title: Kilovoltage intrafraction motion monitoring and target dose reconstruction for stereotactic volumetric modulated arc therapy of tumors in the liver.
abstract: OBJECTIVE
  To use intrafraction kilovoltage (kV) imaging during liver stereotactic body radiotherapy (SBRT) delivered by volumetric modulated arc therapy (VMAT) to estimate the intra-treatment target motion and to reconstruct the delivered target dose.
  
  
  METHODS
  Six liver SBRT patients with 2-3 implanted gold markers received SBRT in three fractions of 18.75 Gy or 25 Gy. CTV-to-PTV margins of 5 mm in the axial plane and 10 mm in the cranio-caudal directions were applied. A VMAT plan was designed to give minimum target doses of 95% (CTV) and 67% (PTV). At each fraction, the 3D marker trajectory was estimated by fluoroscopic kV imaging throughout treatment delivery and used to reconstruct the actually delivered CTV dose. The reduction in D95 (minimum dose to 95% of the CTV) relative to the planned D95 was calculated.
  
  
  RESULTS
  The kV position estimation had mean root-mean-square errors of 0.36 mm and 0.47 mm parallel and perpendicular to the kV imager, respectively. Intrafraction motion caused a mean 3D target position error of 2.9 mm and a mean D95 reduction of 6.0%. The D95 reduction correlated with the mean 3D target position error during a fraction.
  
  
  CONCLUSIONS
  Kilovoltage imaging for detailed motion monitoring with dose reconstruction of VMAT-based liver SBRT was demonstrated for the first time showing large dosimetric impact of intrafraction tumor motion.
authors.affiliation: Department of Oncology, Aarhus University Hospital, Denmark; Institute of Clinical Medicine, Aarhus University, Denmark. Electronic address: per.poulsen@rm.dk.
authors.forename: Per Rugaard
authors.initials: PR
authors.lastname: Poulsen
authors.affiliation: Department of Oncology, Aarhus University Hospital, Denmark; Department of Medical Physics, Aarhus University Hospital, Denmark.
authors.forename: Esben S
authors.initials: ES
authors.lastname: Worm
authors.affiliation: Department of Medical Physics, Aarhus University Hospital, Denmark.
authors.forename: Jørgen B B
authors.initials: JB
authors.lastname: Petersen
authors.affiliation: Department of Oncology, Aarhus University Hospital, Denmark; Institute of Clinical Medicine, Aarhus University, Denmark.
authors.forename: Cai
authors.initials: C
authors.lastname: Grau
authors.affiliation: Department of Oncology, Aarhus University Hospital, Denmark; Department of Medical Physics, Aarhus University Hospital, Denmark.
authors.forename: Walther
authors.initials: W
authors.lastname: Fledelius
authors.affiliation: Department of Oncology, Aarhus University Hospital, Denmark; Institute of Clinical Medicine, Aarhus University, Denmark.
authors.forename: Morten
authors.initials: M
authors.lastname: Høyer
mesh_terms: D000368:Aged; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D008113:Liver Neoplasms / Q000473:pathology* / Q000556:secondary / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D016634:Radiosurgery / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods
keywords: Dose reconstruction; Image-guided radiotherapy; Intrafraction motion monitoring