Radiopharmaceutics

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.

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.

IntroductionIsotopes 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.

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).

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.

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.

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 260000000000

15 15

226Ra 580000 16000 15000

Ideal radiopharmaceutical propertiesShort half-life isotope(Ideally 1.5

times the duration of the diagnostic

procedure.)Energy of Gamma Rays: (Ideal: 100-

250 keV)

Pure gamma emitterTarget to Non target RatioLocalization only in tissue desiredEasy preparationEconomy price

radioactive decay types:

When an unstable nucleus decays, It may give out:1- Alpha particle decay2- Beta particle decay3- Gamma ray

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.

1- Alpha particle decayAlpha 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.Alpha particles are relatively slow and

heavy and have a low penetrating power .Because they have a large charge, alpha particles ionize other atoms strongly.

2- 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 a medium penetrating power.Beta particles ionize atoms that they pass, but not as strongly as alpha particles do.

3- Gamma ray

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

Radioactive materials1- 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

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

Neutron-induced reactions

It is the bombardment of a nonradioactive target nucleus with a source of thermal neutrons in a device called a Radionuclide Generator.

Radionuclide Generator

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

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

Application of radiopharmaceuticals1- 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 called gamma

camera

Good luck!