title: MRI-based tumor motion characterization and gating schemes for radiation therapy of pancreatic cancer.
abstract: OBJECTIVE
  To characterize pancreatic tumor motion and to develop a gating scheme for radiotherapy in pancreatic cancer.
  
  
  METHODS
  Two cine MRIs of 60s each were performed in fifteen pancreatic cancer patients, one in sagittal direction and one in coronal direction. A Minimum Output Sum of Squared Error (MOSSE) adaptive correlation filter was used to quantify tumor motion in craniocaudal, lateral and anteroposterior directions. To develop a gating scheme, stability of the breathing phases was examined and a gating window assessment was created, incorporating tumor motion, treatment time and motion margins.
  
  
  RESULTS
  The largest tumor motion was found in craniocaudal direction, with an average peak-to-peak amplitude of 15mm (range 6-34mm). Amplitude of the tumor in the anteroposterior direction was on average 5mm (range 1-13mm). The least motion was seen in lateral direction (average 3mm, range 2-5mm). The end exhale position was the most stable position in the breathing cycle and tumors spent more time closer to the end exhale position than to the end inhale position. On average, a margin of 25% of the maximum craniocaudal breathing amplitude was needed to achieve full target coverage with a duty cycle of 50%. When reducing the duty cycle to 50%, a margin of 5mm was sufficient to cover the target in 11 out of 15 patients.
  
  
  CONCLUSIONS
  Gated delivery for radiotherapy of pancreatic cancer is best performed around the end exhale position as this is the most stable position in the breathing cycle. Considerable margin reduction can be established at moderate duty cycles, yielding acceptable treatment efficiency. However, motion patterns and amplitude do substantially differ between individual patients. Therefore, individual treatment strategies should be considered for radiotherapy in pancreatic cancer.
authors.affiliation: Department of Radiotherapy, University Medical Center Utrecht, The Netherlands. Electronic address: h.heerkens@umcutrecht.nl.
authors.forename: Hanne D
authors.initials: HD
authors.lastname: Heerkens
authors.affiliation: Department of Radiotherapy, University Medical Center Utrecht, The Netherlands.
authors.forename: Marco
authors.initials: M
authors.lastname: van Vulpen
authors.affiliation: Department of Radiotherapy, University Medical Center Utrecht, The Netherlands.
authors.forename: Cornelis A T
authors.initials: CA
authors.lastname: van den Berg
authors.affiliation: Department of Radiotherapy, University Medical Center Utrecht, The Netherlands.
authors.forename: Rob H N
authors.initials: RH
authors.lastname: Tijssen
authors.affiliation: Department of Radiotherapy, University Medical Center Utrecht, The Netherlands.
authors.forename: Sjoerd P M
authors.initials: SP
authors.lastname: Crijns
authors.affiliation: Department of Surgery, University Medical Center Utrecht, The Netherlands.
authors.forename: Izaak Q
authors.initials: IQ
authors.lastname: Molenaar
authors.affiliation: Department of Surgery, University Medical Center Utrecht, The Netherlands.
authors.forename: Hjalmar C
authors.initials: HC
authors.lastname: van Santvoort
authors.affiliation: Department of Radiotherapy, University Medical Center Utrecht, The Netherlands.
authors.forename: Onne
authors.initials: O
authors.lastname: Reerink
authors.affiliation: Department of Radiotherapy, University Medical Center Utrecht, The Netherlands.
authors.forename: Gert J
authors.initials: GJ
authors.lastname: Meijer
mesh_terms: D000368:Aged; D045853:Exhalation; D005260:Female; D006801:Humans; D001239:Inhalation; D019028:Magnetic Resonance Imaging, Cine / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009068:Movement; D010190:Pancreatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000517:prevention & control; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*
keywords: Gating; MRI; Magnetic resonance imaging; Motion; Pancreatic cancer; Radiotherapy