title: Dosimetric impact of online correction via cone-beam CT-based image guidance for stereotactic lung radiotherapy.
abstract: OBJECTIVE
  To evaluate the dosimetric impact of online cone-beam computed tomography (CBCT) guided correction in lung stereotactic body radiation therapy (SBRT).
  
  
  METHODS
  Twenty planning and 162 CBCT images from 20 patients undergoing lung SBRT were analyzed. The precorrection CBCT (CBCT after patient setup, no couch correction) was registered to planning CT using soft tissue; couch shift was applied, with a second CBCT for verification (postcorrection CBCT). Targets and normal structures were delineated on CBCTs: gross tumor volume (GTV), clinical target volume (CTV), cord, esophagus, lung, proximal bronchial tree, and aorta. Dose distributions on all organs manifested on each CBCT were compared with those planned on the CT.
  
  
  RESULTS
  Without CBCT guided target position correction, target dose reduced with respect to treatment plan. Mean and standard deviation of treatment dose discrepancy from the plan were -3.2% (4.9%), -2.1% (4.4%), -6.1% (10.7%), and -3.5% (7%) for GTV D(99%), GTV D(95%), CTV D(99%), and CTV D(95%), respectively. With CBCT correction, the results were -0.4% (2.6%), 0.1% (1.7%), -0.3% (4.2%), and 0.5% (3%). Mean and standard deviation of the difference in normal organ maximum dose were 2.2% (6.5%) before correction and 2.4% (5.9%) after correction for esophagus; 6.1% (14.1%) and 3.8% (8.1%) for cord; 3.1% (17.5%) and 6.2% (9.8%) for proximal bronchial tree; and 17.7% (19.5%) and 14.1% (17%) for aorta.
  
  
  CONCLUSIONS
  Online CBCT guidance improves the accuracy of target dose delivery for lung SBRT. However, treatment dose to normal tissue can vary regardless of the correction. Normal tissues should be considered during target registration, according to target proximity.
authors.affiliation: Department of Radiation Oncology, Clinirad, Angelina Caron Hospital, Curitiba, Parana, Brazil.
authors.forename: Ana Paula
authors.initials: AP
authors.lastname: Galerani
authors.forename: Inga
authors.initials: I
authors.lastname: Grills
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Hugo
authors.forename: Larry
authors.initials: L
authors.lastname: Kestin
authors.forename: Nasiruddin
authors.initials: N
authors.lastname: Mohammed
authors.forename: K Kenneth
authors.initials: KK
authors.lastname: Chao
authors.forename: Andrew
authors.initials: A
authors.lastname: Suen
authors.forename: Alvaro
authors.initials: A
authors.lastname: Martinez
authors.forename: Di
authors.initials: D
authors.lastname: Yan
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D054893:Cone-Beam Computed Tomography; D005260:Female; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging*; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D008297:Male; D008875:Middle Aged; D009068:Movement; D058958:Organs at Risk / Q000000981:diagnostic imaging; D016634:Radiosurgery / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012119:Respiration; D047368:Tumor Burden