title: The use of photon beams of a flattening filter-free linear accelerator for hypofractionated volumetric modulated arc therapy in localized prostate cancer.
abstract: OBJECTIVE
  To evaluate the potential usage of flattening filter-free (FFF) photon beams in the treatment of prostate cancer.
  
  
  METHODS
  Volumetric-modulated arc therapy (VMAT) treatment planning was performed for 7 patients using TrueBeam(®) linear accelerator and photon beams with (X6, X10) and without (X6FFF, X10FFF) flattening filter. Prescribed dose was 19 × 3 Gy = 57 Gy. One or two 360° arcs with dose rate of 600 MU/min for flattened beams, and 1,200 MU/min for FFF beams were used.
  
  
  RESULTS
  No difference was detected between the four beams in PTV coverage, conformity, and homogeneity. Mean body dose and body volume receiving 50% of the prescribed dose decreased with increasing mean energy (r(2) = 0.8275, p < 0.01). X6FFF delivered 3.6% more dose compared with the X6 (p < 0.01). X10FFF delivered 3.0% (p < 0.01), and the X10 5.8% (p < 0.01) less mean body dose compared with X6. There was a significant increase in the mean dose to the rectum for the X10 compared with X6 (2.6%, p < 0.01). Mean dose to the bladder increased by 1.3% for X6FFF and decreased by 2.3% for X10FFF. Using a single arc and FFF, treatment time was reduced by 35% (2 SD = 10%).
  
  
  CONCLUSIONS
  FFF beams resulted in dose distributions similar to flattened beams. X10FFF beam provided the best solution, sparing rectum and bladder and minimizing whole-body dose. FFF beams lead to a time efficient treatment delivery, particularly when combined with hypofractionated VMAT.
authors.affiliation: Department of Radiation Oncology, University Hospital Zurich, Zurich, Switzerland. daniel.zwahlen@gmx.ch
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Zwahlen
authors.forename: Stephanie
authors.initials: S
authors.lastname: Lang
authors.forename: Jan
authors.initials: J
authors.lastname: Hrbacek
authors.forename: Christoph
authors.initials: C
authors.lastname: Glanzmann
authors.forename: Stephan
authors.initials: S
authors.lastname: Kloeck
authors.forename: Yousef
authors.initials: Y
authors.lastname: Najafi
authors.forename: Tino
authors.initials: T
authors.lastname: Streller
authors.forename: Gabriela
authors.initials: G
authors.lastname: Studer
authors.forename: Kathrin
authors.initials: K
authors.lastname: Zaugg
authors.forename: Urs M
authors.initials: UM
authors.lastname: Luetolf
mesh_terms: D005374:Filtration / Q000295:instrumentation; D006801:Humans; D008297:Male; D058958:Organs at Risk / Q000528:radiation effects; D010315:Particle Accelerators; D017785:Photons / Q000627:therapeutic use*; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000517:prevention & control*; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods; D061089:Radiotherapy, Image-Guided / Q000295:instrumentation* / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation / Q000379:methods*; D012007:Rectum / Q000528:radiation effects; D013997:Time Factors; D001743:Urinary Bladder / Q000528:radiation effects