Module 4

Question 1

Units of measurement abbreviations

Answer 1

SI - international 
Roentgen - system 
Rad - milliroentgen
Rem Gray - (mR) millirad
(Gy) - (mrad) millirem
Sievert - (mrem) milligray 
(Sv) - millisievert (mSv) microsievert (μSv)

Question 2

Radiation Absorbed dose (D)

Answer 2

Amount of x-ray energy absorbed by a unit mass of tissue

• unit: Gray (Gy)
• SI unit joules per kilogram
• 1Gy = 100 rads

Question 3

Equivalent Dose (HT)

Answer 3

Allows the different radiobiological effectiveness (RBE) comparison
Radiation weighting factor WR
represents different biological effects of different radiation on different tissues
the unit of equivalent dose allows comparisons to be made between one type of radiation and another

Question 4

Effective Dose (E)

Answer 4

Conversion of dose to specific area to whole body is called the tissue weighting factor (WT)

E = H X WT

Unit: sievert (Sv)

measures the potential risk to health

Question 5

Effective dose in dental radiography

Answer 5

Bitewing/periapical = 0.0003 - 0.022 mSv
Panoramic = 0.0027 - 0.038 mSv
Upper Standard occlusal = 0.008 mSv
Lateral cephalometric and other medical exposures = 0.0022 - 0.0056 mSv

   chest lateral x-ray = 0.038 mSv
   skull lateral x-ray = 0.016 mSv
   barium swallow = 1.5 mSv
   CT scan (chest) = 1.4 mSv

Question 6

Collective Dose

Answer 6

Measured in man - Sv
Collective dose = effective dose (E) x population
in the UK in 2008 the collective dose was calculated by the health protection agency to be more 24,700 man-Sv

Question 7

Dose limits

Answer 7

International commission for radiological protection (ICRP) sets the annual maximum dose for limits for radiation workers

Classified Workers:
Old dose limits - 50mSv
Current dose limits - 20mSv

Non classified workers:
Old dose limits - 15mSv
Current dose limits - 6mSv

General public:
Old dose limits - 5mSv
Current dose limits - 1mSv

Question 8

Estimated annual dose

Answer 8

the radiological protection division of the health protection agency estimates the annual doses from various sources.
Dose rates are a measure of the dose per unit of time
Average annual dose:
Cosmic radiation - 330
External radiation from earth crust - 350
Ionising radiation from foodstuff - 250
Radioactive waste - 1
Medical and dental diagnostics - 410

Question 9

Risk factors

Answer 9

Intra oral film
traditional equipment - 1 fatal cancer in every 2 million
recommended equipment - 1 fatal cancer in every 20 million

panoramic radiograph - 1 in 1,000,000

The younger the patient the greater the risk

smoking 10 cigarettes a day - 1 in 200
natural causes aged 40 - 1 in 700
accidents in the home - 1 in 10,000
accidents on the road - 1 in 10,000
accidents at work - 1 in 50,000

Question 10

Multiplication of risk according to age

Answer 10

Under 10   = x3
10-20         = x2
20-30        = x1.2
30-50        = x0.5
50-80        = x0.3
80+            = negligible

Question 11

Biological effects - Direct action (damage)

Answer 11

energy from ejected electron (photoelectrons) or the x-ray photon is transferred to the cells DNA, RNA or protein enzymes.
this direct action causes damage by rupturing the helix causing point mutation, the correct information is not passed on
Can lead to:
Abnormal replication 
Cell death
Radiation induced malignancy 
Reproductive stem cell interaction
Radio induced congenital abnormality

Question 12

Biological effects - indirect action

Answer 12

Most common reaction as 80% of our body consists of water
when radiation hits the water molecules ionization occurs. this produces ions and free radicals.
free radicals combine to form
Hydrogen Peroxide (a cellular poison)
and
Hydroperoxyl radical (a toxic substance)
they can transfer excess energy to other molecules - breaking the chemical bonds

Question 13

Deterministic Effects

Answer 13

• will definitely happen from a specific high dose of radiation
• severity increases with increased absorbed dose
• threshold dose exists, there will be no effect below this dose
• early tissue reactions happening shortly after exposure
• late tissue reactions appearing months or years after exposure

Question 14

Stochastic Effects

Answer 14

• may happen with any level of radiation
• no safe dose level, no threshold dose has the possibility of an stochastic effect
• every dose has the possibility of an stochastic effect
• the lower the dose the less probability of damage
• type of damage can not be determined
• severity of the damage not related to dose size
• cancer induction
• heritable/genetic effects

Question 15

Genetic Effects

Answer 15

Gene or chromosomes mutate can be spontaneous or caused by radiation
the damage of the DNA of the sperm or egg cells only happens if the reproductive organs are radiated this can lead to congenital abnormalities
no threshold dose - may happen

Question 16

Effects on an unborn child

Answer 16

3-7 weeks after conception is the most sensitive time
Radiation can cause:
- congenital abnormalities
- mental retardation
- cancer induction
- death
as a referrer you are responsible for checking the patients last menstrual period (if applicable)