title: Safety of high-dose-rate stereotactic body radiotherapy.
abstract: OBJECTIVE
  Flattening filter free (FFF) beams with high dose rate are increasingly used for stereotactic body radiotherapy (SBRT), because they substantially shorten beam-on time. The physical properties of these beams together with potentially unknown radiobiological effects might affect patient safety. Therefore here we analyzed the clinical outcome of our patients.
  
  
  METHODS
  Between 3/2010 and 2/2014 84 patients with 100 lesions (lung 75, liver 10, adrenal 6, lymph nodes 5, others 4) were treated with SBRT using 6 MV FFF or 10 MV FFF beams at our institution. Clinical efficacy endpoints and toxicity were assessed by Kaplan-Meier analysis and CTCAE criteria version 4.0.
  
  
  RESULTS
  Median follow-up was 11 months (range: 3-41). No severe acute toxicity was observed. There has been one case of severe late toxicity (1%), a grade 3 bile duct stricture that was possibly related to SBRT. For all patients, the 1-year local control rate, progression free survival and overall survival were 94%, 38% and 80% respectively, and for patients with lung lesions 94%, 48% and 83%, respectively.
  
  
  CONCLUSIONS
  No unexpected toxicity occurred. Toxicity and treatment efficacy are perfectly in range with studies investigating SBRT with flattened beams. The use of FFF beams at maximum dose rate for SBRT is time efficient and appears to be safe.
authors.affiliation: Department of Radiation Oncology, University Hospital Zurich, Rämistrasse 100, 8091, Zurich, Switzerland. sonja.stieb@usz.ch.
authors.forename: Sonja
authors.initials: S
authors.lastname: Stieb
authors.affiliation: Department of Radiation Oncology, University Hospital Zurich, Rämistrasse 100, 8091, Zurich, Switzerland. stephanie.lang@usz.ch.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Lang
authors.affiliation: Department of Radiation Oncology, University Hospital Zurich, Rämistrasse 100, 8091, Zurich, Switzerland. claudia.linsenmeier@usz.ch.
authors.forename: Claudia
authors.initials: C
authors.lastname: Linsenmeier
authors.affiliation: Department of Radiation Oncology, University Hospital Zurich, Rämistrasse 100, 8091, Zurich, Switzerland. shaunnicholas.graydon@usz.ch.
authors.forename: Shaun
authors.initials: S
authors.lastname: Graydon
authors.affiliation: Department of Radiation Oncology, University Hospital Zurich, Rämistrasse 100, 8091, Zurich, Switzerland. oliver.riesterer@usz.ch.
authors.forename: Oliver
authors.initials: O
authors.lastname: Riesterer
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000601:surgery*; D011836:Radiation Tolerance; D016634:Radiosurgery; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012449:Safety; D016896:Treatment Outcome; D055815:Young Adult