Physics - Radiation Biology Flashcards
Define Exposure and what are the units?
Ability of X-rays to ionize air. Roentgens (R)
Define Absorbed Radiation Dose or Radiation Dose. What are the units?
Amount of energy absorbed per unit mass at a specific point. Measured in Gy or Rads (1 Gy = 100 rads(
What is equivalent dose? What are the units?
Absorbed dose of different types of radiation creates different damage. EqD = Dose * weight. Weight for x-rays and gamma => 1. For Alpha => 20. Measured in Sievert
What is effective dose and what are the units?
Efd = Eqd * tissue weighting factor. Measured in Sieverts.
What does KERMA stand for?
Kinetic energy released per unit mass
What is KERMA trying to tell you?
Primary energy transfer after exposure. No secondary effects accounted for.
At low energy KERMA (> = < ) absorbed dose?
= As it will all be absorbed by PE domination.
At high energy KERMA will be (> = < ) absorbed dose?
Kerma > dose => Some electrons will pass through the patient not contributing to dose.
Overall Tissue dose (> =
Tissue dose > Kerma by about 10% due to scatter not accounted for in the kerma equasion.
What is kerma-area product? (Also called dose area product)
KAP = Dose * cross sectional area
How is KAP affected by the source distence?
It’s not. It’s the same along all points. Dose decreases via inverse square but distance increases via divergence also by the square.
How does changing geometric mag change the KAP and entrance KERMA?
Increases entrance dose (increase burn risk) as you’ve moved the patient closer to the detector but NO change in KAP
How does collimation change KAP?
Decrease (KAP = Dose * cross sectional area
How does collimation change the air kerma?
Increases slightly due to more power need
KAP is a good indicator of which risk type?
Stochastic
