Finals Material Flashcards
What do the initials in the following acronyms stands for:
GTV, CTV, PTV
GTV: gross tumors volume
CTV: clinical target volume
PTV: plan target volume
Which term/acronym is the volume which accounts for organ movement and setup uncertainties
PTV
This type of technique gives the shape of a diamond
“crossfire” technique which is 2Ap obliques and 2 PA obliques
2 EQUALLY weighted parallel opposed AP-PA fields will give a shape of :
An hour glass
AP-PA and a right and left laterals are nicknamed what
4 field “box” or “brick”
Prior to the availability of IMRT- a technique using AP,RPO, LPO fields were frequently used to treat what area
Cervical esophagus
A 3 field recital cease use PA and right and left laterals with wedges. The wedges should be placed with the ______ towards the posterior of the patient’s anatomy
Heel towards the posterior of the patient anatomy
A wedge technique may be used on breast tangents. To compensate for the slope of the breast, where would the heel of the wedge be placed
Towards the nipple
Name the technique which was used for ovarian cancer- total abdomen, pelvis, and sub diaphragmatic lymph nodes
Moving strip technique
Next the 2 factors which affect the Roentgen to cGy conversion factor
Density of the irradiated material (Z)
Energy of the beam
Lines that connect points of equal dose are called
Isodose curves
Name any 2 factors which affect the shape of the isodose chart
Field size
Beam energy
The point which is labeled 100% on an isodose chart is called
Normalization point
The point labeled 100% for a treatment which uses MORE THAN ONE BEAM (FIELD) is generally placed where
At the isocenter
What is the most accurate method to measure a radiation beam and create an isodose chart
Ionization chamber
The rapid fall off of dose at the edge of the beam is called
Penumbra
Formula for TAR
TAR= TAR0 + SAR
When doing the clarkson calculation on a blocked field, which part of the TAR value is being “adjusted”
(Sc) for the lack of scatter
TARo denotes the tissue air ratio value for field 0x0. This field size indicates the field from the portion of the beam created when the electrons hit the target. This is called the _____ beam
Primary
The blocked equivalent square can also be called
Effective field size
Write the 3 metals which makes up the Thoreaus filter in order from the tube to the patient
Tin (Sn), Cooper (Cu), Aluminum (Al).
Tissue air ratio (TAR) at Dmax is also known as
Back scatter factor
TAR is NOT dependent on
SSD
When using either TAR or TMR for monitor unit calculations, the field size and machine output are measured at what distance
100 cm- SAD
The ratio of dose at depth compared to the dose at Dmax when bOTH measurements are take at the same distance from the radiation is defined as
TMR- tissue maximum ration
Cherry end is a lead alloy and consists of what 4 metals
Lead, tin, bismuth, and cadiminum
In order to ensure adequate shielding of normal tissue s, the thickness of a block or MLC must be at least how many HVL thick
5 HVL thick
If the treatment is given through a “hole”, in the block, like an electron cutout, this type of block is called
A negative block
If the Gantry rotates 360 while the radiation beam in on, this type of treatment is called
Rotational therapy
Name the radiation field which treats the lymph nodes ABOVE the diaphragm
Mantle field
How many centimeters of cerobend are needed to have the Same shielding ability as 1cm of pure lead
1.25
Name the machine which uses Thoreaus filter
Orthovoltage machine
PDD compares the dose at some depth to the dose at ___
Dmax
Sc and Sp correct for the change in scatter when the field size is different than the reference field size. What is the reference field size?
10x10
Sc is _____ than 1 when the treatment field size is larger than the reference field size
Greater than
Sp is ____ than 1 when the treatment field size is smaller than the reference field size
Lesser than
When using PDD to calculate the correct number of MU to deliver the prescribe tumor dose, the machine output (aka reference dose rate) used must be know at what distance from the radiation source?
Treatments SSD and Dmax depth
Field size will ____ as PDD increase
FS increase as PDD increase
PDD ____ as you go deeper into the patient
Decreases
When using PDD to calculate the correct number of MU to deliver a prescribe dose, where is the field size measured
On the skin surface
The PDD value at Dmax for any field size ,beam energy, or SSD is equal to
100% or 1
As beam energy increases, what happens to PDD
Energy increase, PDD increases
As field size increase, what happens to PDD
FS increase, PDD increase
As SSD increase, what happens to PDD
SSD increase,PDD increase
As you go deeper into the patient, what happens to PDD
Deeper, PDD decrease
Mayneord factor is an application of which law
Inverse square law
When would you use sterling formula (aka equivalent square)
When the treatment fields are not square field size. So this is an estimate of a rectangle to a square
If the SSD decreases, how would this affect the back scatter factor
SSD does NOT affect BSF
List in order from the MOST to the LEAST penetrating beam machine
(Gorillas Can Swing Over Short Mountains)
Megavoltage - MOST Supervoltage Orthovoltage Superficial Contact Grenz Ray
Which machine type uses 10-15kVp beam
Grenz Ray
Which machine toe measured its HVL in millimeters of Copper
Orthovoltage
Which machine type uses beam energy greater than or equal to 1000kVp
Megavoltage
This is the intersection point of the Collimator axis and the gantry axis of rotation
Isocenter
Unit of exposure in air
Roentgen (R)
This distance between the patient skin and the depth of max ionization (Dmax) is called
The build up region
Tissue equivalent material is called Bolus. Examples includes
Wax
Superfluous
Water
The most frequently used beam modifying device is
Wedges
The standard range of wedge angle is from ___ to ____
15 degrees to 60 degrees
When the upper Collimator moves during the treatment and gives a “wedge effect”. This type of wedge is called
EDW- enhance dynamic wedge
Name the type of wedge which is generally used on a Cobalt 60, where it’s toe is aligned at the field edge and there is a separate wedge for each field width
Individual wedge
In order to Make up for the lack of tissue and maintain skin sparring, what can be used to account for a sloping skin surface
Compensators or wedges
The area where there is a lack of tissue is called
Air gap
Identify the factor which adjusts the PDD when the treatment SSD is different than the SSD used to measure PDD table
The Mayneord Factor (F)
” f “ factor is the roentgen to cGy conversion factor and is affected by
Density of irradiated material
Beam energy
How do you calculate dose using “ f” factor
(Exposure R)(f of the material)
Point where maximum absorb dose occurs for a single photon field
Dmax
What is the Dmax for cobalt 60
0.5cm
What is the Dmax for 6MV
1.5cm
What is the Dmax for 10Mv
2.5cm
What is the Dmax for 18Mv
3.5cm
Dmax is affected primarily by
Beam energy
Dmax occurs at the _____ for low energy
At the skin surface
Dmax occurs _____ for high energy
Beneath the skin surface
The distance between the patient skin surface and Dmax
Build up region
Blade pairs capable of independent movement
Asymmetrical jaws
PDD field size is measured on the
Skin
The amount of radiation coming from the machine at a specific distance
Reference dose rate
(Roentgen)x(BSF)x(“f” factor) is the machine output for
Low energy machines like orthovoltage
Amount of radiation scattered “back”, adding to the skin dose
Back scatter factor
For energies with HVL greater than 1mmCu, BSF
Decreases due to more forward scatter
Increase in FS cause an ______ in BSF
Increase FS cause increase n BSF due to more tissue being covered
The Mayneord factor is used when
There is a change in SSD
As FS increase, TAR
Increase
As energy increase, TAR
Increase
As you go deeper into the patient, TAR
Decrease due to moving further away from the source
As SSD increase, TAR
Is not affected. SSD does it change TAR
Blocks must be at least _____ thick to allow for less than 5% transmission
5HVL
Cerrobend is made of
Bacon, lettuce, tomato with cheese
Bismuth
Lead
Tin
Cadmium
Main advantage of cerobend
Low melting point
Divergent blocks have ____ edges
Slanted edges
Non divergent blocks have ___ edges
Non slanted edges
Positive block treats ____
Around.
Negative blocks treats _____
Through the hole
This technique is used to treat BELOW the diaphragm
Inverted Y
Clarkson calculation is also called
Irregular field calculation
Clarkson calculation is done for
Calculation to correct for the lack of scatter due to blocking
Isodose curves is measured by
Radiographic films
Solid sta detectors (TLD )
Ion chamber (most reliable)
Factors affecting isodose charts
Energy
FS
SSD
Source size
For a single field, the normalization point is placed at
Dmax
For multiple fields, the normalization point is placed at
The isocenter
Isodose shift methods is used for
Sloping skin surface
MLC and cerobend modify the ____ of the beam
Shape of the beam
Wedges modify the ____ of the beam
Shape of the beam and changes the whole isodose chart
Angle through which an isodose curve is tilted at the central Ray of the beam
Wedge angle
90- (.5hinge)
Angle between the central Ray of 2 beams
Hinge
180- (2 x wedge)
Type of wedge that accommodates all field size
Universal wedge
Contours are measurements of the patient both ____ and ____
Internally and externally
The most accurate method of obtaining a patient contour
CT Scan
