title: [A bi-isocentric irradiation technique in radiotherapy for nasopharyngeal carcinoma].
abstract: OBJECTIVE
  Although the problem of fields gap in radiotherapy for nasopharyngeal carcinoma (NPC) was solved by mono-isocentric technique, the dose distribution was heterogeneous with "hot" and/or "cold" spots. This study was to explore the best way to solve the problems of both fields gap and dose distribution using bi-isocentric technique.
  
  
  METHODS
  Mono-isocentric and bi-isocentric irradiation techniques were used to simulate irradiation, respectively. Mono-isocentric irradiation technique was used to design the beam-split facio-upper neck field and the tangential low neck-supraclavicular field at the match plane. Bi-isocentric irradiation technique was used to design the facio-upper neck field and the tangential low neck-supraclavicular field at the match plane, namely the upper border of the tangential field and the lower border of the facio-upper neck fields.
  
  
  RESULTS
  Both mono-isocentric and bi-isocentric irradiation techniques were conformed well to QA at the junction of the neighboring portals, without "hot" or "cold" spots, by dosimetry. But the CADplan Three Dimensions Treatment Planning System showed that the dose distributional uniformity of sagittal plane in nasopharynx was much better in bi-isocentric technique than in mono-isocentric irradiation technique, without cold region in gross tumor volume (GTV) and/or hot region in normal tissue.
  
  
  CONCLUSIONS
  Bi-isocentric irradiation technique takes a perfect match-plane and a satisfied dose distributional uniformity.
authors.affiliation: Department of Radiation Oncology, Xinhua Hospital, Shanghai Second Medical University, Shanghai 200092, P. R. China. xiashian52@sohu.com
authors.forename: Shi-An
authors.initials: SA
authors.lastname: Xia
authors.forename: Song-Fang
authors.initials: SF
authors.lastname: Zhang
authors.forename: Yong-Qing
authors.initials: YQ
authors.lastname: Tu
authors.forename: Guo-Hua
authors.initials: GH
authors.lastname: Wu
authors.forename: Qing
authors.initials: Q
authors.lastname: Lin
authors.forename: Yuan
authors.initials: Y
authors.lastname: Yao
mesh_terms: D006801:Humans; D009303:Nasopharyngeal Neoplasms / Q000532:radiotherapy*; D011874:Radiometry / Q000295:instrumentation / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D011881:Radiotherapy, Computer-Assisted / Q000379:methods*