title: A comparison of helical tomotherapy to circular collimator-based linear-accelerator radiosurgery for the treatment of brain metastases.
abstract: OBJECTIVE
  To compare stereotactic radiosurgery treatment plans for the treatment of patients with brain metastases generated using Tomotherapy and a circular collimator-based SRS approach.
  
  
  METHODS
  Twenty patients, previously treated with circular collimator-based radiosurgery, were replanned using Tomotherapy treatment planning software. Tomotherapy planning emphasized dose fall off peripheral to the target by allowing for inhomogeneous target coverage. Conformity and dose falloff were compared with the circular collimator-based plans using the following metrics: prescription isodose to tumor volume ratio, conformation number, and homogeneity index to assess effects on targets, whereas a combined conformity gradient index and the volume of the 12-Gy isodose volume were used to assess differences in dose to normal brain.
  
  
  RESULTS
  Although a similar homogeneity index was achieved for both sets of plans, plan conformity was generally improved using the tomotherapy system whereas dose falloff at the target periphery was shallower. The 12-Gy isodose volume increased on average by 3.4 mL (range, -1.9 to +12.1 mL), for the 20 patients studied, but in spite of this, based on modeled predictions, the risk for symptomatic radiation necrosis associated with Tomotherapy SRS for each patient still falls within the clinically observed ranges for Gamma Knife SRS.
  
  
  CONCLUSIONS
  Tomotherapy can be used to create treatment plans that meet the dosimetric and clinical requirements for stereotactic radiosurgery.
authors.affiliation: Department of Human Oncology, University of Wisconsin School of Medicine and Public Health, Madison, 53792, USA.
authors.forename: Emilie T
authors.initials: ET
authors.lastname: Soisson
authors.forename: Minesh P
authors.initials: MP
authors.lastname: Mehta
authors.forename: Wolfgang A
authors.initials: WA
authors.lastname: Tomé
mesh_terms: D001932:Brain Neoplasms / Q000401:mortality / Q000532:radiotherapy* / Q000556:secondary*; D006801:Humans; D016634:Radiosurgery / Q000295:instrumentation / Q000379:methods*; D015996:Survival Rate; D036542:Tomography, Spiral Computed / Q000379:methods*; D016896:Treatment Outcome