1. RADIOPHARMACEUTICALS

2. ISOTOPES :
Isotopes are atoms of the same element with the same number of protons but different number of neutrons.
The isotopes of a particular element have the same chemical and physical properties.
Examples of isotopes are :
C , C

3. TYPES OF ISOTOPES : Two major types of isotopes are found in nature :
stable isotopes and unstable (radioactive) isotopes.
Stable isotopes maintain their elemental integrity and do not decompose to other isotopic or elemental forms. E.g. 12 C
Unstable or radioactive isotopes decompose by emission of nuclear particles (alpha particles, beta particles, gamma rays, x-rays) into other isotopes of the same or different elements. E.g. 14C

4. Alpha particles, α
α particles which constitute alpha radiation consists of 2 protons and 2 neutrons.
Characteristics :
a) They are equivalent to the nuclei of helium atoms 4 He 2
b) They are heavy and positively charged (+2).
c) The particles move at a relatively slow speed, averaging 0.1 the speed of light (3x1010 ) cm/s.
d) Their penetrating power is very low and can be stopped by a sheet of paper or a very thin sheet of aluminium foil.
e) These particles will travel only 3 to 8 cm in air.
f) Energy value, typically 4 Mev.

5. Alpha particles, α
g) α radiation is usually emitted only from elements having atomic numbers greater than 82.
h) The emission of alpha radiation is illustrated below with radium -226 (the radium isotope having a mass number of 226) :
Ra ———> Rn α (or He)
The low penetrating power of alpha particles makes isotopes emitting this type of radiation not useful for biological applications because these particles cannot penetrate tissue.

6. Beta particles, β
β radiation is of two types because there are two types of electrons : negative electron (negatron) and positive electron (positron).
The positron is identical with the negatron in all respects except for its charge of +1 instead of -1. It is also known as the antiparticle of the electron.
When these electrons are emitted from radioactive nuclei, they are called β-particles.
Negatrons (β –) are emitted by unstable nuclei having neutrons in excess of protons.
So, a transformation of a neutron to a proton occurs with the emission of beta radiation (β –).

7. Beta particles, β
Elements undergoing this type of transformation will decay to the element having the next highest atomic number.
n ———> p β –
An example of β decay is shown below :
C ———> N β –

8. Beta particles, β
Positrons (β +) are emitted from nuclei having a proton/ neutron ratio above stable limits.
So a proton can be transformed into a neutron, with the emission of beta – radiation (β +)
p ———> n β +
An example of β decay is shown below :
Zn ———> Cu β +
Positrons are not important in biological applications because they are short-lived and undergoes reactions with electrons to produce gamma radiation.
β e – ———> 2 γ

9. Beta particles, β Characteristics:
They have the mass of an electron (approximately 9.1 x g).
They move at a faster velocity.
Their emissions from elements do not alter the atomic mass but changes the atomic number.
They have more penetrating power than alpha particles and can travel from 10 to 15 mm in water or penetrate almost 1-inch thicknesses of aluminium.
Maximum energy is 1.5 Mev and mean energy is 0.6 Mev.
Many isotopes emitting β – have useful biological applications as the radiation will penetrate tissues.

10. Gamma Radiation, γ
Gamma radiation is electromagnetic but α and β radiations are particulate.
It means γ radiation demonstrates both wave and particle properties.
Gamma rays are radiated as discrete packets of energy (quanta). These are also known as photons.

11. Characteristics:
The rays are of a short wavelength and travel at the speed of light.
Since it is of electromagnetic radiation, it has no mass or charge.
They have very high energy (2 Mev).
They have excellent penetrating power and very thick lead or concrete shielding is required to protect against this radiation.

12. Mode of radioactive decay:
Type of Radiation
Alpha particle
Beta particle
Gamma ray
Symbol or
Charge +2 -1
Speed
slow
fast
Very fast
Ionising ability
high
medium
Penetrating power
low
Stopped by:
paper
aluminium
lead

13. Radiation measurement:
The basic unit for quantifying radioactivity (i.e. describes the rate at which the nuclei decay).
Curie (Ci):
Curie (Ci), named for the famed scientist Marie Curie
Curie = 3.7 x atoms disintegrate per second (dps)
Millicurie (mCi) = 3.7 x 107 dps
Microcurie (μCi) = 3.7 x 104 dps
Becquerel (Bq):
A unit of radioactivity. One Becquerel is equal to 1 disintegration per second.

14. Radiopharmaceuticals
Radiopharmaceuticals are medicinal formulations containing radioisotopes which are safe for administration in humans for diagnosis or for therapy. Or
A radioactive drug that can be administered safely to humans for diagnostic and therapeutic purposes.

15. Radionuclide + Pharmaceutical
Radiopharmaceutical products include inorganic compounds, organic compounds, peptides, proteins, monoclonal antibodies and fragments and oligonucleotides labeled with radionuclide with half-lives varying from a few minutes to several days.
Radionuclide + Pharmaceutical

16. Radiopharmaceuticals
Radiopharmaceuticals used in cancer treatment are small, simple substances, containing a radioactive isotope or form of an element.
They are targeted to specific areas of the body where cancer is present.
Radiation emitted from the isotope kills cancer cells.
1616

17. Application of radiopharmaceuticals
Treatment of disease: (therapeutic radiopharmaceuticals)
Chromic phosphate P32 for lung, ovarian, uterine, and prostate cancers
Sodium iodide I 131 for thyroid cancer
Samarium Sm 153 for cancerous bone tissue
Sodium phosphate P 32 for cancerous bone tissue and other types of cancers
Stronium chloride Sr 89 for cancerous bone tissue

18. Chromic phosphate P 32
Chromic phosphate P 32 is a suspension that is delivered through a catheter, or tube, inserted into the sac surrounding the lungs, or into the abdominal or pelvic cavities.
The usual dosage is millicuries for abdominal administration and 10 millicuries for administration to the lung sac.
Chromic phosphate P 32 also may be injected into the ovaries or prostate.

19. Sodium Iodide I 131
Sodium Iodide I 131 is taken by mouth as a capsule or a solution.
The usual dose for treating thyroid cancer is millicuries, depending on age and body size. Doses may be repeated.
Treatment usually requires two to three days of hospitalization. For this therapy to be effective there must be high levels of thyroid-stimulating hormone (TSH, or thyrotropin) in the blood. This hormone can be injected

20. Strontium-89/ samarium Sm 153 lexidronam
Strontium-89 is injected into a vein. The usual dosage is 4 millicuries, depending on age, body size, and blood cell counts. Repeated doses may be required.
The usual dosage of samarium Sm 153 lexidronam is 1 millicurie per kg (0.45 millicurie per lb) of body weight, injected slowly into a vein.
Repeated doses may be necessary. Because samarium Sm 153 lexidronam may accumulate in the bladder, it is important to drink plenty of liquid prior to treatment and to urinate often after treatment. This reduces the irradiation of the bladder.

21. sodium phosphate P 32
The dosage of sodium phosphate P 32 depends on age, body size, blood cell counts, and the type of treatment.
The usual dosages range from 1–5 millicuries. Repeated doses may be required.

22. Radiation Contamination:
There are several types of radiation that can be emitted from radioactive substances.
The basic types of radiation are alpha, beta and gamma.
Radiopharmaceuticals administered to patients are usually either beta or gamma emitting or a combination of both.
Beta radiation doesn't penetrate more than a few millimeters through tissue.
Gamma emitting radioactive materials can penetrate through tissue and therefore pose an external radiation hazards.

23. Radiation Contamination:
There is an important difference between radiation exposure and radioactive contamination.
Radiation exposure of a person can occur at a distance from the radioactive materials or source.
Radiation exposure usually occurs as a result of gamma rays being emitted by the radioactive materials and traveling through air.
Gamma rays that are absorbed by the body can cause harm.

24. Radiation Contamination:
If a person is contaminated it means that the person has come into contact with a radioactive substance and that this material is present on skin, clothing or on objects.
Contamination is hazardous because the radioactive materials can be inhaled or ingested.

25. Production of radionuclides:

26. 1- Charged particle bombardment
Radionuclides may be produced by bombarding target materials with charged particles in particle accelerators such as cyclotrons.
A cyclotron consists of :
Two flat hollow objects called Dees.
The dees are part of an electrical circuit.

27. Cont…
On the other side of the dees are large magnets that (drive) steer the injected charged particles (protons, deutrons, alpha and helium) in a circular path.
The charged particle follows a circular path until the particle has sufficient energy that it passes out of the field and interact with the target nucleus.

28. Cyclotron

30. 2- Neutron bombardment
Radionuclides may be produced by bombarding target materials with neutrons in nuclear reactors.
The majority of radiopharmaceuticals are produced by this process.

31. 3- Radionuclide generator systems
Principle:
A long-lived parent radionuclide is allowed to decay to its short-lived daughter radionuclide and the latter is chemically separated in a physiological solution.
Example:
technetium-99m, obtained from a generator constructed of molybdenum-99 absorbed to an alumina column.

32. 99Mo/99mTc Generator: