Radiopharmaceuticals: Lesson 23: Radiopharmaceuticals

1. Introduction to Radiopharmaceuticals:

Radiopharmaceuticals are chemical compounds that are labeled with a radioactive isotope, allowing for the tracking and imaging of biological processes within the body. They are widely used in medicine, particularly in the diagnosis and treatment of cancer.

2. 18F-flourodesoxyglucose (18FDG):

• Use: 18FDG is a commonly used radiopharmaceutical in cancer diagnosis. It is used to assess glucose (sugar) metabolism in the body. Cancer cells often have a higher metabolic rate than normal cells, and therefore will absorb more 18FDG. This allows doctors to detect tumors and monitor the effectiveness of treatment.

• Imaging modality: 18FDG is used with positron emission tomography (PET) scanners. PET scanners work by detecting positrons (positively charged particles) emitted from 18FDG in the body. These positrons collide with electrons in the body, producing two gamma photons (gamma rays) that travel in opposite directions. The PET scanner detects and measures these photons to reconstruct a 3D image of the body.

3. Imaging modalities used in the morphological and functional assessment of organs:

• Gamma camera/ SPECT (Single Photon Emission Computed Tomography): This device uses a radioactive isotope emitting gamma rays to generate images of organs in the body.

• PET (Positron Emission Tomography): This device uses radioactive isotopes emitting positrons to generate images of organs in the body.

4. Operating principle of SPECT:

• SPECT uses radioactive isotopes that emit gamma rays. The gamma rays emitted from the radioactive isotopes injected into the body are captured by the SPECT scanner and used to reconstruct a 3D image of the organs in the body.

5. Operating principle of PET:

• PET uses radioactive isotopes that emit positrons. Positrons emitted from the radioactive isotopes injected into the body collide with electrons and produce two gamma photons that travel in opposite directions. The PET scanner captures these photons and uses them to reconstruct a 3D image of the organs in the body.

6. Substances used in gamma cameras:

• 99mTc: Used to investigate bone fractures, bone and joint diseases.

• 201 Thallium: Used to investigate areas of the myocardium suffering from ischemia.

7. Substances used in SPECT:

• 131 Iodine, 99 Technetium: Used to investigate brain function, brain diseases.

• 197 HgCl2: Used to investigate kidney function, kidney diseases.

• 99 Technetium: Used to investigate thyroid diseases.

8. Units for assessing the biological impact of radiation:

• Absorbed dose (Gy): The absorbed dose is the amount of energy that ionizing radiation delivers to a unit mass of matter.

• 1 Gy is equivalent to 1 Joule/kg of matter.

• Absorbed dose assesses the biological impact of radiation.

• Equivalent dose (Sv): Equivalent dose is calculated by multiplying the absorbed dose (Gy) by the radiation weighting factor.

• The radiation weighting factor is a coefficient reflecting the relative harmfulness of different types of radiation.

• The unit of equivalent dose is Sievert (Sv).

9. “Finding other chemicals that also bind to this radioactive nucleus” is the purpose of radiochemical purity testing:

• Radiochemical purity is a very important concept in the field of radiopharmaceuticals. It refers to the identification and removal of chemical impurities that may be associated with the radioactive nucleus.

• Radiochemical purity testing aims to ensure that radiopharmaceuticals used in medicine are safe and effective.

• A radiopharmaceutical with high purity will ensure that the radioactive nuclei are only bound to the desired chemical and not other chemical impurities that could be harmful to the patient.

Note:

• Radiopharmaceuticals can be harmful to the body if not used correctly.

• Doctors must be careful when prescribing and monitoring patients who use radiopharmaceuticals.

• Patients must follow the instructions of their doctor and medical staff to ensure safe and effective treatment.