title: Rules of parotid gland dose variations and shift during intensity modulated radiation therapy for nasopharyngeal carcinoma.
abstract: BACKGROUND
  To determine the position and dose delivery changes rules of parotid gland (PG) during the course of intensity modulated radiation therapy (IMRT) in nasopharyngeal carcinoma patients (NPC).
  
  
  METHODS
  One hundred and forty one competed tomography (CT) images from 47 NPC patients (three images for each patient were acquired before treatment, at the 15th and 25th fraction during the treatment) who underwent radical IMRT were selected for this study. A total of 70-76Gy at 2.12-2.3 Gy/fraction/d was given to the GTVnx in 33 fractions. The distances between the lateral/medial aspects of PG and midline (DLM and DMM) at the level of odontoid process were measured. The dose differences between plan and actual delivery were calculated.
  
  
  RESULTS
  The volume reductions of PGs between fractions 15 and 25 were larger than those in the first 15 fractions (4.68 ± 3.23 cc vs. 2.46 ± 4.55 cc for the right PG and 5.96 ± 2.99 cc vs. 2.06 ± 2.99 cc for the left PG). However, the percentage of gland volume receiving ≥ 30 Gy (V30) of bilateral PGs decreased more significantly in the first 15 fractions than that between fractions 15 and 25 (5.61 ± 16.04% vs. 1.14 ± 21.54% for the right PG and 6.87 ± 15.58% vs. 0.81 ± 15.94% for the left PG). The gross tumor volume of the nasopharynx (GTVnx) decreased more significantly in the first 15 fractions than that between the 15th and 25th fraction (8.23 ± 13.61 cc vs. 3.30 ± 8.09 cc). The DMM of ipsilateral PGs reduced in the first 15 fractions (0.80 ± 2.96 mm) but increased between fraction 15 and 25 (-2.19 ± 3.96 mm). While ipsilateral PG shifted into target volume but shifted out target volume between fraction 15 and 25. Parotid glands V30 was correlated with GTVnx, GTVnx reduction and DMM reduction (p<0.01).
  
  
  CONCLUSIONS
  Our results indicate that the reduction of GTVnx leads to the positional change of the parotid gland, which results in more significant dose change of the parotid gland in the first 15 fractions than that between fraction 15 and 25.
authors.affiliation: Department of Radiation Oncology, Affiliated Taizhou Hospital of Wenzhou Medical University, Zhejiang, 317000, China. ww11520@hotmail.com.|Laboratory of Cellular and Molecular Radiation Oncology, Affiliated Taizhou Hospital of Wenzhou Medical University, Zhejiang, 317000, China. ww11520@hotmail.com.
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.affiliation: Department of Radiation Oncology, Affiliated Taizhou Hospital of Wenzhou Medical University, Zhejiang, 317000, China. yhh93181@hotmail.com.|Laboratory of Cellular and Molecular Radiation Oncology, Affiliated Taizhou Hospital of Wenzhou Medical University, Zhejiang, 317000, China. yhh93181@hotmail.com.
authors.forename: Haihua
authors.initials: H
authors.lastname: Yang
authors.affiliation: Department of Radiology, Affiliated Taizhou Hospital of Wenzhou Medical University, Zhejiang, 317000, China. miyc@enzemed.com.
authors.forename: Yucheng
authors.initials: Y
authors.lastname: Mi
authors.affiliation: Department of Radiation Oncology, Affiliated Taizhou Hospital of Wenzhou Medical University, Zhejiang, 317000, China. huw@enzemed.com.|Laboratory of Cellular and Molecular Radiation Oncology, Affiliated Taizhou Hospital of Wenzhou Medical University, Zhejiang, 317000, China. huw@enzemed.com.
authors.forename: Wei
authors.initials: W
authors.lastname: Hu
authors.affiliation: Department of Radiation Oncology, Affiliated Taizhou Hospital of Wenzhou Medical University, Zhejiang, 317000, China. dingwj@enzemed.com.|Laboratory of Cellular and Molecular Radiation Oncology, Affiliated Taizhou Hospital of Wenzhou Medical University, Zhejiang, 317000, China. dingwj@enzemed.com.
authors.forename: Weijun
authors.initials: W
authors.lastname: Ding
authors.affiliation: Department of Radiation Oncology, Affiliated Taizhou Hospital of Wenzhou Medical University, Zhejiang, 317000, China. xieyy@enzemed.com.|Laboratory of Cellular and Molecular Radiation Oncology, Affiliated Taizhou Hospital of Wenzhou Medical University, Zhejiang, 317000, China. xieyy@enzemed.com.
authors.forename: Youyou
authors.initials: Y
authors.lastname: Xie
authors.affiliation: Department of Radiation Oncology, Affiliated Taizhou Hospital of Wenzhou Medical University, Zhejiang, 317000, China. xs_caiyj@enzemed.com.|Laboratory of Cellular and Molecular Radiation Oncology, Affiliated Taizhou Hospital of Wenzhou Medical University, Zhejiang, 317000, China. xs_caiyj@enzemed.com.
authors.forename: Yujie
authors.initials: Y
authors.lastname: Cai
authors.affiliation: Enze Medical Research Center, Affiliated Taizhou Hospital of Wenzhou Medical University, Zhejiang, 317000, China. chenxf@enzemed.com.
authors.forename: Xiaofeng
authors.initials: X
authors.lastname: Chen
mesh_terms: D000328:Adult; D000368:Aged; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009303:Nasopharyngeal Neoplasms / Q000532:radiotherapy*; D009367:Neoplasm Staging; D010306:Parotid Gland / Q000473:pathology* / Q000528:radiation effects; D011379:Prognosis; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*