Image Guided Radiotherapy in Urological Cancers

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Image Guided Radiotherapy in Urological Cancers

• Dr Ann Henry
• Consultant Clinical Oncologist
• Cookridge Hospital, Leeds

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Overview

• What is Image guided radiotherapy
• What IGRT technologies are available and how do
  you make a choice
• How is it being implemented clinically
• What are the implications for the management of
  urological cancers

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DIAGNOSIS

IMAGING
VERIFICATION

The
Radiotherapy
CANCER STAGING

XRT DELIVERY
Chain
TARGET VOLUME DEFINITION
SIMULATION

PLANNING
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3D conformal treatment planning
Conformal XRT Delivery
Current 2D verification
3D IGRT
EPID bony landmark verification
Actual target volume verification
Patient re-positioning to compensate for
geometric errors
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What is driving IGRT ?

• Technological developments
• Increased awareness of set-up and internal organ
  motion errors
• Introduction of more conformal treatments i.e.
  IMRT and dose escalation
• Trend to hypo-fractionation, particularly
  prostate XRT
• Current verification based on 2D bony landmarks
  inadequate

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IGRT Available Technology

• Implanted markers and EPID
• Ultrasound e.g. BAT and Sonarray systems
• CT on rails e.g. Siemens Primatom system
• kV imager on linac gantry e.g. Elekta Synergy,
  Varian On Board Imager (OBI)
• Linac integrated into ring gantry of MV CT
  scanner e.g. TomoTherapy Hi-Art system
• Linac on robotic arm e.g. Cyberknife

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Implanted markers and EPI

• Requires uses of dense markers usually gold or
  platinum. Can be spherical (approx 2mm diameter)
  or cylindrical (approx 3x1mm).
• Implanted using modified TRUS biopsy needle
• At least 3 markers inserted to allow
  triangulation and assessment of 3D displacements
• Usually requires a-Si flat panel imagers
• Advantages Easy to use to verify position and
  technology available in most departments
• Disadvantages Invasive, no information on
  changes in organ volume

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B-mode Acquisition and Targeting (BAT system).
Sonarray similar.
Disadvantages may be unreliable with large inter
and intra-observer variability. From Langen et
al Int J Rad Oncol Biol Physics 57(3) 635-644.
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Megavoltage cone beam CT

• TomoTherapy Hi-Art system available commercially
• Has CT gantry with mobile 6MV linac within
• Delivers IMRT only
• All in one solution with TPS, on-treatment MV
  cone beam imaging and exit dosimetry
• Metal artefacts e.g. hip replacements not seen
  with MV cone beam CT
• Disadvantages Cost and need for backup plans to
  cover down time

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MV CT (TomoTherapy Hi-Art)
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Elekta Synergy
Acquires kV cone beam CT, fluoroscopy and static
kV images. Varian OBI uses similar technology.
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Cone Beam CT ? cone beam more scatter
therefore image quality not as good as diagnostic
CT ? 2D rows detectors ? Single gantry rotation
Image acquired over 30 s to 1 minute
Conventional CT ? fan beam ? 1D (single) row
detectors ? Multiple gantry rotations Image
acquired in secs
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Cyberknife

• 1 Ceiling mounted diagnostic x-ray sources
• 2 Compact linac on robotic arm
• 3 a-Si flat panel detectors
• Usually used to deliver extra-cranial
  stereo-tactic single or hypo- fractionated
  treatments

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Adapted from Steve Webb, IGRT meeting 11/9/06
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Random Error Blurs dose distribution
Systematic Error Shifts dose distribution
On-line correction compensates for both
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On-line vs. Off-line

• On-line
• Image and adjust position as necessary
• Corrects for random and systematic errors
• More time consuming and requires immediate
  decisions
• Most appropriate at sites subject to large random
  errors or when delivering hypo-fractionated
  treatments

• Off-line
• Retrospective analysis
• Corrects for systematic error only
• Less time consuming and clinicians opinion can be
  sought
• Most frequently used
• Appropriate at sites where systematic gt random
  errors

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Errors in Prostate Radiotherapy Delivery

• Standard EPI verification based on bony anatomy
  doesnt assess prostate motion
• Prostate displacement more dependent on
  physiological changes (rectal gt bladder filling)
  and predominantly results in AP shifts
• Planning scan represents snapshot of prostate
  position and if not representative introduces
  systematic error
• Serial imaging in first week can be used to
  quantify systematic errors and correct by
  shifting patient. Re-planning infrequently needed
  as the prostate is a rigid structure which
  doesnt deform significantly

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Serial cone beam kV CT Prostate
Day 1
Day 2
Planning
Day 4
Day 3
Day 3
Day 4
Courtesy of Christie Hosptial
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Bladder Coronal cone beam kV CT (systematic
error)
Courtesy of Christie Hospital
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Clinical imaging of urological patients at
Cookridge Hospital

• Previously EPI D1 and 2 and average error
  corrected for if gt 5mm in any direction
• Urological patients treated on Synergy imaged
  D1-3 and average error in prostate position
  corrected for if gt 3mm by shifting pt position
• Imaged weekly thereafter. If any additional error
  gt 3mm noted then 3 serial images acquired and
  error averaged and corrected for.
• Currently requires weekly image review by
  clinician or radiologist.

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Elekta Synergy software and kV cone beam CT
display. Can be fused with planning CT on bony
anatomy or soft tissue and error quantified.
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Planning scan (green) fused with cone beam kV CT
(purple) demonstrating displacement.
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Checkerboard display of planning and cone beam CT
scans.
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Checkerboard display showing larger rectal volume
on treatment.
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Large volumes of bowel gas causing image artefact.
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Cone beam kV CT of post-op prostate patient
demonstrating surgical clips.
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The worst case scenario geographic miss and
large volume rectum in PTV
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Departmental Audit

• On completion of treatment of first 30 urological
  patients aim to quantify set-up and prostate
  positioning errors.
• kV imaging not available to all patients and will
  try to identify those that benefit most for
  example those with large rectal or bladder
  volumes at planning.
• Plan to review CTV-PTV margins used in planning
  in light of results.

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Clinical Implications of IGRT

• IGRT individualises treatment delivery to
  compensate for internal organ motion and set-up
  errors
• Accurate 3D verification will allow safe
  implementation of IMRT/dose escalation
  particularly when utilising hypo fractionated
  schedules
• To fully realise clinical benefit implementation
  needs to be radiographer lead using clear site
  specific verification protocols
• Choice of technology usually depends on existing
  equipment and cost
• Will allow accurate audit of departmental error
  in treatment delivery
• Potential to develop accurate radiobiological
  models
• IGRT allows more accurate and safe treatment
  delivery