RADIOPHARMACEUTICALS AND HALF LIFE BY VANA JAGAN MOHAN RAO

1. BY
VANA JAGAN MOHAN RAO M.S.Pharm, MED.CHEM
NIPER-KOLKATA
Asst.Professor, MIPER-KURNOOL
Email: jaganvana6@gmail.com

2. What is Radiopharmaceuticals?
A radiopharmaceutical is a
radioactive compound used for the
diagnosis and therapeutic treatment
of human diseases.
A radiopharmaceutical has two
components:
a radionuclide and
a pharmaceutical.

3. Introduction
In designing a radiopharmaceutical, a
pharmaceutical is first chosen on the basis of
its preferential localization in a given organ or
its participation in the physiologic function of
the organ.
Then a suitable radionuclide is tagged onto
the chosen pharmaceutical such that after
administration of the radiopharmaceutical,
radiations emitted from it are detected by a
radiation detector.

4. Introduction
Isotopes of an atom have the same number of protons, but a
different number of neutrons.
Radioisotopes & Radionuclides: Unstable isotopes which are
distinguishable by radioactive transformation.

5. Radioactivity: the process in which an unstable
isotope undergoes changes until a stable state is
reached . When the atomic nucleus undergoes
spontaneous transformation, called radioactive
decay, radiation is emitted (alpha particles, beta
particles and gamma rays).

6. Introduction
• Radiation refers to particles or waves coming
from the nucleus of the atom (radioisotope or
radionuclide) through which the atom
attempts to attain a more stable configuration.

7. Important parameters
Radioactive decay is the process in which an
unstable atomic nucleus spontaneously loses
energy by emitting ionizing particles and
radiation.
Physical half-life is the period of time required
to reduce the radioactivity level of a substance to
exactly one half its original value due solely to
radioactive decay.
Biological half-life the time required for a living
organism to eliminate one-half of a radioactive
substance which has been introduced into it.

8. Effective half life
The time required for a radioactive element in
an animal body to be diminished by 50% as a
result of radioactive decay and biologic
elimination.
Te = ( Tp X Tb) ( Tp + Tb )
isotope T(ph) T(b) T(e)
3H 4500 12 12
99mTc 0.25 1 0.2
235U 26000000000
0
15 15
226Ra 580000 16000 15000

9. Ideal radiopharmaceutical properties
 Short half-life isotope(Ideally 1.5 times the duration
of the diagnostic procedure.)
 Energy of Gamma Rays: (Ideal: 100-250 keV)
 Pure gamma emitter
 Target to Non target Ratio
 Localization only in tissue desired
 Easy preparation
 Economy price

10. RADIOACTIVE DECAY TYPES
When an unstable nucleus decays, It may give out:
1. Alpha particle decay
2. Beta particle decay
3. Gamma ray

11. Penetrating power
Alpha particles may be
completely stopped by a
sheet of paper, beta particles
by aluminum shielding.
Gamma rays can only be
reduced by much more
substantial mass, such as a
very thick layer of lead.

12. Alpha particledecay
Alpha particles are made of 2 protons and 2
neutrons.
This means that when a nucleus emits an
alpha particle, its atomic number decreases by
2 and its atomic mass decreases by 4.
Alphaparticles are relatively slow and
heavy and have a low penetrating power .
Because they have a large charge, alpha
particles ionize other atoms strongly.

13. Beta particle decay
Beta particles have a charge of minus 1. This
means that beta particles are the same as an
electron.
This means the atomic mass is unchanged
the atomic number increases or decreases by 1.
They are fast, and light.
Beta particles have amedium penetrating power.
Beta particles ionize atoms that they pass, but not
as strongly as alpha particles do.

14. Gamma ray
Gamma rays are waves, not particles.
This means that they have no mass and no
charge.
Gamma rays have a high penetrating power.
Gamma rays do not directly ionize other atoms,
although they may cause atoms to emit other
particles which will then cause ionization.

15. Radioactive materials
1 Natural radioactivity:
Nuclear reactions occur spontaneously
2 Artificial radioactivity:
The property of radioactivity produced by
particle bombardment or electromagnetic
irradiation. All radionuclides commonly
administered to patients in nuclear medicine
are artificially produced.

16. Types of artificial radioactivation:
A- Charged-particle reactions(cyclotron)
B- Photon-induced reactions(nuclear
reactor)
C- Neutron-induced reactions(radionuclide
generator)

17. Neutron-induced reactions
It is the bombardment of a non-
radioactive target nucleus with a source
of thermal neutrons in a device called a
Radionuclide Generator.

18. Radionuclide Generator
 Radionuclide generators contain a parent
radionuclide that decays to produce a
radioactive daughter. The parent is usually
produced in specialized nuclear reactor

20. Example:
technetium-99m, obtained from a
generator constructed of molybdenum-99
absorbed to an alumina column.
Parent: 99Mo as molybdate
Half-life: 66 hr.
daughter:
half-life:6hr

21. Application of radiopharmaceuticals
1 Treatment of disease:
They are radiolabeled molecules designed to deliver
therapeutic doses of ionizing radiation to specific
diseased sites.
2 As an aid in the diagnosis of disease:
The radiopharmaceutical accumulated in an organ of
interest emit gamma radiation which are used for
imaging of the organs with the help of an external
imaging device