RT208-INTRODUCTION

What is Radiobiology?

• Study of effects of ionizing radiation on biologic tissue.

• Radiation: Energy emitted by matter in the form of electromagnetic waves or high-speed particles.

Forms of Radiation

• Radiation in the form of waves:

  • X-rays

  • Gamma rays

• Radiation in the form of particles:

  • Negatron

  • Positron

  • Electrons

  • Protons

  • Neutrons

Exposure to Radiation

• External Exposure: Radiation from a source outside the body impacting tissues as it passes through.

  • Common Sources:

    • Medical imaging (X-rays, CT scans)

    • Cosmic rays (high-altitude flights)

    • Industrial sources (gamma rays in material testing)

• Internal Exposure: Radioactive materials ingested, inhaled, or absorbed, allowing radiation interaction with internal tissues.

  • Common Sources:

    • Contaminated food or water (sewage treatment plants)

    • Inhalation of radon gas

    • Radiation therapy (ingested radioisotopes)

Classification of Radiation

• Non-Ionizing Radiation:

  • Found at the long wavelength end of the spectrum.

  • Energy is low enough to excite molecules and atoms, causing them to vibrate faster.

• Ionizing Radiation:

  • Has more energy than non-ionizing radiation, sufficient to cause chemical changes by breaking chemical bonds.

  • Can ionize matter directly and indirectly.

Types of Ionizing Radiation

• Directly Ionizing Radiation: Causes ionizations directly upon absorption, leading to damage.

• Indirectly Ionizing Radiation: Absorbs energy to produce fast-moving charged particles, which then cause damage.

Radioactive Units

• Becquerel (Bq): SI unit for measuring activity of a radioactive substance (1 Bq = 1 decay/second).

• Curie (Ci): Old unit of radioactivity (1 Ci = 3.7 x 10^10 Bq).

• Gray (Gy): SI unit of absorbed radiation dose, important for determining potential biological harm (1 Gy = 1 joule/kg of tissue).

• Rad (Radiation Absorbed Dose): Older unit of absorbed radiation dose (1 Rad = 0.01 Gy).

• Sievert (Sv): SI unit of radiation equivalent, accounting for biological effects (1 Sv = 1 Gy x radiation weighting factor).

  • Gamma radiation: weighting factor of 1.

  • Alpha radiation: weighting factor of 20.

• Rem: Older unit of radiation dose equivalent (1 Rem = 0.01 Sv).

• Roentgen (R): Unit for exposure to ionizing radiation in air (1 R = 2.58 x 10^-4 coulombs/kg of air).

Units of Radioactive Contamination

• Becquerel per square meter (Bq/m²): Measures radioactive contamination on surfaces.

• Counts per minute (CPM): Used in labs/environmental monitoring to quantify radioactive decays detected per minute.

Sources of Medical Radiation Exposure

• Diagnostic Radiology: Uses X-rays to visualize internal structures of the body.

  • Examples:

    • X-rays (chest, bone fractures, mammograms).

    • CT (produces detailed cross-sectional images).

• Dental Radiology: Specialized imaging for teeth and jaw.

  • Examples:

    • Intraoral X-rays (individual teeth).

    • Panoramic X-rays (entire mouth).

    • Cone Beam CT (3D imaging for orthodontics and implants).

• Cardiovascular-Interventional Radiology: Minimally invasive procedures using real-time imaging.

  • Examples:

    • Angiography (blood vessels).

    • Stent Placement (open blocked arteries).

    • Pacemaker Implantation (using fluoroscopy).

• Nuclear Medicine: Uses radiopharmaceuticals to diagnose/treat diseases.

  • Diagnostic Procedures:

    • Technetium-99m (imaging bones, thyroid, heart, kidneys).

    • F-18 (detects cancers and brain activity).

  • Therapeutic Procedures:

    • Iodine-131 (treats hyperthyroidism, thyroid cancer).

    • Lutetium-177 (targets cancers like neuroendocrine tumors and prostate tumors).

• Radiation Oncology: Uses high-energy radiation to destroy cancer cells or shrink tumors.

  • Examples:

    • External Beam Radiation Therapy (EBRT).

    • Brachytherapy (placing radioactive sources near tumors).

    • Stereotactic Radiosurgery (high-precision radiation for brain tumors).