title: Interfractional variations of tumor centroid position and tumor regression during stereotactic body radiotherapy for lung tumor.
abstract: OBJECTIVE
  To determine interfractional changes of lung tumor centroid position and tumor regression during stereotactic body radiation therapy (SBRT).
  
  
  METHODS
  34 patients were treated by SBRT in 4-5 fractions to a median dose of 50 Gy. The CT scans acquired for verification were registered with simulation CT scans. The gross target volume (GTV) was contoured on all verification CT scans and compared to the initial GTV in treatment plan system.
  
  
  RESULTS
  The mean (±standard deviation, SD) three-dimension vector shift was 5.2 ± 3.1 mm. The mean (±SD) interfractional variations of tumor centroid position were -0.7 ± 4.5 mm in anterior-posterior (AP) direction, 0.2 ± 3.1 mm in superior-inferior (SI) direction, and 0.4 ± 2.4 mm in right-left (RL) direction. Large interfractional variations (≥5 mm) were observed in 5 fractions (3.3%) in RL direction, 16 fractions (10.5%) in SI direction, and 36 fractions (23.5%) in AP direction. Tumor volume did not decrease significantly during lung SBRT.
  
  
  CONCLUSIONS
  Small but insignificant tumor volume regression was observed during lung SBRT. While the mean interfractional variations of tumor centroid position were minimal in three directions, variations more than 5 mm account for approximately a third of all, indicating additional margin for PTV, especially in AP direction.
authors.affiliation: Department of Radiation Oncology, The Affiliated Cancer Hospital of Zhengzhou University, 127 Dongming Road, Zhengzhou, Henan 450008, China.
authors.forename: Yanan
authors.initials: Y
authors.lastname: Sun
authors.affiliation: Department of Radiation Oncology, The Affiliated Cancer Hospital of Zhengzhou University, 127 Dongming Road, Zhengzhou, Henan 450008, China.
authors.forename: Yufei
authors.initials: Y
authors.lastname: Lu
authors.affiliation: Red Cross Blood Center of Henan, 9 Tongle Road, Zhengzhou, Henan 450053, China.
authors.forename: Siguo
authors.initials: S
authors.lastname: Cheng
authors.affiliation: Department of Radiation Oncology, The Affiliated Cancer Hospital of Zhengzhou University, 127 Dongming Road, Zhengzhou, Henan 450008, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Guo
authors.affiliation: Department of Radiation Oncology, The Affiliated Cancer Hospital of Zhengzhou University, 127 Dongming Road, Zhengzhou, Henan 450008, China.
authors.forename: Ke
authors.initials: K
authors.lastname: Ye
authors.affiliation: Department of Radiation Oncology, The Affiliated Cancer Hospital of Zhengzhou University, 127 Dongming Road, Zhengzhou, Henan 450008, China.
authors.forename: Huiyun
authors.initials: H
authors.lastname: Zhao
authors.affiliation: Department of Radiation Oncology, The Affiliated Cancer Hospital of Zhengzhou University, 127 Dongming Road, Zhengzhou, Henan 450008, China.
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Zheng
authors.affiliation: Department of Radiation Oncology, The Affiliated Cancer Hospital of Zhengzhou University, 127 Dongming Road, Zhengzhou, Henan 450008, China.
authors.forename: Dingjie
authors.initials: D
authors.lastname: Li
authors.affiliation: Department of Radiation Oncology, The Affiliated Cancer Hospital of Zhengzhou University, 127 Dongming Road, Zhengzhou, Henan 450008, China.
authors.forename: Shujuan
authors.initials: S
authors.lastname: Wang
authors.affiliation: Department of Radiation Oncology, The Affiliated Cancer Hospital of Zhengzhou University, 127 Dongming Road, Zhengzhou, Henan 450008, China.
authors.forename: Chengliang
authors.initials: C
authors.lastname: Yang
authors.affiliation: Department of Radiation Oncology, The Affiliated Cancer Hospital of Zhengzhou University, 127 Dongming Road, Zhengzhou, Henan 450008, China.
authors.forename: Hong
authors.initials: H
authors.lastname: Ge
mesh_terms: D000328:Adult; D000368:Aged; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D009362:Neoplasm Metastasis; D016634:Radiosurgery; D014057:Tomography, X-Ray Computed