L4 Dose and Measurement

Question 1

What does radiation absorbed dose mean?

Answer 1

Radiation absorbed dose (D)

• Measurement of the emount of energy absorbed from the radiation beam per unit mass of tissue
• Units: milligray (mGy) and microgray (uGy)

Question 2

What does equivalent dose mean?

Answer 2

Equivalent dose (H)

• Radiation absorbed dose x weighting factor
• Indicates the radiobiological effectiveness (RBE) of different types of radiation. i.e. allows for the differing biological effects of different types of radiation and thus provides a common unit.
• Units: Sievert (Sv) milliSievert (mSv) microSievert (uSv)

Question 3

What does effective dose mean?

Answer 3

Effective dose (E)

• Measure which allows doses from different investigations of different parts of the body to be compared, by converting all doses to an equivalent whole body dose.
• Equivalent dose x tissue weighting factor
• Units: Sv, mSv, uSv

When people refer to “dose” they are almost always talking about the effective dose.

Question 4

What is the typical effective dose from an intra-oral radiograph?

Answer 4

0.3-22uSv
Best practice = 2uSv

Equivalent to 8 hours natural background radiation.

Question 5

What is the typical effective dose from a panoramic radiogrpah?

Answer 5

2.7-38uSv

Best practice = 20uSv

Equivalent to 3 days natural background radiation.

Question 6

What is the risk of a fatal malignancy from an intraoral radiograph?

Answer 6

With rectangular collimation and F-speed film or digital radiogrpahy:
1 fatal malignancy per 10 million exposures

Question 7

What is the risk from 1 panoramic radiograph?

Answer 7

1 fatal malignancy per 1 million exposures

Question 8

What is the estimated genetic risk from dental radiology in the UK?

Answer 8

1 congenital abnormality every 3 years, reproductive system not in primary beam so risk is practically negligible.