Radiation Safety

Question 1

What is attenuation?

Answer 1

decrease in x-ray beam intensity due to interactions in matter

Question 2

Increased patient size _______ attenuation

Answer 2

increases

Question 3

Increasing atomic number _______ attenuation

Answer 3

increases

Question 4

bone vs fat ______ attenuation

Answer 4

increases

Question 5

Increased kVp ___________ attenuation and ________ beam energy

Answer 5

decreases
decreases

Question 6

increased attenuation __________ transmission reading in detectors

Answer 6

decreases

Question 7

transmission
what happens and what is the radiation interaction

Answer 7

x-ray beam passes all the way through the patient
nonionizing- nothing happens

Question 8

coherent scattering
what happens and what is the radiation interaction

Answer 8

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

Question 9

Photoelectric absorption
what happens and what is the radiation interaction

Answer 9

x-ray photon is fully absorbed by electron and electron is ejected out of orbit
ionizing (broken molecule and damaged cells)

Question 10

Compton scattering
what happens and what is the radiation interaction

Answer 10

electron ionizes but part of the energy results in scatter
ionizing

Question 11

Radiation exposure is calculated with units of

Answer 11

coulombs/kilogram (C/kg)

Question 12

effective dose and equivalent dose are measured in

Answer 12

millisieverts (mSv)

Question 13

absorbed does the the

Answer 13

energy of radiation absorbed by the patient

Question 14

exposure is the

Answer 14

number of ionization events in air

Question 15

effective does is used to

Answer 15

project the risk of radiation induced cancer

Question 16

air kerma is measured in units of ____________ and t the measurement defining what

Answer 16

gray or milligray
the energy o ions created in air from radiation

Question 17

high transmission reading is the result of

Answer 17

a high number of photons passing through the material without being attenuated

Question 18

biological effects can be __________ or __________.

Answer 18

deterministic or stochastic

Question 19

what are deterministic effects and do they have a threshold?

Answer 19

predictable
yes

Question 20

What are stochastic effects and do they have a threshold?

Answer 20

non predictable
no thresholds

Question 21

Dose threshold where effects take place for deterministic effects
miscarriage:
oligospermia:
cataracts:
erythema:
epilation:

Answer 21

miscarriage: 100mGy
oligospermia: 150 mGy
cataracts: 2000 mGy
erythema: 2000mGy
epilation: 3000mGy

Question 22

What are 2 examples of stochastic effects?

Answer 22

cancer
heritable (genetic) effects

Question 23

What is the size of the head phantom that physicists use to calculate CTDI

Answer 23

16 cm

Question 24

What is the size of the body phantom that physicists use to calculate CTDI

Answer 24

32 cm

Question 25

what is the unit of measurement for CTDI

Answer 25

mGy

Question 26

CTDI reference levels
adult head-
Pedi head-
adult abdomen-
pedi abdomen-
adult chest-

Answer 26

adult head- 75
Pedi head- 40
adult abdomen- 25
pedi abdomen- 20
adult chest-20

Question 27

how is DLP or dose-liner product calculated

Answer 27

CTDI x scan length

Question 28

factors affecting patient dose:
tube current (mA) controls what
As mA increases
-patient dose
-CTDI
-DLP

Answer 28

intensity
As mA increases
-patient dose - increases
-CTDI - increases
-DLP - increases

Question 29

factors affecting patient dose:
tube potential (kVp) aka as
As kVp increases
- patient dose
-CTDI
-DLP

Answer 29

tube voltage or beam energy
As kVp increases
- patient dose - increases
-CTDI - increases
-DLP - increases

Question 30

factors affecting patient dose:
pitch aka
As pitch increases
-patient dose
-CTDI
-DLP

Answer 30

table movement/ beam width (helical only)

-patient dose - decreases
-CTDI - decreases
-DLP - decreases

Question 31

factors affecting patient dose:
beam width aka
As beam width increases
-patient dose
-CTDI
-DLP

Answer 31

collimation

-dose - decreases
-CTDI - decreases
-DLP - decreases

Question 32

To optimize patient dose
-mA
-kVp
-pitch
-beam width
-centering of patient

Answer 32

-mA - decreased
-kVp - decreased
-pitch - higher
-beam width- largest
-centering of patient - isocenter

Question 33

3 different types of dose modulation

Answer 33

-variable mA (z-axis modulation)
-automatic exposure control (AEC)
-automatic tube current modulation (ATCM)

Question 34

What happens during z-axis modulation (Vriable mA)

Answer 34

densest part receives the highest dose

Question 35

what happens during x-y modulation

Answer 35

dose changes with projection
AP doses use lower dose than lateral projections

Question 36

What are 2 different types of dose warnings

Answer 36

dose notification
dose alerts

Question 37

Dose notifications are displayed when

Answer 37

predicted CTDI is set to exceed the dose notification value

Question 38

Dose notification examples of high reference levels
Adult head-
pedi head (2-5) -
pedi head (<2) -
adult torso -
pedi torso -

Answer 38

Adult head- 80
pedi head (2-5) - 60
pedi head (<2) - 50
adult torso - 50
pedi torso -10

Question 39

Dose alerts are displayed when

Answer 39

accumulative CTDI for a series of scan is set to exceed 1000mGy

Question 40

what are 2 types of shielding used in CT

Answer 40

lead shields
bismuth shield

Question 41

lead shields must
1.
2.

Answer 41

1. wrap the patient 360
2. never be inside the scan field

Question 42

What happens if the lead shield is inside the scan field?

Answer 42

beam hardening and increased patient dose