Biological Effects of Ionising Radiation

Question 1

when ionisation occurs what is deposited locally

Answer 1

energy (35eV)

Question 2

what happens when radiation passes through matter

Answer 2

it will ionise atoms along its path

Question 3

where can evidence of DNA damage be seen

Answer 3

in the faulty repair of chromosome breaks

Question 4

where is DNA damage seen

Answer 4

in individuals who are exposed to large doses

Question 5

what is the direct effect of radiation damage on DNA

Answer 5

radiation interacts with the atoms of a DNA molecule or another important part of the cell

Question 6

what is the indirect effect of radiation damage on DNA

Answer 6

radiation interacts with water in the cell, producing free radicals which can cause damage

Question 7

why are double strands of DNA more difficult to repair

Answer 7

it usually occurs due to alpha radiation and if the repair is faulty it can lead to mutations which affects cell function

Question 8

what does the biological effect of DNA damage depend on

Answer 8

type of radiation, amount of radiation, time over which the dose is received, the tissue or cell type irradiated

Question 9

why is radiation delivered at a lower dose less damaging

Answer 9

cells can repair less serious DNA damage before further damage occurs

Question 10

what organs are at risk from cancer following large radiation exposures

Answer 10

oesophagus, thyroid, lungs, skin, breast, stomach, liver, colon, gonads

Question 11

what is the radiosensitivity of tissues dependent on

Answer 11

function of the cells that make up the tissues
if cells are actively dividing

Question 12

what kind of cells are very radiosensitive

Answer 12

stem cells

Question 13

why are stem cells radiosensitive

Answer 13

they divide very frequently

Question 14

what cells are highly radiosensitive

Answer 14

bone marrow, lymphoid tissue, GI, gonads, embryonic tissues

Question 15

what cells are moderately radiosensitive

Answer 15

skin, vascular endothelium, lungs, lens of eye

Question 16

what are the least radiosensitive cells

Answer 16

CNS, bone and cartilage, connective tissue

Question 17

what are the possible outcomes after radiation hits a cell nucleus

Answer 17

no change
mutation repaired
cell death
cell survives but is mutated - cancer?

Question 18

what is absorbed dose

Answer 18

measures the energy deposited by radiation
in Grays

Question 19

what is equivalent dose

Answer 19

absorbed dose multiplied by a weighting factor depending on the type of radiation
in Sieverts (Sv)

Question 20

what does the linear no threshold model estimate

Answer 20

long term biological damage from radiation

Question 21

what does the linear no threshold model assum

Answer 21

the damage is directly proportional to radiation dose and radiation is always harmful with no safety threshold

Question 22

what is response linearity

Answer 22

several small exposures would have the same effect as one large exposure

Question 23

what are the 2 types of radiation effects

Answer 23

deterministic and stochastic

Question 24

what is the deterministic effects of radiation

Answer 24

tissue reactions
only occur above a certain dose
severity of effect is related to the dose received

Question 25

what is the stochastic effects

Answer 25

probability of occurrence is related to the dose received

Question 26

what is somatic stochastic effect

Answer 26

results in disease or disorder

Question 27

what is genetic stochastic effect

Answer 27

abnormalities in descendents

Question 28

what is the effect of radiation exposure during pregnancy

Answer 28

damage or kill enough of the cells for the embryo to undergo resorption

Question 29

what dose can be lethal for an embryo

Answer 29

100mGy

Question 30

what dose can lead to growth retardation in a foetus

Answer 30

> 250mGy

Question 31

why does pregnancy not need to be taken into account for dental x-rays

Answer 31

because the dose is so low

Question 32

what is the annual background radiation dose

Answer 32

2.2mSv

Question 33

what is the equivalent dose of an intra oral

Answer 33

0.005mSv

Question 34

how far should the controlled beam extend from the x-ray tube and patient

Answer 34

1.5m

Question 35

what does justification mean when taking radiographs

Answer 35

practices must have sufficient benefit to individuals or society in order to offset the detriment

Question 36

what does optimisation mean when taking radiographs

Answer 36

individual doses and the number of people exposed should be kept ALARP

Question 37

what does dose limitation mean

Answer 37

system of individual dose limits so that the risks to individuals are acceptable

Question 38

how can patient doses be reduced

Answer 38

use E speed film or faster
use a kV range of 60kV to 70kV
focus to skin distance should be >200m
use rectangular collimation

Question 39

what are diagnostic reference levels

Answer 39

dose levels for typical examinations for standard sized patients

Question 40

what does DRLs allow for

Answer 40

identification of units giving higher doses

Question 41

what are the adult DRLs for intra oral examinations on phosphor plates

Answer 41

1.2mGy

Question 42

what are the child DRLs for intra oral examinations on phosphor plates

Answer 42

0.7mGy