Radiatiopharmaceuticals

Prof. Dr. Omar Shebl Zahra

Prof. of Clinical Oncology & Nuclear medicine

Faculty of Medicine – Alex. University

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Overview

Lecture 1

Nuclear pharmacy is a specialty of pharmacy practice dedicated to the compounding and dispensing of radioactive materials for use in nuclear medicine procedures.

Recalling chemistry, the nucleus of an atom consists of protons and neutrons.

If a nucleus for whatever reason has an excess of either one of these constituents, it will try to "get rid of" the excess component and return to a stable state. 

By doing so, the atom is said to give off this energy in the form of radiation.  There are quite a few naturally occurring radionuclides, most of them are man-made. 

An unstable nucleus can give off its energy in a variety of ways. 

The type of emission that is given off will determine whether or not the radionuclide will be useful for imaging or treating a patient. 

The radiologic specialty of nuclear medicine uses small quantities of radioactive materials with a known type of emission. 

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However we should know that

Electromagnetic radiation is emitted from the sun, from signals sent from radio & TV stations, from radar used to track airplanes & even visible light. 

In this particular field, we are interested in a type of radiation termed radionuclides. 

A radionuclide is an atom that has an unstable nucleus. 

 

By "tagging or labelling" the radioactive source to some compound that is known to localize in a specific area of the body, the compound will carry the radioactive material to the desired site. 

By using a specific detection device called a gamma camera, it is possible to detect the emissions given off by the radioactive material and create images of the relative distribution of the radioactive source in the body.

As nuclear medicine procedures became more widely used, the need for someone to prepare the labelled products for administration to the patients became more evident. 

While many large hospitals were able to use pharmacists with training in the handling of radioactive material, smaller hospitals were unable to utilize nuclear medicine procedures because they did not have the staff to prepare the necessary doses in a cost effective manner. 

Where a traditional pharmacist will dispense doses in milligram weight units, a nuclear pharmacist will dispense in millicurie activity units. 

Where a traditional pharmacist dispenses tablets and capsules, a nuclear pharmacist dispenses the radioactive material in liquid or capsule form. 

Where a traditional pharmacist will generally dispense the prescription to the patient, the nuclear pharmacist will dispense to a hospital or clinic nuclear medicine department where the dose will be administered to the patient. 

In most nuclear pharmacies, the nuclear pharmacist is responsible for obtaining the desired radioactive material, either from a manufacturer, or from an in house generator system.   

The most commonly used isotope in nuclear medicine is Technetium-99m that is readily and continuously available from a generator system. 

The generator forms the radionuclide that is retained on an internal column until the generator is "milked". 

When "milking" the generator, sodium chloride is passed over the column, which removes the radioactive material.  The eluate is then collected in a shielded evacuated vial. 

After performing quality assurance tests on the eluate, it can be used in the preparation of the final radiopharmaceutical products.

In order to provide protection while handling radioactive material, most compounding is done behind leaded glass shielding and using leaded glass syringe shields and lead containers to hold the radioactive material. 

Lead is an excellent shielding material that serves to protect the nuclear pharmacist from the radioactive emissions from our products. 

Nuclear pharmacists work with large quantities of radioactive material on a day-to-day basis, but by using simple techniques, the amount of radiation exposure to the nuclear pharmacist is very low.

Here are many different products that can be used.  Most radiopharmaceuticals are available as "kit" formulations. 

All materials necessary for preparation are available in the non-radioactive kit with the exception of the radioactive isotope.  When the radioactive isotope is added to the kit, the chemical reactions required for binding the isotope occur within the vial. 

In most cases, when the tagging reaction is complete, the final product will be ready for quality control verification and unit dose dispensing.

In addition to preparing and dispensing the radioactive products, nuclear pharmacists are available to provide drug information to other health professionals, to aid the nuclear medicine staff in the selection of products, and to assist in the interpretation of unusual studies. 

Nuclear pharmacists receive extensive training on the various radiopharmaceuticals that are used, as well as training on the safe handling of radioactive materials and the procedures that will minimize radiation exposure to themselves and to others. 

Radiation is energy that comes from a source and travels through space and may be able to penetrate various materials. Light, radio, and microwaves are types of radiation that are called non-ionizing.

The kind of radiation discussed in this document is called ionizing radiation because it can produce charged particles (ions) in matter.

Ionizing radiation is produced by unstable atoms. Unstable atoms differ from stable atoms because unstable atoms have an excess of energy or mass or both. Radiation can also be produced by high-voltage devices (e.g., x-ray machines).

ionizing radiation

Unstable atoms are said to be radioactive. In order to reach stability, these atoms give off, or emit, the excess energy or mass. These emissions are called radiation.

The kinds of radiation are electromagnetic (like light) and particulate (i.e., mass given off with the energy of motion). Gamma radiation and x rays are examples of electromagnetic radiation.

Gamma radiation originates in the nucleus of a radioactive material.

Beta and alpha radiation are examples of particles which are also emitted from the a radioactive nucleus.

Interestingly, there is a "background" of natural radiation everywhere in our environment.

It comes from space (i.e., cosmic rays) and from naturally occurring radioactive materials contained in the earth and in living things.

Source Exposure

External Background Radiation 60 mrem/yr, US Average

Natural K-40 and Other Radioactivity in Body 40 mrem/yr

Air Travel Round Trip (NY-LA) 5 mrem

Chest X-Ray Effective Dose 10 mrem per film

Radon in the Home 200 mrem/yr (variable)

Man-Made (medical x rays, etc.) 60 mrem/yr (average)

Radiation Exposure from Various Sources

Types of Radiation

The radiation one typically encounters is one of four types: alpha radiation, beta radiation, gamma radiation, and x radiation.

Neutron radiation is also encountered in nuclear power plants and high-altitude flight and is emitted from some industrial radioactive sources.

Gamma radiation and x rays are highly penetrating electromagnetic radiation.

Gamma radiation or x rays are able to travel many feet in air and many inches in human tissue. They readily penetrate most materials and are sometimes called "penetrating" radiation. X rays are like gamma rays. X rays, too, are penetrating radiation.

They are produced by Sealed radioactive sources that emit gamma radiation and machines that emit x rays respectively.

Gamma radiation and x rays are electromagnetic radiation like visible light, radio-waves, and ultraviolet light. These electromagnetic radiations differ only in the amount of energy they have.

Gamma rays and x rays are the most energetic of these.  Dense materials are needed for shielding from gamma radiation.

Clothing provides little shielding from penetrating radiation, but will prevent contamination of the skin by gamma-emitters.  

Radiation Measurement

In the United States, radiation absorbed dose, dose equivalent, and exposure are often measured and stated in the older units called rad (or Gray), rem (or Sivert), or roentgen (R), respectively.

1 Gray = 100 rad 1 mGray = 100 mrad 1 Sivert = 100 rem 1 mSivert = 100 mrem

This exposure can be from an external source irradiating the whole body, an extremity, or other organ or tissue resulting in an external radiation dose.

Alternately, internally deposited radioactive material may cause an internal radiation dose to the whole body or other organ or tissue.

Radioactive Material

The size or weight of a quantity of material does not indicate how much radioactivity is present. A large quantity of material can contain a very small amount of radioactivity, or a very small amount of material can have a lot of radioactivity.The amount of radioactivity present is traditionally determined by estimating the number of curies (Ci) present. The more curies present, the greater amount of radioactivity and emitted radiation.

specific activity = curies per unit mass of a radioisotope

radioactive half-life = time taken for half the radioactive atoms in a radioactive material to decay.

Common fractions of the curie are the millicurie (1 mCi = 1/1,000 Ci) and the microcurie (1 μCi = 1/1,000,000 Ci)

The SI system uses the unit of becquerel (Bq) as its unit of radioactivity. One curie is 37 billion Bq.

Since the Bq represents such a small amount, one is likely to see a prefix noting a large multiplier used with the Bq as follows:

37 GBq = 37 billion Bq = 1 curie

Thank you and Good Luck

Prof. Dr. Omar Shebl Zahra