title: Objected constrained registration and manifold learning: a new patient setup approach in image guided radiation therapy of thoracic cancer.
abstract: OBJECTIVE
  The management of thoracic malignancies with radiation therapy is complicated by continuous target motion. In this study, a real time motion analysis approach is proposed to improve the accuracy of patient setup.
  
  
  METHODS
  For 11 lung cancer patients a long training fluoroscopy was acquired before the first treatment, and multiple short testing fluoroscopies were acquired weekly at the pretreatment patient setup of image guided radiotherapy (IGRT). The data analysis consisted of three steps: first a 4D target motion model was constructed from 4DCT and projected to the training fluoroscopy through deformable registration. Then the manifold learning method was used to construct a 2D subspace based on the target motion (kinetic) and location (static) information in the training fluoroscopy. Thereafter the respiratory phase in the testing fluoroscopy was determined by finding its location in the subspace. Finally, the phase determined testing fluoroscopy was registered to the corresponding 4DCT to derive the pretreatment patient position adjustment for the IGRT. The method was tested on clinical image sets and numerical phantoms.
  
  
  RESULTS
  The registration successfully reconstructed the 4D motion model with over 98% volume similarity in 4DCT, and over 95% area similarity in the training fluoroscopy. The machine learning method derived the phase values in over 98% and 93% test images of the phantom and patient images, respectively, with less than 3% phase error. The setup approach achieved an average accumulated setup error less than 1.7 mm in the cranial-caudal direction and less than 1 mm in the transverse plane. All results were validated against the ground truth of manual delineations by an experienced radiation oncologist. The expected total time for the pretreatment setup analysis was less than 10 s.
  
  
  CONCLUSIONS
  By combining the registration and machine learning, the proposed approach has the potential to improve the accuracy of pretreatment setup for patients with thoracic malignancy.
authors.affiliation: Radiation Oncology Department, Cancer Institute of New Jersey, University of Medicine and Dentistry of New Jersey, 195 Little Albany Street, New Brunswick, New Jersey 08901, USA. chent4@umdnj.edu
authors.forename: Ting
authors.initials: T
authors.lastname: Chen
authors.forename: Salma K
authors.initials: SK
authors.lastname: Jabbour
authors.forename: Songbing
authors.initials: S
authors.lastname: Qin
authors.forename: Bruce G
authors.initials: BG
authors.lastname: Haffty
authors.forename: Ning
authors.initials: N
authors.lastname: Yue
mesh_terms: D059925:Anatomic Landmarks / Q000000981:diagnostic imaging*; D001185:Artificial Intelligence; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D010363:Pattern Recognition, Automated / Q000379:methods; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique; D013899:Thoracic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*
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