title: Variable dose interplay effects across radiosurgical apparatus in treating multiple brain metastases.
abstract: OBJECTIVE
  Normal brain tissue doses have been shown to be strongly apparatus dependent for multi-target stereotactic radiosurgery. In this study, we investigated whether inter-target dose interplay effects across contemporary radiosurgical treatment platforms are responsible for such an observation.
  
  
  METHODS
  For the study, subsets ([Formula: see text] and 12) of a total of 12 targets were planned at six institutions. Treatment platforms included the (1) Gamma Knife Perfexion (PFX), (2) CyberKnife, (3) Novalis linear accelerator equipped with a 3.0-mm multi-leaf collimator (MLC), and the (4) Varian Truebeam flattening-filter-free (FFF) linear accelerator also equipped with a 2.5 mm MLC. Identical dose-volume constraints for the targets and critical structures were applied for each apparatus. All treatment plans were developed at individual centers, and the results were centrally analyzed.
  
  
  RESULTS
  We found that dose-volume constraints were satisfied by each apparatus with some differences noted in certain structures such as the lens. The peripheral normal brain tissue doses were lowest for the PFX and highest for TrueBeam FFF and CyberKnife treatment plans. Comparing the volumes of normal brain receiving 12 Gy, TrueBeam FFF, Novalis, and CyberKnife were 180-290% higher than PFX. The mean volume of normal brain-per target receiving 4-Gy increased by approximately 3.0 cc per target for TrueBeam, 2.7 cc per target for CyberKnife, 2.0 cc per target for Novalis, and 0.82 cc per target for PFX. The beam-on time was shortest with the TrueBeam FFF (e.g., 6-9 min at a machine output rate of 1,200 MU/min) and longest for the PFX (e.g., 50-150 mins at a machine output rate of 350 cGy/min).
  
  
  CONCLUSIONS
  The volumes of normal brain receiving 4 and 12 Gy were higher, and increased more swiftly per target, for Linac-based SRS platforms than for PFX. Treatment times were shortest with TrueBeam FFF.
authors.affiliation: Department of Radiation Oncology, University of California, San Francisco, 505 Parnassus Avenue, Room L-08, San Francisco, CA , 94143, USA. lijunma@radonc.ucsf.edu.
authors.forename: Lijun
authors.initials: L
authors.lastname: Ma
authors.affiliation: Department of Radiation Oncology, BC Cancer Agency, University of British Columbia, Vancouver, Canada.
authors.forename: Alan
authors.initials: A
authors.lastname: Nichol
authors.affiliation: Department of Radiation Oncology, University of Oklahoma, Oklahoma City, OK, USA.
authors.forename: Sabbir
authors.initials: S
authors.lastname: Hossain
authors.affiliation: Department of Radiation Oncology, University of Louisville, Louisville, KY, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: Wang
authors.affiliation: Washington Fremont Hospital Gamma Knife Center, Fremont, CA, USA.
authors.forename: Paula
authors.initials: P
authors.lastname: Petti
authors.affiliation: Department of Radiation Oncology, BC Cancer Agency, University of British Columbia, Vancouver, Canada.
authors.forename: Rosemin
authors.initials: R
authors.lastname: Vellani
authors.affiliation: Department of Radiation Oncology, University of Oklahoma, Oklahoma City, OK, USA.
authors.forename: Chris
authors.initials: C
authors.lastname: Higby
authors.affiliation: Department of Radiation Oncology, University of Oklahoma, Oklahoma City, OK, USA.
authors.forename: Salahuddin
authors.initials: S
authors.lastname: Ahmad
authors.affiliation: Department of Radiation Oncology, University of California, San Francisco, 505 Parnassus Avenue, Room L-08, San Francisco, CA , 94143, USA.
authors.forename: Igor
authors.initials: I
authors.lastname: Barani
authors.affiliation: Department of Radiation Oncology, University of Utah, Salt Lake City, UT, USA.
authors.forename: Dennis C
authors.initials: DC
authors.lastname: Shrieve
authors.affiliation: Department of Radiation Oncology, University of California, San Francisco, 505 Parnassus Avenue, Room L-08, San Francisco, CA , 94143, USA.|Washington Fremont Hospital Gamma Knife Center, Fremont, CA, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Larson
authors.affiliation: Department of Radiation Oncology, Sunnybrook Odette Cancer Center, University of Toronto, Toronto, Canada.
authors.forename: Arjun
authors.initials: A
authors.lastname: Sahgal
mesh_terms: D001932:Brain Neoplasms / Q000473:pathology / Q000601:surgery*; D006801:Humans; D009362:Neoplasm Metastasis; D016634:Radiosurgery / Q000295:instrumentation* / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*
keywords: Brain metastases; Gamma Knife; Intensity modulation; Stereotactic radiosurgery
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