A Device for RealTime 3D ImageGuided IMRT

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A Device for Real-Time 3D Image-Guided IMRT

• James F. Dempsey, Ph.D.1, Benoit Dionne, M.S.2,
  Jeffrey F. Fitzsimmons, Ph.D.3, Alireza
  Haghighat, Ph.D.2, Jonathan G. Li, Ph.D.1, Daniel
  A. Low, Ph.D.4, Sasa Mutic, M.S.4, Jatinder R.
  Palta, Ph.D.1, H. Edwin Romeijn, Ph.D.5, and
  Glenn E. Sjoden, Ph.D.2
• 1)Department of Radiation Oncology, University of
  Florida, Gainesville, Florida 32610, U.S.A.
• 2)Department of Nuclear and Radiological
  Engineering, University of Florida, Gainesville,
  Florida 32611
• 3)Department of Radiology, University of Florida,
  Gainesville, Florida 32610, U.S.A.
• 4)Department of Radiation Oncology, Washington
  University, St. Louis, Missouri 63110, U.S.A.
  5Department of Industrial and Systems
  Engineering, University of Florida, Gainesville,
  Florida 32611, U.S.A.

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Conflict of Interest Statement

• James F. Dempsey owns stock in and is the
• C.S.O. of ViewRay Inc. and as such may
• benefit financially as a result of the
• outcomes of work or research reported in
• this presentation

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Outline

• Motivation, why are we doing this?
• Introducing the ViewRay, Inc. Renaissance ?
• not commercially available or cleared by FDA and
  NRC clinical use
• MRI for real-time imaging
• 60Co ? -Ray IMRT
• Summary

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Why Would We Want Real-Time 3D Image-Guidance?
patients are dynamic -they move, breath, shrink,
grow,
Intra-fraction motion occurs continuously -from
the base of the tongue to bottom of the pelvis-
real-time imaging is the only comprehensive
answer
4D CT Data from Low et al. Int. J. Rad. Oncol.
Biol. Phys., In Press.
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Introducing the ViewRay Renaissance

• The ViewRay RenaissanceTM (patent pending)
• Low-field Open MRi imaging
• Real-time volumetric parallel
• Volume repeatedly acquired every 2.0-0.5 seconds
• Imaging simultaneous to irradiation
• Cobalt teletherapy ?-ray IMRT
• 5-9 cone-beam MLC delivered IMRT
• Small Scale Super Computer
• Daily 4D assessment of motion
• Daily IMRT planning
• Reconstruction of daily delivered dose
• Know where the dose goes every dayTM

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Prototype of the RenaissanceTM Device

• Co-registered and gantry mounted
• Open split solenoid super conducting MRI
• 0.3 T
• MLC-Based cone beam IMRT unit with axial patient
  access
• Multiple sources
• Other delivery approaches?
• Imaging during beam-on
• Daily optimization
• Daily recording of delivered dose

IMRT gamma- ray unit
MRI unit
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The RenaissanceTM A Device for Real-Time 3D
Image-Guided IMRT

• Commercial device under development in
  collaboration between ViewRay, Inc. and academic
  research team
• The RenaissanceTM (patent pending not approved
  for clinical use)
• Compatible combination of MRI and Cobalt Therapy
  IMRT Unit
• Low-field Open parallel MRI imaging
• Volume repeatedly acquired every 2.0-0.2 seconds
• Imaging simultaneous to irradiation
• Cobalt teletherapy ?-ray IMRT
• 5-9 cone-beam MLC delivered IMRT
• Small Scale Super Computer
• Daily 4D assessment of motion
• Daily IMRT planning
• Reconstruction of daily delivered dose

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Why Cobalt or ?-Ray IMRT?

• Because it works!!!
• High quality optimization enables gamma-ray IMRT
• 40 seconds to optimize on single PC
• Compatible w/ MRI
• 1.5 cm diameter 60Co source
• 250R/min. _at_ 1 meter
• MLC _at_ 60 cm
• 7 beam plan
• Targets to 73.8 and 54 Gy
• Spare tissue, saliva glands, cord, brain stem,
  and mandible

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Quality ?-Ray IMRT Example

• Targets w/ gt95 Vol. coverage
• lt12 hot spot for high dose target
• Sparing for 3 out of 4 saliva glands lt50 vol. _at_
  30 Gy
• lt3 Tissue gt 50 Gy
• Cord, brain stem, and mandible below tolerance

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5 Beam 6MV vs ?-Ray IMRT

• Comparison of 60Co and 6MV 5 beam IMRT for
  Prostate Cancer Case (Pinnacle3 7.x, Philips)
• Target Coverage very good for both
• At higher doses near tolerance DVHs are very
  similar
• Femoral head sparing best with 60Co
• Optimization Algorithm more important than beam
  quality

6MV Solid Lines 60Co Dashed Lines
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Axial Prostate 6MV vs. 60Co
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Sagittal Prostate 6MV vs. 60Co
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Coronal Prostate 6MV vs. 60Co
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Why MRI?

• No moving parts!
• Very, very fast volume acquisition!
• Parallel or dynamic MRI
• No ionizing radiation dose to the patient!
• MRI can image metabolic physiologic information

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Why Low Field MRI?

• Low field MRI is a must for radiation therapy
• High field causes a loss of spatial integrity
• Magnetic Susceptibility artifacts due to the
  patient
• Scale with Bo field strength
• E.g. 1 cm distortion at 3T becomes 1 mm
  distortion at 0.3T
• High field ruins the dose distribution

See Petersch et al. Radiotherapy and Oncology 71
(2004) 5564 0.3 T -gt 3.24 mm max distortion 1.5
T -gt 16.2 mm max distortion
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Low Field MRI Preserves the Dosimetry

• Significant distortion of the dose in water at
  1.5 Tesla 6MV
• Air cavities increase interface dose
• Penumbra distorted
• No problem for Cobalt and low field MRI (0.3T)
• Air cavities have low interface dose
• Penumbra unperturbed
• Contamination
• electrons swept away

See Raaysmaker et al. Phys. Med. Biol. 49 (2004)
41094118 Raaijmakers et al. Phys. Med. Biol. 50
(2005) 13631376
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Parallel MRI (pMRI) Enables Real-time Imaging

• Current MRI scanners already operate at the
  limits of potential imaging speed based on
  rapidly switched gradient systems (for safety
  concerns).
• Huge advances from pMRI
• up to 32 independent receiver channels, which
  theoretically
• allowing 32 increased image acquisition speed
• 48 Slices 160 x 256 can be acquired in 1 s
• Lose factor of 5 in 1.5T -gt 0.3T
• Gain factor of 32 w/ pMRI
• Sodickson et al. Acad Radiol. 2005
  May12(5)626-35.

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MRI Improves 60Co IMRTElectron Contamination is
Swept Away

• Even a low-field Open MRI will provide enough
  field strength to sweep contamination electrons
• In a 0.3 Tesla field the radius of curvature for
  a 1 Mev electron in vacuum is 1.3 cm
• Contamination electrons cannot reach the patient
  lower skin dose to patient
• Can be modeled by Monte Carlo Simulation
• See paper for measurements of sweeping effect
• Jursinic and Mackie Phys. Med. Biol. 41 (1996)
  14991509.

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Elimination of Contamination Electrons

• Electrons are shown in blue/white
• Photons are shown in pink

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Summary Outlook

• ViewRay, Inc. has been formed w/ experienced
  management to build the device
• Technology is patent pending
• Technically feasibility of the device has been
  established
• Uses existing technologies
• Low Field Parallel MRI
• Cobalt therapy
• MLC-based IMRT
• Compatibility established
• Dosimetric quality established
• Development collaboration team established with
• University of Florida 6 Departments
• Washington University Dept. of Radiation Oncology
• National high magnetic field laboratory
• MRI design manufacture contract under
  negotiation
• Employs existing source supplier identified
• Seeking funding and collaboration
• Private
• NIH
• Strong clinical collaborators