Biological Effects of Ionising Radiation

Question 1

How does ionising radiation turn atoms into ions?

Answer 1

It has enough energy to knock away electrons orbiting the nucleus of an atom

Question 2

During the ionisation process, how much energy roughly is deposited locally?

Answer 2

35eV

Question 3

What is the most significant effect of ionising radiation in healthcare settings?

Answer 3

Damage to DNA

Question 4

Radiation can damage DNA directly or indirectly, what is the difference?

Answer 4

Direct effect =
- radiation interacts with the atoms of a DNA molecule of another important part of the cell

Indirect effect =
- radiation interacts with water in the cell, producing free radicals which can cause damage

Question 5

The biological effect of radiation (on tissues) will depend on what factors?

Answer 5

• type of radiation
• amount of radiation (dose)
• time over which the dose is received (dose rate)
• the tissue or cell type irradiated

Question 6

What is the radiosensitivity of tissues dependent on?

Answer 6

• function of the cells that makeup the tissue
• if the cells are actively dividing

Question 7

What type of cells are very radiosensitive?

Answer 7

stem cells (as they divide frequently)

Question 8

Give examples of highly radiosensitive tissues:

Answer 8

• bone marrow
• lymphoid tissue
• gastrointestinal
• gonads
• embryonic tissue

Question 9

Give examples of moderately radiosensitive tissues:

Answer 9

• skin
• vascular endothelium
• lung
• lens of eye

Question 10

Give examples of low radiosensitive tissues:

Answer 10

• CNS
• bone & cartilage
• connective tissue

Question 11

What can occur if radiation hits a cells nucleus?

Answer 11

1. no change
2. DNA mutation
   
   • mutation repaired
   • cell death
   • cell survives but is mutated

Question 12

What is the absorbed dose measurement? (radiation)

Answer 12

Measures the energy deposited by radiation and has units of Gray (Gy)

Question 13

What is the equivalent dose measurement? (radiation)

Answer 13

Absorbed dose multiplied by a weighting factor depending on the type of radiation
- measured in Sieverts

Question 14

What is the effect of radiation during pregnancy?

Answer 14

• could damage or kill enough of cells for embryo to undergo resorption
• lethal to fetus
• growth retardation

Question 15

Can pregnant patients receive dental X-rays?

Answer 15

yes because the dose to the foetus is so low

Question 16

What are examples of background radiation sources?

Answer 16

• cosmic rays
• internal radionuclides from diet
• radionuclides in the air
• external gamma radiation
• air travel

Question 17

How far from the X-ray tube and patient is the ‘controlled area’ where staff stand during dental radiographs?

Answer 17

at least 1.5m away

Question 18

What is involved in the radiation protection philosophy?

Answer 18

• justification of radiograph
• dosage and number of people exposed should be ALARP (as low as reasonably possible)
• individual dose limits to reduce risk

Question 19

What type of collimators should be used to keep the radiation dose to dental patients ALARP?

Answer 19

rectangular collimators

Question 20

How can patient doses be reduced in dental radiography ?

Answer 20

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

Question 21

What is the current DRLs and national reference levels for adults?

Answer 21

• 0.9mGy (digital sensors)
• 1.2mGy (phosphor plats & film)

Question 22

What is the current DRLs and national reference levels for children?

Answer 22

• 0.6mGy (digital sensors)
• 0.7mGy (phosphor plates & film)