This document provides an overview of radiopharmaceuticals, detailing their applications in medicine for treating and diagnosing various conditions using radioactive isotopes. It describes the types of radioactive emissions (alpha, beta, and gamma), the principles of radioactive decay, and methods for measuring radioactivity. Additionally, it highlights specific radioisotopes used in therapy and diagnosis, illustrating their properties and clinical applications.

1. UNIT-V
Radiopharmaceuticals
Presented by
Ms. Kiran Divekar
Assistant Professor
Pharmaceutical Chemistry

2. Radioactivity
The phenomenon of spontaneous emission of certain kind of
invisible radiation by certain substance is called Radioactivity.
The substances which emit such radiation is called Radioactive
substance.
It was discovered accidentally by the French Scientist Henry
Becquerel.
Radiopharmaceuticals are used in medicines. It is used to treat
cancerous tumors, to diagnose thyroid disorders and other metabolic
disorders including brain function.

3. Radioactive radiations are composed of three important rays α, β & γ
which differ very much in their nature and properties
1. α –rays:
 These rays or particles are positively charged.
 It consists of two unit positive charge and has a mass which is nearly four
times that of hydrogen atom.
 These are heavy, slow moving and their penetrating power is slow.
 These rays ionise the gas through which they pass
 During the emission of α-particle from a radioactive element, atomic
number decreases by 2 units and mass number decrease by 4 units
Radioactive Rays

4.  These rays or particles are negatively charged.
 They have negligible mass.
 These are having smaller mass, higher speed and thus β-particles are
much more penetrating than α-particle.
 They have lower ionising power than α-rays.
 During the emission of β-particle from a radioactive element, atomic
number increases by 1 unit and there is no change in mass number.
2. β –rays:

5. 3. γ-rays:
 These rays are neutral i.e., do not carrying charge.
 The particle of these rays has negligible mass.
 As they do not have any mass, their ionising power is also very poor.
 It not affected by magnetic field and are having the speed of light.

9. Atoms of an element which have the same atomic number but have
different mass number are called Isotopes.
In other words, isotopes are atoms of the same element whose nuclei
contain the same number of protons but different number of neutrons.
When the radioactive isotopes undergo nuclear reactions and they
produce α, β & γ particles. The original nuclide is called the parent and the
product is termed as daughter.
This phenomenon of nuclear changes is termed as disintegration or
radioactive decay.
Isotopes

11. According to the law of Radioactive Decay, the quantity of a
radioelement which disappears in unit time (rate of disintegration) is directly
proportional to the amount present.
It is independent of temperature, so its energy of activation is zero.
Various forms of equation for radioactive decay are:
Radioactive Decay
Where λ is a constant, and is known as decay or disintegration constant

12. Integrating the equation
C is the constant of integration and log N stands for logeN. Since the number
of atoms of the radioactive substance present initially i.e. t=0 is N0
Substituting the value of integration constant

13. Converting log to the base e to the base 10, we get:
Where,
Nt =Number of atoms that nucleid present after time t.
N0 = Initial number of atoms of the nucleus at time 0
λ-= Decay constant
This equation is similar to that of the first order reaction, hence it is
seen that radioactive disintegration are example of first order reactions.

14. Units of Radioactivity is Curie.
Its symbol is Ci or C. It refers to the activity of one gram of radioactive
material and is equal to 3.7 x 1010
disintegration per second (dps).
Units of Radioactivity
Marie Curie Pierre Curie
1 Curie = 3.7 x 1010
dps
The millicurie and micro curie are equal to 10-3
or 10-6
respectively.
1 Millicurie = 3.7 x 107
dps
1 Microcurie =3.7 x 104
dps
But now a days, the unit curie is replaced by Rutherford (Ra).

15. Rutherford (Rd) is defined as the amount of a radioactive substance which
undergoes 106
dps
Roentagen (R): It is the unit of exposure,
1R= 2.58 x 10-4
CKg-
(C=A Coulomb)
RAD: It is the unit of absorbed dose,
1 rad =10-2
Jkg-1
However in SI system,
Becquerel (Bq): It is defined as one disintegration per second
1Bq=1 disintegration per second
106
Bq =1 rd
3.7x1010
Bq= 1C

16. The half-life period is defined as the time required for a radioactive isotope
to decay to one half of its initial value.
It is denoted by t1/2
Where λ is disintegration constant.
Each radioactive isotope has its own characteristic of half life.
Shorter the half-life period of an element, greater is the number of
disintegrating atoms and hence greater is its radioactivity.
Half-Life of Radioelement

17. The half life periods or half lives of different radioelements vary
widely ranging from fraction of seconds to millions of years.
Half-lives for various radionuclides vary considerably
e.g. Polonium: 122 has half life of 3x10-7
seconds.
Uranium 238 has 4.5x104
years
Average half life period:
The reciprocal of the radioactive constant or decay constant is called
average half life period. It is denoted by τ(tau)

18. To measure the radiation of alpha, beta and gamma rays many
techniques involving detection and counting of individual particles or
photons have been available.
It include:
1. Ionisation Chamber
2. Proportional counter
3. Geiger-Muller counter
Measurement of Radioactivity

19. 1. Ionisation chamber:
An ionisation chamber consists of chamber filled with gas and
fitted with two electrodes kept at different electrical potentials and a
measuring device to indicate the flow of electric current.
The fill gas can be Ar, He, air etc. These are available in various
size and shapes. They have poor resolution due to large number of
charge carriers. They are operated in current mode.

20. 2. Proportional counter:
If the electric field gradient between the anode & cathode is
increased by increasing the applied voltage, the electrons produced in the
primary ionisation further ionise the gas molecule e.g. the number of ion
pair is multiplied.
For each primary electron liberated, a large number of additional
electrons are liberated. The current pulse through electrical current is
greatly amplified. In a certain original number of ion pairs. Proportional
counters operate in this voltage region. The usually operated in pulse mode
and are used in the form of gas filled or gas flow counters for a, b and
fission frequent counting The most common file pass is "P-10"consisting of
90% Ar and 10% methane. The energy resolution of the proportional
counter is in the range of 5-10%.

22. 3. Geiger-Muller counter:
It is one of the oldest radiation detector types in existence, having been
introduced by Geiger and Muller in 1928.
 It is referred to as G-M counter or simply tube.
 The simplicity, low cost and of ease of operation of these detectors
have lead to the continued use to the present time.
 They can detect α, β & γ raditions.
 It consists of a cylinder made up of stainless steel or glass coated with
silver on the inner side which acts as cathode.
 Coaxially inside the tube a mounted fine wire works as an anode.

23.  It is having the mixture of ionising gas which contain a small proportion
quenching vapour.
 The function of quenching vapour are
i) to prevent the false pulse
ii) to absorb the photons emitted by excited atoms and molecule
returning to their ground state
 Chlorine bromine, ethyl alcohol and ethyl formate are commonly used
quenching agents.
 Radiation when enters the tube through a thin section of outer wall
causes ionization of atoms of the gas.
 When a high voltage is maintained between two electrodes, the
electrons and charged ions are attracted by the anode and cathode
respectively.
 Each particle of radiation produces a brief flow or pulse of current which
can be recorded by a scalar.

25. Scintillation Detectors:
Scintillation detectors rely on the atomic or molecular excitation
produced.
Deexcitation then results in the emission of light a process known
as fluorescence. This light then act as a detectable signal. It consists of a
cell, a photomultiplier tube coupled with phosphar or flour to convert
scintillations into electrical pulses, an amplifier and a scalar.
Both inorganic and organic scintillations can be used as detector

26. There are two main types of scintillator:
1.Inorganic, such as Sodium Iodide :
Single crystals of Nal, doped with an activator such as Thallium to
modify the energy levels which are used to form detectors.
They are insulators and have a wide gap between the valence band
and conduction band. Suitable activators are used to create excited states
which decay by emission of light in the visible range.
Other scintillation like Csl (TI), CsI (Na), Hi I (Er), BaF2
2. Organic Scintillator:
It is used for simple α & β counting with 100% efficacy. Anthrene
have high scintillation efficacy and stilbene low scintillation efficacy.
It suffer from the limitation of poor energy resolution

28. A care should be taken to protect people and personal from harmful
radiation during handling and storage of radioactive material emits.
The following precautions are taken while working with radio
detectors, radio assays, traces experiments, manufacturing or handling of
radioactive materials
1. These materials should be handled with forceps or suitable
instruments and direct contact should be avoided.
STORAGE, HANDLING AND PRECAUTIONS OF RADIOACTIVE MATERIAL

29. 2. Any substance which is taken internally (foods, drinks, smokes etc.) should
not be carried in laboratory where radioactive materials are used.
3. Sufficient protective clothing or shielding must be used while handling the
materials.
4. Radioactive materials should be kept in suitable labelled containers shield
by lead bricks and preferably in remote corner.

30. 5. Areas where radioactive materials are used or stored should be
monitored constantly (tested regularly for radioactivity).
6 The final disposed of radioactive material
should be done with great care to animals
and environment.

31. Radioisotopes are used in medicine in two different ways.
They may be :
(1) radiation source in therapy,
(2) radioactive tracers for diagnostic purposes.
In therapeutic use of radioisotopes, the radiations emitted produce
destructive effects on existing cells and prevent the formation of new cells
and tissues. For this reason, the radioisotope therapy is applied to those
disease conditions in which extensive cellular metabolic malfunction exists.
The therapeutically used radioisotopes depend mainly on their ability
to ionise atoms. The energy measurement involved in radiations and
resulting in ionization is expressed in millions of electron volts called as
MeV.
Applications of Radioisotopes:

32. The strength or the energy of alpha, beta and gamma is
expressed as MeV.
All radiations cause ionization of atoms in their paths. The
radiation of short wavelength (gamma rays) have high penetrating
power than long wavelength (beta rays).
Besides, the greater the MeV of the rays more destructive it
becomes to the surrounding tissues.

33. 1. Sodium iodide131
 Iodide I-131 (as Sodium iodide I-131) is a radioisotopic drug
used for the treatment and palliation of thyroid malignancy.
 Iodine-131 is notable for causing mutation and death in
cells that it penetrates, which is due to its mode of beta decay.
 As a result of beta decay, approximately 10% of its energy and
radiation dose is via gamma radiation, while the other 90%
(beta radiation) causes tissue damage without contributing to
any ability to see or image the isotope.

34.  Low levels of beta radiation are also known for causing
cancer as this dose is highly mutagenic.
 For this reason, less toxic iodine isotopes such as I-123 are
more frequently used in nuclear imaging, while I-131 is
reserved for its tissue destroying effects.
 Therapeutic solutions of Sodium Iodide-131 are indicated for
the treatment of hyperthyroidism and thyroid carcinomas
that take up iodine.
 It is also indicated for use in performance of the radioactive
iodide (RAI) uptake test to evaluate thyroid function.

35.  Indium In-111 is a radioisotope with a physical half-life of 2.83
days, used to label agents for diagnosis, disease progression
and treatment.
 It is commonly used in Nuclear Medicine Diagnostic Imaging
by radio-labeling targeted molecules or cells.
 During its radioactive decay, it emits low energy gamma (γ)
photons.
2. Indium In-111

36. 3. Chromium 51
 Chromium-51 is a synthetic radioactive isotope
of chromium having a half-life of 27.7 days.
 Decaying by electron capture with emission of gamma
rays (0.32 MeV);
 It is used to label red blood cells for measurement of
mass or volume, survival time, and sequestration
studies, for the diagnosis of gastrointestinal bleeding,
and to label platelets to study their survival.
 It has a role as a radioactive label.

37. 4. Technetium-99

38.  The radioisotope most widely used in medicine is technetium 99,
employed in some 80% of all nuclear medicine procedures.
 It is an isotope of the artificially-produced element technetium and it
has almost ideal characteristics for a nuclear medicine scan.
 It has a half-life of six hours which is long enough to examine metabolic
processes yet short enough to minimize the radiation dose to the
patient.
 The most important isotope, because it is the only one available on a
large scale,
 It is produced in kilogram quantities as a fission product in nuclear
reactors.
 Technetium metal looks like platinum but is usually obtained as a gray
powder

39. 5. Calcium47
Half – life: 4.5 days
The isotope of Calcium-47 has unique radioactive tracing
properties and is one of the most valuable tools in nutritional
studies and medicine.
Whenever introduced into a cancer patient, Calcium-47's
isotope starts emitting abnormal concentrations of gamma
rays that help locate the tumor more accurately.
Calcium-47 is used in medicine to investigate bone
metabolism problems or to diagnose calcium disorders.
It is also used in the biomedical research of animals to study
the cellular body function and the formation of bones in
mammals.

40. 6. Erbium169
9.4 d
Half life 9.4 days

41.  Pure erbium is a silvery white metal that is relatively stable in air. It
slowly reacts with water and quickly dissolves in diluted acids, except
hydrofluoric acid.
 Thirty radioisotopes have been characterized.
 Natural erbium is a mixture of six stable isotopes: erbium-166 (33.5
percent), erbium-168 (26.98 percent), erbium-167 (22.87 percent),
erbium-170 (14.91 percent), erbium-164 (1.6 percent), and erbium-
162 (0.14 percent).
 Erbium-169 is one of radioisotopes that can be used for radiation
synovectomy (radio synovectomy) in the treatment of inflammatory
joint diseases (arthritis) due to its β- particle emission.
Synovectomy is a procedure where the synovial
tissue surrounding a joint is removed.

42. 7. Gallium68
 It has 31 known isotopes and 11 metastable isomers.
 Gallium-68 is a positron emitter that decays with a half-life of 67.71
min.
 Gallium-68 a positron emitter radionuclide, with great impact on the
nuclear medicine, has been widely used in positron emission
tomography (PET) diagnosis of various malignancies in humans during
more recent years especially in neuroendocrine tumors (NETs).