CTP1 Exam 2 UPDATED QUESTIONS AND
CORRECT ANSWERS
PDD equation - CORRECT ANSWER PDD = (D(d)/ D(dmax)) * 100
What are D0, Dmax, D10 for 6x PDD - CORRECT ANSWER 30%, 1.5 cm, 67%
What are D0, Dmax, D10 for 18x PDD - CORRECT ANSWER 20%, 3.5cm, 80%
How is PDD measured - CORRECT ANSWER in water chamber with reference and
signal ion chambers. The signal chamber moves ant to post (up and down)
How is an isodose line derived? - CORRECT ANSWER from PDD and profiles
When should you not normalizes an isodose line? - CORRECT ANSWER within 2cm
of the field edge
Normalization equation - CORRECT ANSWER (100/ what you are normalizing
to)*100
Purpose of wedges - CORRECT ANSWER tilt the isodose lines
missing tissue compensation
Old definition of a wedge angle - CORRECT ANSWER depth where 50% line is
new definition of wedge angle - CORRECT ANSWER depth of 10 cm
How does wedge angle change with depth? - CORRECT ANSWER wedge angle will
decrease with depth because the scatter will begin to fill in the gradient
,What is a compensator - CORRECT ANSWER 3-D wedge: looks like mountains,
abstract shape
Factors affecting compensators - CORRECT ANSWER energy
field size
depth
compensator shape
What are partial transmission blocks - CORRECT ANSWER uses cerrobend
what is the HVL for cerrobend - CORRECT ANSWER 15 mm
Hour glass effect - CORRECT ANSWER for AP/PA field
nothing outside to scatter in when things scatter out, creating an hourglass shape
where are hot spots for AP/PA set up - CORRECT ANSWER at dmax and laterally due
to horns from flattening filter
How do hot spots change with energy for AP/PA set up - CORRECT ANSWER as
energy decreases, hot spots will increase
how do hot spots change with seperation for AP/PA set up - CORRECT ANSWER as
seperation increases, hot spots will increase
how do hot spots change with field size for AP/PA set up - CORRECT ANSWER as
field size increases, hot spots will decrease slightly
for AP/PA set up (sep=20cm) where are the hot spots for 4X - CORRECT
ANSWER 20%
, for AP/PA set up (sep=20cm) where are the hot spots for 6X - CORRECT
ANSWER 15%
for AP/PA set up (sep=20cm) where are the hot spots for 10X - CORRECT
ANSWER 12%
for AP/PA set up (sep=20cm) where are the hot spots for 15X - CORRECT
ANSWER 10%
for AP/PA set up (sep=20cm) where are the hot spots for 18X - CORRECT
ANSWER 8%
How do we minimize integral dose? - CORRECT ANSWER use highest energy
use greater SSD
How does IMRT affect integral dose? - CORRECT ANSWER IMRT will increase
integral dose
dose for inhomogeneities in air upstream - CORRECT ANSWER dose is less due to
lack of backscatter
dose for inhomogeneities in air inside - CORRECT ANSWER increase in dose,
particles can travel further
dose for inhomogeneities in air interface - CORRECT ANSWER lower than expected
due to re-build up effect
dose for inhomogeneities in air beyond - CORRECT ANSWER increase in dose
dose for inhomogeneities in bone upstream - CORRECT ANSWER increase in dose
due to high backscatter
CORRECT ANSWERS
PDD equation - CORRECT ANSWER PDD = (D(d)/ D(dmax)) * 100
What are D0, Dmax, D10 for 6x PDD - CORRECT ANSWER 30%, 1.5 cm, 67%
What are D0, Dmax, D10 for 18x PDD - CORRECT ANSWER 20%, 3.5cm, 80%
How is PDD measured - CORRECT ANSWER in water chamber with reference and
signal ion chambers. The signal chamber moves ant to post (up and down)
How is an isodose line derived? - CORRECT ANSWER from PDD and profiles
When should you not normalizes an isodose line? - CORRECT ANSWER within 2cm
of the field edge
Normalization equation - CORRECT ANSWER (100/ what you are normalizing
to)*100
Purpose of wedges - CORRECT ANSWER tilt the isodose lines
missing tissue compensation
Old definition of a wedge angle - CORRECT ANSWER depth where 50% line is
new definition of wedge angle - CORRECT ANSWER depth of 10 cm
How does wedge angle change with depth? - CORRECT ANSWER wedge angle will
decrease with depth because the scatter will begin to fill in the gradient
,What is a compensator - CORRECT ANSWER 3-D wedge: looks like mountains,
abstract shape
Factors affecting compensators - CORRECT ANSWER energy
field size
depth
compensator shape
What are partial transmission blocks - CORRECT ANSWER uses cerrobend
what is the HVL for cerrobend - CORRECT ANSWER 15 mm
Hour glass effect - CORRECT ANSWER for AP/PA field
nothing outside to scatter in when things scatter out, creating an hourglass shape
where are hot spots for AP/PA set up - CORRECT ANSWER at dmax and laterally due
to horns from flattening filter
How do hot spots change with energy for AP/PA set up - CORRECT ANSWER as
energy decreases, hot spots will increase
how do hot spots change with seperation for AP/PA set up - CORRECT ANSWER as
seperation increases, hot spots will increase
how do hot spots change with field size for AP/PA set up - CORRECT ANSWER as
field size increases, hot spots will decrease slightly
for AP/PA set up (sep=20cm) where are the hot spots for 4X - CORRECT
ANSWER 20%
, for AP/PA set up (sep=20cm) where are the hot spots for 6X - CORRECT
ANSWER 15%
for AP/PA set up (sep=20cm) where are the hot spots for 10X - CORRECT
ANSWER 12%
for AP/PA set up (sep=20cm) where are the hot spots for 15X - CORRECT
ANSWER 10%
for AP/PA set up (sep=20cm) where are the hot spots for 18X - CORRECT
ANSWER 8%
How do we minimize integral dose? - CORRECT ANSWER use highest energy
use greater SSD
How does IMRT affect integral dose? - CORRECT ANSWER IMRT will increase
integral dose
dose for inhomogeneities in air upstream - CORRECT ANSWER dose is less due to
lack of backscatter
dose for inhomogeneities in air inside - CORRECT ANSWER increase in dose,
particles can travel further
dose for inhomogeneities in air interface - CORRECT ANSWER lower than expected
due to re-build up effect
dose for inhomogeneities in air beyond - CORRECT ANSWER increase in dose
dose for inhomogeneities in bone upstream - CORRECT ANSWER increase in dose
due to high backscatter
