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CSB094 PLANNING > DCAT > Flashcards

DCAT Flashcards

1
Q

How to solve motion problems

A

Treat patients faster
Motion management

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2
Q

What kind of motion can be controlled by 4DCT

A

Intrafractional motion

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3
Q

Why do we reduce motion

A

Tumour margins could be reduced
- OAR / Normal tissue sparing can be improved
- Potentially dose escalate
- Improve clinical outcomes

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4
Q

Motion management solutions

A

Enhanced immobilisation
Respiratory management
4D imaging

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5
Q

4DCT

A
  • Respiratory cycle correlated CT Scan
  • Acquisition of multiple images at slice positions, each image tagged with breathing signal
  • Images are sorted based on breathing
    signal
  • full tumour trajectory tracking
  • DICOM exported to TPS
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6
Q

ITV

A

The range where tumour can be due to motion
Overall target is still large but it is not irradiating as much normal tissue as normal PTV

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7
Q

Cine view

A

The Cine View gives a simulation of the tumour
and the tissues that move as the patient breathes
* You can select the image sets that are in the cine and change the orientation of the image
* This view is available for transverse, sagittal and coronal slices

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8
Q

How to create ITV

A
  1. Drawing on individual image sets: takes long
    - Combining all phase based GTV with Automargin
  2. Using Specialty Imagesets
    - Maximum Intensity Projection (MIP)
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9
Q

Lowest diaphragm

A

Inhalation

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10
Q

Specialty image pixel values

A

MIP Maximum Intensity Projection
- MinIP Minimum Intensity Projection
- AvgIP Average Intensity Projection

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11
Q

MIP

A

Maximum Intensity Projection:

  • Displays the maximum CT number of all the pixels at the same spatial location over the
    respiratory cycle
  • Basically shows entire extent of tumour motion/trajectory
  • Use with caution for tumours close to the diaphragm or chest wall: anatomically misrepresent
  • brighter as it is taking higher intensity
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12
Q

MIP challenges

A

Sometimes difficult to define edge
For e.g.- tumours may seem like it is attached to the diaphragm when in reality it is not

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13
Q

MiniIp

A

Minimum Intensity Projection:
- Displays the minimum CT number of all the pixels at the same spatial location over the
respiratory cycle
- Basically shows where some part of the tumour is always present throughout respiration
- Useful for liver tumours that present as low density areas
- shows where the tumour is (100% of the time it is there)

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14
Q

AvgIP

A

Average Intensity Projection:
- Displays the average CT number of all the pixels at the same spatial location over the respiratory cycle.
- Considered to be appropriate for use as the
treatment planning CT
* Reducing the need for an additional planning scan
* Lowering radiation exposure to patient

Used for treatment planning

Reduces radiation exposure as an additional image is not required

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15
Q

What happens if planned on MIP or MINIP

A

More MU as more modulation would be required for OAR constraints

Deeper depth and more deposition of energy
Maximum dose for MIP is much lower
Most variation of dose on skin

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16
Q

What is DCAT

A

DCAT is similar to VMAT as the treatment is delivered continuously as the
gantry rotates around the patient, but without segments dissecting the target
User defines: gantry start and stop, couch and Colli, relative weighting for arcs, constant dose rate

17
Q

Why DCAT

A

DCAT is similar to VMAT but without segments dissecting the target, mitigating the mLC interplay effect

Is better for lung as it is a moving target which sometimes be missed due to MLC interplay of VMAT

18
Q

DCAT advantages

A

Differing control points - oar sparing
Conformality
Variable dose rate
Variable target margin
Accounts for motion
Faster
Maximise dose rate
Most robust

19
Q

DCAT disadvantages

A

Only suitable for simple targets
More central and spherical in shape
Worse dose distribution

20
Q

How is interfractional motion controlled for lung treatments

A

Adaptive RT

21
Q

Which bin indicates max exhale

A

10th bin

22
Q

Treatment considerations

A

Motion:
- physiological movements - respiration and cardiac motion (systematic)
- Uncontrollable movements - swallowing, coughing (random)

Imaging artefacts:
- lengthen/shorten apparent targets
- target displacement: gaps in image

Dose delivery artefacts

Increasing target volume sizes
- increased treatment portal sizes
-increased OAR and normal tissue irradiation

CSB094 PLANNING (8 decks)

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