Dose Calculation and Verification Flashcards
Dose Calculation
how is beam energy determined?
by the depth of the tumor and the separation of the patient
photon beams penetrate __more//less__ than electron beams
MORE
PDD (Percent Depth Dose) at the patient’s skin surface is around ___%
30%
electron beams are used for ______ tumors
superficial
the PDD at the patient’s skin surface for electron beams is about __-__%
80-90%
electron treatments are usually prescribed to the ___-___% isodose line
80-90%
general rule for electrons:
MeV is about __x the max depth of the tumor
3x
______________ is used to find the area of IRREGULARLY shaped fields
Clarkson Integration
T/F:
Clarkson Integration takes scatter from the blocked area into consideration for calculations
TRUE
what does SAR stand for?
Scatter Air Ratio
what is the main cause of collimator scatter?
photon scatter within the gantry head
a bigger field size creates __more//less__ scatter
MORE
photon scatter mostly occurs with what type of FILTER?
flattening filter
____ scatter = scatter that happens within the patient or phantom
phantom scatter
phantom scatter can or cannot be directly measured?
cannot be directly measured
both _____ factor and ____ ____ factor compare the dose rate in free space to the dose rate within a phantom at dmax
backscatter factor (BSF)
peak scatter factor (PSF)
fill in the blanks with –> BSF (backscatter factor) and PSF (peak scatter factor)
_____ is used for low-energy beams
____ is used for high energy beams ABOVE 4 MV
what scatter factor is used for energy beams above 4 MV?
peak scatter factor (PSF)
________ = the depth where electronic equilibrium is reached and 100% dose is delivered
dmax
the dmax for higher energies is ___deeper//more superficial____
DEEPER
as PHOTON energy increases, what happens with skin sparring?
skin sparring increases
_______ = ratio that compares the absorbed dose at a depth to the absorbed dose at a specific reference dose (dmax)
PDD (percent depth dose)
when is PDD used/calculated?
only used to calculate MU in SSD treatments
what are the 4 components PDD changes with?
energy
depth
field size
SSD
an increase in ____, ____ ____, and _____ cause the PDD to increase
energy, field size, SSD
PDD and field size have a direct or indirect relationship?
DIRECT
-increase of FS causes an increase of PDD due to more scatter (direct relationship)
PDD __decreases//increases___ as the SSD increases
increases
depth and PDD have an direct or indirect relationship?
INDIRECT /”inverse”
-as the depth within the patient increase PAST dmax, the PDD decreases
what equation makes up for the change in dose at different depths of the CAX (central axis) due to the inverse square law
Mayneord F factor
