What is an isotope?

Radiofarmaceutical product: isotope + tracer

Medical isotopes form the basic ingredient of radiopharmaceutical products which are used to detect (diagnose) or combat cardiovascular diseases and cancer cells (therapy). The radiopharmaceutical product that a patient receives consists of two components: medical isotopes and a tracer.

Isotopes are atoms of the same element. The nucleus of an atom consists of neutrons and protons. An element, for example Uranium, consists of a fixed number of protons. This fixed number is characteristic for the element. The number of neutrons determines which isotope is formed from the combined protons and neutrons.

How are they made?
Matter can be made radioactive by exposing it to high-energy particles. This can be done in many different ways, but the most relevant routes are those via neutrons or via charged particles. The fission process in the reactor produces neutrons that can activate matter. For example, the non-radioactive lutetium (Lu-176) can be converted to the radioactive Lu-177 through exposure to neutrons.

Charged particles, such as positively charged hydrogen particles (protons), can be accelerated to a high speed (= high energy) with an accelerator. This energy can be determined in such a way that these particles form radioactive material. There are both circular accelerators (cyclotrons) and straight accelerators (LINAC, ‘linear accelerator’), but their function is always the same: to accelerate charged particles. The non-radioactive oxygen-18 can be converted by exposure to protons to the radioactive fluorine-18, a commonly used accelerator isotope. The fluorine-18 is used for diagnostics with PET cameras.

Can every medical isotope that is currently being created in a reactor also be created in an accelerator? The answer is: No, this is not possible. The reverse also applies: not every medical isotope made in an accelerator can be made in a reactor. This has to do with the properties of the raw materials in relation to the radiation that an accelerator or reactor produces. These are physical properties that determine how much radioactivity can be made with a reactor or with an accelerator. What is important is whether the medical isotope can be produced with the proper quality (purity, specific activity) and correct amount (radioactivity).

Reactor rods

The radioactive materials used in diagnosis and therapy are called medical (radio) isotopes. To ensure that they reach the correct organ, the isotope is linked to a non-radioactive material. By administering this combination to a patient, a special camera can be used to detect a ‘trace’ of radiation, from which the nuclear specialist can see how an organ functions or where a cancer is active.

Tracer and radiopharmaceutical
By combining the correct isotope (or radionuclide) with a specially developed protein (the trace material or tracer) it is possible to map a specific disease process. The combination is also called the radiopharmaceutical. The radiopharmaceutical is specifically selected for examination or treatment (therapy) of the patient, so that it has the correct biological and radiation properties.