A Comparison Between Two Leading Stereotactic Platforms in the Treatment of Multiple Metastases

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A Comparison Between Two Leading Stereotactic
Platforms in the Treatment of Multiple Metastases

• Sandra Vermeulen MD, James Raisis MD, Francisco
  Li MS, Per Kjäll PhD
• Northwest Hospital Gamma Knife, Seattle
• Seattle Cyberknife, Seattle
• R D Physics, Eletka Instruments AB, Stockholm,
  Sweden

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Radiosurgical Stereotactic Platform Objectives

• Precision
• Reproducibility
• Operator Friendly
• Patient comfort
• Treatment time constraints
• Frame, No frame

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Cyberknife Credentials

• Approved by the FDA since 2001
• More than 120 hospitals and medical centers
  provide CyberKnife technology
• Greater than 40,000 patients treated worldwide
• More than 400 peer review papers have been
  published
• Patient mix 50 cranial, 50 extra-cranial

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Cyberknife
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Cyberknife Characteristic that Differ from Gamma
Knife

• No immbolization frame
• Real-time imaging required
• Motion tracking required
• Capable of Fractionation
• important if tumors engulf optic apparatus,
  spinal cord or other sensitive structures
• Large tumors
• Extra-cranial targeting below the clavicle
  possible
• More staffing requirements
• More complex QA requirements

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Brain Metastases

• Most patients have multiple lesions
• MRI screening evaluations show 80 of patients
  have more than 1 metastases and 50 have 3 or
  more
• Many patients require more than one SRS session
  during the course of their disease
• Are CK and GK beam profiles the same for 1, 4 or
  10 metastases?

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Index Conformity (PIV/TV ratio) of Radiosurgical
Treatment Plans

• Defined in the RTOG radiosurgical guidelines
  90-05 as a measure of the conformity of the
  Prescribed Dose (PIV) to the Target Volume (TV).

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CK Cone Size Selection

• CK cone diameters (mm) available
• 5, 7.5, 10, 12.5, 15, 20, 25, 30, 35, 40, 50, 60
• An output factor is a ratio of dose for a given
  field size to that for a reference field size
• The output factor of the 5 mm cone has not been
• verified by the manufacturer

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Extreme Brain Metastases Case

• MH is a 35y/o mother of 2 with a 4 year history
  of metastatic breast cancer involving brain, lung
  and bone.
• Systemic treatment includes chemotherapy,
  monoclonal antibodies and hormones
• SRS by CK has been given twice for BM (6 lesions
  have been treated over 2 years)
• Patient has been followed for 6 months with 10
  intracranial lesions, all under 1 cm
• With a continued KPS of 80, patient has refused
  WBRT because of the risk of dementia and the GK
  because of the frame placement

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CyberKnife Single Matrix and Multiple Matrix
Plans
Single Matrix
Multiple Matrix
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Cyberknife Conformity Index Multiple and Single
Matrix
Multiple Matrix, 2.08 CI/2.17 nCI
Single Matrix, 1.68 CI/1.70 nCI
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Cyberknife Dose Stacking
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Gamma Knife Single Matrix and Multiple Matrix
Plans
Multiple Matrix, nCI 1.04
Single Matrix, nCI 1.14
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Cyberknife Limitations in the Treatment of
Multiple Metastases

• When treating more than 4 lesions, target
  conformity is lost and normal brain inclusion
  within lower non-prescription isodose volumes is
  increased.
• Output measurement of 5 mm cone not verified by
  manufacturer (most center do not treat tumors
  smaller than 4 mms)

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Conclusion

• The dosimetry of either GK or CK in the treatment
  of lt 4 metastases which are greater than 5 mms
  is comparable by radiosurgical standards
• When treating gt 4 metastases, a larger number of
  lesions can be treated with GK than CK with
  better dosimetry and less normal brain inclusion
  within lower isodose volumes.