Radioactive sources

 In nature there are nearly 300 nuclei,
consisting of different elements and their isotopes.
 Isotopes are nuclei having the same number of
protons but different number of neutrons.
 Radioactivity is the release of energy and
matter that results from changes in the
nucleus of an atom.

 Radioisotopes: A version of a chemical
element that has an unstable nucleus and
emits radiation during its decay to a stable
form.

Radioisotopes come from:
 Nature, such as radon in
the air or radium in the
soil.
 Nuclear reactors by
bombarding atoms with
high-energy neutrons.

Three predominant types of
radiation are emitted by
radioisotopes:
1. alpha particles (+)
2. beta particles (-)
3. gamma rays.
 The different types of radiation
have different penetration
powers.

 Rapidly dividing cells are particularly sensitive to damage by
radiation. For this reason, some cancerous growths can be
controlled or eliminated by irradiating the area containing the
growth.
 Internal radionuclide therapy is by administering or planting a
small radiation source, usually a gamma or beta emitter, in the
target area.
 Short-range radiotherapy is known as brachytherapy.
BRACHYTHERAPY

 External irradiation (sometimes called teletherapy)
 Teletherapy is the use of radioactive material for
production of external beam of gamma rays for Rx
at a distance from the radioactive source(tele means
“at a distance”)
 Teletherapy can be carried out using a gamma beam
from a radioactive cobalt-60 source.
TELETHERAPY

 High specific activity
 Adequate photon energy
 Appropriate half-life
 Easy to make (or activate)
 Easy to handle
 Reasonable cost

 Brachytherapy (BT) (brachy is Greek for “short
distance”) consists of placing sealed radioactive
sources very close to or in contact with the target
tissue.
 The main advantage of brachytherapy technique is it
delivers localized high dose to the tumor volume.

 Ra-226: 0.975 Ci/g
 Ir-192: 9220 Ci/g
 An Ir-192 source can have much higher activity than
a Ra-226 source for a given mass or size.
 This is one of reasons that Ir-192 is used as HDR
source (about 10 Ci).

RADIUM 226
 It is a part of the radioactive series.
 Starting with uranium-238 and ending with the stable
isotope lead- 210.
 Half life – 1620 years

 Decays by alpha emission to radon-222 (daughter
product.)
 An encapsulated radium source emits a photon
spectrum with maximum energy of 2.45 Mev.
 It was used for treatment of cancer of the uterine cervix
and implants.

 Product of uranium-238 fission.
 Decays by β minus emission.
 Half life – 30.17 years
 Emits a photon energy 0.662 Mev.

 Its lower photon energy eased the
radiation protection requirements.
 Its solid physical form and lack of alpha
emission made it safer in the tube being
damaged. So caesium considered as
safer than radium.

Spherical caesium 137 source as used in
afterloading machine

 Produced by neutron activation of the
stable cobalt-59.
 Short half life – 5.26 years
 Decay by β minus emission.
 It emits gamma energies of 1.17 and
1.33 Mev.
 High specific activity
 More expensive than caesium.

 Produced by the neutron activation of
iridium-191.
 Half life- 74 days.
 Decays by beta emission.
 This emits a complex photon spectrum
with maximum energy of 0.38 Mev.
 Its used in the form of a wire, used for
low dose rate (LDR) manual implants.

Diagramatic representation of iridium 192 wire

 The central radioactive core is an
iridium / platinum alloy.
 Its surrounded by a 0.1mm thick
platinum sheath.
 It is available in 0.3 mm or 0.6 mm
overall diameter as wires or pins.
 Thin wire is coiled as 500 mm length.
 High specific activity.
 Its used for high dose rate afterloading
machines.

 Daughter product of xenon 125.
xenon 124.
 Iodine 125 decays electron capture.
 Half life - 59.6 days
 Gamma ray has an energy of 35.5 Kev.

 Emits characteristic radiation of 27.4
and 31.4 Kev.
 This low energy gives a half value
thickness of lead of 0.025 mm, which
makes radiation shielding highly
effective.
 Iodine 125 is incorporated with
implantable seeds.
 Several types of seeds are available
from different manufacturers.

TWO TYPES OF IODINE 125 SEEDS
DIAGRAMMATIC REPRESENTATION OF
FOR EXAMPLE

Figure shows the structure of Oncura type of
6702 and 6711 seeds.
 6702 has the iodine 125 absorbed on to an ion
exchange resin.
 It contains no radiographic marker.
 Its used for temporary implants.
 6711 has iodine 125 adsorbed on to a silver
rod.
 Silver acts as radiographic marker for
imaging.
 Its used or prostate implants.
 Size of both seeds – 4.5 mm long and 0.8 mm
diameter.

 Produced by the neutron activation of
the stable palladium 102 and the
interaction of protons or deuterons on
rhenium 103.
 It decays by electron capture.
 Half life – 17 days

 Emits a mixture of gamma rays and
characteristic radiaton.
 Its with a slightly lower mean energy of
about 21 kev.
 It is encapsulated into seeds.
 Used for prostate implantation.

the stable gold 197.
 Decays by beta emission to an isotope
of mercury.
 Half life – 2.7 days

 It emits a 0.412 Mev gamma photon.
 It is encapsulated in platinum.
 Used for permanent implantation,
especially head and neck region.

 It is a fission product.
 Used in brachytherapy as a beta emitter for
superficial treatements.
 Decays by beta minus emission to yttrium 90.
 Half life – 28.7 years.

 Beta energy is too small ( 546 kev ).
 Daughter element yttrium 90 (half life -
64 hours) also decay by beta minus
emission.
 Beta energy – 2.27 Mev
 This material has been used for surface
applicators – ophthalmic applicator.

 Beta particles provide the required
surface dose with rapid fall- off beneath.
 They were made from a strontium
compound.
 It incorporated into a silver sheet.
 Then formed into an applicator with
shielding on the reverse side.
 Several shapes and sizes are currently
available.

Fission product
Decays by beta emission to an
isotope of rhenium.
Half life- 1.02 years
Beta energy – 3.54 Mev
Plaques are similar to the strontium
90 plaques.

 Active material is incorporated into a
silver sheet forming the surface of the
plaque.
 Plaque is provided with suture holes to
allow it to be fixed.
 Several shapes and sizes are currently
available.

Various other radionuclides have been
used in brachytherapy.
 Californium 252
 Phosphorous 32
 Samarium 145
 Tantalum 182

 Artificial radionuclides are used.
 The source is in direct contact with a tissue or is
sealed in an envelope.
 OPEN SOURCE
1. Can be applied metabolic way. Therapy of thyroid
gland by radioactive iodine 131, which is
selective captured by the thyroid.
2. Infiltration of the tumour by the radionuclides
solution of a postrate tumour by the colloid gold
Au-198. This way of application is seldom used
today as well.

 CLOSED SOURCES
1. Needles with a small amount of radioactive
substance. They usually contain Co-60 or Cs-
137 . The needles are applied interstitially.
2. Sources are also inserted in to the body cavities
3. Large irradiation devices for teletherapy. The
radionuclides is enclosed in a shielded
container. The radioactive material is moved in
to working position during irradiation. The
most commonly used are Co-60 or Cs-137.

Radioactive sources

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Radioactive sources