title: Hypofractionated radiotherapy for lung tumors with online cone beam CT guidance and active breathing control.
abstract: BACKGROUND
  To study the set-up errors, PTV margin and toxicity of cone beam CT (CBCT) guided hypofractionated radiotherapy with active breathing control (ABC) for patients with non-small cell lung cancer (NSCLC) or metastatic tumors in lung.
  
  
  METHODS
  32 tumors in 20 patients were treated. Based on the location of tumor, dose per fraction given to tumor was divided into three groups: 12 Gy, 8 Gy and 6 Gy. ABC is applied for every patient. During each treatment, patients receive CBCT scan for online set-up correction. The pre- and post-correction setup errors between fractions, the interfractional and intrafractional, set-up errors, PTV margin as well as toxicity are analyzed.
  
  
  RESULTS
  The pre-correction systematic and random errors in the left-right (LR), superior-inferior (SI), anterior-posterior (AP) directions were 3.7 mm and 5.3 mm, 3.1 mm and 2.1 mm, 3.7 mm and 2.8 mm, respectively, while the post-correction residual errors were 0.6 mm and 0.8 mm, 0.8 mm and 0.8 mm, 1.2 mm and 1.3 mm, respectively. There was an obvious intrafractional shift of tumor position. The pre-correction PTV margin was 9.5 mm in LR, 14.1 mm in SI and 8.2 mm in AP direction. After CBCT guided online correction, the PTV margin was markedly reduced in all three directions. The post-correction margins ranged 1.5 to 2.1 mm. The treatment was well tolerated by patients, of whom there were 4 (20%) grade1-2 acute pneumonitis, 3 (15%) grade1 acute esophagitis, 2 (10%) grade1 late pneumonitis and 1 (5%) grade 1 late esophagitis.
  
  
  CONCLUSIONS
  The positioning errors for lung SBRT using ABC were significant. Online correction with CBCT image guidance should be applied to reduce setup errors and PTV margin, which may reduce radiotherapy toxicity of tissues when ABC was used.
authors.affiliation: Department of radiation oncology, Cancer centre, West China Hospital, Sichuan University, Chengdu 610041, China.
authors.forename: Yali
authors.initials: Y
authors.lastname: Shen
authors.forename: Hong
authors.initials: H
authors.lastname: Zhang
authors.forename: Jin
authors.initials: J
authors.lastname: Wang
authors.forename: Renming
authors.initials: R
authors.lastname: Zhong
authors.forename: Xiaoqing
authors.initials: X
authors.lastname: Jiang
authors.forename: Qinfeng
authors.initials: Q
authors.lastname: Xu
authors.forename: Xin
authors.initials: X
authors.lastname: Wang
authors.forename: Sen
authors.initials: S
authors.lastname: Bai
authors.forename: Feng
authors.initials: F
authors.lastname: Xu
mesh_terms: D000328:Adult; D000368:Aged; D002289:Carcinoma, Non-Small-Cell Lung / Q000532:radiotherapy*; D054893:Cone-Beam Computed Tomography; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D009068:Movement; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012119:Respiration; D012149:Restraint, Physical / Q000379:methods; D055815:Young Adult