title: A dosimetric evaluation of flattening filter-free volumetric modulated arc therapy in nasopharyngeal carcinoma.
abstract: OBJECTIVE
  To explore the dosimetric effects of flattening filter-free (FFF) beams in volumetric modulated arc therapy (VMAT) of nasopharyngeal carcinoma via a retrospective planning study.
  
  
  METHODS
  A linear accelerator (LINAC) was prepared to operate in FFF mode and the beam data were collected and used to build a model in TPS. For 10 nasopharyngeal carcinoma (NPC) cases, VMAT plans of FFF beams and normal flattened (FF) beams were designed. Differences of plan quality and delivery efficiency between FFF-VMAT plans and filter filtered VMAT (FF-VMAT) plans were analyzed using two-tailed paired t-tests.
  
  
  RESULTS
  Removal of the flattening filter increased the dose rate. Averaged beam on time (BOT) of FFF-VMAT plans was decreased by 24.2%. Differences of target dose coverage between plans with flattened and unflattened beams were statistically insignificant. For dose to normal organs, up to 4.9% decrease in V35 of parotid grand and 4.5% decrease in averaged normal tissue (NT) dose was observed.
  
  
  CONCLUSIONS
  The TPS used in our study was able to handle FFF beams. The FFF beam prone to improve the normal tissue sparing while achieving similar target dose distribution. Decreasing of BOT in NPC cases was valuable in terms of patient's comfort.
authors.affiliation: Department of Radiotherapy, Cancer Hospital and Institution, Chinese Academy of Medical Sciences, Panjiayuan NaiLi 17#, Chaoyang Dist, Beijing, China.
authors.forename: Guishan
authors.initials: G
authors.lastname: Fu
authors.affiliation: Department of Radiotherapy, Cancer Hospital and Institution, Chinese Academy of Medical Sciences, Panjiayuan NaiLi 17#, Chaoyang Dist, Beijing, China.
authors.forename: Minghui
authors.initials: M
authors.lastname: Li
authors.affiliation: Department of Radiotherapy, Cancer Hospital and Institution, Chinese Academy of Medical Sciences, Panjiayuan NaiLi 17#, Chaoyang Dist, Beijing, China.
authors.forename: Yixin
authors.initials: Y
authors.lastname: Song
authors.affiliation: Department of Radiotherapy, Cancer Hospital and Institution, Chinese Academy of Medical Sciences, Panjiayuan NaiLi 17#, Chaoyang Dist, Beijing, China.
authors.forename: Jianrong
authors.initials: J
authors.lastname: Dai
keywords: Flattening filter-free; nasopharyngeal carcinoma; radiotherapy; volumetric modulated arc therapy