CSB069 > IGRT Technologies > Flashcards

IGRT Technologies Flashcards

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1
Q

What is image guidance?

A
  • IGRT involves any use of imagnig to aid decision making
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2
Q

What is the main IGRT decision in RT?

A
  • whether to treat and how and when to treat

- confidence in accuracey of treatment delivery is crucial in the decision making process

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3
Q

What is the goal of RT?

A
  • goal to maximise the therapeutic ratio
  • deliver tumourcidal dose to target
  • minimise dose to OAR
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4
Q

Why do we use IGRT?

A
  • reduce PTV margins
  • reduce setup errors
  • account for organ motion
  • increase accuracey of beam placement
  • increase precision of dose delivery
  • lead to reduced toxicity
  • permit dose escalation
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5
Q

What is the clinical benefit of IGRT for prostate?

A
  • significant reduction in late urinary toxicitiy
  • no difference in PSA relapse-free surivial
  • high risk patients, significant improvment was obseved at 3 years
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6
Q

What are the IGRT technologies?

A
  • planar
  • volumetric
  • non-ionising
  • new technologies
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7
Q

What is planar MV imaging?

A
  • portal imaging
  • projection using treament beam
  • used for setup pre-treatment target verification
  • low contrast between soft tissue and bone
  • useful for soft-tissue/air interface
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8
Q

What are the types of MV imaging?

A
  • liquid ion chamber EPID

- a silicone EPID

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9
Q

What sites if MV still used?

A
  • whole brain
  • breast
  • MLC shape verification
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10
Q

What are the cons of kV imaging?

A
  • more expensive then MV

- requires additional linac hardware

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11
Q

What are the pros of kV imaging?

A
  • better resolution and constrast then MV
  • lower imaging dose
  • similar workflow to MV
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12
Q

What are fiducial and why are they used for prostate?

A
  • small gold seeds

- surrogate for prostate and allows physicians to overcome bladder and rectal filling and patient motion

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13
Q

What are pros of fiducials?

A
  • surrogate of prostate motion
  • fast method of localisation
  • staff have great confidence when aligning (low intra and inter-observer variability)
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14
Q

What are the cons of fidicuals?

A
  • expense
  • invasive procedure and risk of infection
  • some patients ineligible e.g. warfarin dependency
  • rely of three discrite points to localise prostate
  • evaluation of nearby organs and deformation of target is difficult
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15
Q

What is the imaging for CK?

A
  • two ceiling mounted KC sources

- two floor-mounted aSi detectors

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16
Q

What is the exactrac imaging?

A
  • two floor mounted kV source
  • two ceiling-mounted aSi detectors
  • available add on to linac
  • allows frameless radiosurgery
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17
Q

What are the differences between CK and exactrac imaging?

A
  • CK kV source on ceiling where as ET kV source in floor

- CK imaging every 15 seconds where as ET imaging when floor is rotated

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18
Q

What is the imaging for VERO SBRT?

A
  • ring gantry similar to tomo but gantry and couch can move unlike tomo
  • MV source (unrestricted imaging angles) and kV source
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19
Q

How many sources can be used with VERO imaging?

A
  • can do MV or MVCT with one source but two gives better quality
  • best for movable tumours but can be used for all parts of body
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20
Q

What are the in room CT technologies

A
  1. fan beam:
    - CT on rails
    - tomotherapy
  2. cone beam
    - CBCT (kV)
    - MVCT (MV)
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21
Q

What is CT on rails?

A
  • diagnostic CT directly opposite
  • single couch for both gantries as couch rotates between the linac and CT
  • CT slides over patient
  • assumes fixed relationship between the isocentre of CT and linac
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22
Q

Why is CT-on-rails no used in AUS?

A
  • expensive and significant decrease in departmental efficiency
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23
Q

What is the workflow of CT on rails?

A
  • patient setup on CT couch
  • CT scan done
  • table rotated 180 degrees
  • patient positioned at treatment iso
  • CT reviewed
  • table adjusted
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24
Q

What is the comparison between CT on rails and CBCT?

Study These Flashcards
A
  • couch sag occurs at CT on rails gantry which can’t be corrected
  • image quality better for CT on rails
  • time lag between image aquisition and treatment increases organ motion (prostate)
25
What is the helical tomotherpay imaging?
- MV source placed on ring gantry - MV fan beam - provides less tissue contrast then kV CT but less artefacts for high atomic material - dose higher then CBCT
26
What are the two models for CBCT projections?
- full fan | - hald fun
27
When is a full-fan used?
- head region because of its narrow FOV
28
What does CBCT allows?
- daily iso localisation - monitor patient throughout treatment - can replan/adapt treatment depending on weight loss, disease progressio or response
29
What is an imaging using electromagnetic transponders?
- Calypso | - commonly for prostate but can be used for any site
30
What are the pros of Calyso?
- continous, real time monitoring of prostate | - non-ionizing = no additional radiation dose
31
What are the cons of Calypso?
- expense - training - not all patients suitable (abdomen measurment)
32
What are the components of Calypso?
- electromagnetic transponders - 4D electromagnetic array - 4D console - infrared cameas - 4D tracking system
33
How do the electromagnetic transponders work?
- permanently implanted in prostate priot to EBRT - transmits RF wave to calypso system - inactive until energised by calypso system
34
How does the 4D electromagnetic array work?
- electromagnetic energy source excties the Beacon transponders - recievers detect the transponder coordinates
35
What happens when not using Calypso for VMAT?
- rapid, high dose rate treamtne that may miss target - motion doesnt stop once the arc begins - target position at setup doesn't always translate to target position during treatment
36
Why is ultrasound not popular?
- inaccurate treatment localisation - ultrasound probe pressure - inter-user variability
37
What are the pros of ultrasound guidance?
- 3D US is inexpensiv - non ionising - real time guidance method
38
What is a 3D ultrasound guidance example?
- Clarity | - US probe calibrated to same isocentre as CT system
39
How does Clarity work?
- serie of relfective markers used to track its position in space - enables the volumtric US image to be automatically fused with planning CT - provides additional info for contouring - no extra appointment time needed
40
What is BAT?
- 3D ultrasound used for patient alginment in treatment room - required 90 seconds for scanning and repositioning - treatment couch position tracked using same system as US probe
41
What sites are clairty and BAT used for?
- breast (post-op cavity definition) | - prostate
42
What are some cons of 3D ultrasound?
- hard to incoroporate due to increased training time
43
What is a form of optical tracking?
- varian RPM
44
What is the varian RPM?
- non-invasive, video based system - uses an infrared tracking camera and a reflective marker array - relfectors act as surrogate for patients respiratory cycle
45
What does the RPM measure?
- the patient's respiratory pattern and range of motion
46
When is RPM used?
- breath hold procedures | - lungs, liver, pancreas and breast
47
What is optical surface imaging?
- utilises two or three ceiling mounted 3D camera units, designed to image the patient at simulation or treatment
48
How does alignRT work?
- reference surface model is produced by importing controus from CT data or acquired 3D surface at sim - each treatment fraction, system verifies patient posiiton - couch shifts calculated to correct for inconsistencies between actual and planned positions
49
What is a con of alignRT?
- no information on internal motion
50
What is Halcyon?
- multi-arc VMAT - 800MU/min dose rate - 6MV - 4 revolutions per min - flattening filter free - 100cm wide bore
51
What is the IGRT for halycon?
- 15 sec for kV-CBCT | - 7 sec for 2D MV image
52
What is MRIdian system?
- real time MRI guidance | - uses 3 cobalt sources for treament
53
What is the advantage of MRI IGRT?
- ability for treatment adaptation based on functional imaging - superior soft tissue contrast
54
What is a challenge with MRI linac?
- bore size if 70cm - increased complexity of imaging will impact clinical decision making - safety and QA implication - education for RO and RT
55
What is the future of real time tracking?
- MLC shape able to follow taret through IGRT
56
What are the three frequency of IGRT?
- periodic (weekly) - daily pre-treatment - real-time tracking
57
What are the types of ionising IGRT?
1. Linac - MV - kV/CBCT - fiducial based 2. CK and exactrac - kV 3. Tomo - MVCT 4. VERO - MV - kV - CBCT 5. CT on rails 6. Halcyon - CBCT - MV
58
What are the types of non-ionising IGRT?
- Calypso - ultrasoud (Clarity and BAT) - optical surface imaging (Align RT) - MRI linac
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