CALCULATIONS & MATH TUTORIALS Flashcards
REMINDER only use inverse square law when ______ and ____ are involved together
distance and dose
the radiation beam intensity will ___increase/decrease__ with ___increasing/decreasing__ distance due to the beam’s divergence
beam intensity//dose will decrease with increasing distance, due to beam’s divergence
would you use inverse square law or direct proportion to - compare similar triangles, use for field size and SSD, and magnification
direct proportion
inverse square law or direct proportions show change in dose with distance
inverse square law
T/F: divergence is predictable
true
magnification is based on inverse square law or direct proportions?
direct proportions
overdose or underdose, we use inverse square law or direct proportion? - commonly phrased “patient was accidentally treated at x distance, or x dose”
inverse square law
Mayneord F is a type of direct proportion or inverse square law?
inverse square law
for a direct proportion that is a square, you must do the eq once or twice?
once - example 8 x 8
for a direct proportion that is a rectangular, you must do the eq once or twice?
twice - example 9.3 x 8
according to inverse square law - if you double your dose, what happens to your distance?
quarter your distance
according to inverse square law - if you double your distance
Intensity needs to go up by 4
if a patient was treated at 109 SSD, instead of 100 SSD… were they overdose or underdosed?
underdosed… we are treating patient further away from source … lowering table
we kick the couch to avoid beam divergence and match with the ______
field size
ISF stands for what?
Inverse Square Factor
Inverse Square Factor only incorporates the Intensity, or Distance?
Distance
if it is an under dose … small number goes on top or bottom of ISF?
we want a smaller number as answer, so small number would go on top
if it is an over dose … small number goes on top or bottom of ISF?
we want larger number as answer, so larger number would go on top
do not forget to _____ distance part of ISF/Inverse Sqaure Law!!!!
square it!
for a dose error question - if it is UNDER dose do we want ISF to be greater than, or less than 1?
less than 1
for a dose error question - if it is OVER dose do we want ISF to be greater than, or less than 1?
greater than 1
________ is the ratio of the size of an object in the image to the actual size of the object in real life *hint - ______ factor
magnification factor
degree to which an image is larger than the actual object = _________
magnification factor
due to what is why an image is always larger than the actual object for xrays -
beam divergence
magnification factor can be effected by what? (2)
xray source to image receptor distance -
and object to be imaged distance to image receptor
_______ = the thickness of an absorber required to attenuate the intensity of the beam to half its original value
HVL (half value layer)
after a 100% beam comes in contact with a HVL absorber, what will be the intensity after? what if you add another HVL?
50% –> 100/2
if another HVL is added then do 50/2 to get 25%
for blocks - transmission rate must be less than what?
5%
_______ is used to help calculate for primary barriers
workload
______ shows the beam ON time per week
workload
workload shows the beam ON time per month, week, day, or minute ?
per week!
workload = the weekly dose delivered at ____ distance from source
1 meter
what is workload expressed in?
rad / week at 1 meter
you DO or DO NOT square the fields before plugging them into Blocked Equivalent Square calculation?
do not!
what is fun way to remember conversions?
KHDBDCM -
King Henry Died By Drinking Choco Milk
