Lecture 8

Question 1

How low should the level of radiation be?

Answer 1

• ALARA = as low as reasonably acheivable

Question 2

What is the difference between stochastic and deterministic effects of radiation?

Answer 2

• Deterministic effects: effects that occur due to the dose of radiation - once threshold has been reached effect is likely to occur. The severity of the condition is dose related
• Stochastic effects: probability effects - increased dose causes increased chance of disease. The severity is not related to dose

Question 3

What are two conditions that are deterministic?

Answer 3

• Radiodermatitis
• Skin cancer

Question 4

What dose of radiation is considered to cause increased risk of cancer?

Answer 4

• >100 mSv in a short period of time

Question 5

What is the unit of measuring absorbed radiation and what is it equivalent to?

Answer 5

• 1 Gy = 1 joule/kg of tissue
• The gray

Question 6

What is the radiation dose equivalent and what is the unit?

Answer 6

• The dose equivalent is the aborbed dose multiplied by the radiation weighting factor for the type and energy of the radiation
• The unit for measuring dose equivalent is the sievert (Sv)

Question 7

What is the effective radiation dose and what is the measurment for it?

Answer 7

• The effective dose: The dose equivalent multiplied by the tissue weighting factor
• Unit for effective dose = sievert (Sv)

Question 8

What are the annual dose limits for radiation in WA?

Answer 8

• Effective dose limit = 20 mSv/year averaged over 5 consecutive calendar years
• No more than 50 mSv in any one year

Question 9

Where should radiation badges ideally be worn?

Answer 9

• Badges should be worn under apron at chest or waist height

Question 10

What are the three main principles of radiation safety?

Answer 10

1. Time - reduce the time exposed to radiation
2. Distance - increase distance from the primary beam
3. Shielding - protective clothing - lead gowns, thyroid protectors etc.

Question 11

When applying the inverse square law - if you double distance from the primary beam the exposure will be reduced by ___(1)____.

Answer 11

• Formula = 1/D² = 1/2² = 1/4

Question 12

How thick should the lead gown be if <100kV and if >100kV?

Answer 12

• 0.25mm lead if < 100 kV
• > 100 kV then 0.5mm

Question 13

How much lead is required in small animal facilities for the X-ray tables?

Answer 13

• 0.5 mm Pb at the sides
• 1 mm of Pb beneath

Question 14

When are protective screens required in radiation practice?

Answer 14

• Workloads >2000 mAs/wk must use protective screens