21.5 Uses of Radioisotopes

Radioisotopes revolutionize medicine, offering powerful diagnostic and treatment tools. From tracers that illuminate hidden health issues to targeted therapies zapping cancer cells, these atomic marvels push healthcare forward.

Technetium-99m leads the pack in medical imaging, while radiation therapy and chemotherapy duke it out in cancer treatment. Each approach has its strengths, shaping modern medicine's ability to detect and defeat disease.

Medical Applications of Radioisotopes

Radioactive tracers in medicine

• Radioactive tracers are chemical compounds containing a radioactive isotope injected into the body or ingested orally
  • Emit radiation that can be detected using imaging techniques like gamma cameras or positron emission tomography (PET) scanners
  • Creates images showing the distribution of the tracer in the body helps diagnose abnormalities or diseases in specific organs or tissues
• Tracers accumulate in specific organs or tissues based on their chemical properties
  • Iodine-131 concentrates in the thyroid gland used to diagnose and treat thyroid disorders
  • Thallium-201 is used to assess blood flow to the heart muscle helps detect coronary artery disease
• Tracers can also be used in therapeutic applications to deliver targeted radiation to specific areas of the body
  • Iodine-131 treats hyperthyroidism and thyroid cancer by destroying overactive or cancerous thyroid cells
  • Yttrium-90 microspheres are used to treat liver cancer by delivering high doses of radiation directly to the tumor
• Radiopharmaceuticals, which are radioactive tracers specifically designed for medical use, play a crucial role in diagnostic and therapeutic procedures

Production of technetium-99m

• Technetium-99m ($^{99m}$Tc) is a metastable nuclear isomer of technetium-99 produced by the decay of molybdenum-99 ($^{99}$Mo) in a generator
  • Has a half-life of 6 hours making it suitable for medical imaging
  • Emits gamma radiation which is easily detected by gamma cameras
  • Low-energy gamma rays minimize patient radiation exposure
• $^{99m}$Tc is chemically versatile and can be incorporated into various compounds targeting different organs or tissues
  • $^{99m}$Tc-sestamibi for cardiac imaging assesses blood flow to the heart muscle
  • $^{99m}$Tc-methylene diphosphonate for bone scans detects areas of increased bone metabolism (fractures, infections, tumors)
• $^{99m}$Tc is widely used in nuclear medicine for diagnostic imaging accounting for approximately 80% of all nuclear medicine procedures
  • Applications include bone scans, cardiac imaging, brain imaging, and renal function studies
  • Readily available, cost-effective, and provides high-quality diagnostic images with minimal patient radiation exposure
• The production and use of $^{99m}$Tc rely on the process of radioactive decay, where unstable atomic nuclei release energy in the form of radiation

Radiation therapy vs chemotherapy

• Radiation therapy uses high-energy radiation to kill cancer cells and shrink tumors
  • Delivered externally using a machine (external beam radiation therapy) or internally using radioactive implants (brachytherapy)
  • Targets specific areas of the body minimizing damage to healthy cells
  • Side effects are usually localized to the treated area (skin irritation, fatigue)
• Chemotherapy uses drugs to kill rapidly dividing cells including cancer cells
  • Administered orally or intravenously affecting the entire body
  • Targets cells that divide quickly which can include healthy cells like hair follicles and gastrointestinal cells
  • Side effects are often systemic (hair loss, nausea, immune system suppression)
• Both therapies can be used alone or in combination depending on the type and stage of cancer
  • Radiation therapy is often used for localized tumors (breast, prostate) or to alleviate symptoms (bone metastases)
  • Chemotherapy is typically used for systemic treatment of cancer that has spread to multiple parts of the body (leukemia, lymphoma)
• The choice between radiation therapy and chemotherapy depends on factors such as:
  1. Type and stage of cancer
  2. Location of the tumor(s)
  3. Patient's overall health and preferences
  4. Potential side effects and long-term risks (secondary cancers, organ damage)

Radiation Safety and Imaging Techniques

• Ionizing radiation, which can cause cellular damage, is carefully controlled in medical applications to minimize risks
• Radiation safety protocols are essential in all medical procedures involving radioisotopes to protect patients and healthcare workers
• Nuclear imaging techniques, such as PET and SPECT scans, use radioisotopes to create detailed images of internal body structures and functions