Radiation Biology and Its Effects

Radiation Biology

• Radiation's effects on humans stem from atomic interactions, ionizing or exciting orbital electrons, causing energy deposition in tissue.
• Atom ionization alters chemical binding properties.
• Molecule breakage or atom relocation within molecules can disrupt proper function and potentially cause cell death.
• Ionized atoms can regain neutrality by attracting free electrons.
• Cells and tissues can regenerate.

Early Radiation Effects

• Effects observed within minutes or days of exposure.

Late Radiation Effects

• Effects observed months or years after exposure.

Radiobiology

• Study of ionizing radiation's effects on biological tissue.
• Aims to accurately describe radiation's impact on humans to ensure safe diagnosis and therapy.

Body Composition

• Body primarily comprised of hydrogen, oxygen, carbon, and nitrogen. (H=60%, O=25.7%, C=10.7, N=2.4%)
• Radiation interacts at the atomic level.
• 4 main macromolecule types in the body: water, lipids, carbohydrates, and nucleic acids.

The Cell Theory

• Cells are the basic functional units of all plants and animals.
• Interactions at an atomic level can result in cellular dysfunction.

Molecular Composition

• 5 principal types of molecules in the body: water, protein, lipids, carbohydrates, nucleic acids (DNA and RNA).

Water

• Comprises about 80% of the human body.
• Important for delivering energy to target molecules within the body and contributes to radiation effects.

Proteins

• Account for about 15% of the human body.
• Consist of amino acids held together by peptide bonds. Some essential, meaning body cannot produce these.
• Important functions including structure, enzymes, hormones, and antibodies.

Carbohydrates

• Composed of carbon, hydrogen, and oxygen.
• Provide fuel for cell metabolism.
• Glucose is the ultimate fuel source.

Lipids

• Composed of carbon, hydrogen, and oxygen.
• Serve as fuel and thermal insulators.

Nucleic Acids

• DNA and RNA.
• DNA is highly radiosensitive and contains hereditary information.
• RNA is crucial for cell growth and development, and protein synthesis.
• Located in the nucleus and cytoplasm

Cells: Radiosensitivity

• Cell proliferation rate and maturity influence radiosensitivity. Immature cells are more radiosensitive.
• General factors that determine cell radiosensitivity include function of an organ, cell maturation rate, and inherent sensitivity of the cell type.

Cell Types: Genetic & Somatic

• Genetic cells (oogonia and spermatogonia in females and males respectively) when undergoing proliferation result in germ cells. Germ cells pass genetic effects to offspring.
• Somatic cells, when undergoing proliferation result in cells affecting the individual.

Biological Effects of Radiation

• Radiation effects are based on the deposited energy per unit mass, referred to as Linear Energy Transfer (LET).
• High LET radiation (alpha particles, neutrons) deposits a lot of energy concentrated in a small area.
• Low LET radiation (x-rays, gamma rays) deposits energy more widely and penetrates better.

Different Radiation Effects

• Stochastic (probabilistic): effects with no threshold dose, such as cancer and genetic mutations, increasing probability with a higher dose.
• Non-stochastic (deterministic): effects with a threshold dose, such as radiation burns and cataracts, increasing severity with a higher dose beyond the threshold. Radiation hormesis is a hypothesis that low doses of radiation are useful.