Radiation Protection Unit 2 Chapter 4 radiation quantities and units

Objectives Differentiate between kVp and mAs as technical factors Describe absorption verses attenuation Differentiate between primary, exit, image –forming, and scattered radiation. List and discuss 2 types of photon transmission. List the events that occur when x-radiation passes through matter. Identify the x-ray photon interactions with matter which are important in diagnostic radiology. Describe the effect of kVp on image quality and patient absorbed dose. Discuss the historical evolution of radiation quantities and units Explain the concepts of skin erythema dose, tolerance dose and threshold dose. List examples of early somatic effect, late somatic effects and late stochastic effects. Differentiate between somatic and genetic effects. Differentiate among the radiation quantities exposure dose and effective dose and identify the appropriate symbol for each quantity. List and explain the International System (SI) units for radiation exposure, air kerma, absorbed dose, equivalent dose and effective dose. Define or describe: DAP, tissue weighting factor, LET, and effective dose.  

History November 1895- Roentgen discovered x-rays December 1895 Reported findings- discovery 1896- 23 cases of radiodermatitis was reported 1898- Thomas Edison invented fluoroscope 1904- 1st x-ray fatality Clarence Dally- Edison’s friend and assistant- radiation induced CA Suffered with severe x-ray burns and amputation of both arms 1870’s and 1880’s- Sir William Crooks – invented the 1st x-ray tube- partial vacuum 1913- William D. Coolidge- invented the vacuum tube

Injuries Between 1911 and 1914- at least 54 cancer deaths and 198 cases of radiation induce malignancy Earliest unit of measurement – skin erythema dose- amount of radiation required to cause redness to the skin after irradiation – Gray- Not accurate 1928- Roentgen was accepted as unit of exposure 1931- 1stdoes limiting recommendation made by Advisory Committee on x-ray and radium protection. .2R/day Now called National Council on Radiation Protection and Measurement 1937 “Roentgen” became internationally accepted as unit of exposure since it had be defined

Dose over the ages Annual Maximum Permissible Dose ( MPD)- expressed in Roentgen 1931- 50 1936-30 1948- 15 1958- 5

Injury types Occupational exposure- exposure to radiation works – early as 1910 Seen in radiologists and non-radiologists Somatic damage-biologic damage to the body- reported as early as 1896 Early deterministic somatic effects- appear within minutes, hours, days or weeks- dose dependent organic damage- will most likely occur once a threshold has been met Late deterministic somatic effects / late stochastic effects-recognized in 1936- months or years after exposure and genetic effects Late Deterministic- increases the chances of occurring Late Stochastic- do not have a threshold – arbitrary Tolerance dose- measurement of how much a person could be exposed to radiation without apparent acute effects Threshold dose- a dose lower than the tolerance dose- Radiodermatitis- reddening of the skin Blood disorders- aplastic anemia from bone marrow failure Leukemia- over production of white blood cells

Radiation Quantities - main Units 1. Exposure (X) Roentgen 2. Air kerma (J/kg)2 or Gya or Gyt 3. Absorbed Dose ( D) Rad or Gray 4. Equivalent Dose ( EqD) Rem or Sievert 5. Effective Dose ( EfD) Sievert or Milli-Sievert

R=traditional unit C/kg = SI unit 1. Exposure- Roentgen Amount of radiation that may strike an object – used for x-ray equipment calibration R=traditional unit C/kg = SI unit Roentgen ( R) – a unit of radiation exposure that will liberate a charge of 2.58 x 10-4 coulombs per kg of air Amount of charge released by x-rays as they pass thru dry air conversions : Roentgen to Coulomb 1 R = 2.58 x 10 -4 C/Kg Coulomb to Roentgen C/Kg 1 C/kg = 3876 ≈ 3880 R 2.58 x 10 -4 C/Kg 1 coulomb = 1 ampere-second basic unit of electrical charge ( how much electricity is transferred by a current of 1 A in 1 second) Unit of exposure in air What comes out of the machine Refers to energies of less than 3 MeV

Gya ( air) or Gyt ( tissue) 2. Air kerma SI unit- measurement of radiation to an object- in air –radiation intensity in air Used for x-ray tube output and inputs to image receptors Gradually replacing the traditional quantity, exposure J/Kg for Air Gray (Gy) Gya ( air) or Gyt ( tissue) Expressed as a the kinetic energy( Joules) released in a unit of mass (kilogram) DAP- Dose Area Product- modern measurement to determine entire amount of energy delivered to the patient by the beam- Used with radiographic and Fluoro units Kinetic energy released in matter Kinetic energy released in material Kinetic energy released per unit mass May start seeing use in clinical settings

3. Absorbed dose- Rad or Gray RAD- traditional unit Gray – SI Unit ( usually expressed as mGy or cGy) Gyt Unit of quantity, absorbed dose- amount absorbed by the patient RAD= Radiation absorbed dose or ( D )or absorbed dose How much energy is transferred to an irradiated object by ionizing radiation Proportional to the degree of attenuation : the more attenuation , the higher the dose received, the more biological damage Traditional unit: 1 Rad is = to the radiation necessary to deposit energy of 100 ergs in 1 gram of material Erg- unit of energy transfer 1 RAD = 100 erg/g 1 RAD = 1/100 Gray so 5000 Rad = 50 Gy 500 rad= 5 Gyt or 500 rem = 5 Sv

Surface integral dose (sid) Exposure area product or amount of radiant energy transferred by radiation to the body during an x-ray Traditional unit R-cm2 SI unit Gy-m2

Let (linear Energy Transfer) The amount of energy transferred on average by incident radiation to an object per unit length of travel through the object Radiation that has a high LET transfers a large amount of energy into a small area- more damage Low LET – travels farther but less damage to one specific area X-ray are considered low LET radiation; they don’t deposit as much energy in a given space as opposed to other radiations High LET= high QF= higher biological damage

Quality Factor – (qf) Factor used to determine the ability of a dose of radiation to cause biological damage Different for different types of radiation: example :alpha more damaging than x-ray so alpha gets a higher rating Number assignment of radiation types QF is based on LET

3. Equivalent Dose (EqD)– ReM or sievert Rem= traditional unit Sievert ( Sv) – SI Unit REM= Radiation Equivalent Man Used in rad protection for occupationally exposed individuals Measures the biological effectiveness of radiation The absorbed does equivalent of any type of ionizing radiation that produces the same biological effect as one rad of x-radiation Different types of radiation produce different amounts of biological damage Use radiation weighting factor (WR ) factor takes into account the type and energy of the radiation Same numeric value as the QF

Eqd Cont’d - Determine absorbed dose Equivalent Dose= absorbed dose x radiation weighting factor SI Eqd= D x WR which is Sv = Gy x WR TRADITIONAL REM= RAD x QF 1 Sv= 1000 mSv

SI Sieverts or milli-Sieverts Traditional Rem 5. Effective Dose ( efd) used to measure the overall risk of exposure to humans from radiation “sum of the weighted equivalent doses for all irradiated tissues or organs “ NRCP report 116 SI Sieverts or milli-Sieverts Traditional Rem EfD= D x WR x WT WT – tissue weighting factor- risk associated with irradiation of different body tissues- risk of developing CA when all tissues are given the same amount of radiation Utilizes BERT – for comparisons for environment sources

Collective effective dose ( colEfd) used to describe the radiation exposure of a population or group from low doses of radiation Product of the exposure of the persons exposed SI Unit = person-Sievert traditional = man-rem If 200 people received an avg EfD of .25 Sv. The ColEfd = 200 x .25 = 50 person sieverts

Total Effective dose equivalent (tede) Used in radiation dosimetry Defined by the Nuclear Regulatory Commission ( NRC) to monitor and control human radiation exposure – all sources of radiation Sum of effective dose equivalent from external radiation and CEDE ( committed effective dose equivalent) internal exposure “committed dose”- probability of health effects from intake of radioactive material into the body Nuc Med techs and IR radiologists- use to monitor high dose occupational workers TEDE whole body limit 0.05 Sv (worker) or 0.001 Sv for general population

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SI Units Presently in Use Radiation quantities Exposure Air kerma Absorbed dose (D) EqD EfD Radiation units Coulombs per kilogram (C/kg) Gray (Gy) Gy Sievert (Sv) Sv Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Traditional Nonmetric Units Gradually Becoming Obsolete Radiation quantities Exposure Absorbed dose (D) Equivalent dose (EqD) Effective dose (EfD) Units of measure R Rad Rem Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

A pt receives 3000rad: what is the dose in SI? a. 6000Gy b. 3000 cGy c. 300rad d. 30R rad and cGy are equal so B 2. 10 Sieverts equal ___________ rem. 1 Sv = 100 rem so 10 x 100= 1000 3. 1000 rem =____________Sieverts . rem / 100 1000/100 = 10 Sv 4. 1 Rem = __________ mSv . 100 rem = 1000 mSv so 1000 / 100 = 10 mSv 5. Convert 8000 rad to Gy:___________ 8000/ 100 = 80 Gy 6. Convert 7 Gy to rad: _____________ 7 x 100= 700 rad Resources:   Radiation Protection in Medical Radiography by Mary Alice Statkeiwicz Sherrer, Paula Visconti, E. Russell Ritenour and Kelli Welch Haynes. 6th and 7th Edition. Elsevier online. Essentials of Radiographic Physics and Imaging. James N. Johnston and Terri L Fauber. 1st Edition. Elsevier Online.

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