BRACHYTHERAPY
BRACHYTHERAPY
• Source Strength Specification
• Radioactive sources
• High-dose-rate Brachytherapy
• Pulsed-dose-rate Brachytherapy
• Applicators and instruments
• Brachytherapy Dosimetry and Dose Distribution
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BRACHYTHERAPY
• Involves placing radioactive material
directly into or immediately adjacent to
the tumor.
• Brachy – “short”
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ADVANTAGES OF
BRACHYTHERAPY
• High dose of radiation is delivered to tumor in short time, So
biologically very effective
• Normal tissue spared due to rapid dose fall off
• Better tumor control
• Radiation morbidity minimal
• Radiation reactions localized &manageable
• Treatment time short – reduces risk of tumor repopulation
• Therapeutic ratio high
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DISADVANTAGES OF
BRACHYTHERAPY
• Invasive
• Need anesthesia
• Limited availability
• Any small error leads to high normal tissue dose
and treatment failure
• Radiation hazards exposure
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IDEAL
RADIOISOTOPE
• Easily available & Cost effective
• Gamma ray energy high enough to avoid increased
energy deposition in bone & low enough to minimise
radiation protection requirements
• Preferably monoenergetic: Optimum 300 KeV to 400
KeV(max=600 kev)
• Half life: – Moderate (few years) half life removable
implants – Shorter half life for permanent implants
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PHYSICAL STATES OF
BRACHYTHERAPY
SOURCE
• Tubes
• Needles
• Seeds
• Fluids
• Ophthalmic Applicators
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TUBES
Are standard capsules for the radioactive source used
for the treatment of gynecological malignancies.
Encapsulated with platinum.
Examples:
• Radium-226
• Cobalt 60
• Cesium-137
NEEDLES
• Radioactive substance use for interstitial
treatment are usually encapsulated in a
shield shape needles.
• Longer than tubes but small in diameter.
SEEDS
Seeds are left in placed permanently.
Examples
• Iodine-125
• gold 198
• Iridium 192
RADIOISOTOPES
Isotopes Energy (MeV) Half-life Source form
Ra-226 0.83 1,626 yrs Tubes/needles
Cs-137 0.662 30 yrs Tubes/needles
Ir-192 0.397 73.8 days Seeds
Co-60 1.25 5.27 yrs Spheress
I-125 0.028 59.6 days Seeds
Pd-103 0.021 17 days Seeds
Au-198 0.412 2.7 days Seeds
Sr-90 2.24 28.9 days Plauqe
I -131 0.60 8.06 days Oral solution
P-32 1.71 14.3 days Fluid 11
RADIUM – 226
• Decays alpha emission and part of a long decay chain with
natural Uranium and concludes in an isotopes of stable lead.
• Use of radium was very practical because it has a very high
specific activity.
• Specific activity is the activity per unit mass of radioactive
material. It dictates the total activity that a small source can
have.
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CESIUM – 137
• One of the most widely used of the radium substitutes and has
largely replaced radium as the primary isotope for brachytherapy of
the uterus and cervix.
• It reduces the radiation safety hazard.
• Less problematic when it comes to storing compared with radium.
• Cesium sources in a wide variety of needle or tube configurations.
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IRIDIUM – 192
• Supplied in form of wires of Iridium – platinum alloy or a small
seeds of this alloy attached to the nylon ribbon with spacing of
1 cm between seeds.
• Undergoes beta decay and has average energy of 380 KeV
• They were being inserted into the tissue carrier needles that
penetrate through the tumor or around the tumor.
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COBALT – 60
• They are not commonly used in brachytherapy applications.
• Undergoes a two tiered beta decay after its neutron activation
that produces 1.117 and 1.33 MeV gamma rays which
averaged of 1.25 MeV.
• It has been used for ophthalmic applicators in some
application in some needles and tubes.
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GOLD – 198
• Popular replacement for radium – 222 in permanent implants.
• Radiation safety is less problem and more dose is absorbed
locally.
• They are formed in a cylinder grains or seeds.
• They have an activity of approximately 5 mCi/seeed.
• Gold gives tissue a very high dose rate in a short time, a
method called high-dose rate therapy.
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IODINE – 125
• Becoming more common in interstitial seed plants.
• Daughter product from activation of xenon- 124 and xenon –
125.
• Making iodine therapy a low dose rate therapy.
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TYPES
BRACHYTHERAPY
DEPENDS ON
• Source position
• Source loading pattern
• Duration of implant
• Dose rate
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SEVERAL
BRACHYTHERAPY
APPLICATION
(SOURCE POSITION)
INTERSTITIAL
TECHNIQUE
• Consists of surgically placing small
radioactive sources directly into the target
tissue with the use of needles.
• Hollow stainless-steel needles are inserted
through the lesion with both ends visible,
plastic tubing with button affixed through
each needle
• The most widely used source for the treatment of
gynecological cancers is 137Cs.
• It is often necessary to use sources of different
strengths to achieve the desired dose
distribution.
• In modern remote afterloading devices 192Ir is
the commonly used radionuclide
INTRACAVITARY
TECHNIQUE
Intracavitary brachytherapy is mostly used for
cancers of the uterine cervix, uterine body
and vagina. Various applicators are in use to
hold the sources in an appropriate
configuration.
A cervix applicator consists of a central tube
(tandem) and lateral capsules (ovoids or
colpostats).
FLETCHER SUIT
SYSTEM
• Tandem – long narrow tube that inserts to
the opening into the cervix into the uterus
• Ovoids – (colpostats) oval shaped and
inserted to lateral fornices of vagina
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SURFACE MOULD
THERAPY
Consist of applicator array of radioactive
sources usually designed to deliver a
uniform dose distribution to the skin of
mucosal surface.
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INTRALUMINAL
TECHNIQUE
Places the implant in in a special applicator
inside a body passage. It may be used for
esophageal and lung cancer and can be
given along with external radiation therapy.
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INTRAVASCULAR
TECHNIQUE
Used as a treatment for restenosis and
recurrent arterial blockage following
angioplasty or stenting of a blocked
artery
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BRACHYTHERAPY
TREATMENTS
CLASSIFIED WITH
RESPECT TO SOURCE
LOADING
• Hot Loading
• After loading
• Remote after loading
• Manual after loading
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HOT LOADING
The applicator is preloaded and
contains radioactive sources at the time
of placement into the patient
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AFTERLOADING
• The applicator is placed first into the
target position and the radioactive
sources are loaded later.
• Manual after loading
• Remote after loading
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MANUAL REMOTE
AFTER LOADING
• Ir192 wires • consists of pneumatically or motor-
driven source transport system
• sources manipulated into applicator
by means of forceps & hand-held tools
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THE USE OF REMOTE
AFTERLOADING DEVICES
OFFERS SEVERAL PRACTICAL
ADVANTAGES OVER MANUAL
PROCEDURES, SUCH AS
• Increased patient Remote afterloading devices are used in
treatment capacity; both interstitial and intracavitary clinical
applications.
• Consistent and
reproducible treatment The anatomic sites commonly treated with
delivery; these devices are similar to those treated
with conventional brachytherapy
• Reduced radiation procedures
exposure of staff
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THE ESSENTIAL
COMPONENTS OF ALL
REMOTE AFTERLOADING
SYSTEMS ARE:
• A safe to house the radioactive source;
• Radioactive sources, single or multiple;
• A local or remote operating console;
• A source control and drive mechanism;
• Source transfer guide tubes and treatment
applicators;
• A treatment planning computer. 34
• The three commonly used
radioactive sources in remote
afterloading devices are 60Co,
137Cs and 192Ir.
• Currently the most commonly used
source for afterloading is 192Ir
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DOSE RATE
1. Low-dose rate(LDR)
• Emit radiation at a rate of 0.4–2 Gy/hour.
2. Medium-dose rate (MDR)
• characterized by a medium rate of dose delivery, ranging
between 2-12 Gy/hour.
3. High-dose rate (HDR)
• when the rate of dose delivery exceeds 12 Gy/h.
4. Pulsed-dose rate (PDR)
• involves short pulses of radiation, typically once an hour, to
simulate the overall rate and effectiveness of LDR treatment.
5. Ultra low dose rate
• Dose range 0.03 to 0.3 Gy/Hr 36
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BRACHYTHERAPY
TREATMENT CLASSIFIED
WITH RESPECT TO
TREATMENT DURATION
• Temporary
• Permanent
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TEMPORARY
IMPLANT
Dose is delivered over a short period of time and the
sources are removed after the prescribed dose has beam
reached.
• It may be LDR or HDR.
• The specific treatment duration will depend on many
different factors, including the required rate of dose
delivery and the type, size and location of the cancer.
Example
• Cesium 137
• Iridium 192
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PERMANENT
IMPLANT
• Dose is delivered over a lifetime of the source until
complete decay.
• seed implantation
• Placing small LDR radioactive seeds (about the size of a
grain of rice) in the tumor or treatment site and leaving
them there permanently to a gradually decay.
Example:
• Iodine 125
• Palladium 103
• Gold 198
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BRACHYTHERAPY
APPLICATORS AND
INSTRUMENTS
• External applicator or molds
• Interstitial applicators
• Intracavitary applicators
• Intravascualr stent application
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BRACHYTHERAPY
DOSIMETRY AND
DOSE DISTRIBUTION
• Paterson-Parker (Manchester) System
• Paris System
• Quimby/Memorial Dosimetry System
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RADIUM
SUBSTITUTE
Used to indicate any isotope used in brachytherapy.
Based on the original radium work.
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PATERSON-PARKER
(MANCHESTER)
SYSTEM
• Manchester system
• Establishes a set of guidelines that, if
followed, will provide dose of 10% within the
implanted area.
• Devised to deliver a reasonably uniform
dose to a plane or volume.
• The system assumes the use of linear
sources to be implanted in tissue in planes
or other geometric shapes and gives rules
for placing the radium sources in this case.
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• The sources are distributed non-
uniformly following certain rules, based
on the size of the target volume, with
more source strength concentrated in
the periphery.
• Usually the prescribed dose is about
10% higher than the minimum dose
within the treated volume.
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PLANAR VOLUME
IMPLANTS
• Square and rectangle • If the shape of the implanted
implants volume resembles a three
• The planes should be 1 dimensional shape more than
a plane.
cm apart and parallel.
• Cylinders, ellipsoids, spheres
and cubes.
• This type of calculations are
done for seed implants of the
prostate and other implants
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PARIS SYSTEM
• Utilizes uniform distribution of the
radioactivity and the rules can be applied to
volumes of any shape.
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THE THREE PRINCIPLES OF PARIS
SYSTEM
• The radioactive sources must be rectilinear and arranged so that their
centers are in the same plane, which is perpendicular to the direction
of the sources and it is called the central plane. The dose is defined
and calculated in this plane but not restricted to the plane.
• The linear activity must be uniform along each source and same for all
sources.
• The radioactive sources must be placed uniformly. This is the case
even more than one plane is used.
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QUIMBY SYSTEM
• Quimby calculated and tabulated dose
distributions for linear radium sources
with different active lengths and wall
thickness.
• The tabulated data give the centigrays per
hour at locations along as well as away
from the axis of 1 mg –radium radium
source.
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PATIENT
IMMOBILIZATION
• Aid in treatment setup and reproducibility.
• Provide immobilization of the patient or
treatment area with minimal discomfort to
the patient
• Support the conditions prescribe in the
treatment plan
• Increase precision and accuracy of the
treatment.
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• Patient positioning devices designed to
place the patient in particular position
for treatment. Ensuring that the patient
does not move.
• Simple immobilization devices
• Complex immobilization devices
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• Masking tape or paper • Foaming agents
tape • Alpha cradle
• Plastic or cloth strap with • Vac-Lok
Velcro • Thermoplastic folds
• Rubber bands
• Bite bocks
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