1) Radioisotopes are atoms of an element that have the same number of protons but a different number of neutrons. They can be stable or unstable. Unstable isotopes decay by emitting particles like alpha or beta particles or gamma rays. 2) The fundamental unit of radioactivity is the Curie, defined as 3.7x1010 disintegrations per second. Some common units used are millicurie and microcurie. 3) Radioisotopes are used safely in medicine if their emissions have low energy, they have a short physical half-life, and a short biological half-life. Common medical isotopes include carbon-14, sodium-24, hydrogen-3, and tech

1. Radioisotopes
&
Radiopharmaceuticals

2. Isotopes
Isotopes are atoms of an element having the same number of protons and different
number of neutrons. Alternatively
Isotopes may be defined as the atoms of an element which have the same atomic
number but different atomic masses or mass numbers.
Example: Hydrogen has three isotopes.
Two major types of isotopes are found in nature.
Stable isotopes maintain their elemental integrity and do not decompose to other
isotopic or elemental forms.
Unstable or radioactive isotopes decompose or decay by emission of nuclear
particles, into other isotopes of the same or different elements.
Carbon has five isotopes.
Two are stable:
Three are radioactive:
.
H
1
1 H
2
1
H
3
1
C
12
6
C
13
6
C
10
6 C
11
6 C
14
6

3. Nature of Radio active Isotopes
All elements having atomic weights above 222 are radioactive.
All radioactive compounds have the common property of emitting rays or particles
Natural radio active isotopes emit alpha particles, beta particles and gamma rays.
Artificial radio active isotopes emit mainly beta and gamma rays.
An isotope is said to decay when radiations are given off.
These are classified as follows:
Alpha particles
Beta particles
- Negative particles or Negatrons
- Positive particles or Positrons
Gamma rays
K capture Decay

4. Units of Radioactivity
The fundamental unit of radioactivity is the Curie(Ci)
Curie is defined as the amount of radioactive material in which the
number of disintegrations per second is 3.7  1010
1 Curie (Ci) = 3.7  1010 disintegrations per second (dps)
1 Mill curie (mCi) = 3.7  107 disintegrations per second (dps)
1 Micro curie (Ci) = 3.7  104 disintegrations per second (dps)
Rutherford unit = 1  1010 disintegrations per second (dps)
Mache unit = of 1 Micro curie of radium emanation/water
In the SI unit system, the radio activity unit is 1 nuclear disintegration
per time unit(s), 1 dps, and is called Becquerel (Bq).The unit 1
disintegration per minute, dpm, is often used.
1 Curie (Ci) = 3.7  1010 Bq.
2700
1

5. The safest radioisotopes to use and handle are those in which-
 The particles and rays have relatively low energy
 The physical half life is short
e.g. (2.3h)
(Technetium) (6h)
 The biological half life is short.
I
132
Tc
99
Criteria of Safe Isotopes

6. Toxicity of Radioactive Isotopes
Class 3 Radionuclides (Medium Toxicity-Lower Sub-group B)
This includes most of the radioactive isotopes used in medicine.
e.g.:
Class 4 Radionuclides (Low Toxicity)
This includes isotopes with very weak emissions or a short effective
half-life. e.g.: 3H, 91Y, 99Te
C
14
Na
24
H
3
Te
99
91Y

7. Isotopes in Medicine
 Radioisotopes are used in medicine in two different ways:
- as radiation sources or
- as radioactive tracers
 As radiation sources their principal role is in therapy.
 As radioactive tracers they are used mainly for diagnostic purposes.
 A radiopharmaceutical is a preparation, intended for in vivo use,
containing a radionuclide in the form of an element, a simple salt
or a complex and may exist in the form of a solid, liquid or gas.
 Radiopharmaceuticals are used for diagnosis and therapy.
 For diagnostic applications, a radiopharmaceutical should not be
pharmacologically active in that it should not produce a
physiological effect.
 For therapy,the radiopharmaceutical preparation contains enough
radioactivity to produce the intended specific changes in tissue.

8. Radio Pharmaceutical Preparations
Iodine - 125 and Iodine - 131
Sodium Iodide 125 Solution
Sodium Iodide 131 Capsules and Solution
They are used as diagnostic aid to determine thyroid
function. The usual oral dose is 50 to 100 Ci.
Technetium - 99m
Technetium Tc 99m Injections
They are used for the diagnostic study of lungs,bone
imaging and renal imaging.Usual intravenous dose
is 10-15 Ci.

9. Radiopaque Contrast Media
Radiopaque media are chemical compounds containing elements of
high atomic number which will stop the passage of X-rays.
These types of compounds are used as diagnostic aids in radiology.
The most common radiopaques contain barium and iodine.
Barium sulfate is the agent of choice in radiographic studies of the
gastrointestinal tract.
The major criterion of Barium sulfate is it’s insolubility in acidic
gastric juice.
The major side effect associated with the use of Barium sulfate is
constipation.
The usual oral dose of Barium sulfate is 200-300g.