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ABR Part 1 - Big Mix

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What are the Hounsfield Units for air, lung, fat, muscle, and bone?

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What are the Hounsfield Units for air, lung, fat, muscle, and bone?

Air = -1000
Lung = -700
Fat = -100
Muscle = 40
Bone = 700 - 3000

What is the OER for 15 MeV neutrons?

Ultrasound dB equation

dB = -10*log(I_echo/I_incident)

When is a characteristic x-ray vs. an Auger e- likely to occur?

-Characteristic x-rays favored for Z>30
-Auger effect for Z<30

Characteristics and examples of late responding tissues

-Spinal cord, kidney, muscle, lung, bladder
-α/β<~3
-Good ability to repair
-More sensitive at higher doses

How do you calculate heat units for an x-ray tube?

HU = kVp x mAs x 1.4

What is the true negative fraction (specificity)?

Measures the probability of a negative test.
specificity = TN/(FP+TN)
**Be able to draw truth table

Describe transient equilibrium

-Parent half-life is longer than daughter half-life, but not infinitely long
-Daughter activity increases then exceeds parent activity
-After the maximum activity is reached, both activities decay in parallel

What is PRF in ultrasound?

-Pulse repetition frequency: the number of pulses (lines of sight) sent out per second
PRF = frame rate * lines per image

Field size for MU calcs: where are S_c, S_p, and PDD defined?

S_c defined at isocenter
S_p defined at normalization depth
PDD defined at treatment depth

What is the specific activity of a radionuclide?

a = λN_a/A

λ=ln2/T_1/2
N_a=Avogadro's Number
A=atomic mass number

Threshold dose for deterministic effects after fetal exposure

What happens when overall treatment time is prolonged?

Local tumor control decreases (for rapidly growing tumors)

What is the cutoff energy for free air ion chambers?

What is effective uptake half-life?

T_ue = (T_u*T_p)/(T_u+T_p)