Dosimetry Flashcards
What is dosimetry?
The measurement and calculation of radiation doses
What are the key learning outcomes in dosimetry?
- Understand radiation dose quantities
- Practical use in clinical practice
- Principles of Diagnostic Reference Levels
- Automatic Exposure Controls and optimization
What are the radiation core safety principles?
Justification
-risk vs benefit
Optimisation
-ALARP
Limitation
-staff and public
What does ALARP stand for?
As Low As Reasonably Practicable
What is KERMA?
Kinetic Energy Released per Unit Mass
Kair
Included effects of bremsstrahlung
Unit-Gray
What is absorbed dose and its units?
Measured in Gray (Gy)
Amount of energy deposited in a material
What is and How is equivalent dose calculated?
Considers harmfulness of radiation
Equivalent dose = Absorbed dose * x weighting factor
What unit is used for equivalent dose?
Sievert (Sv)
What is Linear Energy Transfer (LET)?
LET is the energy deposited per unit distance
Defines how damaging radiation is and determines its biological consequence
Higher LET+ more irreparable DNA breaks
Alpha particles have a HIgh LET
True or False: Gamma rays, x rays, electrons have a high LET.
False
What does the effective dose account for?
The sensitivity of different organs to radiation.
Some organs in the body are more sensitive to radiation than others.
A tissue weighting factor is applied
What is the purpose of tissue weighting factors (WT)?
To account for the relative contribution of each organ to effective dose
What is the significance of the reference air kerma?
Used as a surrogate for Entrance Surface Dose (ESD)
What is the typical risk range for developing childhood cancer from radiation exposure?
1 in 1,000,000 to 1 in 200
Higher dose and exam location = higher risk
What is DAP in dosimetry?
Dose (exposure) Area Product
Product of the exposure and the area it covers
What does CTDI stand for?
CT Dose Index
Beam width is not the same as slice thickness
CTDIvol - CT dose index for a volume vacancy be used to measure absorbed dose with a rotational x ray beam
Fill in the blank: The unit for exposure is _______.
coulombs per kilogram (C/kg)
Occupational Exposures in dosimetry
Exposures to a risk in the workplace is covered by the Health and safety at work act (HASAWA)
How are Diagnostic Reference Levels (DRLs) established?
- National dose audits
- Local Diagnostic Reference Levels
- Clinical indications
What is the role of Automatic Exposure Controls (AEC)?
Use of ionisation chambers to optimise exposure
To optimize exposure by monitoring dose received at the detector
Terminates x rays when the dose is what has been specified
What does the acronym ICRP stand for?
International Commission on Radiological Protection
What is the typical annual occupational dose for a radiographer?
< 0.5 mSv
What is the back-scatter factor (BSF) typically used in dose measurements?
1.2 – 1.4
What is the relationship between DAP and distance from the focus?
DAP is independent of the distance to the patient
Area of skin exposed is proportional to the square of the distance from the focus
