Radioactivity, Alpha radiation, Beta radiation, Gamma radiation, Types of radiation, properties of alpha, beta and gamma radiations, Half-life of radioactive substances, Methods to measure radioactivity, Radioactive isotopes, Isotopes of Hydrogen, Isotopes of Carbon, Sodium Iodide -131, Medicinal uses of Sodium Iodide - 131, Storage of radioactive substances, Precautions in the handling of Radioactive substances, Applications of Radiopharmaceuticals

1. RADIOPHARMACEUTICALS
Authored By:
Dr. Alex Martin
Ph.D., M.Pharm, FAGE

2. RADIOACTIVITY
The phenonemon of an unstable nucleus loosing energy via emission of radiations
composed of either subatomic particles or waves through space or through a maaterial
medium.
Energy from
sun is radiated
in the form of
waves.
Energy from unstable
nucleus is emitted in
the form of particles or
in certain forms of
electromagnetic
radiations.
An unstable nucleus gets converted to a stable nucleus via
emmision of a sub-atomic particle or electromagnetic radiation.
Such unstable nuclei may be naturally occuring in nature or may
be artificially produced isotopes of elements.
ALPHA, BETA AND GAMMA RADIATION
Emission of alpha particles by an unstable nucleus is referred to as
Alpha radiation.
Alpha particles consists of two protons and two neutrons bound
together into a particle.
I. ALPHA RADIATION

3. II. BETA RADIATION
Emission of Beta particles by an unstable nucleus is referred to as Beta
radiation.
Beta particles consists of a high speed–high energy electron
spontaneouly emmited by a radioactive atom during its decay.
III. GAMMA RADIATION
Emission of gamma rays by an unstable nucleus during radioactive
decay is referred to as Gamma radiation.
Gamma rays are electromagnetic waves with shortest wavelength and
therefore its component photon has the highest energy. For the reason,
it is the most penetrating.
PROPERTIES OF ALPHA, BETA AND GAMMA RADIATION
A. Alpha radiations have the least penetrating power such
that they can be stopped if obstructed by a thin sheet of
paper.
B. Beta Rays have more penetrating power than the alpha
rays. A medium of higher density is required to stop them,
such as an aluminum foil.
C. Gamma Rays has the highest penetrating power of all.
A denser medium which is as thick as that of a heavy
metal such as lead is required to obstruct them.
1. PENETRATING POWER

4. 2. IONIZING POWER
I. ALPHA PARTICLE
An Alpha particle has the greatest mass of
all three, and therefore has the highest
ionizing power. Within their small range in
Air < 10 cm, they can ionize anything on its
way, acquire two electrons and become a
harmless Helium item. However, their entry
into the body is easily obstructed by clothing
or even dead skin on humans.
II. BETA PARTICLE
A Beta particle is an electron emitted
spontaneously by a decaying
radioactive atom. Because its an
electron, the mass is quite less and
therefore they have lesser ionizing
power and causes lesser injury to
body tissues. However, owing to their
penetrating power, they can cause
grave injuries to human tissues.
III. GAMMA RADIATION
Gamma radiations are electromagnetic waves
that have no mass. For this reason, Gamma rays
have ‘Zero Ionizing Power’. They pass through
the human body without causing any injury.

5. 3. CHARGE
Alpha Particle = +2e
Beta Particle = -e
Gamma ray = 0
4. RANGE
Alpha Particle ~ 10 cm in air
Beta Particle = Up to a few meters in air
Gamma ray = Several meters in air
CHART: PHYSICAL PROPERTIES OF ALPHA, BETA AND GAMMA RADIATION

6. HALF LIFE
1. Half life of a radioactive material is the time required to
reduce to half of its initial volume.
2. Eg: Cobalt-60 is a radioactive element used in radiation
therapy in oncology
Half life of Co-60 = 5.6 years
That means,
8 g of Co-60 = 4g of Co-60 after 5.6 years
4g of Co-60 = 2g of Co-60 after 5.6 years
2g of Co-60 = 1g of Co-60 after 5.6 years
…and so on, Co-60 would have infinite half lives…., till radiations
emitted become negligible.
3. Unstable Co-60
decays and gets
converted to stable
Nickel-60 nucleus
which persists with the
undecayed Co-60.
Therefore, there is no
visible change in
volume or mass from
its initial volume.
4. Half life of a radioactive material depends upon nature of
unstable nuclei and the type of radiation that the radioactive
element is emitting.
a) Alpha decay is slowest.
b) Beta decay is faster
c) Gamma decay is fastest.
Thus, half life for gamma decay will be the least.
Half life for alpha decay will be more.

7. Half life is given as:
t1/2 = 0.693/ƛ
Where, ƛ = radioactive decay constant
t1/2 = Half life
0.693 = Logarithm of 2, representing exponential rate of decay.
METHODS TO MEASURE RADIOACTIVITY
1. Scintillation Counting Method
1. a) It consists of a Scintillation
counter which is usually
composed of materials that
fluoresces when struck by an
ionizing radiation such as
phosphor, thalium activated
Sodium iodide, ZnS or anthracene
incorporated into liquid solvents.
b) When ionizing radiation (alpha,
beta or gamma radiations) passes
through the scintillation counter,
it ionizes the atoms along its
track. This results in very weak
light flashes
2. The light flashes are converted into electrical
signals by photoelectric alloy of cesium and
antimony.
3. The converted electrical signals are amplified for
about a million times by Photomultiplier tube.

8. 4. The resultant output signal is then directed to an anode and then to a counter. The
output pulse recorded is directly proportional to the energy of the radiation that was
incident on the scintillation counter at the first place.
2. GEIGER-MULLER COUNTER
1. Gieger-Muller tube is filled with an inert gas such as argon,
helium or neon at low pressure and a very high voltage.
2. When a particle or photon of incident radiation passes
through the tube, it ionizes the gaseous atoms along its track.
3. The ionization of gaseous atoms is accompanied by release
of electrons which collide with other atoms and results in more
electrons. The additional electrons generated repeat the cycle
of collision and generation of more electrons. This manifold
multiplication of the initial electrical signal within the tube is
referred to as Avalanche Mutiplication.
4. The amplified electrical signal is diverted towards the anode,
and from the anode to a read-out device.
5. The current recorded is directly proportional to the energy
of the photon carried by the incident radiation

9. 3. IONIZATION CHAMBER
1. It consists of a gas-filled chamber with
two electrodes viz. the anode and the
cathode.
2. A voltage is applied between the
electrodes to create an electric field
3. When ionizing radiation enters the
chamber it ionizes the atoms along its
track creating ion-pairs.
4. The resultant positive ions and
electrons move to electrodes of opposite
polarity under influence of electric field.
5. This generates an ionization current which is measured
by an electrometer circuit. The electrometer is capable of
reading very small current in the range of femptoampere
to picoampere.
6. The current measured is
equivalent to the energy of the
photon that was incident on
the ionization chamber.

10. 4. PROPORTIONAL COUNTER
1. It consists of a chamber filled with an
inert gas, usually 90% argon and 10 %
methane, also known as P-10.
2. When an ionizing particle enters the
chamber, it ionizes the atoms of the gas
along its track.
3. This results in the formation of ‘ion
pairs’ vidilicet - the positive ions and the
electrons.
4. The formed ions migrate to the the electrodes of opposite polarity. This area is referred
to as the ‘ion-drift’ region. In this region the electrical field strength is low which is the
reason that the newly formed ‘ion-pair’ are not able to ionize any atoms in this region even
though they collide.
5. But as the ion-pair reach very closely in the immediate vicinity of electrodes, the
electrical field becomes very strong. Due to this reason, the ion-pair tends to ionize atoms
of the gas in this region producing additional electrons. The additional electrons collide
with other gas atoms in this region to produce more electrons. The cycle continues to
produce an electrical signal of significant strength. This region is referred to as the
‘avalanche region’

11. 6. The output electrical signal is fed to the anode and from there to a read out device.
7. As each avalanche is due to only one original ionizing incident, the total ion current (sum
of all avalanches) would be directly proportional to the number of original events.
RADIOACTIVE ISOTOPES
1. Species of the same chemical element that
have different masses and that emit their
excess energy in the form of radiations (Alpa,
Beta or gamma) are referred to as Radioactive
isotopes.
2. Radioactive isotopes have unstable
combination of neutron and protons in their
nucleus. This results in the build up of excess
energy of their nucleus which they release in
the form of radiations in the process of
radioactive decay.
3. The resultant nucleus after emission of
radiations may be a stable nucleus, or it may
be a another unstable nucleus bound to emit
further radiations.

12. An example of this is Hydrogen atom with
three isotopes – Protium, Dueterium and
Tritium. However, only tritium is a
radioactive isotope which emits beta
radiations.
Similarly, Carbon has three naturally
occuring isotopes – C-12, C-13 and C-14,
out of which only one i.e. C-14 is a
radioactive isotope, meaning that its
emits radiations and has a half life.
SODIUM I-131
1. Oral Tablets are
available as white
gelatin capsules.
2. Inert fillers are soaked into solution of
Iodine- 131 such that they adsorb the
medication. Later, these fillers are enclosed
in a capsulated dosage form.

13. 1. I-131 emits beta particles and Gamma rays with a
physical half life of 8.04 days. The resultant stable
nucleus formed is that of Xenon – 131.
PHYSICAL PROPERTIES
2. Gamma ray constant for Iodine –
131 = 2.27 millicurie / hour at 1 cm.
3. Half-
value
thickness
= 0.24cm
of Lead
MEDICINAL USES OF SODIUM IODIDE - 131
Sodium Iodide – 131
undergoes beta mode of
decay, and thus it kills the
cells that it penetrates. As
iodide is rapidly absorbed
in the thyroid tissue, it
aids in eliminating thyroid
cancer cells.
1. In Thyroid Cancer

14. MEDICINAL
USES OF
SODIUM
IODIDE - 131
2. In the
treatment of
thyrotoxicosis
It is used in the
treatment of
thyrotoxicosis
due to Grave’s
Disease. It is
absorbed in the
thyroid tissues
and eliminates
the hyperactive
cells of the
thyroid tissue,
thus bringing
down the
thyroid
hormone level
in the body.
3. In Thyroidectomy
NaI – 131 is used for ablation procedure
wherein the remaining left over thyroid tissue
after thyrodectomy, is destroyed by Beta
radiations.
4. In pheochromocytoma and nueroblastoma
Sodium Iodide – 131 is combined with certain radiopharmaceuticals
that have higher affinity for other tissues. In this way, it serves dual
purpose – one is in providing additive effect in killing malignant cells
and the other is in imaging of the tissue (NaI-131 emits gamma
radiations also).
Eg: I-metaiodobenzylguanidine is used for imaging and treating
pheochromocytoma and nueroblastoma.

15. 5. As
Diagnostic
aid for
determining
tumors
NaI-131 in addition to Beta radiations,
emits gamma radiations too. The
gamma radiations can be easily viewed
by a gamma scanner wherein the
structure appears as a fluorescent
image. As iodine has a high affinity for
thyroid tissue, it accumulated there and
emits gamma rays and thus it detects
thyroid malignancy.
5. Diagnosis of
Thyroid function
It is employed in Radioactive Iodine Uptake
Test. The amount of beta radiations emitted by
the thyroid gland after the administration of
NaI-131 capsule is measured. It is seen that the
measured value is equivalent to the expected
value of radioactivity (as is determined from
dose). If not so, it indicates the inability of
thyroid cells to absorb iodine.
MEDICINAL USES OF SODIUM
IODIDE - 131

16. STORAGE CONDITIONS OF RADIOPHARMACEUTICALS
1. It should be
stored in a place
which is not
readily visited by
laboratory
personnel.
2. The containers that contains
radiopharmaceuticals should be
enclosed with thick glass walls
or perspex to provide for
sufficient shielding and to
permit visual inspection.
3.Radiopharmaceuti
cals that emit
gamma radiations
(such as Sodium
Iodide- 131) should
be enclosed in thick
lead containers to
provide for shielding
against gamma
radiations.
4. Liquid preparations of
radiopharmaceuticals
should be stored in thick
glass vials that is sufficiently
transparent to permit visual
inspection of the
preparation.
5. A separate fridge is to be
assigned for radiopharmaceuticals
that are meant to be regulated in a
cold temperature. A sticker
depicting the sign of radioactive
substances is to be glued over the
fridge.

17. PRECAUTIONS IN HANDLING RADIOPHARMACEUTICALS
1. Protective Clothing
1 a). Wear protective clothing, preferably disposable clothing when
working in radioactive lab. Remove and dispose off the clothing after
work.
1 b). For face, use radiation shields.
1 c). Always wear gloves and shoes. Touch susceptible surfaces via means
of tissue paper.
2. Storage: Store radiopharmaceuticals in suitable containers
that provide sufficient shielding. Ensure that such containers
contain the Nuclear Radiation warning symbol.
Other apparatus which accidentally comes with contact with
radioactive substances should be isolated and appropriate
Nuclear Radiation Warning stickers are to be pasted on their
surfaces.
3. Maintain a separate
fridge for radioactive
substances. Sticker
depicting the presence
of radioactive
substances should be
glued over it. Don’t
store other chemicals
with it.
Precautions

18. 4. Never handle radioactive substances with hand. Always use
forceps to handle radioactive solid particles.
5. Never use pipettes to
suck radioactive liquid
preparations. Use
pipetting device instead.
7. Radioactive liquids
are to be handled in
trays with adsorbent
tissue papers over
these trays. This is to
absorb any liquid that
accidentally spills out.
6. Wastes from radioactive substances should be stored until a time when it
emits harmless quantity of radiation. Only, after then it should be disposed off.
8. Regularly monitor
the storage area for
radioactive
emissions.
PRECAUTIONS

19. 10. Never eat, smoke or drink in the lab
containing radioactive substances.
9. Minimize the items that you bring to a radioactive
lab.
11. Wash your hands thoroughly before leaving the lab.
PHARMACEUTICAL APPLICATION OF RADIOPHARMACEUTICALS
1. NaI-131 In
Thyroid Cancer
Sodium Iodide – 131 undergoes beta
mode of decay, and thus it kills the
cells that it penetrates. As iodide is
rapidly absorbed in the thyroid
tissue, it aids in eliminating thyroid
cancer cells.
2. Co-60
in
Radiation
Therapy
of Cancer
Co-60 which is used in external
beam radiotherapy machines emits
two types of gamma radiations of
monochromatic wavelengths, 1.17
and 1.33 mev. Both types penetrate
the human tissues and kills cells.

20. 3. C-14 in detecting peptic
ulcer causing H.pyroli
infection.
Urea labeled with C-14 is used in Urea
Breath Test in order to detect the presence
of peptic ulcer causing H. pyroli
infestation of the stomach. Urea C-14 is
given in the form of a tablet. The urease
enzyme of H.Pyroli cleaves the drug into
ammonia and radioactive C02. The
radioactive C02 is absorbed into the blood
and exhaled through lungs. The exhaled
radioactive C02 is collected and checked for
radioactivity. The presence of radioactivity
indicates the presence of H.Pyroli
bacterium since only H.Pyroli possess
urease enzyme and humans do not.
4. Palliative treatment of bone
metastasis
Low energy beta emmiting
radionuclide vidilicet Samarium-153,
Strontium-89 and Phosphorous-32
are used to selectively deliver higher
doses of radiations to bone
malignant cells while delivering only
a negligible dose to normal
hematopoietic bone marrow cells.
The procedure provides a rapid pain
relief.
However, the radiation therapy is
terminated following a considerable
reduction in blood cells.

21. 5. Erbium-169 in Radiosynoviorthesis
Erbium -169 is
administered as
an intra-
articular
injection in
interphalangeal
joints to
stabilize the
synovial joints
and thereby
reduce pain and
inflammation
effectively at a
low cost.
Injection of Erbium-169 at the
synovial joints of phalangeal units is
followed by phagocytosis of its own
molecules by hypertrophic
overactive synoviocytes. The result
is the ablation of these inflammed
cells. To maintain hoemostasis,
normal synoviocytes proliferate to
produce new synoviocytes, thus
maintaining the synovial fluid levels
that are secretd by these cells.
6. Ammonia N -13 as
diagnostic agent in PET
It is given as an injection prior
to PET procedure to analyze
myocardial perfusion in
individuals who are suspected
to have coronary artery
disease. The procedure assists
in identifying plaques in
arteries and weaker muscles
and valves of the heart.
Following intravenous injection of Ammonia N-13, it is extracted from the blood into the
myocardial cells where it is metabolized to Glutamine N-13. Glutamine N-13 gets trapped in
the myocardial cells by joining the cellular pool of amino acids. N-13 decays 100% by
positron decay and this emmison of positron permits it to be visualized under PET.

22. THANK YOU…