Measurement of radiation dose Flashcards

1
Q

Define absorbed dose

A

energy imparted to organ or tissue per unit mass

  • average absorbed dose to that tissue
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2
Q

What is absorbed dose measured in?

A

gray (Gy)

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3
Q

Define equivalent dose

A

absorbed dose to organ or tissue weighted for type of radiation

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4
Q

What is equivalent dose measured in

A

Sievert Sv

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5
Q

Define effective dose

A

absorbed dose to organ or tissue weighted for type of radiation AND type of tissue

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6
Q

what is effective dose measured in

A

sieverts

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7
Q

Effective dose is directly related to risk of average person irradiated, what 3 things does this risk depend on

A
  • amount of energy absorbed per uni mass
  • type of radiation
  • radio sensitivity of site where radiation absorbed
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8
Q

Why might radiation have increased risk in children than adults

A
  • they have longer for cancers to be expressed
  • developing tissues may be more radiosensitive
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9
Q

What are 3 ways of dose calculation methods in patients in DR?

A
  1. ESD measurement
  2. DAP measurement
  3. DLP measurement
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10
Q

What does ESD, DAP and DLP stand for ?

A

entrance surface dose

dose area product

dose length product

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11
Q

What is entrance surface dose and how does it work + units

A
  • measurement of absorbed dose (mGy)
  • directly measured at patients skin using TLD
  • calculated from known tube output and other known factors
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12
Q

What does FIA and BSF stand for

A

fraction incident beam absorbed

backscatter factor

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13
Q

what is dose area product and how does it work + units

A
  • measures product of absorbed dose (in air) and x-ray field area
  • mGy.cm^-2
  • independent of focus to skin distance (FSD)
  • measured directly using a dose area product metre (flat area parallel place IC mounted to the tube port)
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14
Q

What is dose length product and how does it work + units

A
  • mGy.cm
  • Directly calculated from CTDI and scan length
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15
Q

What does CTDI stand for

A

computed tomography dose index

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16
Q

What are Monte Carlo simulations?

A
  • mathematical modelling of a limited range of photons
  • frequently used in nuclear medicine dosimetry taking into account half life, radionuclide emission data and biological clearance
  • also used in radiotherapy for beam modelling
17
Q

What does DRL / NDRL / LDRL stand for?

A

diagnostic reference level
national diagnostic reference level
local diagnostic reference level

18
Q

what is diagnostic references level

A

(in IRMER)
- dose levels in medical radiodiagnostic practices or in case of radioactive medicinal products, levels of activity for typical examinations for groups of standard-sized patients

19
Q

What are the difference ways you would calculate dose in plain film, ct, nuclear medicine and routine fluroscopy?

A

Plain film = DAP
CT = DLP
Nuclear medicine = activity
Routine fluoroscopy = DAP

20
Q

what are the disadvantages of using N/LDRL?

A
  • effective dose has limitations
  • weighting factors are tailored to a population
  • not ideal for individual patient risk
  • useful for dose comparisons across modalities
21
Q

What does ICRP stand for?

A

international commission on radiological protection

22
Q

what are the 3 principles from ICRP that controls dose reduction?

A
  • ALARP
  • limitation (time, shielding, distance)
  • justification (benefit vs risk)
  • optimisation (minimum dose for diagnostic image)
23
Q

Compare the risk of radiation to stages of a growing foetus

A

radiation risks are most significant during organogenesis (formation fo organs of organism from embryonic cells) and in early foetal period

24
Q

What is the threshold exposure that typically induces issues with the dental nervous system in foetal?

A

100 mGy

(worth 3 pelvic CT examinations or 20 x-rays)

25
Q

Between radiation induced malformations and radiation induce cancer which is a deterministic or stochastic risk

A

radiation induced malformation = deterministic risk

radiation induced cancer = stochastic risk

26
Q

When can communication of risks associated with pregnancy be negligible?

A

if foetal does is less than 1mGy

27
Q

What risks comes with giving pregnant lady iodine-131 and how

A
  • crosses placenta
  • foetal thyroid accumulates iodine after 10 weeks
  • high foetal thyroid dose can result in permanent hypothyroidism (thyroid gland doesnt produce enough hormones)
28
Q

What must be done if woman is discovered as pregnant after being given I-131 within 12 hrs

A

oral administration of stable potassium iodine

29
Q

How does a TLD work?

A
  • radiation absorbed
  • electrons stimulated into higher energy state
  • dosimeter is heated
  • electrons drop out of higher energy state releasing energy as light photons
  • light is equivalent to dose
30
Q

Define EPD

A

electronic personal dosimeter

31
Q

How does an EPD work

A
  • incident radiation creates electron-hole pairs
  • instant red out

number of holes is equivalent to dose

32
Q

What body part I? Hp(10), Hp(0.07) and Hp(3) used for to measure dose:

A

Hp 10= whole body (effective dose) (measures at 10mm)

Hp 0.07= extremities skin dose (measures at 0.07)

Hp 3= eye ( measures at 3mm)

33
Q
A