Radiation Safety Flashcards
What is attenuation?
decrease in x-ray beam intensity due to interactions in matter
Increased patient size _______ attenuation
increases
Increasing atomic number _______ attenuation
increases
bone vs fat ______ attenuation
increases
Increased kVp ___________ attenuation and ________ beam energy
decreases
decreases
increased attenuation __________ transmission reading in detectors
decreases
transmission
what happens and what is the radiation interaction
x-ray beam passes all the way through the patient
nonionizing- nothing happens
coherent scattering
what happens and what is the radiation interaction
x-ray photon enters the patient and is temporarily absorbed by an electron but is immediately emitted out with all of its original energy just in a different direction
nonionizing
Photoelectric absorption
what happens and what is the radiation interaction
x-ray photon is fully absorbed by electron and electron is ejected out of orbit
ionizing (broken molecule and damaged cells)
Compton scattering
what happens and what is the radiation interaction
electron ionizes but part of the energy results in scatter
ionizing
Radiation exposure is calculated with units of
coulombs/kilogram (C/kg)
effective dose and equivalent dose are measured in
millisieverts (mSv)
absorbed does the the
energy of radiation absorbed by the patient
exposure is the
number of ionization events in air
effective does is used to
project the risk of radiation induced cancer
air kerma is measured in units of ____________ and t the measurement defining what
gray or milligray
the energy o ions created in air from radiation
high transmission reading is the result of
a high number of photons passing through the material without being attenuated
biological effects can be __________ or __________.
deterministic or stochastic
what are deterministic effects and do they have a threshold?
predictable
yes
What are stochastic effects and do they have a threshold?
non predictable
no thresholds
Dose threshold where effects take place for deterministic effects
miscarriage:
oligospermia:
cataracts:
erythema:
epilation:
miscarriage: 100mGy
oligospermia: 150 mGy
cataracts: 2000 mGy
erythema: 2000mGy
epilation: 3000mGy
What are 2 examples of stochastic effects?
cancer
heritable (genetic) effects
What is the size of the head phantom that physicists use to calculate CTDI
16 cm
What is the size of the body phantom that physicists use to calculate CTDI
32 cm
what is the unit of measurement for CTDI
mGy
CTDI reference levels
adult head-
Pedi head-
adult abdomen-
pedi abdomen-
adult chest-
adult head- 75
Pedi head- 40
adult abdomen- 25
pedi abdomen- 20
adult chest-20
how is DLP or dose-liner product calculated
CTDI x scan length
factors affecting patient dose:
tube current (mA) controls what
As mA increases
-patient dose
-CTDI
-DLP
intensity
As mA increases
-patient dose - increases
-CTDI - increases
-DLP - increases
factors affecting patient dose:
tube potential (kVp) aka as
As kVp increases
- patient dose
-CTDI
-DLP
tube voltage or beam energy
As kVp increases
- patient dose - increases
-CTDI - increases
-DLP - increases
factors affecting patient dose:
pitch aka
As pitch increases
-patient dose
-CTDI
-DLP
table movement/ beam width (helical only)
-patient dose - decreases
-CTDI - decreases
-DLP - decreases
factors affecting patient dose:
beam width aka
As beam width increases
-patient dose
-CTDI
-DLP
collimation
-dose - decreases
-CTDI - decreases
-DLP - decreases
To optimize patient dose
-mA
-kVp
-pitch
-beam width
-centering of patient
-mA - decreased
-kVp - decreased
-pitch - higher
-beam width- largest
-centering of patient - isocenter
3 different types of dose modulation
-variable mA (z-axis modulation)
-automatic exposure control (AEC)
-automatic tube current modulation (ATCM)
What happens during z-axis modulation (Vriable mA)
densest part receives the highest dose
what happens during x-y modulation
dose changes with projection
AP doses use lower dose than lateral projections
What are 2 different types of dose warnings
dose notification
dose alerts
Dose notifications are displayed when
predicted CTDI is set to exceed the dose notification value
Dose notification examples of high reference levels
Adult head-
pedi head (2-5) -
pedi head (<2) -
adult torso -
pedi torso -
Adult head- 80
pedi head (2-5) - 60
pedi head (<2) - 50
adult torso - 50
pedi torso -10
Dose alerts are displayed when
accumulative CTDI for a series of scan is set to exceed 1000mGy
what are 2 types of shielding used in CT
lead shields
bismuth shield
lead shields must
1.
2.
- wrap the patient 360
- never be inside the scan field
What happens if the lead shield is inside the scan field?
beam hardening and increased patient dose
