title: Clinical application of flattening filter free beams for extracranial stereotactic radiotherapy.
abstract: OBJECTIVE
  To investigate the clinical application of flattening filter free (FFF) beams at maximum dose rate for stereotactic body radiotherapy (SBRT).
  
  
  METHODS
  Patients with tumors in the lung or abdomen were subjected to SBRT using 6 MV FFF or 10 MV FFF beams. For each patient, three plans were calculated using 6 MV flattened, 6 MV FFF, and 10 MV FFF beams. Treatment times were recorded and analyzed, and tumor displacements were assessed by pre- and post-treatment cone beam computed tomography (CBCT).
  
  
  RESULTS
  Altogether, 26 patients (16 lung, 10 abdominal tumors) were treated. The average dose rate per patient ranged from 442 to 1860 MU/min. Beam-on time was on average 1.6 min (1SD=0.6 min), with the total treatment times recorded at 18.5 min (1SD=3.5 min). The time advantage of using FFF beams was dose-dependent and started at 4 Gy for 6 MV FFF and at 10 Gy for 10 MV FFF beams. The average of the tumor displacements during treatment was 2.0mm (1SD = 1.0mm).
  
  
  CONCLUSIONS
  SBRT using FFF beams is time efficient and associated with excellent patient stability. According to Van Herk's formula, ITV-PTV margins of 6mm are sufficient in our patient cohort. Further studies are necessary to assess clinical outcome and toxicity.
authors: Department of Radiation Oncology, University Hospital Zurich, Zurich, Switzerland.
authors: Stephanie
authors: S
authors: Lang
authors: Binaya
authors: B
authors: Shrestha
authors: Shaun
authors: S
authors: Graydon
authors: Frederique
authors: F
authors: Cavelaars
authors: Claudia
authors: C
authors: Linsenmeier
authors: Jan
authors: J
authors: Hrbacek
authors: Stephan
authors: S
authors: Klöck
authors: Gabriela
authors: G
authors: Studer
authors: Oliver
authors: O
authors: Riesterer
mesh_terms: D000008:Abdominal Neoplasms / Q000000981:diagnostic imaging / Q000601:surgery*; D000368:Aged; D000369:Aged, 80 and over; D054893:Cone-Beam Computed Tomography; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000601:surgery*; D008875:Middle Aged; D016634:Radiosurgery / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*