title: Practically acquired and modified cone-beam computed tomography images for accurate dose calculation in head and neck cancer.
abstract: BACKGROUND
  On-line cone-beam computed tomography (CBCT) may be used to reconstruct the dose for geometric changes of patients and tumors during radiotherapy course. This study is to establish a practical method to modify the CBCT for accurate dose calculation in head and neck cancer.
  
  
  METHODS
  Fan-beam CT (FBCT) and Elekta's CBCT were used to acquire images. The CT numbers for different materials on CBCT were mathematically modified to match them with FBCT. Three phantoms were scanned by FBCT and CBCT for image uniformity, spatial resolution, and CT numbers, and to compare the dose distribution from orthogonal beams. A Rando phantom was scanned and planned with intensity-modulated radiation therapy (IMRT). Finally, two nasopharyngeal cancer patients treated with IMRT had their CBCT image sets calculated for dose comparison.
  
  
  RESULTS
  With 360° acquisition of CBCT and high-resolution reconstruction, the uniformity of CT number distribution was improved and the otherwise large variations for background and high-density materials were reduced significantly. The dose difference between FBCT and CBCT was < 2% in phantoms. In the Rando phantom and the patients, the dose-volume histograms were similar. The corresponding isodose curves covering ≥ 90% of prescribed dose on FBCT and CBCT were close to each other (within 2 mm). Most dosimetric differences were from the setup errors related to the interval changes in body shape and tumor response.
  
  
  CONCLUSIONS
  The specific CBCT acquisition, reconstruction, and CT number modification can generate accurate dose calculation for the potential use in adaptive radiotherapy.
authors.affiliation: Division of Radiation Oncology, Department of Oncology, National Taiwan University Hospital and College of Medicine, Taipei.
authors.forename: Chih-Chung
authors.initials: CC
authors.lastname: Hu
authors.forename: Wen-Tao
authors.initials: WT
authors.lastname: Huang
authors.forename: Chiao-Ling
authors.initials: CL
authors.lastname: Tsai
authors.forename: Jian-Kuen
authors.initials: JK
authors.lastname: Wu
authors.forename: Hsiao-Ling
authors.initials: HL
authors.lastname: Chao
authors.forename: Guo-Ming
authors.initials: GM
authors.lastname: Huang
authors.forename: Chun-Wei
authors.initials: CW
authors.lastname: Wang
authors.forename: Chien-Jang
authors.initials: CJ
authors.lastname: Wu
authors.forename: Jason Chia-Hsien
authors.initials: JC
authors.lastname: Cheng
mesh_terms: D054893:Cone-Beam Computed Tomography / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D009303:Nasopharyngeal Neoplasms / Q000532:radiotherapy; D058958:Organs at Risk / Q000528:radiation effects; D010039:Otorhinolaryngologic Neoplasms / Q000532:radiotherapy*; D010315:Particle Accelerators; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods