1. Radiation Protection Unit 2
Chapter 4 radiation quantities and units

2. 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.

3. History November 1895- Roentgen discovered x-rays
December 1895 Reported findings- discovery
cases of radiodermatitis was reported
1898- Thomas Edison invented fluoroscope
st 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

4. Injuries
Between 1911 and 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
stdoes 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

5. Dose over the ages
Annual Maximum Permissible Dose ( MPD)- expressed in Roentgen

6. 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 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

7. 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

8. 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 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 C/Kg
Coulomb to Roentgen C/Kg C/kg = ≈ 3880 R
2.58 x 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

9. 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

10. 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 Rad = 50 Gy
500 rad= 5 Gyt or rem = 5 Sv

11. 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-cm SI unit Gy-m2

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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 Sv for general population

19. review

20. 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.

21. 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.

22. A pt receives 3000rad: what is the dose in SI?
a. 6000Gy b 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
rem =____________Sieverts .
rem / /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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