title: Clinical study of the time of repeated computed tomography and replanning for patients with nasopharyngeal carcinoma.
abstract: OBJECTIVE
  To study the necessity of repeat computed tomography (CT) scan and replanning and know a more accurate time using weekly kilovoltage cone beam computed tomography (kV-CBCT) scans for patients with nasopharyngeal carcinoma (NPC) during radiotherapy.
  
  
  METHODS
  Thirteen NPC patients treated with IMRT were enrolled into this prospective study. Weekly pretreatment kV-CBCT scans were performed on the 1st, 6th, 11st, 16th, 21st and 26th radiation time, respectively. Target delineations were contoured on all fractionated CBCT images, including the gross tumor volume of the primary nasopharyngeal tumor (GTVnx) and parotid glands. The volumes of GTVnx and parotid glands were calculated automatically using the Pinnacle3 8.0 system. Compared to the original GTVnx, the percentage of shrinking volume (ΔP) ≥ 50% was considered significantly.
  
  
  RESULTS
  As the radiation proceeding, the GTVnx had a trend of shrinkage. Of all 13 patients, 11 cases (84.6%) had the volume shrinking ≥ 50% before the 21st radiation and 12 cases (92.3%) before the 26th radiation. And the parotid volume decreased significantly in the first four-week radiation, 6.45 ± 3.16cm3 (range, 3.06-13.9cm3) for the left parotid gland and 5.78 ± 2.39cm3 (range, 2.70-11.2cm3) for the right. Furthermore, only a little displacement occurred to bilateral parotid glands.
  
  
  CONCLUSIONS
  The replanning for NPC patients with IMRT is necessary, and the time between the 21st to 25th radiations is appropriate.
authors.affiliation: School of Medicine and Life Sciences, University of Jinan-Shandong Academy of Medical Sciences, Shandong, China.|Department of Radiation Oncology VI, Shandong Cancer Hospital Affiliated to Shandong University, Jinon, Shandong, China.
authors.forename: Xiujuan
authors.initials: X
authors.lastname: Gai
authors.affiliation: Department of Radiation Oncology VI, Shandong Cancer Hospital Affiliated to Shandong University, Jinon, Shandong, China.
authors.forename: Yumei
authors.initials: Y
authors.lastname: Wei
authors.affiliation: Shandong Provincial Hospital affiliated to Shandong University, Shandong, China.|Shandong Provincial Western Hospital, Shandong, China.
authors.forename: Hengmin
authors.initials: H
authors.lastname: Tao
authors.affiliation: Department of Radiation Oncology, Shandong Cancer Hospital Affiliated to Shandong University, Shandong, China.
authors.forename: Jian
authors.initials: J
authors.lastname: Zhu
authors.affiliation: Department of Radiation Oncology VI, Shandong Cancer Hospital Affiliated to Shandong University, Jinon, Shandong, China.
authors.forename: Baosheng
authors.initials: B
authors.lastname: Li
mesh_terms: D000293:Adolescent; D000328:Adult; D002277:Carcinoma / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy*; D054893:Cone-Beam Computed Tomography / Q000379:methods; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D000077274:Nasopharyngeal Carcinoma; D009303:Nasopharyngeal Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy*; D009367:Neoplasm Staging; D010306:Parotid Gland / Q000528:radiation effects; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D013997:Time Factors; D014057:Tomography, X-Ray Computed / Q000379:methods; D047368:Tumor Burden; D055815:Young Adult
keywords: cone beam computed tomography (CBCT); displacement; gross tumor volume (GTV); nasopharyngeal carcinoma (NPC); parotid gland