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CSB069 > IGRT Technologies > Flashcards

IGRT Technologies Flashcards

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?

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
Q

What is the helical tomotherpay imaging?

A
  • 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
Q

What are the two models for CBCT projections?

A
  • full fan

- hald fun

27
Q

When is a full-fan used?

A
  • head region because of its narrow FOV
28
Q

What does CBCT allows?

A
  • daily iso localisation
  • monitor patient throughout treatment
  • can replan/adapt treatment depending on weight loss, disease progressio or response
29
Q

What is an imaging using electromagnetic transponders?

A
  • Calypso

- commonly for prostate but can be used for any site

30
Q

What are the pros of Calyso?

A
  • continous, real time monitoring of prostate

- non-ionizing = no additional radiation dose

31
Q

What are the cons of Calypso?

A
  • expense
  • training
  • not all patients suitable (abdomen measurment)
32
Q

What are the components of Calypso?

A
  • electromagnetic transponders
  • 4D electromagnetic array
  • 4D console
  • infrared cameas
  • 4D tracking system
33
Q

How do the electromagnetic transponders work?

A
  • permanently implanted in prostate priot to EBRT
  • transmits RF wave to calypso system
  • inactive until energised by calypso system
34
Q

How does the 4D electromagnetic array work?

A
  • electromagnetic energy source excties the Beacon transponders
  • recievers detect the transponder coordinates
35
Q

What happens when not using Calypso for VMAT?

A
  • 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
Q

Why is ultrasound not popular?

A
  • inaccurate treatment localisation
  • ultrasound probe pressure
  • inter-user variability
37
Q

What are the pros of ultrasound guidance?

A
  • 3D US is inexpensiv
  • non ionising
  • real time guidance method
38
Q

What is a 3D ultrasound guidance example?

A
  • Clarity

- US probe calibrated to same isocentre as CT system

39
Q

How does Clarity work?

A
  • 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
Q

What is BAT?

A
  • 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
Q

What sites are clairty and BAT used for?

A
  • breast (post-op cavity definition)

- prostate

42
Q

What are some cons of 3D ultrasound?

A
  • hard to incoroporate due to increased training time
43
Q

What is a form of optical tracking?

A
  • varian RPM
44
Q

What is the varian RPM?

A
  • non-invasive, video based system
  • uses an infrared tracking camera and a reflective marker array
  • relfectors act as surrogate for patients respiratory cycle
45
Q

What does the RPM measure?

A
  • the patient’s respiratory pattern and range of motion
46
Q

When is RPM used?

A
  • breath hold procedures

- lungs, liver, pancreas and breast

47
Q

What is optical surface imaging?

A
  • utilises two or three ceiling mounted 3D camera units, designed to image the patient at simulation or treatment
48
Q

How does alignRT work?

A
  • 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
Q

What is a con of alignRT?

A
  • no information on internal motion
50
Q

What is Halcyon?

A
  • multi-arc VMAT
  • 800MU/min dose rate
  • 6MV
  • 4 revolutions per min
  • flattening filter free
  • 100cm wide bore
51
Q

What is the IGRT for halycon?

A
  • 15 sec for kV-CBCT

- 7 sec for 2D MV image

52
Q

What is MRIdian system?

A
  • real time MRI guidance

- uses 3 cobalt sources for treament

53
Q

What is the advantage of MRI IGRT?

A
  • ability for treatment adaptation based on functional imaging
  • superior soft tissue contrast
54
Q

What is a challenge with MRI linac?

A
  • bore size if 70cm
  • increased complexity of imaging will impact clinical decision making
  • safety and QA implication
  • education for RO and RT
55
Q

What is the future of real time tracking?

A
  • MLC shape able to follow taret through IGRT
56
Q

What are the three frequency of IGRT?

A
  • periodic (weekly)
  • daily pre-treatment
  • real-time tracking
57
Q

What are the types of ionising IGRT?

A
  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
Q

What are the types of non-ionising IGRT?

A
  • Calypso
  • ultrasoud (Clarity and BAT)
  • optical surface imaging (Align RT)
  • MRI linac

CSB069 (7 decks)

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