Final Flashcards
Visible mass to include lymphadenopathy and metastasis
GTV
Subclinical malignant disease
CTV
To include all geometric variations (ITV+SM)
PTV
Volume to include motion (CTV+IM)
ITV
Normal tissue at risk of radiation damage
OAR
Tissue that receives a dose that is considered significant in relation to normal tissue tolerance
IrV
Isodose levels are modified by changing the energy, field size, beam arrangements, and beam modifiers to produce a desired dose distribution.
True
As source size increases the Penumbra
Increases
As SSD increases the penumbra
Increases
As SDD increase the Penumbra
Decreases
Some MLC’s create a lot of penumbra when the leaves are mounted on diverging carriages
False
What is the most often used type of DVH graph?
Cumulative
Which DVH graphs the volume of a structure receiving dose within a specified dose interval?
Differential
Normalization point is the point chosen by the planner where the ____% Isodose line is placed
100%
Which energy would give the most skin sparring?
18MV
Does dose falloff more rapidly with photons or electrons?
electrons
Does using more beams result in better homogeneity or worse homogeneity?
Better
Cerrobend blocks have more field conformality than MLC’s due to the
MLC leaf size
Single field treatment techniques are usually used for this type of treatment
T-Spine
A disadvantage of a parallel opposed treatment planning technique is
entry and exit dose
An advantage of using a four field technique is
max dose decreases
What does VMAT stand for?
Volumetric modulated arc therapy
A commonly used treatment site that uses a matching field technique is
craniospinal
The angle through which an isodose curve is tilted at the central ray of a beam at specified depth(usually 10cm) is called the
wedge angle
The wedge factor is the ratio of the doses with and without the wedge inserted at a specified depth.
True
Which type of wedge uses the motion of the collimator jaw or leaves during treatment delivery to modify the dose distribution.
Enhanced dynamic wedge
MLC’s can create island blocks. T or F
False
Cerrobend blocks are composed of
Pb, tin, cadmium, bismuth
The melting point for cerrobend is.
158 degrees
What type of beam modifiers can be used to address tissue irregularities for sloping surfaces but today can also be used for tissue inhomogeneities inside the body
Compensators
Bolus is used primarily to
Bring dose to the surface for treating superficial lesions.
As electrons energy increases, skin dose
Increases
Energy/2
Practical range
Energy/3
80% isodose line
Energy/4
90% isodose line
Pb cutout thickness for on skin electron blocking should be at least
MeV/2 in mm of Pb
Data registration and fusion are geometric alignment of images with one another. T or F
True
Axial scanning provides better resolution but helical scanning is faster and delivers less dose. T or F
True
CT scans are used to create DRR’s. T or F
True
PET scans provide information about physiology rather than anatomy. T or F
True
Most common PET radionuclide is
FDG (fluorodeoxyglucose)
What are the 2 main types of image registrations?
Rigid and deformable
What is the main advantage for using deformable registration
patient position does not have to be the same
What best describes an IMRT Treatment?
Delivers non uniform fluence from different beams angles to generate a non uniform dose distribution
IMRT planning assigns non uniform intensities or weights to small subdivisions of beams referred to as:
Beamlets
IMRT is delivered most commonly using
MLC’s
When treating using IMRT and using a step and shoot technique the leaves do not move when the beam is on. T or F
True
When treating using VMAT technique radiation is delivered to the target while simultaneously moving the MLC’s and the gantry. T or F.
True
SRS treatment is usually given in 5 fractions. T or F
False
Isodose levels are modified by changing the energy, field size, beam arrangements, beam modifiers, etc., to produce a desired dose distribution
Isodose Distribution
Isodose levels are lines that pass-through points of equal dose expressed as a % relative to a reference point
Isodose Level Parameters
Two-dimensional graph showing dose delivered to volumes of interest.
Dose Volume Histogram, (DVH)
(Most often used) graphs the volume(in the y-axis that receives the corresponding dose or more in the x-axis
Cumulative DVH
Graphs the volume of a structure receiving dose within a specified dose interval
Differential DVH
Cerrobend blocks have more field conformality than MLC’s due to the leaf size. T or F.
True
Desired modification in the spatial distribution of radiation by insertion of any material in the beam path
Beam modifiers
Eliminates radiation dose to certain parts of an area where the beam is directed
Shielding
Allows normal dose to certain parts of an area where the beam is directed
Compensation
allows for a tilt in the radiation isodose curves
Wedge
Where the distribution of the beam is altered by reducing the central exposure area relative to the peripheral
Flattening
Wedges are commonly made of
Pb or Steel
Angle between isodose curve and central axis
Wedge angle
Ratio of doses with and without the wedge inserted at a specified depth
Wedge factor
Disadvantages of MLC’s include
Island blocking
Jagged field boundary
Field matching difficult
Penumbra is larger
Cerrobend blocks composed of
Bismuth, cadmium, lead, and tin
Used to bring dose to the surface for treating superficial lesions
Bolus
