title: A split-parotid delineation approach for dose optimization in volumetric modulated arc therapy for nasopharyngeal carcinoma patients with parapharyngeal space invasion and level IIa cervical lymph node involvements.
abstract: OBJECTIVE
  This study evaluated the potential benefit of a split-parotid delineation approach on the parotid gland in the treatment planning of patients with nasopharyngeal carcinoma (NPC).
  
  
  METHODS
  50 patients with NPC with parapharyngeal space (PPS) and/or level IIa cervical node involvements were divided into three groups: PPS only, level IIa cervical node only and both. Two volumetric-modulated arc therapy plans were computed. The first plan (control) was generated based on the routine treatment-planning protocol, while the second plan (test) was computed with the split-parotid delineation approach, in which a line through the anterolateral margin of the retromandibular vein was created that divided the parotid gland into anterolateral and posteromedial subsegments. For the test plan, the anterolateral subsegment was prescribed, with a dose constraint of 25 Gy in the plan optimization. Dosimetric data of the parotid gland, target volumes and selected organs at risk (OARs) were compared between the control and test plans.
  
  
  RESULTS
  The mean dose to the anterolateral subsegment of the parotid gland in all three groups was kept below 25 Gy. The test plan demonstrated significantly lower mean parotid dose than the control plan in the entire gland and the anterolateral subsegment in all three groups. The difference was the greatest in Group 3.
  
  
  CONCLUSIONS
  The split-parotid delineation approach significantly lowered the mean dose to the anterolateral subsegment and overall gland without greatly compromising the doses to target volumes and other OARs. The effect was more obvious for both PPS and level IIa cervical node involvements than for either of them alone.
  
  
  CONCLUSIONS
  It is the first article based on the assumption that parotid gland stem cells are situated at the anterolateral segment of the gland, and applied the split-parotid delineation approach to the parotid gland in the treatment planning of patients with NPC with PPS and level IIa cervical node involvements, so that the function of the post-radiotherapy parotid gland might be better preserved.
authors.affiliation: 1 Cancer Hospital, Shantou University Medical College, Shantou, Guangdong, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Xiao
authors.affiliation: 1 Cancer Hospital, Shantou University Medical College, Shantou, Guangdong, China.
authors.forename: Zhixiong
authors.initials: Z
authors.lastname: Lin
authors.affiliation: 1 Cancer Hospital, Shantou University Medical College, Shantou, Guangdong, China.
authors.forename: Wuzhe
authors.initials: W
authors.lastname: Zhang
authors.affiliation: 1 Cancer Hospital, Shantou University Medical College, Shantou, Guangdong, China.
authors.forename: Mei
authors.initials: M
authors.lastname: Li
authors.affiliation: 1 Cancer Hospital, Shantou University Medical College, Shantou, Guangdong, China.|2 Department of Health Technology and Informatics, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR.
authors.forename: Vincent W C
authors.initials: VW
authors.lastname: Wu
mesh_terms: D000328:Adult; D000368:Aged; D002277:Carcinoma; D002574:Cervical Vertebrae / Q000528:radiation effects; D005260:Female; D006801:Humans; D008207:Lymphatic Metastasis; D008297:Male; D008875:Middle Aged; D000077274:Nasopharyngeal Carcinoma; D009303:Nasopharyngeal Neoplasms / Q000532:radiotherapy*; D009333:Neck; D009361:Neoplasm Invasiveness; D058958:Organs at Risk; D010306:Parotid Gland / Q000528:radiation effects*; D011874:Radiometry; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D014057:Tomography, X-Ray Computed
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