title: Predictors of respiratory-induced lung tumour motion measured on four-dimensional computed tomography.
abstract: OBJECTIVE
  The delivery of radical radiotherapy in lung cancer is complicated by respiratory-induced tumour motion. The aim of the study was to correlate tumour motion characteristics with tumour and patient factors, particularly the anatomical lobe and pulmonary zone.
  
  
  METHODS
  Lung tumour volumes on four-dimensional computed tomography were delineated by a single observer at maximal expiration and propagated through all 10 phases of the breathing cycle. Movements were tracked in the superior-inferior (SI), anterior-posterior (AP) and medio-lateral (ML) directions by changes in the tumour centroid coordinates. Tumour motion characteristics were correlated with anatomical lobe, pulmonary zone, tumour volume, T-stage, smoking status and spirometry.
  
  
  RESULTS
  In 101 consecutive patients, the median magnitude of tumour motion in the SI direction was significantly larger in tumours located in lower lobes compared with upper lobes and middle/lingular lobes (0.70 cm versus 0.09 cm versus 0.26 cm, P < 0.01). No significant difference was found in median tumour motion between lower, upper and middle/lingular lobes in the AP (0.16 cm versus 0.13 cm versus 0.16 cm, P = 0.45) and ML (0.08 cm versus 0.08 cm versus 0.13 cm, P = 0.32) directions, respectively. When assessed by zone, the median tumour displacement in the SI direction was significantly larger in the lower zones (0.81 cm) as compared with the middle zones (0.30 cm) and upper zones (0.11 cm), P < 0.01. No difference was observed in the AP (P = 0.45) and ML (P = 0.73) directions. Tumour volume, T-stage and forced expiratory ratio were not statistically significant predictors of respiratory-induced tumour motion.
  
  
  CONCLUSIONS
  Respiratory-induced tumour motion in the SI direction was significantly greater in lower lobe and lower pulmonary zone tumours compared with apical tumours. Tumour volume, T-stage and spirometry did not correlate with the magnitude or direction of respiratory-induced tumour motion. During curative radiotherapy in lung cancer, attention should be paid to motion management, especially for lower lobe tumours.
authors.affiliation: Radiation Oncology and Cancer Imaging, Peter MacCallum Cancer Centre, Melbourne, Australia. Electronic address: kevin.tan11@gmail.com.
authors.forename: K V
authors.initials: KV
authors.lastname: Tan
authors.affiliation: Radiation Therapy Services, Peter MacCallum Cancer Centre, Melbourne, Australia.
authors.forename: R
authors.initials: R
authors.lastname: Thomas
authors.affiliation: Physical Sciences, Peter MacCallum Cancer Centre, Melbourne, Australia.
authors.forename: N
authors.initials: N
authors.lastname: Hardcastle
authors.affiliation: Radiation Therapy Services, Peter MacCallum Cancer Centre, Melbourne, Australia.
authors.forename: D
authors.initials: D
authors.lastname: Pham
authors.affiliation: Physical Sciences, Peter MacCallum Cancer Centre, Melbourne, Australia; Sir Peter MacCallum Department of Oncology, Melbourne University, Melbourne, Australia.
authors.forename: T
authors.initials: T
authors.lastname: Kron
authors.affiliation: Radiation Oncology and Cancer Imaging, Peter MacCallum Cancer Centre, Melbourne, Australia; Sir Peter MacCallum Department of Oncology, Melbourne University, Melbourne, Australia.
authors.forename: F
authors.initials: F
authors.lastname: Foroudi
authors.affiliation: Radiation Oncology and Cancer Imaging, Peter MacCallum Cancer Centre, Melbourne, Australia; Sir Peter MacCallum Department of Oncology, Melbourne University, Melbourne, Australia.
authors.forename: D
authors.initials: D
authors.lastname: Ball
authors.affiliation: Centre for Biostatistics and Clinical Trials, Peter MacCallum Cancer Centre, Melbourne, Australia.
authors.forename: L
authors.initials: L
authors.lastname: Te Marvelde
authors.affiliation: Centre for Biostatistics and Clinical Trials, Peter MacCallum Cancer Centre, Melbourne, Australia.
authors.forename: M
authors.initials: M
authors.lastname: Bressel
authors.affiliation: Radiation Oncology and Cancer Imaging, Peter MacCallum Cancer Centre, Melbourne, Australia; Sir Peter MacCallum Department of Oncology, Melbourne University, Melbourne, Australia.
authors.forename: S
authors.initials: S
authors.lastname: Siva
mesh_terms: D005260:Female; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D008168:Lung / Q000033:anatomy & histology* / Q000503:physiopathology*; D008175:Lung Neoplasms / Q000503:physiopathology* / Q000532:radiotherapy*; D008297:Male; D009367:Neoplasm Staging; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012189:Retrospective Studies
keywords: Four-dimensional computed tomography; motion; respiratory induced