title: A dual computed tomography linear accelerator unit for stereotactic radiation therapy: a new approach without cranially fixated stereotactic frames.
abstract: OBJECTIVE
  To perform stereotactic radiation therapy (SRT) without cranially fixated stereotactic frames, we developed a dual computed tomography (CT) linear accelerator (linac) treatment unit.
  
  
  METHODS
  This unit is composed of a linac, CT, and motorized table. The linac and CT are set up at opposite ends of the table, which is suitable for both machines. The gantry axis of the linac is coaxial with that of the CT scanner. Thus, the center of the target detected with the CT can be matched easily with the gantry axis of the linac by rotating the table. Positioning is confirmed with the CT for each treatment session. Positioning and treatment errors with this unit were examined by phantom studies. Between August and December 1994, 8 patients with 11 lesions of primary or metastatic brain tumors received SRT with this unit. All lesions were treated with 24 Gy in three fractions to 30 Gy in 10 fractions to the 80% isodose line, with or without conventional external beam radiation therapy.
  
  
  RESULTS
  Phantom studies revealed that treatment errors with this unit were within 1 mm after careful positioning. The position was easily maintained using two tiny metallic balls as vertical and horizontal marks. Motion of patients was negligible using a conventional heat-flexible head mold and dental impression. The overall time for a multiple noncoplanar arcs treatment for a single isocenter was less than 1 h on the initial treatment day and usually less than 20 min on subsequent days. Treatment was outpatient-based and well tolerated with no acute toxicities. Satisfactory responses have been documented.
  
  
  CONCLUSIONS
  Using this treatment unit, multiple fractionated SRT is performed easily and precisely without cranially fixated stereotactic frames.
authors.affiliation: Department of Radiology, Division of Radiation Oncology, National Defense Medical College, Saitama, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Uematsu
authors.forename: T
authors.initials: T
authors.lastname: Fukui
authors.forename: A
authors.initials: A
authors.lastname: Shioda
authors.forename: H
authors.initials: H
authors.lastname: Tokumitsu
authors.forename: K
authors.initials: K
authors.lastname: Takai
authors.forename: T
authors.initials: T
authors.lastname: Kojima
authors.forename: Y
authors.initials: Y
authors.lastname: Asai
authors.forename: S
authors.initials: S
authors.lastname: Kusano
mesh_terms: D001932:Brain Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy / Q000556:secondary / Q000601:surgery*; D004867:Equipment Design; D006801:Humans; D010315:Particle Accelerators; D016634:Radiosurgery / Q000379:methods*; D014057:Tomography, X-Ray Computed