RADIATION THERAPY TECHNIQUES
QUESTIONS WITH CORRECT
ANSWERS
Mark all concerning wedges:
- reduce hot spots
- can be hard or dynamic
- used for tissue compensating of sloping surfaces
- known as superflab - Answer- - reduce hot spots
- can be hard or dynamic
- used for tissue compensating of sloping surfaces
Irradiated volume - Answer- Volume of tissue receiving a significant dose (50% or
more of the prescribed dose)
GTV - Answer- The gross, palpable, visible, or clinically demonstratable location
of the cancerous growth
CTV - Answer- Tissue volume that contains the clinical and subclinicall disease
PTV - Answer- Surrounds the clinical and subclinical growth and an additional
margin to compensate for different types and variations and uncertainties of the
beam
Treated volume - Answer- Larger than the target volume, encompasses the
additional margins around the target to allow for limitations of the treatment
technique
Localization - Answer- geometrical definition of the tumor and anatomic structures
using surface or fiducial marks for reference
Verification - Answer- a check that each beam/port covers the intended treatment
area and spares organs at risk
Simulation - Answer- The process carried out by the radiation therapist under the
direction of the radiation oncologist. This is a mock up of the patient positioning for
treatment
IFD - Answer- Patient separation between two beams
Is a photon beam heterogenous or homogenous? - Answer- Heterogenous
,What is the average energy of an 18MV beam? - Answer- 6mv
SAD setup - Answer- iso in 100 or less
SSD setup - Answer- iso is 100 or more
What is the importance of shielding blocking devices - Answer- - high intensity
- high atomic number
- low melting point
Shielding material should the original intensity of the beam to ___% or less -
Answer- 5
MLC or blocks should be at least ___ cm away to avoid ___scatter - Answer- 15-
20, electron
What are the material and amount of those materials in cerrobend? - Answer-
Bismuth - 50%
Lead - 26.7%
Tin - 13.3%
Cadmium - 10%
What is the most toxic ingredient in cerrobend? - Answer- Cadmium
What is true about compensators? - Answer- - maintain skin sparing
- used for tissues with different densities
- allow for normal depth dose for irregular surfaces
What are the different types fo wedge filters? - Answer- - EDW
- Virtual
- Dynamic
- Individualized
What does bolus change? - Answer- The location of DMAX
What does bolus do to skin sparing? - Answer- Decreases skin sparing because
DMAX depth is decreased.
What angle are EDW wedge filters measured at? - Answer- 10cm
Do compensators affect DMAX? - Answer- no
4mv DMAX - Answer- 1cm
, 6mv DMAX - Answer- 1.5 cm
10mv DMAX - Answer- 2.5cm
18mv DMAX - Answer- 3.5cm
24mv DMAX - Answer- 4cm
Attenuation for lung - Answer- .3
Attenuation for bone - Answer- 1.5
Attenuation for air - Answer- .0013
Attenuation for fat - Answer- .91
attenuation for muscle or water - Answer- 1
How much percent of hotspots do we accept? - Answer- 10%
What is the relationship between energy and penumbra? - Answer- increase
energy decrease penumbra
What increases skin sparing? - Answer- increased energy, size of build up,
increased depth at dmax
If you increase field size what happens with scatter and dose - Answer- they both
increase
formula for equivalent square - Answer- 4(A)/P
formula for effective field size - Answer- 4(a-area of blocks)/P
Hinge angle formula - Answer- 180-2(wedge angle)
Wedge angle formula - Answer- 90-(hinge angle/2)
How is treatment time expressed for linear accelerators? - Answer- cGy per MU
attenuation factor formula - Answer- dose with wedge/ dose without wedge
How dow e prevent secondary electron contamination? - Answer- have to be at
least 15 cm away from the patient
How do we calculate dmax dose? - Answer- total dose/%DD
QUESTIONS WITH CORRECT
ANSWERS
Mark all concerning wedges:
- reduce hot spots
- can be hard or dynamic
- used for tissue compensating of sloping surfaces
- known as superflab - Answer- - reduce hot spots
- can be hard or dynamic
- used for tissue compensating of sloping surfaces
Irradiated volume - Answer- Volume of tissue receiving a significant dose (50% or
more of the prescribed dose)
GTV - Answer- The gross, palpable, visible, or clinically demonstratable location
of the cancerous growth
CTV - Answer- Tissue volume that contains the clinical and subclinicall disease
PTV - Answer- Surrounds the clinical and subclinical growth and an additional
margin to compensate for different types and variations and uncertainties of the
beam
Treated volume - Answer- Larger than the target volume, encompasses the
additional margins around the target to allow for limitations of the treatment
technique
Localization - Answer- geometrical definition of the tumor and anatomic structures
using surface or fiducial marks for reference
Verification - Answer- a check that each beam/port covers the intended treatment
area and spares organs at risk
Simulation - Answer- The process carried out by the radiation therapist under the
direction of the radiation oncologist. This is a mock up of the patient positioning for
treatment
IFD - Answer- Patient separation between two beams
Is a photon beam heterogenous or homogenous? - Answer- Heterogenous
,What is the average energy of an 18MV beam? - Answer- 6mv
SAD setup - Answer- iso in 100 or less
SSD setup - Answer- iso is 100 or more
What is the importance of shielding blocking devices - Answer- - high intensity
- high atomic number
- low melting point
Shielding material should the original intensity of the beam to ___% or less -
Answer- 5
MLC or blocks should be at least ___ cm away to avoid ___scatter - Answer- 15-
20, electron
What are the material and amount of those materials in cerrobend? - Answer-
Bismuth - 50%
Lead - 26.7%
Tin - 13.3%
Cadmium - 10%
What is the most toxic ingredient in cerrobend? - Answer- Cadmium
What is true about compensators? - Answer- - maintain skin sparing
- used for tissues with different densities
- allow for normal depth dose for irregular surfaces
What are the different types fo wedge filters? - Answer- - EDW
- Virtual
- Dynamic
- Individualized
What does bolus change? - Answer- The location of DMAX
What does bolus do to skin sparing? - Answer- Decreases skin sparing because
DMAX depth is decreased.
What angle are EDW wedge filters measured at? - Answer- 10cm
Do compensators affect DMAX? - Answer- no
4mv DMAX - Answer- 1cm
, 6mv DMAX - Answer- 1.5 cm
10mv DMAX - Answer- 2.5cm
18mv DMAX - Answer- 3.5cm
24mv DMAX - Answer- 4cm
Attenuation for lung - Answer- .3
Attenuation for bone - Answer- 1.5
Attenuation for air - Answer- .0013
Attenuation for fat - Answer- .91
attenuation for muscle or water - Answer- 1
How much percent of hotspots do we accept? - Answer- 10%
What is the relationship between energy and penumbra? - Answer- increase
energy decrease penumbra
What increases skin sparing? - Answer- increased energy, size of build up,
increased depth at dmax
If you increase field size what happens with scatter and dose - Answer- they both
increase
formula for equivalent square - Answer- 4(A)/P
formula for effective field size - Answer- 4(a-area of blocks)/P
Hinge angle formula - Answer- 180-2(wedge angle)
Wedge angle formula - Answer- 90-(hinge angle/2)
How is treatment time expressed for linear accelerators? - Answer- cGy per MU
attenuation factor formula - Answer- dose with wedge/ dose without wedge
How dow e prevent secondary electron contamination? - Answer- have to be at
least 15 cm away from the patient
How do we calculate dmax dose? - Answer- total dose/%DD
