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Radiotherapy Year 3 > Imaging > Flashcards

Imaging Flashcards

1
Q

What is the aim of 4D adaptive radiotherapy

A

Continually adapt and reoptimise the plan (using IGRT information to establish tumour dose and OAR dose regularly)

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2
Q

What are the categories of IGRT

A

Simple (don’t require serial imaging, gross error check on fraction 1)
Complex (involve serial imaging for systematic error correction)
Adaptive (involving image acquisition so position of field can be changed at time of treatment)

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3
Q

What are the four types of dosimetric adaptation?

A

Scheduled ART
Reactive ART
Proactive ART
Real time ART

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4
Q

What is scheduled ART and an example

A

Replanning is scheduled in advance for predictable or likely changes
Pre-scheduled repeat scan is booked for H&N patients where weight loss is expected

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5
Q

What is reactive ART and an example

A

Acts on observed changes detected during imaging during treatment
Change in patient shape is observed and repeat planning CT is acquired

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6
Q

What is proactive ART and an example

A

Predicts changes likely to occur and prepares a choice of plans (library) to compensate

Bladder radiotherapy: create a number of plans with PTVs of different sizes for different bladder filling

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7
Q

What is real time ART and an example

A

Creates and delivers a new plan online while the patient is in the treatment position
VIEWRAY MRIdian

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8
Q

What do we need to consider for adaptive planning in general?

A

CTV includes sub clinical disease: how can we be sure we are still treating disease we cannot see?

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9
Q

What do we need to consider in reactive ART?

A

Is the dose to targets too high or low, is the dose to critical structures too high
Consider dosimetric, clinical, and patient specific factors

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10
Q

What are issues with plan of the day?

A

What about bladder filling during treatment?
Increased workload of 6 plans per patient - do you QA them all?
How many fractions do you allow of each plan?
How are you sure you are treating on intended plan?

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11
Q

What are the two main types of motion management?

A

Active and passive
Passive accepts that motion exists, attempts to quantify range of motion, creates treatment to incorporate movement prior to delivery

Active could reduce amount of motion, or use real time tracking, or adapt throughout treatment

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12
Q

What is an example of passive motion management?

A

Acquiring a 4D free breathing CT
Delineating ITV across 4DCT
Delivering treatment with free breathing

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13
Q

What are examples of active motion management?

A

Compression
Gated delivery or breath hold
Tracking

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14
Q

Considerations of compression

A

Treatment delivery is not interupted
Reproducibility may be a problem
Patient compliance may be an issue

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15
Q

Considerations of gated delivery or breath hold

A

Reduced duty cycle
Extended beam on time
Minimising breathing motion but increasing possibility of postural changes
Patient compliance

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16
Q

Considerations of using tracking

A

Beam on throughout
Relies on accurate prediction model
Relies on verification during delivery

17
Q

Name some respiratory measuring systems

A

ANZAI
Pressure sensor in elastic belt around diaphragm

Varian RGSC/RPM
Small marker acts as surrogate of breathing motion using IR/visible light camera

C-RAD
Optical surface scanning with no fiducials or markers, can be used to assist patient posture correction

18
Q

What is the most reproducible breath hold position?

A

Full exhale

19
Q

How does scan impact what is seen on CT?

A

CT will capture tumour at random point
PET will capture a time averaged tumour position
4DCT captures entire movement
Breath hold captures tumour at extreme position but is not going to have motion related artifacts and will have most true tumour shape and size

20
Q

What is prospective gating?

A

CT acquisition is only gathered during a defined interval of breathing cycle (acquisition is gated)

21
Q

What is retrospective gating and what are the main types?

A

Data is retrospectively binned into phases, overlapping spirals are acquired, slow CT scan
Bin size is independent of number of bins

Amplitude binning and phase binning

22
Q

What are the drawbacks of retrospective gating?

A

Imaging dose is much higher than comparable 3DCT
Automatic dose control may not be available
Limitations on scan lengths
Imaging anatomy outside of CTs normal FoV may not be possible

23
Q

Is amplitude or phase binning better?

A

Amplitude shows fewer artefacts and is more accurate
Phase is better for reconstruction of peaks

24
Q

What are the challenges of 4D image acquisition?

A

Single movie loop visualisation, is it representative of breathing cycle
Has the surrogate modified the breathing behaviour

25
Q

What are some common 4DCT arefacts

A

Duplication of anatomy due to significant change in amplitude of breathing
Missing data - interpolated between points because no discernible points of data
‘Step’ artefact - system assumes linear breathing but patient is not breathing as expected

26
Q

How does gated RT work?

A

Minimise motion by only treating in certain parts of breathing cycle
Acquire a 4DCT over the entire cycle, assess motion, select phases of 4DCT for planning to restrict motion
Reduces volume to be treated, but requires very regular breathing, audio coaching

27
Q

What is the aim of abdominal compression

A

Restrict motion of the diaphragm and related respiratory motion
Note that frames alone are not sufficient for localisation: need IGRT

28
Q

Why use DIBH

A

Reduces movement, creates more space between heart and breast
Patient holds breath for about 20 seconds, requires coaching, acquire 3DCT in BH

29
Q

What imaging dataset do you want to match to a CBCT?

A

AvIP will have most similar appearance to CBCT, as CBCT averaged over many breathing cycles
Verify passive management with AvIP

30
Q

How would you do real time verification and is it always appropriate?

A

Use 2D MV port during treatment
Not always appropriate: depends on location, tumour size, density which all impact contrast

31
Q

How would you do verification when using compression devices?

A

Same as passive management because it is via physical restriction
Advantageous if TT are quick

32
Q

How would you verify DIBH?

A

Compare reference breathing trace with measurement on day, should be consistent
Triggered 2D imaging in breath hold to verify and correct position
Patient visual feedback helps

33
Q

How would you do verification for gating

A

Compare reference breathing trace with measurment on day
CBCT to set up anatomy and check motion
Trigered 2D imaging on entry and exit from gated window
Fluoro to assess tumour motion

Radiotherapy Year 3 (8 decks)

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