title: First Clinical Investigation of Cone Beam Computed Tomography and Deformable Registration for Adaptive Proton Therapy for Lung Cancer.
abstract: OBJECTIVE
  An adaptive proton therapy workflow using cone beam computed tomography (CBCT) is proposed. It consists of an online evaluation of a fast range-corrected dose distribution based on a virtual CT (vCT) scan. This can be followed by more accurate offline dose recalculation on the vCT scan, which can trigger a rescan CT (rCT) for replanning.
  
  
  METHODS
  The workflow was tested retrospectively for 20 consecutive lung cancer patients. A diffeomorphic Morphon algorithm was used to generate the lung vCT by deforming the average planning CT onto the CBCT scan. An additional correction step was applied to account for anatomic modifications that cannot be modeled by deformation alone. A set of clinical indicators for replanning were generated according to the water equivalent thickness (WET) and dose statistics and compared with those obtained on the rCT scan. The fast dose approximation consisted of warping the initial planned dose onto the vCT scan according to the changes in WET. The potential under- and over-ranges were assessed as a variation in WET at the target's distal surface.
  
  
  RESULTS
  The range-corrected dose from the vCT scan reproduced clinical indicators similar to those of the rCT scan. The workflow performed well under different clinical scenarios, including atelectasis, lung reinflation, and different types of tumor response. Between the vCT and rCT scans, we found a difference in the measured 95% percentile of the over-range distribution of 3.4 ± 2.7 mm. The limitations of the technique consisted of inherent uncertainties in deformable registration and the drawbacks of CBCT imaging. The correction step was adequate when gross errors occurred but could not recover subtle anatomic or density changes in tumors with complex topology.
  
  
  CONCLUSIONS
  A proton therapy workflow based on CBCT provided clinical indicators similar to those using rCT for patients with lung cancer with considerable anatomic changes.
authors.affiliation: Proton and Advanced RadioTherapy Group, Department of Medical Physics and Biomedical Engineering, University College London, London, United Kingdom.
authors.forename: Catarina
authors.initials: C
authors.lastname: Veiga
authors.affiliation: Ion Beam Applications SA, Louvain-la-Neuve, Belgium.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Janssens
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Ching-Ling
authors.initials: CL
authors.lastname: Teng
authors.affiliation: iMagX Project, ICTEAM Institute, Université Catholique de Louvain, Louvain-la-Neuve, Belgium.
authors.forename: Thomas
authors.initials: T
authors.lastname: Baudier
authors.affiliation: iMagX Project, ICTEAM Institute, Université Catholique de Louvain, Louvain-la-Neuve, Belgium.
authors.forename: Lucian
authors.initials: L
authors.lastname: Hotoiu
authors.affiliation: Centre for Medical Image Computing, Department of Medical Physics and Biomedical Engineering, University College London, London, United Kingdom.
authors.forename: Jamie R
authors.initials: JR
authors.lastname: McClelland
authors.affiliation: Proton and Advanced RadioTherapy Group, Department of Medical Physics and Biomedical Engineering, University College London, London, United Kingdom.
authors.forename: Gary
authors.initials: G
authors.lastname: Royle
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Liyong
authors.initials: L
authors.lastname: Lin
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Lingshu
authors.initials: L
authors.lastname: Yin
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: James
authors.initials: J
authors.lastname: Metz
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Solberg
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Zelig
authors.initials: Z
authors.lastname: Tochner
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Charles B
authors.initials: CB
authors.lastname: Simone
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: James
authors.initials: J
authors.lastname: McDonough
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, Pennsylvania. Electronic address: teok@uphs.upenn.edu.
authors.forename: Boon-Keng
authors.initials: BK
authors.lastname: Kevin Teo
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D001834:Body Water / Q000000981:diagnostic imaging; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D005260:Female; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000528:radiation effects; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D058958:Organs at Risk / Q000528:radiation effects; D061766:Proton Therapy / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012189:Retrospective Studies