DOSIMETRIC UNITS AND BIOLOGICAL EFFECTS OF RADIATION (W. R. LEO)

1. DOSIMETRIC UNITSAND BIOLOGICAL EFFECTS OF RADIATION (W. R. LEO) Emrah Tiras, University of Iowa

2. Outline • Dosimetric Units • The Roentgen • Absorbed Dose • Equivalent Dose • Effective Dose • Biological Effects • High Dose Effects • Low Dose Effects EmrahTiras, University of Iowa

3. Dosimetric Units • The quantity of radiation received by an object is measured by several different units. • These units are either; • a measure of the quantity of ionization produced • the amount of energy deposited in the material. • The Roentgen • Roentgen (R) is the unit of measurement for exposure to ionizing radiation (such as X-ray and gamma rays). • 1 R is the amount of radiation required to liberate positive or negative charges of one electrostatic unit of charge (esu) in 1 cm³ of dry air at standard temperature and pressure (STP) • This corresponds to the generation of approximately 2.08×10⁹ ion pairs. • In SI units , 1R = 2.58×10⁻⁴ C/kg. EmrahTiras, University of Iowa

4. Absorbed Dose: • Also known as total ionizing dose(TID). • It measures the total energy absorbed per unit mass and is the fundamental parameter in radiological protection. • Its unit of the measurement is the Gray. • 1 Gray = 1 Joule/ kg • It is not a good indicator of the likely biological effect. • Equivalent Dose(Hт): • It is a measure of the radiation dose to issue where an attempt has been made to allow for the different relative biological effects of different types of ionizing radiation. • It has units of sieverts and Rontgen equivalent man(100 REM= 1 Sievert). • It is calculated by: Hт = WR х DR WR : Radiation weighting factor or quality factor (which indicates each radiation types’ relative biological effectiveness). DR : is the average absorbed dose received by organ R. EmrahTiras, University of Iowa

5. Effective Dose(+equivalent): • is used to compare radiation doses on different body parts on an equivalent basis. • The unit for the effective dose is the Sievert (Sv) and it is measured in Joule/ kg. • E= Σ W(t)хH(t) H(t): weighted average of the equivalent dose to different body tissues. EmrahTiras, University of Iowa

6. Biological Effects of Radiation • Whether the source of radiation is natural or man-made, whether it is a small dose of radiation or a large dose, there will be some biological effects. Radiation Causes Ionization of: ATOMS which may affect MOLECULES which may affect CELLS which may affect TISSUES which may affect ORGANS which may affect THE WHOLE BODY EmrahTiras, University of Iowa

7. Radiation Effects • Biological effects of radiation are typically divided into two categories. High Doses(Acute) and Low Doses(Chronic) • High Doses(Acute) • This category consists of exposure to high doses of radiation over short periods of time. • Producing acute and short time effects. • Tend to kill cells that tissues and organs are damaged. Some High Dose Effects Skin Burns Sterility Hair Loss Cataracts If the dose of the radiation is higher than 150 Rad, it causes death. EmrahTiras, University of Iowa

8. Low Doses • This category represents exposure to low doses of radiation over an extended period of time • Producing chronic or long term effects. • Low doses tend to damage or change cells. • They spread out over long periods of time. • They do not cause any immediate problem to an body organ. Categories of Effects of Exposure to Low Doses of Radiation Genetic Somatic In-Utero EmrahTiras, University of Iowa