title: Single-Isocenter Multiple-Target Stereotactic Radiosurgery: Risk of Compromised Coverage.
abstract: OBJECTIVE
  To determine the dosimetric effects of rotational errors on target coverage using volumetric modulated arc therapy (VMAT) for multitarget stereotactic radiosurgery (SRS).
  
  
  METHODS
  This retrospective study included 50 SRS cases, each with 2 intracranial planning target volumes (PTVs). Both PTVs were planned for simultaneous treatment to 21 Gy using a single-isocenter, noncoplanar VMAT SRS technique. Rotational errors of 0.5°, 1.0°, and 2.0° were simulated about all axes. The dose to 95% of the PTV (D95) and the volume covered by 95% of the prescribed dose (V95) were evaluated using multivariate analysis to determine how PTV coverage was related to PTV volume, PTV separation, and rotational error.
  
  
  RESULTS
  At 0.5° rotational error, D95 values and V95 coverage rates were ≥95% in all cases. For rotational errors of 1.0°, 7% of targets had D95 and V95 values <95%. Coverage worsened substantially when the rotational error increased to 2.0°: D95 and V95 values were >95% for only 63% of the targets. Multivariate analysis showed that PTV volume and distance to isocenter were strong predictors of target coverage.
  
  
  CONCLUSIONS
  The effects of rotational errors on target coverage were studied across a broad range of SRS cases. In general, the risk of compromised coverage increased with decreasing target volume, increasing rotational error and increasing distance between targets. Multivariate regression models from this study may be used to quantify the dosimetric effects of rotational errors on target coverage given patient-specific input parameters of PTV volume and distance to isocenter.
authors.affiliation: Department of Radiation Oncology, Winship Cancer Institute of Emory University, Atlanta, Georgia; Department of Biostatistics and Bioinformatics, Winship Cancer Institute of Emory University, Atlanta, Georgia. Electronic address: justin.roper@emory.edu.
authors.forename: Justin
authors.initials: J
authors.lastname: Roper
authors.affiliation: Department of Radiation Oncology, Winship Cancer Institute of Emory University, Atlanta, Georgia; Department of Biostatistics and Bioinformatics, Winship Cancer Institute of Emory University, Atlanta, Georgia.
authors.forename: Vorakarn
authors.initials: V
authors.lastname: Chanyavanich
authors.affiliation: Department of Radiation Oncology, Winship Cancer Institute of Emory University, Atlanta, Georgia; Department of Biostatistics and Bioinformatics, Winship Cancer Institute of Emory University, Atlanta, Georgia.
authors.forename: Gregory
authors.initials: G
authors.lastname: Betzel
authors.affiliation: Department of Biostatistics and Bioinformatics, Winship Cancer Institute of Emory University, Atlanta, Georgia.
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Switchenko
authors.affiliation: Department of Radiation Oncology, Winship Cancer Institute of Emory University, Atlanta, Georgia; Department of Biostatistics and Bioinformatics, Winship Cancer Institute of Emory University, Atlanta, Georgia.
authors.forename: Anees
authors.initials: A
authors.lastname: Dhabaan
mesh_terms: D001932:Brain Neoplasms / Q000601:surgery*; D016001:Confidence Intervals; D006801:Humans; D015999:Multivariate Analysis; D016634:Radiosurgery / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D061106:Radiotherapy Setup Errors; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012189:Retrospective Studies; D018570:Risk Assessment; D012399:Rotation; D018709:Statistics, Nonparametric; D013997:Time Factors