Treatment & Planing (Exam 1) Flashcards
2 parts of simuaiton
Localization & Verification
Geometric definition of the position and extent of the tumor or anatomical structures by reference of surface marks that can be used for treatment setup and skin care instructions.
Localization
Final check that each of the planned treatment beams overs the tumor or target volume before actual first treatment and match up
Verification
Material with high atomic number, lead, copper, solder wire used on a surface or in a body cavity of a patient to delineate special points of interest or critical structures.
*This will show up on xray
Radiopaque Marker
Measurement of the thickness of a patient among the central axis.
Separation or Intrafield Distance (IFD)
Distance to Isocenter is always 100cm
SSD
Dimensions of the treatment field at isocenter, represented by width x length or length x width
Field Size
Indicates the gross palpable or visible tumor
Gross Tumor Volume (GTV)
Indicates the gross palpable or visible tumor and surrounding volume of tissue that may contain subclinical or microscopic disease.
Clinical Target Volume (CTV)
Indicates the CTV plus margins for geometric uncertainties, such as patient motion, beam penumbra, and treatment setup differences.
Planning Target Volume (PTV)
tumor & any other tissue with presumed tumor.
Target Volume (TV)
encompasses additional margins around the target voume for limitations in treatment technique.
Treatment Volume
volume of tissue receiving a significant dose >50% of specified target dose. Tissue in front of, behind, and around the target volume.
Irradiated volume
An advantage of a source-axis distance treatment compares to a s source-distance treatment (Assuming a patient is NOT required to move in either set up.)
Table adjustments between fields are not normally required
The backscatter factor is effected by
Quantity of radiation
The tissue air ratio (TAR) at the depth of a maximum electron buildup (Dmax) is.
- Always les than or equal to 1
- The backscatter factor
- Dependent on the field size
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 10 MV 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 and field size
Directly proportional with everything except Depth
Tissue-air ratio decreases with decreasing
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 and field size
Directly proportional with everything except Depth
TAR decreases with decreasing
Field Size
When blocking is used in a treatment calculation, the area of the collimator is used in determining
Output factor
Which of the following is not a tissue absorption factor
Output factor
What central axis depth dose quantities would most likely be used to computer an accurate MU setting on an 18-MV unit for an isocentric treatment?
TMR
Two parallel opposed equally weighted 6-MV fields are separated by 20cm of tissue and treated with an SSD technique. The maximum dose will occur
1.5cm 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
1 Gy is the same as:
100 cGy
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 dose is routinely normalized
at the isocenter
What is the reference desert when delivering an external beam radiation therapy treatment using a 10 MV SSD technique
.968
What is the reference desert when delivering an external beam radiation therapy treatment using a 18 MV SSD technique.
.944
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, means:
The gross/palpable or visible/demostrable tumor extent to be irradiated to a specified dose
The term clinical target volume (CTV), as defined by the ICRU, means
a tissue volume that contains a demonstrable GTV and/or subclinical microscopic malignant disease, which has to be eliminated
The field size when using an SSD technique and a photon beam is usually define
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 than 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 beam, and patient motion
The isoventer is
the point around which the source of the beam rotates
what is the reference desert when delivering an external beam radiation therapy treatment using 6MV SSD technique
.993
What is the reference desert when delivering an external beam radiation therapy treatment using a 6MV SAD technique
1.04
What is the percent depth dose of a 12x7cm field delivering a 10MV -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 the 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
depth
field size
When using shielding blocks, which of the following is effected
Equivalent square field
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 as
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 backsatter
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 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
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 length of 17cm
9.9cm
The counterpart of the timer setting of aCo-60 unit is most similar to the _____ of a linac
monitor unit
As energy of a photon beam increases, the dose buildup region ______.
moves deeper below the sin surface.
The angle between the central axes of two beams is called the
hinge angle
The use of a split beam/half beam technique is advantageous due to
preventing beam divergence
Two treatment fields on a patient with cancer of the maxillary sinus have a hinge angle of 90 degrees
15
If one HVL shield is 2.5cm thick how much would the radiation be reduced to with a 5cm thick shield
25%
Calculate the equivalent square of a 4x11cm field
6cm
calculate the equivalent square of a 6x20cm field
9cm
calculate the equivalent square of a 12x17cm field
14cm
calculate the equivalent square of a 7x8cm field
7.5cm
What is the given dose for a patient receiving 250cGy a day treated at a 5 cm depth with SSD technique, if the %DD is 84.5%?
296
GD= (250/.845) = 295.8= 296cGy
Three half-value layers would reduce the intensity of the beam to
12.5%
The field size light should correspond to the _______ %Isodose line.
50
Three half-value layers would reduce the intensity of the beam to:
12.5%
The optimum hinge angle for a pair of 45 degrees wedge filters, neglecting oblique incidence is?
90 degrees
The wedge filter is used during external beam radiation of glottic tumors to
evenly distribute dose
An ideal bolus material should have all of the following except
valence number
Calculate the hinge angle for a 30 degree wedge
120
An area outside the target area which receives a higher dose than the specified target dose is
hot spot
____is the measurement of radiation dose
dosimetry
the ______ is the sameness from side to side of the beam profile
symmetry
The dose is highest at the ______ of a photon beam
central axis
A _____ isodose curve willl have an hourglass shape of the highest intensity isodose line
parallel opposed field
A ____ is the use of independent variable secondary collimator jaws moving during treatment
dynamic wedge
The reference desert for linear accelerators is
1 cGy/MU
Stereotactic radiosurgery utilizes
non-conplaner beams
A ______ method uses more than 4 fields with extensive blocking
conformal
The process of converting dose distribution to percent of a dose at some point is termed
normalization
Isodose distributions are _____ -dimensional representations of the spatial distribution of dose:
three
Wedge-field asides distributions are characterized by increased radiation intensity under the _____ of the wedge:
toe
IMRT is a treatment planning and delivery process that seeks to achieve treatment plan optimization by varying the _____intensity of the treatment beams in addition to their position
intensity
The quality of DRRs can be improved by _______the thickness of CT slices
decreasing
When an immobilization device is needed, it is best
first determine the beam orientation and then build the device
A lung boost is often delivered via
POP AP/PA with a midline block
Without adjustment of output factors, dose rates
increase with decreased field size and decrease with increased distance
A dose of 30000 cGy is to be delivered at a depth of 8cm at a percent depth dose of 76%. What is the dose to an organ at 14cm depth and a percent depth dose of 58%?
3000(.58)/(.76)= 2289
