Measurement of radiation dose Flashcards
Define absorbed dose
energy imparted to organ or tissue per unit mass
- average absorbed dose to that tissue
What is absorbed dose measured in?
gray (Gy)
Define equivalent dose
absorbed dose to organ or tissue weighted for type of radiation
What is equivalent dose measured in
Sievert Sv
Define effective dose
absorbed dose to organ or tissue weighted for type of radiation AND type of tissue
what is effective dose measured in
sieverts
Effective dose is directly related to risk of average person irradiated, what 3 things does this risk depend on
- amount of energy absorbed per uni mass
- type of radiation
- radio sensitivity of site where radiation absorbed
Why might radiation have increased risk in children than adults
- they have longer for cancers to be expressed
- developing tissues may be more radiosensitive
What are 3 ways of dose calculation methods in patients in DR?
- ESD measurement
- DAP measurement
- DLP measurement
What does ESD, DAP and DLP stand for ?
entrance surface dose
dose area product
dose length product
What is entrance surface dose and how does it work + units
- measurement of absorbed dose (mGy)
- directly measured at patients skin using TLD
- calculated from known tube output and other known factors
What does FIA and BSF stand for
fraction incident beam absorbed
backscatter factor
what is dose area product and how does it work + units
- 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)
What is dose length product and how does it work + units
- mGy.cm
- Directly calculated from CTDI and scan length
What does CTDI stand for
computed tomography dose index