Biological Effects Of Ionising Radiation

Question 1

Two types of ionising radiation

Answer 1

By-products of radioactive decay
Artificially produced EM radiation

Question 2

3 by-products of radioactive decay

Answer 2

Alpha particle
Beta particle
Gamma ray

Question 3

What is the result of ionising radiation

Answer 3

Free electron and positively charged ion (Ion Pair)

Question 4

3 steps of radiation interaction

Answer 4

1. When radiation passes through matter it ionises atoms in path
2. Each ion pair deposits around 35ev of energy in air and tissue
3. This energy is greater than energy involved in atomic bonds

Question 5

Most significant effect of ionising radiation

Answer 5

Damage to DNA
E.g. large radiation dose> faulty repair of chromosome breaks>abnormal cells>cancer

Question 6

Two types of DNA damage

Answer 6

Direct
Indirect

Question 7

Direct DNA Damage

Answer 7

Radiation interacts with atoms of DNA molecule or another important part of cell

Question 8

Indirect effect

Answer 8

Radiation interacts with water in cell> H2O becomes ionised> free radical formed> two join forming hydroxyl radical causing DNA damage

Question 9

DNA damage to one strand of helix vs both strands

Answer 9

One strand reads, held in place by other> easily fixed

Both strands break, two remaining ends will seek to rejoin other free ends, not necessarily right ones (DSB)

Question 10

4 factors affecting biological effect of radiation

Answer 10

Type of radiation DSB usually alpha
Amount of radiation (dose)
Time over which dos is received (dose rate)
Tissue or cell type irradiated

Question 11

Dose effect

Answer 11

Low doses>less damage
Linear relationship for alpha particles which kill more cells than a similar dose of X-rays would
N.b WEIGHTING FACTOR

Question 12

Dose Rate Effect

Answer 12

Low dose rate> less damage
Cells can repair less serious DNA damage before further damage occurs
High dose rate, DNA repair capacity of cell likely to be overwhelmed

Question 13

Organ cancer risks

Answer 13

After large radiation exposures, higher incidence of cancer in certain tissues
Depends on organ receiving highest dose

Question 14

What is tissue radiosensitivity dependent on

Answer 14

The function of the cells that make up the cells
If cells are actively dividing

Question 15

Two types of cells and their radiosensitivity

Answer 15

Stem cells
Produce cells for another cell population
Divide frequently
Very radiosensitive

Differentiated cells
Do not exhibit mitotic behaviour
Less sensitive to radiation damage

Question 16

High radiosensitive tissues

Answer 16

More rapid cell division>greater sensitivity to radiation

Bone marrow, lymphoid, GI, gonads, embryonic

Question 17

Moderately radiosensitive tissues

Answer 17

Skin, vascular endothelium, lung, lens of eye

Question 18

Least radiosensitive tissues

Answer 18

CNS, bone and cartilage, connective tissue

Question 19

Possible outcomes when radiation hits cell nucleus

Answer 19

No change

                       - Mutation repaired > viable cell DNA mutation - Cell Death > Unviable cell
                       - Mutated cell > Cancer?

Question 20

Three different types of dose quantities

Answer 20

Absorbed Dose (Gy)
Equivalent Dose (Sv)
Effective Dose (Sv)

Question 21

Absorbed Dose

Answer 21

Measures the energy deposited by radiation
E.g. IO X-ray typical entrance skin dose at colllimator tip is 2mGy

Question 22

Equivalent dose

Answer 22

Is the absorbed dose multiplied by radiation weighting factor depending on radiation
Beta, gamma and X-rays - weighting factor 1
Alpha particles - 20

Question 23

Effective Dose

Answer 23

Is the EQUIVALENT DOSE multiplied by tissue weighting factor
Is probability of cancer induction
Typical intra oral X-ray is 5uSv

Question 24

What does LNT model do

Answer 24

Estimates long term damage from radiation
Assumes always harmful with no safety threshold and several small exposures have same effect as one large

Question 25

Two types of radiation effects

Answer 25

Deterministic- tissue reactions, only occur above threshold dose, severity of effect related to dose received Stochastic- probability of occurrence related to dose received, no threshold to the effect and severity of not dependent on dose. Basis of LNT model

Question 26

Deterministic effects of ionising radiation

Answer 26

Unusual to see in radiology Effects wont show immediately but several days after Certain things happen at certain values e.g. hair loss at 3Sv, lethal dose at 6Sv Typical io xray 5uSv (0.000005Sv)

Question 27

Stochastic effects of ionising radiation

Answer 27

Have no known thresholds Cannot predict if they will happen or how severe they will be Effects can develop years after exposure Can be somatic (resulting in disease or cancer) or genetic (resulting in abnormalities of descendents)

Question 28

Effect of radiation during pregnancy

Answer 28

Doses for any abnormalities to occur are 1000 times greater than that of an IO xray Dose to foetus is so low (0.01uSv and 8uSv which is less than background dose received)

Question 29

what must not happen when taking radiograph of pregnant woman

Answer 29

Foetus must not be irradiated inadvertently nor should X-ray Bea, be directed towards abdomen

Question 30

Examples of natural background radiation

Answer 30

Cosmic rays Radionuclides from diet Radionuclides in air e.g. radon External gamma radiation e.g. soil, rocks Estimated UK background radiation 2.2mSv

Question 31

Lifetime risk of cancer from IO xray

Answer 31

From one in 10m to one in 100m

Question 32

Guidance for X-ray use

Answer 32

Guidance notes for dental practitioners on safe use of X-ray equipment by college of general dentistry

Question 33

IRMER 2017 protecting patient

Answer 33

Justification- must have sufficient benefit to individuals or society in order to offset detriment Optimisation- individual doses and number of people exposed should be kept As Low As Reasonably Practicable (ALARP)

Question 34

How do we keep pt dose ALARP

Answer 34

Using E speed film or faster Using kV rang 60-70kV Focus to skin distance > 200mm

Question 35

Diagnostic Reference Levels in patients

Answer 35

Established dose levels for typical exams on standard sized pts Enables identification of units giving higher doses Adult: 0.9mGy (digital sensors) and 1.2mGy (phosphor plates and film Child: 0.6mGy and 0.7mGy

Question 36

What can we do to improve image quality and therefore reduce pt dose

Answer 36

Reduce damage by inserting CR plates between two plastic sheets Replace/clean damaged detectors Save images with minor artefacts, can be referred to and used in training