Biological Effects of Ionising Radiation & Risk Assessment

Question 1

Why does radiation cause biological effects ?

Answer 1

Ionises atoms when passing through tissues.

Question 2

Define direct effect of ionising radiation.

Answer 2

Interaction with DNA directly or important structures of the cell.

Question 3

Define indirect effect of ionising radiation.

Answer 3

Interaction with water in cell producing free radicals - unstable, highly reactive molecules.

Question 4

What are the 4 factors which extent of biological effect of ionising radiation depends upon ?

Answer 4

Type of radiation, dosage, dosage rate, cell type irradiated.

Question 5

What types of cells are most sensitive to ionising radiation ?

Answer 5

Highly mitotic cells i.e. stem cells.

Question 6

What types of cells are least sensitive to ionising radiation ?

Answer 6

Differentiated cells - show no mitotic behaviour.

Question 7

Name 3 types of tissues which have high sensitivity to ionising radiation.

Answer 7

Bone marrow, lymphoid, gonads, gastrointestinal, embryonic, thyroid.

Question 8

Name 3 types of tissues which have moderate sensitivity to ionising radiation.

Answer 8

Skin, lens of eye, vascular endothelium.

Question 9

Name 3 types of tissues which have low sensitivity to ionising radiation.

Answer 9

CNS, connective tissues, bone and cartilage.

Question 10

Define dose.

Answer 10

Measure of amount of energy transferred and deposited in medium.

Question 11

Define absorbed dose. What is it measured in ?

Answer 11

Energy deposited by radiation - measured in Grays.

Question 12

Define equivalent dose. What is it measured in ?

Answer 12

Absorbed dose x weighting factor - measured in Sv.

Question 13

What is the weighting factor for beta, gamma and x-rays ?

Answer 13

1

Question 14

What is the weighting factor for alpha EM radiation ?

Answer 14

20

Question 15

What is the linear threshold model ?

Answer 15

Estimate of long term biological damage from EM radiation with damage being directly proportional (linear) to dose.

Question 16

Define response linearity.

Answer 16

Several small exposures = effects as 1 large exposure.
Meaning effective dose is directly proportional to cancer risk.

Question 17

What is the probability of cancer after intra-oral radiation ?

Answer 17

< 1: 10 million.

Question 18

What are the two radiation effects.

Answer 18

Deterministic and Stochastic.

Question 19

When do deterministic effects occur following radiation exposure ?

Answer 19

Within days.
Will only occur above threshold dose.

Question 20

What are examples of deterministic effects ?

Answer 20

Cataracts and bone marrow RB depletion - 0.3Sv.
Sterility and hair loss - 0.5Sv.
Fatal - >6Sv to whole body.

Question 21

Define Stochastic effect.

Answer 21

No known threshold dose.
Unpredictable severity.

Question 22

When will Stochastic effects occur following radiation exposure ?

Answer 22

Years after.

Question 23

What are the two subdivisions of Stochastic effect ?

Answer 23

Somatic and genetic.

Question 24

Over what dosage will radiation to abdomen likely void pregnancy ?

Answer 24

> 100mGy.

Question 25

Over what dosage will radiation to abdomen likely cause growth defects during 2-8 weeks.

Answer 25

> 250mGy.

Question 26

Can pregnant women receive intra-oral radiation ?

Answer 26

Yes. Risk is negligible as long as X-ray tube is not pointed towards their abdomen.

Question 27

What distance should controlled area be from xray tube ?

Answer 27

1.5m

Question 28

What are the 4 practices which can be implemented to enhance optimisation and dose limitation in protection of patients during radiation exposure ?

Answer 28

Use of collimator (rectangular).
60-70kV dose.
E-speed film used as less photons required.
>2000cm focus to skin distance.

Question 29

What is a diagnostic reference level ?

Answer 29

Give an indication of the expected radiation dose received by an average-sized patient undergoing a given imaging procedure.