Final Exam RT 202

TYPES OF IONIZATION

particulate -

• radiation given off in particles (alpha, beta)

• possess kinetic energy and are ionizing

alpha-

• unstable nucleus has too many protons and neutrons

• low penetration power

• heavy atoms

• loses 2 protons and 2 neutrons

• 4amu

• +2 charge

• air travel = 1-10 cm

• soft tissue travel = 1mm-100micrometers

• 4-7MeV

• highly ionizing

beta-

• moderately unstable nucleus has too many neutrons

• loses 1 negative or positive charge

• 0amu

• +/- 1

• air travel = 0-10 meters

• soft tissue travel = 0-2 cm

• 0-7 MeV

• stronger penetration power than alpha

electromagnetic -

• travel as photons or wavelengths

• tavel at the speed of light ( 3×10^8 ) ( velocity )

• 0 amu and 0 charge so no nuclear transmutation

gamma -

• when unstable nucleus undergoes radioactive decay

• emitted from nuclei

• air travel = 0-100 meters

• soft tissue travel = 0-30cm

• 0-5 MeV

• low to high penetrating power ( not as ionizing as particulate )

xrays -

• always artificial

• emitted from orbital shell

• air travel = 0-100 meters

• soft tissue travel = 0-30 meters

• 0-25 MeV (much higher than gamma)

• high penetration power

electromagnetic emission spectrum-

xray emission spectrum -

added filtration

• removes quality

• decreases quantity

• small shift to right

• decreases average energy and intensity

• changes in amplitude

target material

• tungsten is best

• gold

• molybdenum

  • have high anomic numbers

generator type

• increases quantity of xrays produced

• increases average kV of beam

kVp curve ( what does the curve mean? left? right? higher? )

xray production

brems

• “breaking radiation”

• the energy given off from the projectile electron when it comes close to the tungsten nucleus and slows down

• occurs at the xray tube

• projectile electron

  • kenetic energy

  • comes close to nucleus

  • nuclear field slows down projectile elecron

• deceleration

  • release of energy from projectile elecron emitted as xrays

• range of energy

  • heterogenous / poly energetic nature of xray beam

  • counts for most amount of xrays in beam

characteristic

discrete energy

part of primary beam

projectile electron knocks out orbital electron creating xrays

• transition

  • release of energy or radiation

• characteristic cascade

  • orbital vacancy filled by outter shell electrons one after another

• calcuation of energy photo emission

  • subtracting binding energies of shells involved

  • Kv of a characteristic xray produced from an electron falling from L to K shell

    =

    69-12= 57 Kv

  • K - 69

    L - 12

    M - 3

    N - 1

    O - .1

    P

( calculate characteristic radiation amounts and compare their emission spectrums -the graph )

brems and characteristic

( define )

( where does the interaction occur? )

Interactions

classical

• unmodified, coherent, thompson scattering

• no ionization - no energy transfer

• low energy, less than 10keV

• from tube

• does not interact with any electrons

• excites atom and leaves

PE

• total absorbtion interaction

• creates contrast

• patient dose

• most important for DX

• 23-150 kVp

• total energy transfer to electron

• Eke = Ei- Eb

compton

• modified, inelastic, incoherent

• partial absorbtion interaction

• scatter

• not useful DX

• 60-90 kVp

• up to 1000 keV

• ejects outer shell electron

• RT dose

• Ei = Es + Eb + Eke

• scatter energy is alwasy higer than compton electron

pair production

• high energy xray photons interacts with electromagnetic field of nucleus

• at least 1.02 MeV of energy

• radiation therapy not xray DX

• annihilation reaction

  • positron combines with negative electron

photodisinegration

• very high energy incident photons are absorbed by nucleus

• xray photon crashed into nucleus

• energy greater than 10 MeV

• nucleus emits a nucleon to stabalize

( what energies are involved? )

( where in the atom the interaction occurs )

( what is produced? )

( which are diagnostic? )

( what affects probability and likelihood of interactions? )

( how contrast and absorbtion affects )

quantities and units

• in air exposure

  • Rentogen

  • C/kg

  • air kerma

  • Gya

  • measures Gamma and X

• absorbed dose

  • Rad

  • Gy

  • Gyt

  • measures Alpha, Beta, Gamma, X

  • PATIENT

• equivalent dose

  • rem

  • Sv

  • measures Alpha, Beta, Gamma, X

  • PERSONNEL

detectors and monitors

film badge

uses a piece of film to measure amount of radiation in darkness of film piece

pocket dosimeter

• ionization chamber

• measures in air exposure

• energy range 0-200mR

• advantages

  • sensitive

  • immediatie reading

  • small and portable

• disadvantages

  • daily identification

  • recalibration

  • daily manipulation

  • limited range of energies

  • no permanent record

TLD

• crystalline material stores radiant energy

• from heat

• delayed emission of light

• light is proportional to dose

• lithium fluoride crystal absorbs radiation energy

• annealing - heating crystal to make it glow

• glow curve plotted

• advantages

  • records exposures as low as 5mRem

  • not affected by humidity or pressure

  • can be worn 3 months

  • reusable

OSL

• scanned by laser then gives off light (proportionate)

• alumium oxide

• more sensitive than TLD

• alumium, copper, tin

• advantages

  • most sensitive

  • 10 micro Sv or 1 mRem

  • can be re-evaluated

  • self contained and pre loaded

  • not affected by humidity

  • long term stability

• disadvantages

  • measures only specific body part

  • no immediate readings

DIS

• ionization chamber

• saved by a memory chip

• EEPROMs store data

• amount of charge created is directly proportionate to amount of exposure

• USB acess

• advantages

  • instant acess

  • reusable

• disadvantages

  • require constant use and measurement of data

geiger-muller

• ionization chamber

• audible sound

• detects gamma, beta, X

• can detect 1 ionizing event

• can detect individual particles

ionization chamber connected to electrometer

• used by medical physicists

• gas filled detector

ionization chamber - type survey meter - cutie pie

• both a rate meter and cumulative exposure instrument

• measures gamma and X

• 10- several thousand microgray/h

• 1 mR/h - several thousand mR/h

• monitoring radiographic xray installations

( how do different monitors work? )

( advantages and disadvantages of personnel monitors )

NCRP reports

NCRP 116

• dose equivalents to personnel and public

NCRP 102

• focuses on patient reduction of exposure

• proper distance

NCRP 105

• filtration

NCRP 160

• medical exposure dose of patients

NCRP 147

• changing equipment over the years trying to improve

• structural shielding design for medical xray imaging facilities

cardinal principles

• minimize time

• protection of patient

  • exposure = exposure rate x time

• maximize distance

  • double distance form source = intensity decreases by a factor of 4

  • triple distance form source = intensity decrases by a factor of 9

• inverse square law

  • point source

• 1 meter rule

  • patient source

  • divide exposure by 1000 if one meter away at 90 degrees

• shielding

  • HVL

  • tenth value layer = 3.3 HVLs

doses

annual occupational effective dose limit - whole body

• 50 mSv/yr

• 5000 mrem/yr

lifetime effective dose - cumEfd

• age x 10 mSv

• age x 1 rem

skin

• 500 mSv/yr

• 50 rem/yr

extremities

• 500 mSv/yr

• 50 rem/yr

lens

• 150 mSv/yr

• 15 rem/yr

educational consideration

• 1 mSv/yr

• 100mrem/yr

embryo/fetus

• monthly = .5 mSv

• gestation = 5 mSv or .5 rem

public exposure

• 1 mSv/yr

negligable dose

• .01 mSv/yr

collective dose ( colEfd)

• cumulative dose to a population or group exposed to a given radiation source

TEDE

• resulting from internal and external sources of radiation

bone marrow average dose in U.S.

• 1 mGyt/yr

• 100rad/yr

GSD

• .20 mSv

• 20mrad

pregnancy

• below 100 mGyt = abortion not indicated

• above 250 mGyt = abortion is recommended

deep dose equivalent

• annual whole body dose

• carried to lifetime dose

• 50 mSv/yr

shallow dose equivalent

• 500 mSv/yr

lifetime dose

• whole body dose

equipment

tube housing

• reduces radiation leakage to less than 1 mGya/hr at 1 meter from housing

• leakage radiation because xrays emit isotropically

source to image receptor distance

• accurate to 2%

reproducibility

• consistency in exposure during repeated exposures

• cannot vary more than 5%

linearity

• consistency with exposures with varying mA station and times

• cannot vary more than 10%

distances

stationary radiographic

• SSD not less than 15”

• SID not less than 40”

mobile radiography

• 1 meter rule

• exposure cord at least 2 meters

stationary fluoro

• SSD SHOULD not be less than 15”

• SSD SHALL not be less than 12”

mobile fluoro

• SHALL not be less than 12”

measurements

tube housing

• less than 1 mGya/hr at 1 meter

permanent filter in fluoro

• 2.5 mm Al

image intensifier

• 2 mm Al

• primary barrier

bucky slot cover

• .25 mm Pb

protective curtain

• .25 mm Pb

• primary barrier

DAP

• SHOULD not exceed 21 mGya/min for each mA of operation

• SHALL not exceed 100 mGya/min

fluoro

how to reduce scatter?

• by reducing pt dose

how to reduce magnification?

• intensifier side as close to pt

how to reduce dose?

• tube under pt

• pulsed radiography

• intensifier side as close to pt as possible

patient protection equipment

shielded when within 5cm or 2in of collimated primary beam

gonadal shield

• .5mm Pb

• flat contact

• shaped contact

• shadow

what positioning reduces dose?

• pa chest for thyroid

• pa pelvis

• pa scoli series to breast tissue

personnel protection equipment

barriers

primary barrier

• any wall perpindicular to primary beam

  • bucky wall

  • floor

  • image intensifier

  • protective curtain

• material

  • 4” masonry

  • 1.6mm Pb

  • lead, concrete, brick, block

secondary barrier

• any wall parallel to brimary beam

  • ceiling

  • doors

  • control booth wall

  • glass window

• material

  • overlap primary by 1/2 “

  • extend to ceiling

  • .8mm Pb

  • 4 thickness gypsum board

controlled area

• less than 1 mSv/wk

• EqD of workers 50 mSv/yr MAX

uncontrolled area

• less than 1 mSv/yr

• MAX is 20 microSv/wk

use factor

indicated by the proportional amount of time during ehich the xray beam is energized

• full occupancy

  • 1U

• partial occupancy

  • ¼ U

• occasional occupancy

  • 1/16 U

workload

number of examinations performed

personnel

• where to stand in mobile and fluoro?

  • behind control booth

• who holds patients and who doesnt

  • patient aid

• lead apron content

  • standard is .5 mm Pb

• pregnancy

  • inform RSO

  • declare yourself a pregnant worker

  • wear a secondary monitor