternative Representation of Dose Distribution (2.F.ix)
3
3
Parameters for reporting
permanent interstitial implants
Description of Volume (3.A.i):
Gross Tumor Volume
Clinical Target Volume
Treated Volume (2.6.4)
Description of Dose (3.A.vi):
Prescribed dose including method of prescription.
Reference Dose in Central Plane
a. Mean Central Dose
b. Minimum Target Dose
Table 3: Levels of priority for reporting implants with a single stationary source line.
Prioritya
Levelb of
computation
Gross Tumor Volume
Clinical Target Volume
Treated Volume
Description of Source and Technique (3.A.ii, 3.A.iii)
RadioNuclide
Length and Shape (Straight/Curved)
Reference air Kerma rate
Strength distribution (uniform linear strength is assumed, if
not, distribution must be specified.)
Diameter of inactive vector (applicator)
1
1
1
1
1
3
1
1
Description of Time Pattern (3.A.iv)
1
1
Total Reference Air Kerma (3.A.v)
1
1
Description of Dose and Prescription point (Distance from the source line position
along the source line)
1
1
Minimum target dose if different from prescribed dose
1
1
Dose at 1 cm from axis of the source line at its center
1
1
Dose at the surface of applicator in contact with tissue
3
3
Additional representation of dose distribution (2.F.ix)
3
3
Dose Rate: Average overall treated dose rate at the point or surface of dose
prescription (2.G.II, 2.G.III)
3
1
Parameters for reporting implants with a single
stationary source line
Description of Volume (3.B.1):
Table 4: Levels of priority for reporting implants with a moving source.
Prioritya
Levelb of
computation
1
1
1
1
1
3
1
1
1
1
Total Reference Air Kerma (3.A.v)
1
1
Description of Dose (3.A.vi): Prescribed dose
Minimum target dose
For single source line or bifurcation, dose at 1 cm
For complex implant, mean central dose
Method of dose optimization, if applicable
1
1
1
1
2
1
2
2
2
3
Description of high and low dose volume (2.F.vi, 2.F.vii)
2
2
Uniformity Parameters Additional representation of dose distribution (2.F.ix)
3
3
Alternative Representation of Dose Distribution (2.F.ix)
3
3
Dose Rates at point or surface of prescription (2.G.ii, 2.G.iii)
3
3
Parameters for reporting temporary interstitial implants
Description of Volume (3.A.i):
Gross Tumor Volume
Clinical Target Volume
Treated Volume (2.F.iv)
Description of Source and Technique (3.A.ii, 3.A.iii)
Radionuclide, source type and source
Type of movement
Range of motion (effective length of source)
Applicator-including diameter of inactive vector.
Number of inactive vectors
Reference air kerma rate
Description of Time Pattern (2.G.iii)
Intervals between fractions
Irradiation time per fraction
Table 5: Levels of priority for reporting implants with a surface applicators.
Prioritya
Levelb of
computation
Description of Clinical Target Volume (3.A.i):
Treated Volume (2.F.iv)
1
1
1
3
Description of Applicator ( 3.A.iii)
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
3
3
3
3
Parameters for reporting
use of surface applicators
Shape (flat/curved, round/square, etc.)
Size
Description of source (3.A.ii)
Radionuclide and chemical form
Concentration (seeds/tubes/plated)c
Description of Time Pattern (2.G.iii)
Intervals between fractions
Irradiation time per fraction
Total Reference Air Kerma (3.A.v)
Description of Dose (3.A.vi):
Prescription Dose and point of dose prescription
Dose at 5 mm in tissue at the center of the applicatord
Minimum target dosee
Description of high dose at tissue surface in contact with applicator,
usually near the –center of the applicator.
Uniformity Parameters
Additional representation of dose distribution (2.F.ix)
Dose Rates:
Average dose rate at the point of dose prescription
(2.G.II)
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