Radiation Effects and Electromagnetic Properties

Radiation Damage

• Radiation damage results from direct or indirect action.
• Direct action occurs when radiation directly affects the biological molecules.
• Indirect action is from free radicals formed by radiation reacting with water.
• Larger molecules are more likely to be affected by radiation.
• Damage to DNA is the main cause of the damaging effects.
• The dose/effect ratio is extremely variable, depending on many factors, like the type of radiation, radiation modes (external or internal), and extent of body surface area.

Biological Effects of IR

• Effects on living organisms vary depending on the type of radiation and the level of exposure.
• Acute effects occur from a high dose in a short period. Chronic effects are from continuous, prolonged, low-dose exposure.
• Somatic effects are on body tissues, and genetic effects are on reproductive cells.
• The most radiosensitive tissues have a high cell division rate, such as bone marrow, skin, and intestinal mucosa, as well as germ cells.

Types of Radiation

• Ionizing Radiation: Capable of directly or indirectly ionizing atoms and molecules. Energy ≥ 10 eV.
  • Corpuscular: Subatomic particles, high speed, often near the speed of light (alpha, beta particles). These are directly ionizing (neutrons are also a possibility of ionizing radiation).
  • Electromagnetic: Photons traveling at the speed of light (x-rays, gamma rays). These are indirectly ionizing.
• Non-ionizing Radiation: Does not have enough energy to ionize atoms and molecules. Energy <10 eV.
  • Optical: Ultraviolet, infrared, visible light (including lasers)
  • Radiofrequency: Including microwaves.
  • Extremely low frequency

Sources of Exposure

• Natural: Cosmic rays, radioactive elements such as uranium, radon (a radioactive, colorless, tasteless gas).
• Artificial: Radiopharmaceuticals, radiotherapy, radiodiagnostics, and research.

Classification of Electromagnetic Radiation

• Ionizing radiation has wavelengths from very short (gamma rays and X rays), to slightly longer (ultraviolet).
• Non-ionizing radiation covers the majority of the spectra, from longer wavelengths (visible light, infrared) to the longest wavelengths (radio waves)

UV Radiation

• UVA (400-320 nm) is the most abundant, penetrates deeply
• UVB (320-290 nm) primarily causes sunburn but is also responsible for some types of skin cancer
• UVC is the most dangerous, mostly absorbed by the atmosphere preventing most from reaching us

Mechanisms of UV Damage

• Direct photochemical mechanism: matter absorbs energy generating an excited molecule.
• Cutaneous chromophores: purine and pyrimidine bases of nucleic acids, melanin, amino acids, lipids. Endogenous -in body. Exogenous -outside body, such as tattoo ink.
• Formation of Thymine Dimers is a serious DNA lesion altering genetic information.

Reactive Oxygen Species

• Generated from radiation interacting with oxygen in tissues, resulting in free radicals such as hydroxyl radicals, and hydrogen peroxide
• Different tissues have varied susceptibility due to differing oxygen tension (pO2) and antioxidant quantity.

Radiotherapy

• Based on directing ionizing radiation at tumor cells to damage their DNA more effectively than healthy cells.
• Oxygen is important for cytotoxicity of cancer cells, and cancer cells with lower oxygen levels are less sensitive to radiotherapy.
• Techniques to increase oxygenation or decrease oxygen in healthy tissues around tumors are being tested to improve the effectiveness of radiotherapy.

Radioisotope Examples

• Fluoro-18(F-18): To detect metabolic activity, especially to diagnose tumors in brain.
• Carbon-11(C-11): For studying cerebral perfusion and other biological reactions in the central nervous system.
• Oxygen-15(O-15): To assess cardiac perfusion and blood flow of the brain.
• Nitrogen-13(N-13): To assess cardiac perfusion.

X-ray Radiography

• X-rays pass through different tissues to varying degrees depending on the atomic number and thickness of the tissue.
• Dense tissues like bones are almost completely crossed, making them light colored on the image (radiograph).
• Partially crossed tissues, like muscles and vessels, appear gray
• Tissues that pass through the rays appear dark, like lungs.

Principles of PET Imaging

• Uses radioisotopes that emit positrons during radioactive decay.
• Detecting emitted positrons allows generating images (PET) that show various biological processes in living tissues.

Explore the complex relationship between frequency and wavelength in electromagnetic radiation through this quiz. Delve into the types of radiation, their energy levels, and the effects of ionizing radiation on biological molecules. Test your knowledge on direct and indirect damage caused by radiation and the role of reactive oxygen species.