Radiobiology and Radiation Protection: Lecture 1

Course Information

• Course Title: Radiobiology and Radiation Protection
• Course Code: IS-RPR 301
• Term: Spring 2024 - 2025
• Instructor: Dr. Mohamed Zakaria El-Sayed
• Instructor's credentials: Assistant Professor of Medical Imaging Sciences, BSc. Medical Imaging Sciences (MIS), College of Health Sciences
• Date: January 15, 2025

/ Lecture 1: Introduction to Radiation Protection & Review of Cell Biology

• Learning Objectives:
  • Introduction to basic concepts in radiation protection
  • Chemical composition of the cell (cell structure, cell division, and the cell cycle)
  • Somatic cells; mitosis
  • Germ cells; meiosis

What is Radiation?

• Radiation occurs when a radioactive source emits energy and travels through space or a medium until it's absorbed by matter.
• Radiation exists as waves or particles.
• Classified into two main types:
  • Ionizing radiation
  • Non-ionizing radiation

Non-ionizing Radiation

• Does not carry enough energy to ionize atoms or molecules.
• Generally considered less harmful than ionizing radiation.
• Examples:
  • Radio waves
  • Microwaves
  • Infrared radiation
  • Visible light
  • Ultraviolet (UV) light

Ionizing Radiation (more than 10eV)

• Carries enough energy to remove tightly bound electrons from atoms, creating ions.
• Can damage living cells and DNA, potentially leading to cancer.
• Examples:
  • Alpha particles
  • Beta particles
  • Gamma rays
  • X-rays
  • Neutrons

Sources of Ionizing Radiation

• Certain cancer treatments (using gamma rays)
• X-rays
• Materials used in nuclear power plants

Ionizing Radiation Exposure

• People are exposed to small amounts of ionizing radiation from the environment (background radiation).
• Exposure to diagnostic imaging, medical treatments, and radioactive materials.

Natural Background Radiation

• Sources:
  • Cosmic radiation (from the sun and stars)
  • Terrestrial radiation (from naturally radioactive materials in soil, rock, air, and water)
  • Internal radiation (from naturally occurring radionuclides in food and air)
  • The sources and levels of natural radiation are subject to variations.

Sources of Radiation Exposure (pie chart):

• Radon
• Medical imaging
• Cosmic
• Other sources
• Consumer products
• Terrestrial
• Internal

Radiation Protection Goals

• Preventing harmful effects of radiation
• Limiting exposure
• Implementation of the ALARA (As Low As Reasonably Achievable) principle
• Establishing dose limits
• Monitoring and control exposures
• Emergency preparedness and response

ALARA (As Low As Reasonably Achievable)

• Aims to keep radiation exposure as low as possible, considering economic and social factors.
• Includes factors: Time, Distance, Shielding

ALARA Rules (patient & personnel)

• Rules for reducing radiation exposure to patients and personnel during procedures.

Cell Cycle

• Cell cycle is a series of events that cells undergo as they grow, replicate their DNA, and divide into two daughter cells.
• Essential for growth, development, tissue repair, and reproduction in all living organisms.

Phases of the Cell Cycle (Mitosis)

• Interphase:
  • G1 Phase (Gap 1): Cell growth, RNA production, protein synthesis (necessary for DNA replication)
  • S Phase (Synthesis): DNA replication
  • G2 Phase (Gap 2): Cell growth and protein synthesis (preparation for mitosis), checks for DNA damage
• M Phase (Mitotic Phase):
  • Mitosis: Division of the nucleus into two identical nuclei

Phases of the Cell Cycle

• Cell cycle length varies from hundreds of hours for stem cells to 24 hours for rapidly dividing cells.

Regulation of the Cell Cycle

• Checkpoints (G1, G2, M/Spindle checkpoint) ensure each phase is completed before the next one begins.

Importance of the Cell Cycle

• Growth and development
• Tissue repair
• Maintaining genetic stability (ensuring each daughter cell receives an exact copy of the parent cell's DNA)

Meiosis

• Type of cell division occurring in testes and ovaries.
• Forms specialized cells (gametes).
• Fundamental in passing genetic information from parent to offspring.
• Begins in a specific cell (germ cell) containing 46 chromosomes (23 pairs).
• Essential to sexual reproduction, enabling genetic diversity and proper chromosome distribution in offspring.

Text Books and Suggested Reading

• Dance, D. R., et al. (2014). Diagnostic radiology physics: A handbook for teachers and students.
• Sherer MA, Visconti PJ, Ritenour ER, Kelli Haynes MS. Radiation protection in medical radiography (8th Edition); 2018.