Principles and Practice Review 1 Flashcards
Which of the following is not found inside the head of a linear accelerator ?
accelerator structure
The backscatter factor is effected by all of the following EXCEPT:
- Treatment field size
- Radiation quality
- Quantity of radiation
Quantity of Radiation
The tissue air ratio (TAR) at the depth of maximum electron buildup (Dmax) is:
- Always less than or equal to 1
- The backscatter factor
- Dependent on the field size
All of the above
The concept of tissue-air ratio (TAR) is most commonly employed for calculations involving:
SSD varying fields
The depth of maximum ionization is most dependent on
Beam energy
A 10MV linear accelerator is used at 100cm SSD. The location of maximum dose is found at a depth of
2.5cm
Percentage depth dose increases with increasing:
- Energy
- Depth
- Field Size
Energy and Field size
Tissue-air ratio decreases with decreasing
- SSD
- Depth
- Field size
Field size
A wedge filter _____ the output of the beam and must thus be taken into account in the treatment calculations
decreases
%DD increases with increasing
- energy
- depth
- field size
energy and field size
TAR decreases with decreasing
- field size
- depth
- SSD
Field size
When blocking is used in a treatment calculation, the area of the collimator is used in determining
- TMR
- Output Factor
- PDD
Output Factor
Which of the following is not a tissue absorption factor?
Output factor
Which of the following central axis depth dose quantities would most likely be used to compute an accurate MU setting on an 18MV unit for an isocentric treatment
TMR
Two parallel opposed equally weighed 6MV fields are separated by 20cm of tissue and treated with an SSD technique. The maximum dose will occur
1.5 under the skin surface
A wedge filter ______ the output of the treatment beam and must thus be taken into account in the treatment calculation
decreases
Mayneord’s factor is used to convert
PDD with a change in SSD from the standard
1Gy is the same as
100cGy
The point of maximum electron equilibrium is referred to as
Dmax
Dose rates:
Increase with increased field size and decrease with increased distance
In a fixed SSD technique the dose is routinely normalized
at Dmax
In an isocentric treatment technique the most done is routinely normalized
at the isocenter
What is the reference desert when delivering an external beam radiation therapy treatment using a 10MV SSD technique?
.968
What is the reference desert when delivering an external beam radiation therapy treatment using a 18MV SSD technique?
2.1
Calculate the equivalent square of a 13x12cm field blocked 12%
11.7
Calculate the equivalent square of a 13x9cm field blocked 7%
10.3
The gross tumor volume (GTV) ], as defined by the ICRU, mean:
The gross tumor volume (GTV) as defined by the ICRU name
The term clinical target volume (CTV), as defined by the ICRU, means
A tissue volume that contains demonstrable GTV a defend volume
The field size when using an SSD technique and a photon mean usually defined
on the skin surface
The angle of beam divergence is
larger farther from the CAX
The three planes in a patient are across the body, along the body in a lateral view, and along the body in an anterior view. Respectively they are referred to as
axial, sagittal, and coronal
When the treatment field is designed by the radiation oncologist, margins are always added around a tumor because of
uncertainties in determining tumor extent, penumbra of the be a, and patient motion
the isocenter is
the point around which the source of the beam rotates
What is the percent depth dose of a 12x7cm field delivering a 10 MV x-ray at a depth of 2.5cm?
100.0
What is the percent depth dose of a 12x7cm field delivering a 18MV x-ray at a depth of 2.5cm?
97.3
What is TAR of a 10x16cm field blocked 5% delivering a 10 MV x-ray at a depth of 10.0cm
.866
The depth of maximum ionization is most dependent upon
beam quality
TAR is dependent upon:
- Energy
- SSD
- Depth
- Field Size
Energy
Depth
Field Size
When using shielding blocks what is effected?
Equivalent square field (ESF)
The intensity of a high energy photon beam at any given distance from a source is:
inversely proportional to the square of the distance
Dose rate for a linear accelerator is expressed at
cGy?MU
TAR is advantageous because
ratios do not depend on source to skin distance
Mayneord factor compensates for a change in central axis depth dose and includes corrections for
inverse square law
Which beam would produce the maximum amount of backscatter
the one with least energy usually 1.25MV
As beam quality increases, maximum dose____.
increases
The %DD for a 12x12cm field, 4MV photon beam, 5cm depth, and 80cm SSD is 82.8. Calculate the %DD for the same field size and depth for 100cm SSD.
84.3
If the field size indicator is set for 20x20cm at 80cm SSD, what is the field size at 84cm?
21x21cm
If a Co-60 unit is used at 80cm SSD for a 15x15cm field size and has a %DD of 58.4 at 10cm depth, what is the %DD for the same field size and depth at 100cm SSD?
60.9
The Dmax for a 10MV photon beam at an 100cm SSD with a 15x15cm field is approximately
2.5cm
Mayneord’s F-factor is of use when there is a change in
SSD
Calculate the equivalent square for a 10x15cm rectangular field
12x12cm
Determine the equivalent square for a rectangular field with a width of 8cm and a length of 15cm
10.4cm
Determine the equivalent square for a rectangular field with a width of 7cm and a length of 17cm
9.9cm
The counterpart of the timer setting of a Co-60 unit is most similar to the ______of a LINAC.
monitor unit
