title: Plan quality and treatment planning technique for single isocenter cranial radiosurgery with volumetric modulated arc therapy.
abstract: OBJECTIVE
  To demonstrate plan quality and provide a practical, systematic approach to the treatment planning technique for single isocenter cranial radiosurgery with volumetric modulated arc therapy (VMAT; RapidArc, Varian Medical systems, Palo Alto, CA).
  
  
  METHODS
  Fifteen patients with 1 or more brain metastases underwent single isocenter VMAT radiosurgery. All plans were normalized to deliver 100% of the prescription dose to 99%-100% of the target volume. All targets per plan were treated to the same dose. Plans were created with dose control tuning structures surrounding targets to maximize conformity and dose gradient. Plan quality was evaluated by calculation of conformity index (CI = 100% isodose volume/target volume) and homogeneity index (HI = maximum dose/prescription dose) scores for each target and a Paddick gradient index (GI = 50% isodose volume/100% isodose volume) score for each plan.
  
  
  RESULTS
  The median number of targets per patient was 2 (range, 1-5). The median number of non-coplanar arcs utilized per plan was 2 (range, 1- 4). Single target plans were created with 1 or 2 non-coplanar arcs while multitarget plans utilized 2 to 4 non-coplanar arcs. Prescription doses ranged from 5-16 Gy in 1-5 fractions. The mean conformity index was 1.12 (± SD, 0.13) and the mean HI was 1.44 (± SD, 0.11) for all targets. The mean GI per plan was 3.34 (± SD, 0.42).
  
  
  CONCLUSIONS
  We have outlined a practical approach to cranial radiosurgery treatment planning using the single isocenter VMAT platform. One or 2 arc single isocenter plans are often adequate for treatment of single targets, while 2-4 arcs may be more advantageous for multiple targets. Given the high plan quality and extreme clinical efficiency, this single isocenter VMAT approach will continue to become more prevalent for linac-based radiosurgical treatment of 1 or more intracranial targets and will likely replace multiple isocenter techniques.
authors.affiliation: Department of Radiation Oncology, University of Alabama at Birmingham, Comprehensive Cancer Center, Birmingham, Alabama.
authors.forename: Grant M
authors.initials: GM
authors.lastname: Clark
authors.affiliation: Department of Radiation Oncology, University of Alabama at Birmingham, Comprehensive Cancer Center, Birmingham, Alabama.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Popple
authors.affiliation: Department of Radiation Oncology, University of Alabama at Birmingham, Comprehensive Cancer Center, Birmingham, Alabama.
authors.forename: Brendan M
authors.initials: BM
authors.lastname: Prendergast
authors.affiliation: Department of Radiation Oncology, University of Alabama at Birmingham, Comprehensive Cancer Center, Birmingham, Alabama.
authors.forename: Sharon A
authors.initials: SA
authors.lastname: Spencer
authors.affiliation: Department of Radiation Oncology, University of Alabama at Birmingham, Comprehensive Cancer Center, Birmingham, Alabama.
authors.forename: Evan M
authors.initials: EM
authors.lastname: Thomas
authors.affiliation: Department of Radiation Oncology, University of Alabama at Birmingham, Comprehensive Cancer Center, Birmingham, Alabama.
authors.forename: John G
authors.initials: JG
authors.lastname: Stewart
authors.affiliation: Department of Neurosurgery, University of Alabama at Birmingham, Birmingham, Alabama.
authors.forename: Barton L
authors.initials: BL
authors.lastname: Guthrie
authors.affiliation: Department of Neurosurgery, University of Alabama at Birmingham, Birmingham, Alabama.
authors.forename: James M
authors.initials: JM
authors.lastname: Markert
authors.affiliation: Department of Radiation Oncology, University of Alabama at Birmingham, Comprehensive Cancer Center, Birmingham, Alabama. Electronic address: jfiveash@uab.edu.
authors.forename: John B
authors.initials: JB
authors.lastname: Fiveash