Units, Detection, and Measurement (PART I)

Wilhelm Conrad Roentgen

a german physics professor that discovered X-rays

November 8, 1895

when were x-rays discovered

modest laboratory at the University of Wurzburg in Bavaria

where were x-rays discovered

image of the hand of Roentgen's wife

first x-ray image

"On a New Kind of Ray", December 1895, Physical Medical Society of Wurzburg

Roentgen announced his scientific findings in an abbreviated manuscript, which was presented to the

1896

cases of somatic damage were reported in Europe

Clarence Madison Dally, October 1904

died of radiation-induced cancer at the age of 39, because of this, Thomas Edison discontinued his x-ray research

1910

cancer deaths among physicians attributed to x-ray exposure were reported

occupational exposure

a radiation exposure received in the course of exercising their professional responsibilities

radiodermatitis

many radiologists and dentists using the new penetrating rays developed a reddening of the skin called

1921: British X-ray and Radium Protection Committee

the committee planned to formulate guidelines for the manufacture and use of radium and x-ray equipment and devices to reduce the chance of occupational injury

1900-1930: Skin Erythema Dose

the received quantity of radiation that causes redness over an area of skin after irradiation

Skin Erythema Dose

often a crude and inaccurate way to quantify radiation exposure

1925: First International Congress of Radiology

this meeting allowed radiologists from all over the world to collaborate, no definite decisions on quantifying the effects of ionizing radiation were made based on the recommendations presented

1925

International Commission on Radiation Units and Measurements (ICRU)

1928: The Second International Congress of Radiology

the "roentgen" was in place as a unit associated with a certain degree of exposure; it was not, yet by any means, scientifically well defined

ICRU

was charged with precisely defining this unit of exposure

International X-ray and Radium Protection Commission

the second international congress also established the ____, predecessor of the International Commission on Radiological Protection (ICRP)

tolerance dose

radiation dose to which occupationally exposed persons could be continuously subjected without any apparent harmful acute effects, such as erythema of the skin

tolerance dose

general belief was that no adverse effects from radiation exposure would be demonstrated at doses lower than this level

threshold dose

tolerance exposure level could be regarded as a

1934: International X-ray and Radium Commission

recommended a tolerance dose daily limit of 0.2 roentgen

1931: Advisory Committee on X-ray and Radium Protection

also recommended a tolerance dose of 0.2 roentgen per day

1936

the committee reduced this dose to 0.1 roentgen per day

1936

scientists began to recognize the delayed tissue reactions and stochastic effects of ionizing radiation that appeared months or years after exposure, and the possibility of genetic or heritable effects' they began to focus on finding ways to minimize the risk of sustaining such damage

- nausea

- fatigue

- diffuse redness of the skin\

- loss of hair

- intestinal disorders

- fever

- blood disorders

- shedding of the outer layer of skin

early tissue reactions (8):

- cataract formation

- fibrosis

- organ atrophy

- loss of parenchymal cells

- reduced fertility

- sterility

late tissue reactions (6):

- cancer

- genetic (hereditary) effects

stochastic effects (2):

1946: US Advisory Committee on X-ray and Radium Protection

became known as the National Committee on Radiation Protection

1956, 1964 - National Council on Radiation Protection and Measurements (NCRP)

the name of this radiation standards organization underwent another change in ___ and again in ___, when it became the

1948: International Systems of Units (SI)

"Système International d'Unités"

International Committee for Weights and Measurements developed this system

1950s: Maximum Permissible Dose (MPD)

MPD replaced the tolerance dose for radiation protection

rem, radiation equivalent man, Roentgen equivalent man

MPD was initially expressed in a unit called ___, also historically known as ___

sievert

the rem has since been replaced by the SI unit

1991: The ICRP adopted the term effective dose (EfD)

based on the energy deposited in biologic tissue by ionizing radiation, it takes into account both of the following:

1. type of radiation (x-radiation, gamma, neutron)

2. variable sensitivity of the tissues exposed to the radiation

Effective Dose (EfD)

it is a measure of the overall risk arising from the simultaneous irradiation of various biologic tissues and organs within an individual

Sievert (Sv)

EfD is expressed in the SI unit

1980: the ICRU adopted SI units

a unified system of metric units for use with ionizing radiation is urged, with full implementation of the units as soon as possible

Gray (Gy) and Centigray (cGy)

are routinely used in therapeutic radiology to specify absorbed dose

sievert (Sv)

replaced the rem for radiation protection purposes

100 rem

1 Sv =

milligray per minute (mGy-a/min), roentgens per minute (R/min)

fluoroscopic patient entrance radiation levels are now specified in ____, but in many facilities they are still measure as exposure rates in ____

- occupational exposure

- medical exposure

- public exposure

types of exposures (3):

occupational exposure

refers to all exposure received in the workplace

medical exposure

includes exposures from diagnostic and therapeutic procedures; include individuals assisting patients with these procedures

public exposure

encompasses all exposures other than occupational and medical exposures

exposure

amount of radiation responsible for the ionization of a well-defined volume of air; it may be determined by measuring the number of electronic-ion pairs

directly

the intensity of x-ray exposure of the air volume and the number of electron-ion pairs are ___ proportional

coulombs per kilogram (C/kg)

SI unit for exposure:

roentgen (R)

conventional unit for exposure:

2.58 x 10⁻⁴ C/kg

1 R = __ C/kg

1.6 x 10¹⁹ electrons

1 C = __ electrons

coulomb (C)

- basic unit of electrical charge

- equal to the "amount" of electrical charge moving past a point in a conductor in 1 second when an electrical current of 1 ampere is used

ampere

SI unit of electrical current:

current

consists of moving electrical charges, the most common of which is the electron

-1.6 × 10⁻¹⁹ C

the charge carried by an electron is equal to:

ampere

quantifies the flow rate of electric charge

coulombs per kilogram (C/kg)

this exposure unit is simply equal to an electrical charge of 1 C produced in a kilogram of dry air by ionizing radiation

kinetic energy released per unit mass

KERMA stands for

KERMA - kinetic energy released per unit mass

it expresses how energy is transferred from a beam of radiation to a material

joules per kilogram (J/kg)

unit for kerma is

air kerma

the total kinetic energy released in a unit mass of air

dose area product (DAP)

- the sum total of air kerma over the exposed area of the patient's surface

- a measure of the amount of radiant energy that has been thrust into a portion of the patient's body surface

mGy•cm²

DAP is usually specified in units of

activity

it is the number of radionuclides disintegrating per second (dps or s⁻¹)

becquerel (Bq)

SI unit for activity:

curie (Ci)

conventional unit for activity:

1 dps

1 Bq = __ dps

3.7 x 10¹⁰ Bq = 2.22 x 10¹² dpm

1 Ci = __ Bq = __ dpm

absorbed dose

it is defined as the amount of energy per unit mass absorbed by an irradiated object

gray (Gy)

SI unit for absorbed dose:

radiation absorbed dose (rad)

conventional unit for absorbed dose:

1 J/kg

1 Gy = __ J/kg

100 rad

1 Gy = __ rad

number of gray x 1,000 = number of milligray

how to convert gray to milligray

number of gray x 100 = number of centigray

how to convert gray to centigray