Lecture 1.pptx.pdf

Radiation Biology Lecture 1 : Introduction to Radiobiology Dr. Abdulaziz Alshihri Assistant Professor Diagnostic Radiology Department Faculty of Applied Medical Sciences Introduction • Objectives • Upon successful completion of this lecture of the course, you should be able to: • • • • The histor...

Radiation Biology Lecture 1 : Introduction to Radiobiology Dr. Abdulaziz Alshihri Assistant Professor Diagnostic Radiology Department Faculty of Applied Medical Sciences Introduction • Objectives • Upon successful completion of this lecture of the course, you should be able to: • • • • The history of Radiation biology Identify the types of ionizing radiation. Identify the medical sources of ionizing radiation. Discuss the five types of interactions between ionizing radiation and tissue atoms 2 The History of Radiation biology • Discovery of X-rays (Late 19th Century): Wilhelm Conrad Roentgen's discovery of X-rays in 1895 marked the beginning of the study of ionizing radiation's biological effects. • Emergence of Radiobiology (Early 20th Century): Early researchers like Marie Curie in 1898 and Henri Becquerel in 1896 conducted pioneering studies on radioactivity and its potential health hazards, laying the foundation for radiobiology. • Radium Therapy (Early 20th Century): The therapeutic use of radium and other radioactive substances emerged in 1920s for treating diseases like cancer, leading to early insights into radiation's effects on living tissues. • Manhattan Project (1940s): During World War II, the Manhattan Project not only developed the atomic bomb but also encouraged intensive research into the biological effects of radiation, particularly on the human body. 3 The History of Radiation biology (cont.) • Radiological Accidents (20th Century): Incidents like the Chernobyl disaster in 1986 and the Hiroshima and Nagasaki bombings in 1945 provided critical data on the immediate and long-term biological consequences of exposure to high levels of ionizing radiation. • Advances in Molecular Biology (Late 20th Century): The integration of molecular biology into radiobiology led to a deeper understanding of radiation-induced DNA damage, cellular repair mechanisms, and the genetic basis of radiation sensitivity. • Modern Radiobiology (21st Century): Modern radiobiology continues to study the complex cellular and molecular responses to radiation exposure, with a focus on developing targeted cancer treatments and improving radiation safety measures. 4 TYPES OF IONIZING RADIATIONS What is radiation in general? • Energy • The ability to do work—that is, to move an object against resistance • How radiation relates to energy • Radiation refers to kinetic energy that passes from one location to another • Radiation is energy transmitted by particles or electromagnetic waves 5 TYPES OF IONIZING RADIATIONS (cont.) Radiation in Biologic Material: • Energy absorption from radiation can lead to excitation or ionization. • Excitation is the raising of an electron to a higher energy level without ejection. • Ionization involves the ejection of one or more orbital electrons. • Ionizing radiation releases large amounts of localized energy (about 33 eV per event) 6 TYPES OF IONIZING RADIATIONS (cont.) Classification of Ionizing Radiation: • Ionizing radiation can be classified as either electromagnetic or particulate. • Electromagnetic radiation includes x-rays and γ-rays, which have the same nature but are produced differently. • X-rays are produced extranuclearly, while γ-rays are emitted by radioactive isotopes and can also come from natural background radiation. 7 TYPES OF IONIZING RADIATIONS (cont.) • To study radiation biology, the radiation can be divided into two parts. o Ionizing radiation  Electromagnetic waves (x-rays, gamma rays, and high-energy ultraviolet radiation [energy higher than 10 electronvolts]) can transfer sufficient energy to some orbital electrons to remove them from the atoms to which they were attached (the process of ionization, the foundation of the interaction of photons with human tissue).  Particulate Radiation o Charged Particles :Charged particle are always “directly” ionizing • Alpha, • Beta (+ and -) • Protons • Heavy nucleui • Electrons o Uncharged Particles: indirectly” ionizing • Neutrons 8 TYPES OF IONIZING RADIATIONS (cont.) Electromagnetic Radiation: • X-rays and γ-rays are both forms of electromagnetic radiation with different production methods. • They are characterized by their wavelengths and frequencies. • X-rays and γ-rays have short wavelengths and high frequencies compared to other electromagnetic radiations. • The concept of x-rays as packets of energy (photons) is crucial in radiobiology. 9 TYPES OF IONIZING RADIATIONS (cont.) • Electromagnetic waves are created as a result of vibrations between an electric field and a magnetic field as they travel through space. • Electromagnetic waves are characterized by their: o Frequency o Wavelength Dual nature of electromagnetic radiation (wave-particle duality) o This form of radiation can travel through space in the form of a wave but can interact with matter as a particle of energy. • • Electromagnetic spectrum: 10 TYPES OF IONIZING RADIATIONS (cont.) • Particulate Radiations: • Besides electromagnetic radiation, other types include electrons, protons, αparticles, neutrons, negative π-mesons, and heavy charged ions. • Electrons are used for cancer therapy and can be accelerated to high energy. • Protons are positively charged and used for cancer treatment, particularly due to their favorable dose distribution. • α-Particles consist of two protons and two neutrons and are emitted during the decay of heavy radionuclides; they are a source of natural background radiation. • Neutrons are electrically neutral and produced through acceleration or nuclear fission; they are also significant in space radiation. • Heavy charged particles are nuclei of elements with some or all electrons stripped and are used in radiation therapy; they require high energy to be 1 produced. • High-energy charged particles in space pose risks to astronauts, including retinal exposure to highenergy ions. 1 TYPES OF IONIZING RADIATIONS (cont.) • Differences in Ionizing Radiation Effects: • In biologic effects, ionizing radiations are usually considered if their photon energy exceeds 124 eV or if they have a wavelength shorter than about 10^-6 cm. • The biological impact depends on the size of individual energy packets (photons), not just the total energy absorbed. • Comparing Energy in Ionizing Radiations: • The energy associated with a lethal dose of x-rays is relatively small, equivalent to a minimal temperature increase or the energy required to lift a person a short distance. • This demonstrates that the potency of ionizing radiation is determined by the size of energy packets, not the total energy absorbed. 1 2 Radiation Sources, and Doses Received Types of Radiation Sources 1. Natural Sources: Radiation from nature that always present in the environment 2. Man-made Sources: Radiation from human-created sources for specific purposes *(Both sources contribute a percentage of the total amount of radiation that humans receive during their lifetime.) 13 Sources of Ionizing Radiation That Humans Are Exposed to Natural radiation (natural background radiation) o o o Terrestrial radiation (e.g., radon, thoron) Cosmic radiation (solar and galactic) Internal radiation from radioactive atoms (also called radionuclides) 14 Sources of Ionizing Radiation That Humans Are Exposed to (Cont.) • Manmade (artifcial) radiation o o o o o o Consumer products containing radioactive material Air travel Nuclear fuel for generation of power Atmospheric fallout from nuclear weapons testing Nuclear power plant accidents (TMI-2 and Chernobyl) Nuclear power plant accidents as a consequence of natural disasters (Fukushima Daiichi) • Medical radiation Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 15 • Medical radiation exposure results from the use of diagnostic x-ray machines and radiopharmaceuticals in medicine. Medical Radiation Sources • Diagnostic Radiology • Interventional Radiology • Nuclear Medicine • Radiation Oncology • Dental Radiology Historical Radiation Exposure • Historically, natural sources contributed more to radiation exposure. • In 1990, over half of the annual U.S. exposure was from natural sources. Shift in Exposure • A 2007 National Council of Radiation Protection and Measurements (NCRP) publication noted a significant shift. • More than half of the U.S. annual exposure is now from medical radiation. • A six-fold increase from 1990 levels. Recent Trends • Collective effective dose has declined. • The 2019 NCRP report (no. 184) recorded a decrease. • 3.0 mSv in 2006 to 2.3 mSv in 2016. 16