Radiobiology & Protection Lecture 1 Introduction PDF

Radiobiology & Protection RMI 212 Lecture 1 Introduction Slide 1 fchs.ac.ae Radiobiology is the study of the effects of ionizing radiation on biological tissue. or Radiobiology is the branch of science concerned with the methods of interacti...

Radiobiology & Protection RMI 212 Lecture 1 Introduction Slide 1 fchs.ac.ae Radiobiology is the study of the effects of ionizing radiation on biological tissue. or Radiobiology is the branch of science concerned with the methods of interaction and the effects of ionizing radiation on living systems. It is a combination of biology, physics and epidemiology. fchs.ac.ae Why Radiobiology? The main goal of radiobiological research is the accurate description of the effects of radiation on humans, so that radiation can be used more safely in diagnosis and more effectively in therapy. fchs.ac.ae History : The beginning of radiobiology was marked by three significant events: Wilhelm Roentgen’s discovery of X- rays in 1895 (Figure1) Henri Becquerel’s observance of Figure 2 Figure 1 rays being given off by a uranium- containing substance in 1896 (Figure2) The discovery of radium by Pierre and Marie Curie in 1898 (Figure3) Figure 3 fchs.ac.ae  RADIOPHYSICS  Introduction: Biophysics is the application of physics to biological systems. This interdisciplinary field is quickly growing in the modern scientific community. fchs.ac.ae 2. The Deposition of Radiation Energy: TOPICS COVERED IN THIS PART:  Definition of ionizing radiation  Types of ionizing radiation and non-ionizing radiation  Definition of LET and quality of ionizing radiation  Generation of free radicals  Direct and indirect action of ionizing radiation fchs.ac.ae Definition of Ionizing Radiation: RADIATION: Radiation is the term given to the energy transmitted by means of particles or waves. It can be ionizing or non-ionizing Slide 7 fchs.ac.ae The absorption of energy from radiation in biologic material may lead to excitation or to ionization. IONIZING RADIATION: If the radiation has sufficient energy to eject orbital electrons from the atom or molecule, the process is called ionization, and that radiation is said to be : Ionizing Radiation NON-IONIZING RADIATION: Can cause excitation of atoms where electrons jump to higher atomic energy levels but are not removed from the atom fchs.ac.ae Types of ionizing radiation and non-ionizing radiation: Slide 9 fchs.ac.ae 1. IONIZING RADIATION:  A. Electromagnetic: X-rays (produced extra-nuclearly) γ-rays (produced intra-nuclearly)  B. Particular: Electrons Protons α-Particles -Particles Neutrons Deuterons Heavy charged particles fchs.ac.ae 2. NON-IONIZING RADIATION 1. UV light 2. Lasers: Light Amplification by Stimulated Emission of Radiation 3. Microwave 4. Radio waves 5. Infrared Waves fchs.ac.ae Types of Radiation fchs.ac.ae Definition of LET and quality of ionizing radiation  Linear Energy Transfer (LET): It describes how much energy an ionizing particle transfers to the material traversed per unit distance Is the energy transferred per unit length of the track. Unit for LET is keV/µm (kiloelectron volt per micrometer) of unit density material. Radiation with LET of 100 keV/µm is the most efficient in producing biological damage. The average separation between ionizing events coincides with the diameter of the DNA double helix fchs.ac.ae  Types of LET:  High LET radiation : This is type of ionizing radiation that deposit a large amount of energy in a small distance. Eg: neutron , alpha particles.  Low LET radiation : This is type of ionizing radiation that deposit a small amount of energy along the track or widely paced ionization event. Eg: electromagnetic radiation fchs.ac.ae LET LOW LET HIGH LET GAMMA RAYS ALPHA PARTICLES IONS OF HEAVY X-RAYS NUCLEI CHARGED PARTICLES LOW ENERGY NEUTRONS fchs.ac.ae LET α X-RAYS fchs.ac.ae  The deposition of energy of different types of radiation dispersion of energy Air tissue Incidence radiation high LET (alpha, neutron, beta) greater radiotoxicity low LET (gamma, x-ray,) LET = linear energy transfer fchs.ac.ae Molecular Effect of Radiation: Radiation Interaction at the Atomic Level At the most basic level, the human body is made up of atoms. The effect of x-ray on human are the result of interaction at atomic levels. The atomic composition of the body determines the character and degree of the radiation interaction. fchs.ac.ae Radiation Interaction At The Atomic Level Most of the body is composed of hydrogen and oxygen. Radiation interaction at the atomic level results in molecular change, and this in turn can produce a cell deficient in normal growth and metabolism. fchs.ac.ae Molecular Composition There are five principle types of molecules in the body: Four are macromolecules , sometimes consisting of thousands of atoms. Proteins Lipids (fats) Carbohydrates Nucleic Acids (DNA) DNA is the most critical & radiosensitive molecule. fchs.ac.ae Molecular Composition 80% Water 15% Protein 2% Lipids 1% Carbohydrates 1% Nucleic Acid (DNA) 1% Other fchs.ac.ae Nucleic Acids There are two basic nucleic acids that are very important to human metabolism. DNA and RNA DNA: located in the nucleus of the cell serves as the control molecule for cell function. DNA contains all of the heredity information for the cell or the entire organism if it is a germ cell. fchs.ac.ae Interactions of Radiation  Types of interaction to radiation 1. DIRECT ACTION 2. INDIRECT ACTION 1) Direct action: Occurs when an ionizing particle interacts with and is absorbed by a biologic macromolecules such a s DNA, RNA, protein or enzyme or any other macromolecule in the cell which become abnormal structures. If the cell can repair the damage, it may survive. If it can't it will die. Since the damage was directly caused, the effect is called Direct Cellular Damage. fchs.ac.ae 2) Indirect action: Radiation interaction with water: The cell is composed of 80% water. The ultimate result of radiation interaction with water molecule is the formation of an ion pair and free radicals. Free radicals have an unpaired electron in their outer shell, a state which confers a high degree of reactivity. fchs.ac.ae Radiation interaction with water: HOH radiation HOH+ + e- HOH + e- HOH- HOH+ H+ + OH * HOH- OH- + H Ion pair (H+, OH-) HOH Free Radicals (H , OH ) fchs.ac.ae Interactions of Radiation The free radicals are extremely reactive and can undergo a number of reactions: 1. Recombine with each other producing no damage (H’ + OH’ → H2O) 2. Join with other free radicals forming a new toxic macromolecules (hydrogen peroxide) that may be damaging to the cell (OH’ + OH’ → H2O2) fchs.ac.ae Interactions of Radiation fchs.ac.ae Fig 2 fchs.ac.ae Direct action & Indirect action fchs.ac.ae Indirect Action: The following outline summarizes the general sequence of events that occurs in the cell via indirect action Sequence of Events in Indirect Action: Incident X-ray photons  Fast electrons  Ion radicals  Free radicals fchs.ac.ae  Macromolecular changes from breakage of chemical bonds  Biological effects: days - cell killing Generation - mutation years - carcinogenesis fchs.ac.ae Possible outcome of radiation injury: A. Repair B. cell dies C. daughter cells die D. no repair E. non identical repair (mutation) before reproduction. fchs.ac.ae