title: Is it necessary to repeat CT imaging and replanning during the course of intensity-modulated radiation therapy for locoregionally advanced nasopharyngeal carcinoma?
abstract: OBJECTIVE
  Our aim was to evaluate the volumetric and dosimetric changes of target volumes and organs at risk (OARs) during intensity-modulated radiation therapy (IMRT) for locoregionally advanced nasopharyngeal carcinoma (NPC) and the necessity of replanning.
  
  
  METHODS
  Twenty locoregionally advanced NPC patients treated by concurrent chemotherapy and IMRT were included. CT and MR images were acquired before treatment and at weeks 2, 3, 4, 5 and 6 during treatment. The target volumes and OARs were contoured based on the fused CT-MRI images and hybrid plans were generated. The changes of volume and dosimetry were measured by comparing original plan and hybrid plans.
  
  
  RESULTS
  Significant volumetric changes of target volumes and parotid gland were observed. The primary nasopharyngeal tumor (GTVnx), CTV1, involved lymph nodes (GTVnd) and left and right parotid glands, shrank at a mean rate of 14.7, 11.56, 11.40, 6.54 and 6.78 % per treatment week, respectively. There were no significant dosimetric changes in GTVnx, GTVnd, CTV1, spinal cord and brain stem while the differences of dose to left and right parotid glands were significant (F = 6.73, P = 0.007; F = 7.43, P = 0.007).
  
  
  CONCLUSIONS
  Remarkable volumetric changes were observed. However, the dosimetric changes were inconspicuous except for the parotid. Replanning might contribute to protect the parotid gland.
authors.affiliation: Department of Radiation Oncology, Cancer Hospital of Fujian Medical University, 91 Maluding, Fuma Road, Fuzhou, 350014, People's Republic of China.
authors.forename: Chuanben
authors.initials: C
authors.lastname: Chen
authors.forename: Xiang
authors.initials: X
authors.lastname: Lin
authors.forename: Jianji
authors.initials: J
authors.lastname: Pan
authors.forename: Zhaodong
authors.initials: Z
authors.lastname: Fei
authors.forename: Lisha
authors.initials: L
authors.lastname: Chen
authors.forename: Penggang
authors.initials: P
authors.lastname: Bai
mesh_terms: D001933:Brain Stem / Q000000981:diagnostic imaging / Q000473:pathology; D002277:Carcinoma; D003131:Combined Modality Therapy / Q000379:methods; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008198:Lymph Nodes / Q000000981:diagnostic imaging / Q000473:pathology; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D064847:Multimodal Imaging / Q000379:methods; D000077274:Nasopharyngeal Carcinoma; D009303:Nasopharyngeal Neoplasms / Q000000981:diagnostic imaging* / Q000188:drug therapy / Q000532:radiotherapy*; D009929:Organ Size; D058958:Organs at Risk / Q000000981:diagnostic imaging* / Q000473:pathology; D010306:Parotid Gland / Q000000981:diagnostic imaging / Q000473:pathology; D011446:Prospective Studies; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects / Q000379:methods*; D013116:Spinal Cord / Q000000981:diagnostic imaging / Q000473:pathology; D014057:Tomography, X-Ray Computed / Q000379:methods*