Biological Effects of Radiation (CTBC 22)

Question 1

When an x-ray enters matter (e.g., human tissue), there are 4 things that can happen:

Answer 1

Transmission
Coherent scattering
Photelectric absorption
Compton scattering

Question 2

During a CT exposure _______ of x-ray photons pass through the patient

Answer 2

billions

Question 3

When x-rays pass through the body without interacting in any way

Answer 3

Transmission (these x-rays aren’t absorbed/scattered, but are measured by the detector array)

Question 4

An x-ray photon absorbed by an electron then immediately emitted from the electron with all its original energy describes

Answer 4

Coherent scattering: these don’t result in ionization/biological harm to the patient, but are “scattered” in a different direction than the original path

Question 5

Non-Ionizing Interactions (2)

Answer 5

Transmission
Coherent Scattering

Question 6

Ionizing Interactions (2)

Answer 6

Photoelectric Absorption
Compton Scattering

Question 7

The removal of a bound electron from an atom

Answer 7

Ionization (the creation of charged particles): results in broken molecules and damaged cells

Question 8

Ionization which occurs when an electron is ejected out of its orbit by fully absorbing an incoming x-ray photon

Answer 8

Photoeletric absorption

Question 9

Ionization which occurs when an electron is ejected out of its orbit by partially absorbing an incoming x-ray photon, resulting in a (residual) scattered x-ray photon

Answer 9

Compton Scatter

Question 10

Decrease in x-ray beam intensity d/t interactions with matter

Answer 10

Attenuation

Question 11

Increasing kVp _______ attenuation and (usually) _______ patient dose

Answer 11

Decreases: increased x-ray energy decreases probability of attenuation
Increases

Question 12

Ionization breaks chemical bonds, which may lead to a cascade of

Answer 12

additional ionizations and broken molecules, possibly damaging the cell

Question 13

Ionizing radiation of cells may result in (3)

Answer 13

Cell will not repair itself and die
Cell will repair itself completely w/no lasting consequences
Cell will repair itself incompletely/incorrectly w/possible mutation/cancer/death

Question 14

When ionizing radiation causes a cell to repair its DNA incompletely/incorrectly, a mutation might occur resulting in

Answer 14

Cancer and eventually death

Question 15

Cataract formation and radiation-induced miscarriage are examples of

Answer 15

Deterministic effects of significant cell death

Question 16

Heritable diseases and cancer are examples of

Answer 16

Probabilistic effects of significant cell mutation

Question 17

_______ effects occur only at specific doses of radiation and not before

Answer 17

Deterministic

Question 18

When the dose-response threshold is determined/known, the severity of the effect _______ with increasing dose

Answer 18

Increases

Question 19

Deterministic effects of radiation are usually relevant only to

Answer 19

Very high doses of radiation

Question 20

Deterministic level for radiation-induced miscarriage

Answer 20

100 mGy (pre-implantation)

Question 21

Deterministic level for decreased sperm count

Answer 21

150 mGy

Question 22

Deterministic level for cataract formation

Answer 22

2000 mGy

Question 23

Deterministic level for Erythema (skin redness)

Answer 23

2000 mGy

Question 24

Deterministic level for Epilation (hair loss)

Answer 24

3000 mGy

Question 25

Most common radiation-induced cancers (6)

Answer 25

Leukemia
Thyroid
Breast
Lung
Bone
Skin

Question 26

Effects based on (random) chance, not a minimum dose

Answer 26

Stochastic effects: Theoretically any radiation dose increases the chance of a stochastic effect

Question 27

Any dose of radiation could cause cancer/the risk of acquiring cancer increases as dose increases

Answer 27

Linear Non-threshold (LNT) model of the probability of radiation-induced cancer