Treatment & Planing (Exam 1) Flashcards by G T

2 parts of simuaiton

Localization & Verification

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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

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Final check that each of the planned treatment beams overs the tumor or target volume before actual first treatment and match up

Verification

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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

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Measurement of the thickness of a patient among the central axis.

Separation or Intrafield Distance (IFD)

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Distance to Isocenter is always 100cm

SSD

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Dimensions of the treatment field at isocenter, represented by width x length or length x width

Field Size

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Indicates the gross palpable or visible tumor

Gross Tumor Volume (GTV)

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Indicates the gross palpable or visible tumor and surrounding volume of tissue that may contain subclinical or microscopic disease.

Clinical Target Volume (CTV)

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Indicates the CTV plus margins for geometric uncertainties, such as patient motion, beam penumbra, and treatment setup differences.

Planning Target Volume (PTV)

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tumor & any other tissue with presumed tumor.

Target Volume (TV)

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encompasses additional margins around the target voume for limitations in treatment technique.

Treatment Volume

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volume of tissue receiving a significant dose >50% of specified target dose. Tissue in front of, behind, and around the target volume.

Irradiated volume

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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

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The backscatter factor is effected by

Quantity of radiation

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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

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The concept of tissue-air ratio (TAR) is most commonly employed for calculations involving.

SSD varying fields

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The depth of maximum ionization is most dependent on

Beam energy

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A 10 MV linear accelerator is used at 100cm SSD. The location of maximum dose is found at a depth of:

2.5cm

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Percentage depth dose increases with increasing

Energy and field size

Directly proportional with everything except Depth

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Tissue-air ratio decreases with decreasing

Field Size

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A wedge filter ________ the output of the beam and must thus be taken into account in the treatment calculations.

decreases

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%DD increases with increasing.

Energy and field size

Directly proportional with everything except Depth

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TAR decreases with decreasing

Field Size

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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

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.

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 _____ 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