title: Dual arc volumetric-modulated arc radiotherapy (VMAT) of nasopharyngeal carcinomas: a simultaneous integrated boost treatment plan comparison with intensity-modulated radiotherapies and single arc VMAT.
abstract: OBJECTIVE
  To compare the performance of volumetric-modulated arc radiotherapy (VMAT) by dual arc with fixed beam intensity-modulated radiotherapies (IMRTs) and single arc VMAT on nasopharyngeal carcinomas (NPC).
  
  
  METHODS
  Twenty NPC cases were re-planned using the planning system of the Pinnacle(3®)SmartArc (SA) module to compare the performance of the following four techniques: seven-field (7F) and 18-field (18F) fixed beam IMRT, and single (SA(1)) and dual arc VMAT (SA(2)). The plan was delivered on an Elekta Synergy™ Linac equipped with an 80-leaf 1cm multileaf collimator. Three dose levels of planning target volumes (PTVs) with 70/59.4/54.0Gy in 33 fractions were prescribed and delivered as a simultaneous integrated boost. The conformity index and homogeneity index of the PTVs, the comprehensive quality index (CQI), the normal tissue complication probability for the organs at risk (OARs), and the planning time, delivery efficiency and accuracy were analysed.
  
  
  RESULTS
  A significantly inferior conformity index at the three dose levels of PTV and homogeneity index of PTV(70) were observed in SA(1) compared with the other techniques. Comparable conformity index and homogeneity index of the PTV were observed among 7F/18F IMRT and SA(2). Based on the CQI of the 11 OARs, the most efficient dose reduction was observed in 18F IMRT followed in order by SA(2), 7F IMRT and SA(1). The planning time was on average 13.2/24.9/40.1/42.8min for 7F/18F IMRT/SA(1)/SA(2), respectively. With regards to the delivery efficiency compared with 7F IMRT, a 51 and 41% reduction in delivery time was achieved by SA(1) and SA(2), respectively. All techniques presented a high quality assurance pass rate (>98%) of the Γ(3mm,3%) criterion.
  
  
  CONCLUSIONS
  In NPC cases, SA(2) gave superior results in terms of PTV coverage and OAR sparing compared with SA(1) and approached the performance achieved by 18F IMRT, but without sacrificing the delivery efficiency.
authors.affiliation: Medical Physics & Informatics Laboratory, Department of Electronics Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung, Taiwan. tflee@cc.kuas.edu.tw
authors.forename: T-F
authors.initials: TF
authors.lastname: Lee
authors.forename: H-M
authors.initials: HM
authors.lastname: Ting
authors.forename: P-J
authors.initials: PJ
authors.lastname: Chao
authors.forename: F-M
authors.initials: FM
authors.lastname: Fang
mesh_terms: D000328:Adult; D002277:Carcinoma; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D000077274:Nasopharyngeal Carcinoma; D009303:Nasopharyngeal Neoplasms / Q000532:radiotherapy*; D058958:Organs at Risk / Q000528:radiation effects*; D017785:Photons / Q000627:therapeutic use*; D011379:Prognosis; D011785:Quality Assurance, Health Care; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated