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