Measurement of radiation dose

Question 1

Define absorbed dose

Answer 1

energy imparted to organ or tissue per unit mass

• average absorbed dose to that tissue

Question 2

What is absorbed dose measured in?

Answer 2

gray (Gy)

Question 3

Define equivalent dose

Answer 3

absorbed dose to organ or tissue weighted for type of radiation

Question 4

What is equivalent dose measured in

Answer 4

Sievert Sv

Question 5

Define effective dose

Answer 5

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

Question 6

what is effective dose measured in

Answer 6

sieverts

Question 7

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

Answer 7

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

Question 8

Why might radiation have increased risk in children than adults

Answer 8

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

Question 9

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

Answer 9

1. ESD measurement
2. DAP measurement
3. DLP measurement

Question 10

What does ESD, DAP and DLP stand for ?

Answer 10

entrance surface dose

dose area product

dose length product

Question 11

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

Answer 11

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

Question 12

What does FIA and BSF stand for

Answer 12

fraction incident beam absorbed

backscatter factor

Question 13

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

Answer 13

• 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)

Question 14

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

Answer 14

• mGy.cm
• Directly calculated from CTDI and scan length

Question 15

What does CTDI stand for

Answer 15

computed tomography dose index

Question 16

What are Monte Carlo simulations?

Answer 16

• 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

Question 17

What does DRL / NDRL / LDRL stand for?

Answer 17

diagnostic reference level
national diagnostic reference level
local diagnostic reference level

Question 18

what is diagnostic references level

Answer 18

(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

Question 19

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

Answer 19

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

Question 20

what are the disadvantages of using N/LDRL?

Answer 20

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

Question 21

What does ICRP stand for?

Answer 21

international commission on radiological protection

Question 22

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

Answer 22

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

Question 23

Compare the risk of radiation to stages of a growing foetus

Answer 23

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

Question 24

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

Answer 24

100 mGy

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

Question 25

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

Answer 25

radiation induced malformation = deterministic risk

radiation induced cancer = stochastic risk

Question 26

When can communication of risks associated with pregnancy be negligible?

Answer 26

if foetal does is less than 1mGy

Question 27

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

Answer 27

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

Question 28

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

Answer 28

oral administration of stable potassium iodine

Question 29

How does a TLD work?

Answer 29

• 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

Question 30

Define EPD

Answer 30

electronic personal dosimeter

Question 31

How does an EPD work

Answer 31

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

number of holes is equivalent to dose

Question 32

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

Answer 32

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)