5. Radiation Physics Flashcards
What are the 3 procedure that need to be carried out before equipment is used?
Critical exam (IRR 17)
Commissioning - Establish baselines, set up for clinical use.
Acceptance testing - Is it as described?
Why is radiation physics important?
Ensure equipment functions correctly:
~ safety
~ images suitable
~ radiation doses as low as possible
What is tube leakage?
Radiation transmitted through tube housing, not the beam.
What is scatter?
Secondary radiation spread out in different directions from the beam.
How do we measure tube leakage and scatter?
Get dose rates within room and behind screen.
What is resolution?
The ability to see fine detail.
What is noise?
Random variation in pixel value
If mean no. of number of photon detected is N
Noise = √N
What are the essential features of quality control (QC) tests?
Repeatable, reliable, quick and easy to analyse.
These features help ensure the reliability and efficiency of testing.
Why is consistent positioning of the test object or detector important in equipment testing?
To ensure that results are repeatable.
How is quality of radiation output assessed?
By the shape of the x-ray spectrum.
What is quality affected by?
Anode material
Tube potential (kVp)
Filtration
How is quantity of radiation output assessed?
By number of x-ray photons
What is quantity affected by?
Tube current
mA
What does beam alignment and collimator accuracy test involve?
Ensuring that the light beam and radiation beam are properly aligned.
What are the common image quality parameters in most imaging systems?
Beam positioning / slice thickness
Uniformity - all regions the same?
Noise - are variations in pixel value hidden by noise?
Resolution
What is spatial resolution?
Can objects close to each other be identified as separate?
What is temporal resolution?
Can system ‘keep up’ with changes in dynamic imaging?
What makes a good phantom?
Mimics the human body closely - if necessary
Stable
Easy to handle/transport
Accurately reflect patient images
What are stochastic effects?
Random effects that may occur after exposure to radiation, such as cancer risk.
What are deterministic effects?
Predictable, effects that have a threshold and become more severe with increasing dose, such as skin burns
What is the purpose of patient dosimetry?
To estimate radiation dose and assess risk to patients and keep doses alara
What is the need to estimate radiation dose?
In order to assess risk to patient
So that: patients can give informed consent to procedures
We can decide whether we need to report a radiation incident
We can optimise procedure.
