Radiation Dose

Question 1

Absorbed radiation dose, strictly from x-rays is expressed as

Answer 1

Rad

Gray

Question 2

Units used to measure the “effective dose” or “dose equivalent” of ANY type of ionizing radiation.

Answer 2

Rem

Sievert

Question 3

1 Sv = ___ rem

Answer 3

100

Question 4

1 rad = ____ rem

Answer 4

1

Question 5

1 Gy = ____ rads

Answer 5

100

Question 6

The amount of radiation in 1rad is equal to?

Answer 6

0.01 joules of energy per kg of matter (patient’s weight).

Question 7

The single greatest natural exposure to radiation in the US comes from?

Answer 7

Radon

Question 8

The average annual dose equivalent from natural sources is?

Answer 8

0. 31 rem

3. 1 mSv

Question 9

Man-made sources of radiation contribute how much annual radiation

Answer 9

0. 31 rem

3. 1 mSv

Question 10

CT scans contribute how much radiation annually

Answer 10

0. 15 rem

1. 5 mSv

Question 11

Other medical imaging contribute how much radiation annually

Answer 11

0. 15 rem

1. 5 mSv

Question 12

Other man-made radiation contribute how much radiation annually

Answer 12

0. 10 rem

1. 0 mSv

Question 13

What is the range of the effective dose from CT

Answer 13

About 1 to 10 mSv

Question 14

“Low-dose CT scans” reduce levels by factors of?

Answer 14

1/2 to 1/5

Question 15

For a body scan, the dose in the center of the patient may be _____ of the skin dose.

Answer 15

1/3

Question 16

Typical effective dose for a Head CT

Answer 16

2 mSv

Question 17

Typical effective dose for an Abdomen CT

Answer 17

8 mSv

Question 18

Typical effective dose for 1 Radiography exposure

Answer 18

0.1 mSv

Question 19

Typical effective dose for 5 Radiography exposures

Answer 19

0.5 mSv

Question 20

Describe the radiation profile of a single slice

Answer 20

It is rounded.

This means there is more radiation applied in the center of the slice and less on the sides.

Question 21

What does the penumbra, on a radiation profile mean?

Answer 21

The radiation is extended outside of the slice into neighboring tissue.

Question 22

The radiation that leaks outside of the intended slice thickness is called?

Answer 22

Radiation penumbra

Question 23

CT Dose Index (CTDI) is what?

Answer 23

An indicator of radiation dose which includes the radiation located within the intended slice thickness as well as that from the penumbra.

Question 24

The CTDI does not factor in variation in dose due to?

Answer 24

Gaps or overlaps in adjacent slices

Question 25

CTDI did not account for what?

Answer 25

Helical scanning, | Simultaneous acquisition of multiple slices in a single rotation, or cone beam irradiation.

Question 26

Multiple Slice Average Dose (MSAD) is an indicator of radiation dose that?

Answer 26

Corrects the CTDI by factoring in gaps or overlaps between the slices or helices due to the selected table increment or pitch.

Question 27

Since a slice obtained with MDCT is not individually collimated, where does the radiation penumbra occur?

Answer 27

Only the end slices of the slice volume

Question 28

The CTDI 100 accounts for what?

Answer 28

1. The possibility of having multiple slices in one rotation (MSDS) 2. Slice thickness

Question 29

CTDI(100) What does the 100 stand for?

Answer 29

100 Refers to the 100 mm pencil ionization chamber the physicists use to measure the radiation.

Question 30

CTDI 100 Is typically measured where

Answer 30

At both the periphery and in the center of the CTDI Phantom

Question 31

What is the disadvantage of CTDI 100

Answer 31

It only considers serial scans and does not consider helical scAns with varying pitches

Question 32

CTDI W or weighted-CTDI is?

Answer 32

A weighted average of the center and peripheral CTDI 100 to arrive at a single measurement based on a single rotation of a multi row detector scanner

Question 33

CTDI is an indicator of Average radiation dose along?

Answer 33

The x-direction and y-direction

Question 34

CTDI w =

Answer 34

(1/3) CTDI100 center + (2/3) CTDI100 periphery

Question 35

CTDI vol represents

Answer 35

The average dose in the central region of a multiple rotation exam

Question 36

CTDI vol Accounts for

Answer 36

Helical studies performed on multi row detector scanners and it indicates the average radiation dose over all three directions. Accounts for overlaps and gaps in the rotations

Question 37

CTDI vol Does not account for what?

Answer 37

The number of rotations, the total length of the volume. Ex: A limited volume pelvic exam would have the same CTDI as a abdomen pelvic exam

Question 38

DLP dose length product Accounts for

Answer 38

(total number of slices) x (slice thickness)

Question 39

DLP =

Answer 39

CTDI vol (mGy) x Total scan length (cm)

Question 40

DLP Is expressed in what units

Answer 40

mGy-cm

Question 41

DLP Does not consider what

Answer 41

The size of the patient or the body part exposed to radiation

Question 42

What is the measurement of radiation dose that would allow risk assessment of inducing cancer?

Answer 42

Effective dose

Question 43

Effective dose is calculated by

Answer 43

Multiplying the absorbed dose by a weighting factor assigned to each organ or body region. If more than one area is exposed, then the total body effective dose is the sum of the effective dose for each individual exposed area.

Question 44

Effective dose is expressed in what units

Answer 44

Sv