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Biophysics 2 (Theory) > 8. Dosimetry of ionizing radiations > Flashcards

8. Dosimetry of ionizing radiations Flashcards

1
Q

3 tasks for dosimetry

A

Estimation of health risk for prevention.

Estimation of biological damages.

Design of therapeutic procedures.

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2
Q

3 requirements for dose values

A

• proportional to the damagas and expected risk

  • additive
  • independent of other factors
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3
Q

What are the 3 dose concepts?

A
  1. physical dose concepts
  2. Biological dose concepts
  3. Derived dose cocepts
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4
Q

2 things that characterize physical dose concepts

A
  1. Absorbed dose
  2. Exposure
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5
Q

physical dose concept

What is validity of absorbed dose?

A

For any kind of material and any type of radiation without restriction

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6
Q

physical dose concept

Formula of absorbed dose?

A

Energy absorbed per unit mass

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7
Q

physical dose concept

Why isn’t the determination of absorbed energy a simple task?

A

Because it has a relatively small value

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8
Q

physical dose concept

It is difficult to measure the amount of charges generated by ionizing radiation in body tissues and in liquids generally

→ it is practical to take measurements in the ____ phase

A

gaseous

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9
Q

physical dose concept

What is exposure? Its formula and unit?

A

It measures the amount of positive or negative charges generated by x-ray or Gamma radiation in air of unit mass (during electron equilibrium)

Unit: C/kg

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10
Q

physical dose concept

What is validity of exposure?

A

in the air, only γ and X –rays, measured in electron equilibrium*

Unit: C/kg

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11
Q

physical dose concept

How are 2nd electrons generated?

A

During the course of measurement

→ irradiation generates secondary electrons are both inside and outside volume V (cavity filled with air)

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12
Q

physical dose concept

What is electron equilibrium? When is this condition most satisfied?

A

If the number of 2nd electrons leaving and entering volume of the cavity (V) are equal

→ It is most satisfied when air is surrounded by air

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13
Q

3 things to be considered about Electron-equilibrium

A
  • composition of surrounding material (chamber wall) – air-equivalent wall!
  • thickness of the wall
  • Photon energy: E< 0.6 MeV
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14
Q

physical dose concept

What is the relationship between biological effects and absorbed dose?

A

They are proportional to each other

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15
Q

physical dose concept

How to calculate absorbed dose from exposure?

A

Take the amount of energy necessary to produce one ion pair multiplied by exposure

Dair =f0X (f0 = 34 J/C)

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16
Q

physical dose concept

Will the dose absorbed by tissue be relevant to degree of damage?

A

YES

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17
Q

In case of low energies (< 0.6 MeV), is there a difference between tissue and air in the process of absorption of X-ray and gamma radiation?

A

Yes

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18
Q

If intensities of radiation of volumes compared are equal, what is the relationship between absorbed energies and mass attenuation coefficient (µm)

A

The absorbed energies are in same proportion as the mass attenuation coefficient (µm)

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19
Q

2 things that characterize biological dose concepts

A

Equivalent dose

Effective dose

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20
Q

Is the absorbed dose enough to measure the possible biological consequences? Why?

A

No, because the biological consequences are influenced by

  • The type of radiation → radiation weighting factor
  • The sensitivity and biological function of target → tissue weighting factor
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21
Q

What is equivalent dose? Formula? Unit?

A

The dose of radiation R absorbed by tissue T (DT,R) through a “radiation” weighting factor wR

Units: J/Kg or Sievert (Sv)

22
Q

Why are the fates of the rabbits different?

A

Because alpha radiation has a very significant weighting factor and high linear transfer energy

23
Q

What is linear energy transfer?

A

the amount of energy that an ionizing particle transfers to the material traversed per unit distance.

-> the energy transferred to the material surrounding the particle track, by means of secondary electrons. (nEionpair/l)

24
Q

Equivalent dose (H)

Is „Efficiency” of various forms uniform? Why?

A

No, because there could be Different in linear transfer energy and radiation weighting factor

25
Q

What is the formula if someone is exposed to more than one type of radiation

A
26
Q

What is effective dose? Formula? Unit?

A

The sum of weighting factors for various tissue multiplied by equivalent dose in the given tissue

Unit of E** : **Sievert (Sv)

27
Q

What is the role of effective dose (E)?

A
  • Consider sensitivity of different tissues
28
Q

What does WT denote in this formula of effective dose (E)?

A

The probability of stochastic damage of the irradiated tissue or organ

→ estimation of the relative sensitivity of tissue

29
Q

What is the sum of these weighting factors?

A
30
Q

2 things that characterize the derived dose concepts

A

Collective dose

Dose rate

31
Q

derived dose concepts

What is collective dose?

A

Sum of the doses received by a given number of people (Ni) in the course of a given time interval.

32
Q

derived dose concepts

What is the formula for collective dose?

A

If Ni person was exposed to Ei effective dose, collective dose is given by the following formula.

33
Q

What does this formula describe?

A

The collective dose by which the radiation burden of a given population is described.

34
Q

What is dose rate?

A

Received dose over time.

Unit: varies with the type of radiation and the time period (pl. Gy/month, mSv/year etc.)

35
Q

Examples of stochastic effects?

A

e.g.tumours, heriditary diseases

36
Q

How to estimate the probability of stochastic effects?

A
  • *HT (equivalent dose) and**
  • *E (effective dose)** provide a basis for estimating the probability of stochastic effects for doses below the threshold of deterministic effects.
37
Q

What are examples of deterministic effects?

A
  • e.g. erythema, epilation, cataract
38
Q

What are the 3 types of dose and dose rate measuring devices?

A
  1. Electronic detectors
  2. Chemical detectors
  3. Solid materials
39
Q

Principle of operation of electronic detectors (for dose measurements)

A

absorbed energy generates free charges

40
Q

3 examples of electronic detectors (for dose measurements)

A
  1. gas-ionization detectors
  2. scintillation detectors
  3. semi-conductor detectors
41
Q

How does ionization chamber work?

A

As charges move towards the electrodes, they produce an electric current proportional to the dose rate.

The change in capacitor charge is proportional to the dose.

42
Q

How to measure dose with ionization chamber?

A

As charges move towards the electrodes, they produce an electric current proportional to the dose rate.

The change in capacitor charge is proportional to the dose.

43
Q

What does ionization
on voltage depend on?

A

Current impulses induced by incoming particles

44
Q

What are the 3 types of scintillation detectors?

A

Liquid scintillator

Plastic scintillator

Inorganic crystals

45
Q

3 things that characterize Liquid scintillator

A

– Solution of fluorescent compounds

– Primary excitation of solvent and follow-up excitation of diluted compound

– Light emission

46
Q

Characterize plastic scintillator

A

Solid materials

47
Q

Describe inorganic scintillator

A

– Primary excitation of crystal, follow-up excitation of luminescent atoms

48
Q

Describe SEMICONDUCTOR DIODE DOSIMETE

A

It measures radiation dose from the quantity of electron-hole pairs generated in doped-semiconductor diodes (Si, Ge).

The current is proportional to the dose rate.

49
Q

In basic setup, an ionization chamber can be used as( 1)___

→ the electric current is (2)___ to the particles generated per unit time and is related to the (3)___

A
  1. dose rate indicator
  2. proportional
  3. dose rate
50
Q

Principle of operation of chemical detectors (for dose measurements). Give an example

A

based on radiochemical alterations

E.g, Film dosimeters follow-up evaluation

51
Q

Principle of operation of solid materials (for dose measurements). Give an example

A

based on physical parameters of solid materials

→ thermoluminescent detector – TLD (LiF, CaF2, BeO, Al2O3)

52
Q

thermoluminescent detector – TLD

The relationship between the number of emitted photons and absorbed dose

A

The number of emitted photons is proportional to the absorbed dose

Biophysics 2 (Theory) (13 decks)

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