title: Clinical realization of sector beam intensity modulation for Gamma Knife radiosurgery: a pilot treatment planning study.
abstract: OBJECTIVE
  To demonstrate the clinical feasibility and potential benefits of sector beam intensity modulation (SBIM) specific to Gamma Knife stereotactic radiosurgery (GKSRS).
  
  
  METHODS
  SBIM is based on modulating the confocal beam intensities from individual sectors surrounding an isocenter in a nearly 2π geometry. This is in contrast to conventional GKSRS delivery, in which the beam intensities from each sector are restricted to be either 0% or 100% and must be identical for any given isocenter. We developed a SBIM solution based on available clinical planning tools, and we tested it on a cohort of 12 clinical cases as a proof of concept study. The SBIM treatment plans were compared with the original clinically delivered treatment plans to determine dosimetric differences. The goal was to investigate whether SBIM would improve the dose conformity for these treatment plans without prohibitively lengthening the treatment time.
  
  
  RESULTS
  A SBIM technique was developed. On average, SBIM improved the Paddick conformity index (PCI) versus the clinically delivered plans (clinical plan PCI = 0.68 ± 0.11 vs SBIM plan PCI = 0.74 ± 0.10, P=.002; 2-tailed paired t test). The SBIM plans also resulted in nearly identical target volume coverage (mean, 97 ± 2%), total beam-on times (clinical plan 58.4 ± 38.9 minutes vs SBIM 63.5 ± 44.7 minutes, P=.057), and gradient indices (clinical plan 3.03 ± 0.27 vs SBIM 3.06 ± 0.29, P=.44) versus the original clinical plans.
  
  
  CONCLUSIONS
  The SBIM method is clinically feasible with potential dosimetric gains when compared with conventional GKSRS.
authors.affiliation: Department of Radiation Oncology, University of California, San Francisco, California. Electronic address: lijunma@radonc.ucsf.edu.
authors.forename: Lijun
authors.initials: L
authors.lastname: Ma
authors.affiliation: Department of Radiation Oncology, University of California, San Francisco, California.
authors.forename: Erica
authors.initials: E
authors.lastname: Mason
authors.affiliation: Department of Radiation Oncology, University of California, San Francisco, California.
authors.forename: Penny K
authors.initials: PK
authors.lastname: Sneed
authors.affiliation: Department of Radiation Oncology, University of California, San Francisco, California.
authors.forename: Michael
authors.initials: M
authors.lastname: McDermott
authors.affiliation: Department of Radiation Oncology, University of California, San Francisco, California.
authors.forename: Alexei
authors.initials: A
authors.lastname: Polishchuk
authors.affiliation: Department of Radiation Oncology, University of California, San Francisco, California.
authors.forename: David A
authors.initials: DA
authors.lastname: Larson
authors.affiliation: Department of Radiation Oncology, Sunnybrook Odette Cancer Center, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Arjun
authors.initials: A
authors.lastname: Sahgal
mesh_terms: D001932:Brain Neoplasms / Q000556:secondary / Q000601:surgery; D004833:Epilepsy, Temporal Lobe / Q000601:surgery; D005240:Feasibility Studies; D006801:Humans; D002538:Intracranial Arteriovenous Malformations / Q000601:surgery; D008577:Meningeal Neoplasms / Q000601:surgery; D008579:Meningioma / Q000601:surgery; D009464:Neuroma, Acoustic / Q000601:surgery; D010865:Pilot Projects; D016634:Radiosurgery / Q000295:instrumentation / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D014277:Trigeminal Neuralgia / Q000601:surgery