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registry > Procedures Pt. 2 > Flashcards

Procedures Pt. 2 Flashcards

1
Q

3 major components incorporated into all CT sim scanners?

A

Gantry: contains the rotating x-ray tube, is essentially the circular “donut” into which the patient is inserted during the scan. (Aperture size-the size of the hole in which the pt. is positioned a.k.a. the bore size, is very important and usually 80-90cm). The Gantry includes the x-ray tube, the detector array, high voltage generator, slip ring, and the mechanical support devices.

Detectors-used to convert radiation to light

Couch-this is where the patient is positioned. it raises up and down and moves the patient in and out through the scanner bore.

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2
Q

common matrix size for CT sim

A

512x512 with a 262,144 pixels

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3
Q

CT sim shift method:

A

reference marks are placed on the patient before the CT scan in a location that is close to the desired treatment isocenter. After the scan the doctor contours the target volume and determines the tx isocenter coordinates. on the first day of tx the patient is positioned with the initial marks then shifted to the new location using calculated shifts from the tx plan. the new marks are the isocenter for tx

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4
Q

CT sim no-shift method:

A

pt is scanned and while the pt is still on the CT couch, images are reviewed by the physician and the tx isocenter is determined based on the areas contoured on the CT images. the isocenter is then programmed into moveable lasers then the patient is marked accordingly

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5
Q

techniques for isocenter localization

A

1) external skin fiducials 2) computing isocenter based on field border placement 3) placement of isocenter based on tx volume or contour information hat is GTV?

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6
Q

What is GTV?

A

Gross Target Volume - palpable or visible extent of tumor

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7
Q

What is CTV?

A

GTV (palpable or visible extent of tumor) plus margin for subclinical disease extension

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8
Q

What is PTV?

A

CTV (GTV (palpable or visible extent of tumor) plus margin for subclinical disease extension) plus margin for tx reproducibility (pt/organ movement, daily setup error)

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9
Q

Define Treatment Volume:

A

Volume enclosed by appropriate isodose in achieving the tx purpose

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10
Q

What does Inverse Square Law mean?

A

means that while distance is doubled, a quantity of radiation is spread over an area 4 times as great, thereby reducing the intensity of the beam in any area to 1/4 its original value.

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11
Q

What does the treatment record document?

A

delivery of treatments; displays fractional and cumulative doses, machine settings and verification imaging; and documents of the ordering and execution of prescribed changes

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12
Q

What does field arrangement depend on?

A

location of the tumor and nearby critical structures

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13
Q

What is the most basic multiple-field technique?

A

POP - parallel opposed portals

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14
Q

What does the hinge-angle parallel opposed fields equal?

A

180 degrees

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15
Q

How many angles do parallel opposed fields enter a pt?

A

any two angles i.e. right-and-left laterals, AP/PA, and obliques

180 degrees apart

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16
Q

What does AP/PA stand for?

A

anteroposterior and posteroanterior - a POP tx field technique

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17
Q

What are obliques?

A

anterior and posterior obliques - a POP tx field technique

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18
Q

What are right-and-left laterals?

A

two positions for a tx field that lie 180 degrees apart for a parallel opposed tx technique which would be on the right and left sides f the pt

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19
Q

What are tangential fields, tangents, or “tangs”?

A

opposing fields for superficial volumes on curved surfaces such as the breast or ribs which flash off the surface of the patients

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20
Q

what does the hinge angle for tangential fields vary between?

A

180-186 degrees

this is to accommodate divergence of the beams to create a coincident deep edge to the treated volume

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21
Q

What does the wedge-pair technique do?

A

changes the volume receiving radiation by decreasing the hinge angle between two tx fields. the relative dose in the area formed between the narrowing hinge-angle increases while the angle between the field pairs decrease

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22
Q

What do wedges do?

A

distribute the does more homogeneously throughout the target

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23
Q

What is the reason for multiple fields?

A

increases the dose where beams intersect and decreases the dose to surrounding tissues

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24
Q

T/F: Deep-seated tumors rely on increasing complexity of beam arrangements

A

True

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25
Q

What is the four-field technique? (aka four-field box or brick)

A

fields arranged 90 degrees from one another and generally require no more than beam shaping for optimal dose distribution in the target areas. commonly used in eep-seated tumors of the pelvis or abdomen

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26
Q

What demonstrates the ultimate multiple-field technique?

A

Arc Therapy

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27
Q

How is radiation delivered in standard arc therapy?

A

while the gantry moves through its arc of rotation, thus effectively delivering radiation through a continuous sequence of individual overlapping tx portals.

28
Q

How does conformal arc therapy reach the outermost ages of the target volume?

A

conformal arcs incorporate changing jaws in the dimension of the moving gantry to the outermost edges of the target volume

29
Q

What should be checked and completed before initiating the treatment beam in arc therapy?

A

verification of pt clearance; accessory medical equip.; tx table; and all stretchers, chairs, and stools must be completed

You should also be able to visualize the pt at all times during tx

30
Q

What does conformal therapy do?

A

applies three-dimensional localization of the tumor volume to the definition of tx fields

31
Q

What is the benefit of CT simulation?

A

tx planning systems can define beam directions which cannot be viewed w two-dimensional imaging

32
Q

How is divergence of the photon beam and bulging of electron dose distribution which poses a challenge for the alignment of adjacent tx fields resolved?
(areas of over or under dose are both of concern)

A

Abutting fields at the skins surface or at some depth with or without coplanar alignment of treatment-beam edges

33
Q

define coplanar:

A

in the same plane.

34
Q

What is the goal of radiation therapy tx planning?

A

to deliver an evenly distributed radiation dose to the target volume while minimizing the dose to surrounding normal tissue

35
Q

How is normal tissue protected?

A

by controlling beam direction and shape

36
Q

What is IMRT?

A

an advanced form of three-dimensional conformal tx planning that uses “inverse planning” techniques, in which the clinical objectives are specified first and a computer program is used to automatically determine the optimal beam parameters needed for the desired dose distribution

37
Q

IMRT requires a committed program for delivery, what does this consist of?

A

it is highly physics-intensive, requiring specially equipped accelerators and/or MLC units, inverse tx planning, and sophisticated dose measurement and QA tools including V & R systems to manage large and complex tx plans

38
Q

During IMRT, what is emphasized for tx delivery?

A

immobilization and setup verification

39
Q

What does IMRT stand for?

A

Intensity-Modulated Radiation Therapy

40
Q

What does BEV stand for? What is it?

A

Beam’s Eye View. viewpoint of the radiation beam as it travels from the radiation source

41
Q

Accelerators that use MLCs to produce IMRT treatments may apply either of two methods. What are they?

A

Segmental MLC or the step and shoot method

42
Q

What is the step and shoot and shoot IMRT method?

A

positions leaves of MLC in the first position, and the beam is initiated. while the first boomlet is delivered, the beam turns off, the accelerator moves the beams to the next position, turns the beam on and off, and so forth, proceeding through each leaf position until the tx is delivered

43
Q

With abutting or gapped, what may be used to blur dose inhomogeneities at a junction?

A

feathering

44
Q

What are beam modifiers?

A

devices that change the shape of the tx field or distribution of radiation at depth

45
Q

when is it necessary to use a gap?

A

abutting edges produce “hot” matches where beams overlap immediately below the surface. the area of overlap must be carefully evaluated for total dose tolerance. when an area of low dose is acceptable at and near the surface, adjacent fields may be separated by a calculated gap.

46
Q

What is SAD?

A

Source to Axis Distance - distance from the radiation source to the isocenter of the tx machine. when the gantry rotates around the pt, the SSD continually changes; however, the SAD is at a fixed distance and will not change (usually 100 cm)

47
Q

What is an isocentric SAD setup?

A

the isocenter is established at some reference point inside the pt. the gantry (source) rotates around this point (axis). since the field size is defined at the isocenter, the collimated field size is defined by the field size set inside the pt and not the field size on the skin surface as seen in the non-isocentric, SSD tx setup

(SAD = SSD + depth to isocenter)

48
Q

What is an advantage to SAD treatments?

A

once the isocenter for the tx has been established, there is no movement of the pt for ea of the subsequent tx fields. less movement between fields lowers the chance of tx errors because of positioning variations during pt movement

49
Q

What is SSD?

A

Source to Skin Distance. the distance from the radiation source to the patients skin, usually measured using a Optical Distance Indicator (ODI) or rangefinder

50
Q

What is a fixed SSD setup?

A

pt is treated using a fixed distance from the radiation source (usually 100 cm) to the patients skin surface. the pt must be moved to this same distance between ea tx

51
Q

What are the advantages of SSD treatments?

A

the ability to obtain a larger field size at a greater distance from the radiation source, and a slight increase in the percentage depth dose. the dose distribution in the pt becomes more homogenous from entrance to exit (increased % of rad within the pt relative to the % of the max entrance dose (Dmax)). However, at an increased distance it will take longer to get the same dose to a point in the pt.

52
Q

What does FOV stand for and mean?

A

Field of View

the max diameter of the area of the scan that can be seen in the reconstructed image

53
Q

What does DRR stand for and mean?

A

Digitally Reconstructed Radiograph
computer generated two-dimensional radiograph displaying skeletal anatomy rendered from a three-dimensional data set such as CT or MRI

54
Q

What is patient separation also referred to as? define it.

A

patient thickness. the measurement of pt thickness from the point of beam entry to the point of beam exit. separation can be measured directly using calipers or indirectly by using ODI (rangefinder) settings

55
Q

How do you measure pt thickness indirectly?

A

set 100 SSD to the surface of the skin and use a ruler to measure the distance from the top of the table to the lateral laser crossing at the skins surface

56
Q

What is inverse square?

A

a mathematical relationship that describes the change in beam intensity caused by the divergence of the beam. This is NOT a direct proportion like field size magnification because it takes into account the increased area of the beam opposed to the perimeter dimensions like field size.

— as the radiation beam diverges away from the source, the area increases and the intensity decreases

57
Q

__________ has a greater effect on radiation output than a change in field size

A

change in distance

58
Q

Define Mayneord’s Formula

A

a special application of inverse square that is rarely used in clinical practice. It approximates the new percentage depth dose for a change in distance from the source

59
Q

What is penumbra?

A

the area of decreased dose at the edge of the beam. It is the dose measured between the 20% and 80% isodose lines. Lower energy beams have more penumbra due to lateral scatter.

60
Q

What is Dmax?

A

Dose maximum - the depth of maximum build up where 100% of the dose is deposited. This is the depth of electronic equilibrium (amount of energy lost is equal to the energy gained)

61
Q

What is Mayneord’s F Formula used for?

A

can be used to estimate the change in percentage depth dose when the distance is either extended or shortened and the field size setting remains the same.

62
Q

What are some graphic representations of the dose from a radiation source?

A

beam profiles, percentage depth dose curves, and isodose curves

63
Q

What are beam profiles?

A

they illustrate radiation sensitivity across the beam at a given depth

64
Q

What are isodose curves?

A

they show the dose that is delivered at various depths across a beam. isodose lines connect points having the same dose

65
Q

Define machine output data:

A

referred to as the dose rate of the machine, it is the amount of radiation exposure produced by a tx machine using a specified reference field size (usually 10cmX10cm) at a specified reference distance(100 cm from the source) and in a specified material (usually phantom)

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