5 - Radiation Safety

Question 1

define the “absorbed dose”

• what is its SI unit?
• measured in?
• subunit?

Answer 1

absorbed dose is the measure of the amount of energy absorbed from the radiation beam per unit mass of tissue

• Gray (Gy)
• joules/kg
• miligray (mGy)

Question 2

what does the equivalent dose take into account?

Answer 2

• it takes into account the different levels of radio-biological effectiveness of different types of radiation (radiation weighting factor)

Question 3

what is the radiation weighting factor?

Answer 3

the biological effects of different types of radiation on different tissues

Question 4

radiation weighting factor of:
x-rays, gamma rays, beta particles, and alpha particles
- what does this difference mean?

Answer 4

x-rays, gamma rays, beta particles = Wr 1
alpha particles = Wr 20

• the biological effect of a particular absorbed dose of alpha particles would be more severe than a absorbed dose of x-rays

Question 5

how to calculate equivalent dose?

Answer 5

absorbed dose x radiation weighting factor

Question 6

equivalent dose: what is the SI unit? what are its subunits?

Answer 6

SI unit: Sievert (Sv)

subunits: millisieverts (mSv), microsievert (uSv)

Question 7

why is the equivalent dose same as the absorbed dose in x-rays?

Answer 7

because the radiation weighting factor for xrays is 1.

Question 8

what does the effective dose allow?

Answer 8

it allows doses from different investigations of different parts of the body to be compared, by converting all doses to an equivalent whole body dose

Question 9

what is tissue weighting factor?

Answer 9

the numerical value assigned to each different tissue based on its radiosensitivity

Question 10

how is effective dose calculated?
SI unit?
subunit?

Answer 10

• equivalent dose x relevant tissue weighting factor
• Sievert (Sv)
• millisievert (mSv)

Question 11

radon gas: 
how does it occur?
where does it build up? 
what circumstances affect its level of buildup?
yearly average dose?

Answer 11

• comes from naturally occurring uranium in the ground
• builds up indoors
• nature of the ground, atmospheric conditions, pattern of ventilation
• 1300 microsieverts

Question 12

gamma rays:
emitted by?
dose depends on?
yearly average?

Answer 12

• natural radioactivity in the earth and building materials
• depends on rocks/soils and building materials
• 350 microsieverts

Question 13

cosmic rays: radiation dose increases with?

Answer 13

latitude and altitude

Question 14

arrange in descending order the dose from these radiographic examinations:
CT head
Chest xray 
Panoramic
Periapical
CT abdomen

Answer 14

CT abdomen (8 mSv)
CT head (2 mSv)
Chest xray (0.02 mSv/20 microSv)
Panoramic (4-30 microSv)
Periapical (1-8 microSv)

Question 15

2 classifications of the biological effects of ionizing radiation?

Answer 15

• deterministic effects (tissue reactions)

- stochastic effects

Question 16

explain the somatic and genetic effects of radiation?

Answer 16

• somatic: affect those irradiated

- genetic: affecting the offspring of those irradiated

Question 17

what are deterministic effects of radiation?

should they occur in dentistry?

Answer 17

somatic, non-cancer damaging effects that will definitely result from a high specific dose of radiation.

• threshold dose exists at which effect begins to take place
• dose proportional to severity of effect

-they should not occur in dentistry

Question 18

examples of deterministic effects?

Answer 18

• hair loss
• skin erythema
• cataracts
• GI upset
• suppression of erythropoiesis

Question 19

effects on the unborn child:
related to?
susceptible when?
results in?

Answer 19

• dose (deterministic)
• when the organs are developing (2-9weeks)
• results in malformations or death

Question 20

what are stochastic effects of radiation?

could they occur in dentistry?

Answer 20

those which occur or develop on a random basis without a threshold, meaning that any dose of radiation can bring on a stochastic effect. however, probability increases with dose

• stochastic effects of radiation do occur in dentistry

Question 21

examples of non-deterministic (stochastic) effects?

Answer 21

leukaemia and solid tumours

Question 22

genetic effects:
radiation to reproductive organs may lead to?
threshold?

Answer 22

radiation to reproductive organs may damage DNA in sperm/egg
lead to congenital abnormalities in offspring or those irradiated but no certainty
- no threshold

Question 23

what are characteristics of the most radiosensitive cells?

Answer 23

• high mitotic rate
• undergo many future mitoses
• most primitive in differentiation
  + lymphocytes and oocytes which are highly differentiated and non-dividing

Question 24

effects of radiation: explain the direct and indirect effects

Answer 24

direct: interacts with biologic macromolecules (DNA, RNA, proteins and enzymes) causing ionisation and damage

indirect: hydrogen and hydroxyl free radicals are produced by action of radiation on water (abundant in the body). free radicals form toxic substances such as hydrogen peroxide
- most common type of damage

Question 25

changes in biological molecules: how is damage done to DNA?

Answer 25

damage to mechanism for cell death, mutation and carcinogenesis via:

• breaking strands
• loss/change of base
• disrupt bond between strands

Question 26

young patients: are they more radiosensitive? why?

Answer 26

young patients have cells which are still dividing, therefore are more radiosensitive. they also have longer lifespan to allow the effect to develop

Question 27

3 principles of radiation protection? + explain each

Answer 27

justification: exposure cannot be carried out until justified. benefit from examination but outweigh risk of exposure
optimisation: operator must ensure that exposure is kept as low as reasonably practicable, and consistent with intended diagnostic purpose

dose limitation

Question 28

warnings for controlled area?

Answer 28

• visible light and audible noise when xrays being produced
• operator should be able to prevent access to controlled area
• use of control panels, switches, isolators outside controlled area

Question 29

lead protection: justified? what to use when the thyroid may be in the primary beam?

Answer 29

• no justification for use of lead aprons, do not protect against radiation scattered internally within body
• thyroid collars should be used

Question 30

pregnancy: when is fetus most susceptible?

Answer 30

during organogenesis (2-9weeks)