Radiation Protection-

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Diagnostic efficacy

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degree to which the diagnostic study accurately reveals the presence or absence of disease in the patient.

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Radiation safety program

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executes alara principle, perform periodic exposure audits

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BERT

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background equivalent radiation time
(does not imply radiation risk, easy to explain to patients, always part of environment)

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Wave particle duality

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x ray acts as both a wave and a particle of energy

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Electromagnetic Spectrum

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described by frequency
unit is hertz(Hz)

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Frequency

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cycles per second

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What is the difference between KeV and kVp

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Kev is electron volts
Kvp is the amount of energy selected

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Electromagnetic spectrum is divided into what?

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ionizing radiation- x rays, gamma, high energy ultraviolet radiation(anything above 10 electon volts)

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Another category of ionizing radiation?

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alpha, beta, neutrons, protons

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Equivalent dose (eqd)

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used for radiation protection, exposure from types of ionizing radiation,

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Effective dose

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need to know equivalent dose to know effective dose
takes into account all types of ionizing radiation to the organs
gives a specific weighted factor

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Radiation equivalent dose and biologic effects from acute whole body exposures

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Blood changes= .25 sv
Nausea and diarrhea= 1.5
Erythema= 2
Gonads, temporary sterility= 2.5
50% chance of death= LD 50/30
death= 6

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Manmade radiation

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consumer products, air travel, nuclear fuel, nuc. weapons, medical radiation.

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Anode

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xrays are made here
high atomic number
high melting point
conducts

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Inherent vs. added filtration

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inherent- includes xray tube and anything in it(oil, window, led housing)
added- aluminum, collimator

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What is the average energy of the selected xray beam?

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one third the amount

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attenuation

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both absorption and scatter radiation

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Direct transmission

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hits image receptor without interacting with the patient

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How is xray fomed?

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by both direct and indirect transmission

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Fog

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undesirable additional density

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Coherent scattering(thompson scatter, rayleigh, classic, elastic, unmodified)

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when a low energy photon(less than 10 KeV) interacts with an atom. significant in mamo. No ionization of the biologic atom occurs.

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Compton(incoherent, inelastic, or modified)

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responsible for most scattered radiation, outershell electron
potential health hazard(occupational dose)

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Photoelectric

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innershell electron(usually k shell)
characteristic photons (when one electron drops into the next)
responsible for both patient dose and contrast

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Probability of occurrence of the photoelectric absorption- probability of occurrence of photoelectric absorption depends on the energy of the incident x ray photons and the atomic number z of the atoms comprising the irradiated object, it increases as the energy of the incident photon decreases and the atomic number of the irradiated atoms increases.

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a structure that is twice the size of another object, absorbs twice as many photons

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The less a given sturcture attenuates radiation

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the darker its image will be.

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As absorption increases

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the potential for biologic damage increases

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Pair Production

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forms a negatron and a positron, used in PET scans, annihilation occurs creating .511 Mev a negatron and a positron, does not occur unless the energy of the incoming incident photon is 1.022 MeV

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Photodisintegration

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only occurs in 10 MeV
used in radiation therapy
collides with the nucleus

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Nov 8 1895

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wilhelm roentegen

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Clerance madison dally

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1st person to die from radiation

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Somatic damage

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biologic damage to the body

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Short term effects

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nausea, fatigue, diffuse redness of the skin, loss of hair, intestinal disorders, fever, blood disorders, shedding of the outer layer of the skin

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long term or late somatic

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cancer, embryologic effects, formation of cataracts

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genetic effects

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biologic effects of ionizing radiation of generations yet unborn

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Roentgen

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measures x ray exposure in air

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rem

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radiation eqivalent man or eqivalent dose

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EfD

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is the quantity that attempts to summarize the overall potential for biologic damage to a human from exposure to ionizing radiation

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the quantity equivalent dose uses radiation weighting factors Wr to adjust the quantity absorbed dose to reflect the difference in biologic harm produced by different types and energies of ionizing radiation

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the quantity effective dose uses tissue weighting factors (Wt) to adjust the quantity equivalent dose to reflect the difference in harm to the person as a whole depending on the tissues organs that have been radiated. effective does takes both the type of radiation and part of the body radiated

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Compton scatter in a material

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does not depend on the atomic number of the material

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The si unit of the absorbed dose is the gray when is defined a s the energy absorption of 1 joule per kilogram

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x

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High let

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produces more biologic damage

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The annual occupational EfD limit of 50 mSv (5 rem)in any single year as a consequence of their work related activities.

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10% or more radiation, person should wear monitor

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What is a film badge?

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Used to monitor large numbers of personnel in a cost effective manner. Record whole body radiation exposure accumulated as a low rate over a long period of time. Can read from .1 mSv to as high as high as 5000 mSv(500 rem).

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Main advantage of film badge

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permanent legal record of personal exposure

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OSL

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most common type of device used for monitoring of occupational exposure in diagnostic imaging.
Uses aluminum oxide, uses a laser light to read it.
Advantages are reading as low as 1 millirem

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Pocket ionization chamber

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most sensitive, provides an immediate readout, disadvantage is there is no legal record and are not cost effective.

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Thermoluminescent dosimeter-

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contains lithium fluoride. crystals absorb energy and are excited to a higher energy level. light is emitted, and produces a reading(only monitor that can be reused)

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Organic

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contains carbon

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Mitosis

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everything but genetic cells

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Meosis

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Genetic cells divide

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What is considered high LET?

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alpha particles,

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What is considered low let radiation?

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gamma rays and x rays

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x rays and gamma rays

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have no mass and no charge

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low let radiation interacts with biologic tissue

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causes damage primarily through an indirect action that involves the production of molecules called free radicals

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free radicals

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solitary atoms or most often a combination of atoms that behave as extremely reactive single entities as a result of the presence of unpaired electrons

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Low LET

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indirect

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RBE-relative biological effectiveness

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capabilities of radiation with differing lets to produce a particular biologic reaction

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Wr

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EqD

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Oxygen enhancement ratio

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biologic tissue is more sensitive in a oxygenated state

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free radical

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increases damage to the cell

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oxygen fixation hypothisis

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o2 state is permanently damaged, without oxygen, is not.

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indirect effect

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interaction of radiation with h20

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direct effect

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ionization of atoms on the dna

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point mutation

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single strand break in the dna

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double strand break

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occurs with two sugar phosphate chains

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chromosome aberations

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occurs early in interphase

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target theory

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dna serves as a target. occurs through direct and indirect

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apoptosis

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programmed cell death

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Chromosome breakage

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potential outcome when ionizing radiation interacts with dna.

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Law of Bergonie and Tribondeau

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observed the effects of ionizing radiation on testicular germ cells of rabbits they had exposed to x rays.

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200 rads to ovaries

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250 for guys

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somatic effects

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when living organisms that have been exposed to radiation experience biologic damage

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nonstochastic deterministic somatic effeccts

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effects are cell killing and directly related

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what happens when low doses are delivered over a long interval of time?

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late radiation effects

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early effects

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appear within minutes, hours, days, or weeks. severity of these effects is dose related. diagnostic imaging exams do not usually impose radiation doses sufficient to cause early deterministic effects.

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accute radiation syndrome

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occurs in humans after a whole body large dose is received over a short period of time

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symptoms of acute radiation syndrome

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hematopoietic syndrome, gastrointestinal syndrome, cerebrovascular syndrome

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stages of acute radiation syndrome

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prodromal period, the initial stage, occurs within hours after a whole body absorbed dose of 1 gy(100 rad)

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latent period

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occurs 1 week after

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recovery can occur in three months of acute radiation syndrome

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cc

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small intestine

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most severely affected part of the gastrointestinal tract.

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Late somatic effects

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effects that appear months or years after exposure to ionizing radiation. they can be directly related to the dose received and occur months or years after a high level radiation exposure are

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stochastic

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randomly occurring, non threshold, greater the dose, the greater the chance of having and effect however the greater the dose dose not mean it will be more severe.

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stochastic

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genetic defects and cancer

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biologic damage

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cataracts, genetic mutations

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ICRP(international commission on radiological protection

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evaluates information on biologic effects of radiation and provides radiation protection incidence through general recommendations on occupational and public dose limits

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NCRP(national council on radiation protection and measurements

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reviews regulations formulated by the IRCP and decides ways to include those recommendations in u.s. radiation protection criteria

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(unscear)United Nations Scientific committee on the effects of atomic radiation

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evaluates human and environmental radiation and derives radiation risk assessments from data and research conclusions

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National academy of sciences/national research council committee on the biological effects of ionizing radiation(nas/nrc-beir)

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reviews studies of biologic effects of ionizing radiation and risk assessment and provides the information to organizations such as the icrp for eval.

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FDA

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conducts an ongoing product radiation control program regulating the design and manufacturing of electric products including x ray equipment

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NCRP report no 116

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provides the most recent guidance on radiation protection

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background and medical

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not included in occupational exposure

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Cumulative effective dose limits for the whole body

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mSv x age Age in rem

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Exposure for the fetus

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.5 mSv per month
5 mSv for gentation

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lens of eyes

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150 mSv

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localized areas of the skin, hands, and feet

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500 mSv

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x ray tube housing leakage

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100mR per hr at 1 meter

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Indicator for SID

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can be accurate within 2%

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off focus radiation

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not produced at the anode inside the tube

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PBL

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positive beam limitation

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SID with PBL requirement

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2 % accuracy

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x ray beam

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heterogeneous

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HVL half value layer

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decreases beam intensity of primary beam by 50%(mm/Al)

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5% variance (reproducibility)

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radiation intensity on radiation exposures

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exposure linearity

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consistency in output radiation intensity at selected kVp settings when settings are changed from one milliamperage and time combination to another

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95%

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recorded image from visable light photons emitted by intensifying screens

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film rare earth screens

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made with rare earth phosphors named gadolinium. they emit more light than regular screens by 15-20 percent.

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faster screen speed

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less dose to patient

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kvp and and screen film

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two most important technical considerations in the amount of patient dose

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quantum mottle

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image noise

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Usage of a grid

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more than 10 cm

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higher grid ratio

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higher patient dose

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Scintillator(amorphus silicon)(DR)

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converts x rays to visible light in system

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CCD's (DR)

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converts electrical signals by an array of transistors.

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photomultiplier tube (CR)

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ultraviolet light to electronic signal

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air gap technique

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cleans up scatter (c spine image)

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Imaging procedures are specified in four ways

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entrance skin exposure, skin dose, gonadal dose, and bone marrow dose.

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TLD's (thermolucent dosimeter)

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most often used to measure skin dose directly(lithium fluoride)

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Genetically significant dose

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assess the impact of gonadal dose. GSD is the equivalent dose to the reproductive organs

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bone marrow dose

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dose of radiation delivered to the organ.

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1 mSv

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nonoccupational exposure

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At a 90 degree angle to the primary x ray beam, at a distance of 1 m, the scattered x ray intensity is approximately 1/ 1,000 of the intensity of the primary x ray beam.

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xx

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.5 mm lead equivalent

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width of lead apron

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primary = 1/16

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secondary= 1/32, scattered and leakage

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control booth

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considered a secondary protective barrier

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lead apron

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.25 minimum
most commonly is .5

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thyroid shield

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.5

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lead glasses

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.35 mm

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during fluor procedures

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minimum of .5 lead aprom

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lead gloves

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.5 mm

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protective curtain

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.25

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bucky slot curtain

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.25mm

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Image intensifier is positioned as close to the patient as possible

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the x ray beam intensity is minimized

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dose limit to skin and hands

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500 mSv (50 rem)