Biological Effects of Radiation and Radiation Dose

Question 1

long term effects of radiation are called …

Answer 1

stochastic effects

Question 2

The short term effects of radiation are called…

Answer 2

deterministic effects

Question 3

define absorbed dose

Answer 3

amount of energy deposited per unit mass of the tissue, Grey (Gy)

Question 4

define Equivalent Dose

Answer 4

-used to assess how much biological damage is expected from the absorbed dose

• used for Different types of radiation Some are more harmful to tissue than others

Question 5

define effective dose

Answer 5

is the measure of potential long term effects that may occur in the patient (i.e. cancer).

It takes into account the fact that different tissues in the body have different radio sensitivity - Units Sievert (Sv)

Question 6

what should effective dose be used for

Answer 6

compare risks from different modalities or examinations that have differing dose distributions

Question 7

what should effective dose be not used for ?

Answer 7

Should not be used to calculate dose to an individual

Question 8

Criticisms of Effective Dose

Answer 8

• tissue weighting factors are averaged over all ages and both genders in the general population and so it cannot be applied to an individual patient

Question 9

why is tissue weighting factors not being able to apply to an individual patient a bad thing, give an example (hint: 15 female, 35 male)

Answer 9

*effective dose calculations from a chest radiograph could be the same in a 15-year-old female patient and a 35-year-oldmale

Question 10

what is a dosimeter ?

Answer 10

any device that can measure radiation

Question 11

what is the simplest form of a dosimeter ?

Answer 11

• Ionisation chamber
• The ionisation chamber is the simplest of all gas-filled radiation detectors,
• Converts electromagnetic energy into electrical energy

Question 12

ionisation chamber is an example of dap, what does dap stand for ?

Answer 12

Dose Area Product

Question 13

what does dap do ?

Answer 13

combines two quantities, Absorbed dose in air and the field size = Gray centimetre squared

Question 14

give an example of dap calculation

Answer 14

*A 5 x 5 cm x-ray field with a dose of 1 mGy

= 1 x (5 x 5) = 25 mGycm2

Question 15

describe the mosfet process (5 steps)

Answer 15

1. Uses semiconductor (Good controller of electrical current)
2. Voltage between the electrodes
3. When irradiated electrons become delocalised/ liberated

4.Results in a VOLTAGE SHIFT between the components

5. SHIFT is proportional to the dose

Question 16

describe the process of Thermoluminescent dosimeter (TLD)

Answer 16

1. Uses the property of thermoluminescence
2. uses the atomic model of two energy bands

3.Electrons absorb energy move from lower to higher energy level

4.Emitted light measured and converted to electrical charge

5.Charge proportional to dose

Question 17

briefly describe the monte Carlo simulation ?

Answer 17

• simulation of a phantom being exposed to a large number of photons of varying energies:
• each photon is followed through a sequence of interaction points and subsequent energy losses and outgoing directions

-At each interaction point the energy deposited to the organ is calculated and used in the dose calculatiom

Question 18

negative of the entrance surface dose

Answer 18

Dose used to calculate effective dose/risk

*So not a direct measurement of organ dose

cant do in real people

Question 19

what are phantoms made of

Answer 19

-made up of contiguous slices with different tissues represented by different densities of epoxy resin

-attenuation properties that are equivalent to real tissue