Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Residency > First Year Exam: CT Sim and Motion Management > Flashcards

First Year Exam: CT Sim and Motion Management Flashcards

1
Q

At what point in the pre-treatment workflow is isocenter set?

A

Treatment planning by dosimetry

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

How do therapists, on the day of treatment, know where isocenter is? Give the steps required to make this happen.

A
  1. Sim therapist marks user origin on patient using BBs
  2. Dosimetrist sets user origin on TPS
  3. Dosimetrist marks isocenter on TPS
  4. Dosimetrist provides therapists with couch shifts to go from user origin to new isocenter
  5. Therapists, on VSim day or first treatment, will make location of new isocenter on patient by moving patient using couch shifts and using lasers to mark new iso
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Give two scenarios in which it’s beneficial for dosimetry to set the isocenter, and not any therapists.

A
  1. Half beam blocking, only dosimetry will know where a half beam block has to occur. Of course HBB depends directly on location of isocenter, so dosi needs to set
  2. Wanting to use small MLCs to shape target
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What slice thicknesses do we use for…
HDR:
Stereotactics:
Everything else:

A

HDR: 0.625 mm
Stereotactics: 1 mm
Everything else: 2.5 mm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the main downside to using a smaller slice thickness?

A

You worsen low contrast resolution (since you’re reconstructing the same image but with less data per voxel)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the main benefit to using a smaller slice thickness?

A

Helps avoid volume averaging effects and gives more accurate spatial dose distribution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What measures higher spatial resolution, small or large FOV?

A

Small FOV

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

In one short sentence, what is pitch?

A

Amount of table movement per gantry rotation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What does a small pitch yield in terms of data and dose? What about a large pitch?

A

Small pitch: more data per slice, but also more dose
Large pitch: less data per slice, but also less dose

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the mA range used in CT?

A

10-800 mA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What image quality metric does mA affect?

A

contrast

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are 4 typical kVp’s used for CT sims? Which do we use in our clinic for all sims?

A

80, 100, 120, 140

We use 140 kVp in our clinic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the main difference in simming considerations for palliative vs curative treatments?

A

Palliative - sim with patient comfort as the main concern, we wan them to get through treatment reproducibly

Curative - sim with dosimetry in mind, because it’s higher dose and we need to focus more on getting the best delivery

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are the 5 most common CT artifacts?

A

Ring
Beam hardening
Streaking (or starvation)
Motion artifacts
Partial volume averaging

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What causes ring artifacts?

A

Bad detector that goes out of calibration and doesn’t properly record incoming data

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What does a beam hardening artifact look like? Why does it happen?

A

The effective energy of a beam changes with attenuation, leading to errors in attenuation coefficients and numbers

Appears as a region of low HU near bone or other large density. The beam in that region is hardened, so the soft tissue attenuates relatively less than it would if it weren’t hardened. The reconstruction algorithm then calculates a lower HU value

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What causes streaking artifacts?

A

Photon starvation due to complete beam attenuation from very high density material

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What causes partial volume averaging artifacts?

A

More than one tissue type in a CT slice becomes averaged into a single voxel, yielding an incorrect CT number

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How do you handle contrast in a CT?

A

Contour the contrast and override HU to set it to water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

In general, what is the function of contrast used in CT?

A

To either distend portions of the stomach, bowel or bladder, or to outline structures such as loops of bowell, vessels, and lymphatic system

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is the typical threshold suspected motion error used in our clinic that would warrant the use of motion management?

A

~1 cm

22
Q

How is an ITV drawn?

A

Using the maximum projection from the 4DCT

23
Q

Which CT do you play on for lungs?

A

average intensity projection, or free breathing

24
Q

What is a slow CT and how long does it usually take?

A

It’s a CT that’s used to scan slowly so there are multiple breathing cycles and it results in an average intensity projection

~60 seconds

25
Q

Describe the use of Inhale/Exhale CTs

A

You take a CT during inhale and exhale and you assume these are the sup/inf max and min to use for the MIP contour

26
Q

How is a breathing cycle established for 4DCT?

A

By placing an RPM block on the patient’s chest and tracking the vertical motion of the block

27
Q

How many bins (phases of breathing cycle) does a 4DCT take?

A

10

28
Q

If motion of target is < 1 cm, what does the physician use to contour lung target?

A

Physician contours on the 30% bin because it’s between inspiration and expiration (less movement)

29
Q

Which scan is used for treatment planning?

A

Average MIP

30
Q

When do you use minimum intensity projection?

A

Contouring liver target, where the tumor is the lowest HU value than the surrounding normal liver tissue

(unlike lung where it’s the opposite, so you use maximum)

31
Q

Why do some sites not do IMRT for lung treatments?

A

Tumor may modulate in and out of open and closed MLC areas. This can result in unintentionally hot or cold spots if the of the MLCs are missing or not

32
Q

Give a general description on how Calypso works

A

Used for target localization and/or tracking during treatment

3 tiny EM transponder beacons implanted into prostate

Emit signals when excited by non-ionizing EM field generated by array

Signal is triangulated like GPS

33
Q

What is the slant board weight limit?

A

300 lb

34
Q

What is the slant board used for?

A

Breast patients

35
Q

What is typical setup considerations/techniques for a prostate patient?

A

Full bladder
Empty rectum
Vacloc immobilization
(Possible use of calypso)

36
Q

When is a belly board used?

A

For prone rectal patients

37
Q

What are some parameters defined by a protocol in CT Sim? (I’ve got 8 listed)

A

Slice thickness

kVp

mA

mAs

FOV

Patient positioning

Types of contrast to use

Immobilization devices

38
Q

Should prostate patients have a full or empty bladder? Why?

A

Full bladder

39
Q

What is approximate motion of a lung tumor in the axial plane?

A

Within 2 mm

The vast majority of tumor motion in lung is superior/inferior, so it won’t show much in axial

40
Q

What is the upper end of dosimetric single fraction errors from IMRT or wedged plans?

What about throughout the course of a 30 fx treatment?

A

Single fraction - can be upwards of 20% error

30 fx - Errors average out and reduce to about 1-2%

41
Q

What is an “Interplay Effect”

A

An effect that occurs when two distinct timelines of motion are in effect simultaneously

An example of this is movement of MLCs in sliding window IMRT and movement of tumor

Interplay effects usually result in inhomogenous dose distributions

42
Q

What is the main benefit to using respiratory motion management?

A

You cand ecrease your treatment volume

43
Q

How are breast patients usually set up? (not prone breast)

A

Arm up on side being treated

Placed on an incline with slant board (300 lb limit)

Can be DIBH, 4D, or free breathing

44
Q

When a 4D scan is performed, what images/scans are actually usually taken?

A

Scout image

A free breathing CT without contrast

A free breathing CT with contrast

The 4DCT

45
Q

When the physicians come into CT sim, what are they usually reviewing?

A

Sometimes they review the scan itself, but not always

Most of the time they come in the review setup, immobilization, isocenter lcoation, and sign any notes that need to be signed (this is all mostly for billing purposes)

46
Q

In general, what sites of the body MIGHT you see motion management done for?

A

Thorax and Abdomen

They’re the most likely locations for respiratory motion

47
Q

At what expected tumor motion would you want to use respiratory motion management?

A

>= 5 mm suspected movement

48
Q

What is the general design of an AlignRT system?

A

Dual camera optical stereoscopic approach

Tracks a 3D contour

Consists of two pods

The pods have two cameras each, and one projector each

49
Q

What are some different types of non-radiographic systems? (4 major types, give the most commonly known example of each one) (think what we use in our clinic)

A

Radiofrequency (like Calypso)

Optical dual camera (like AlignRT)

Single camera (like RPM)

Infrared dual camera (like ExacTrac)

50
Q

Quickly: how does calypso work?

A

Small transponders (or beacons) are implanted in a body site

The beacons are alternating current circuits

An array of source coiuls produces an oscillating electromagnetic field which induces a resonance inside of the transponders

The decay of the resonant signal is detected by a second array of receiver coils

Triangulation is used to determine transponder location

51
Q

What systems are shown below?

A
52
Q

Does AlignRT utilize deformable or rigid registration?

A

Rigid

Residency (23 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions