title: Endobiliary Stent Position Changes during External-beam Radiotherapy.
abstract: OBJECTIVE
  Endobiliary stents can be used as surrogates for pancreatic localization when using cone-beam computed tomography (CBCT) during external-beam radiotherapy (EBRT). This work reports on interfraction stent position changes during EBRT for locally advanced pancreatic cancer (LAPC).
  
  
  METHODS
  Six patients with endobiliary stents who underwent EBRT for LAPC were assessed. Measurements from the most superior aspect of the stent (sup stent) and the most inferior aspect of the stent (inf stent) to the most inferior, posterior aspect of the L1 vertebra central spinous process were determined from daily treatment CBCTs and compared with those determined from the planning computed tomography (CT) scan. Changes in stent-L1 measurements were interpreted as changes in relative stent position.
  
  
  RESULTS
  Three patients showed mean interfraction stent position changes of ≥1 cm when treatment measurements were compared with planning measurements. The sup stent for patient A moved to the right (2.66 ± 2.77 cm) and inferiorly (3.0 ± 3.12 cm), and the inf stent moved to the right (1.92 ± 2.02 cm) inferiorly (3.23 ± 3.34 cm) and posteriorly (1.41 ± 1.43 cm). The inf stent for patient B moved superiorly (2.23 ± 0.49 cm) and posteriorly (1.72 ± 0.59 cm). The sup and inf stent for patient F moved inferiorly (0.98 ± 0.35 cm and 1.21 ± 0.38 cm, respectively). The remaining three patients C, D, and E showed interfraction position changes of <1 cm.
  
  
  CONCLUSIONS
  Endobiliary stent migration and deformation were observed in a small subset of patients. Further investigation is required before confirming their use as surrogates for LAPC target localization during image-guided EBRT.
authors.affiliation: CRUK/MRC Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford, United Kingdom ; Radiotherapy Department, Churchill Hospital, Oxford University Hospitals NHS Trust, Oxford, United Kingdom.
authors.forename: Kwun-Ye
authors.initials: KY
authors.lastname: Chu
authors.affiliation: CRUK/MRC Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford, United Kingdom ; Radiotherapy Department, Churchill Hospital, Oxford University Hospitals NHS Trust, Oxford, United Kingdom.
authors.forename: Cynthia L
authors.initials: CL
authors.lastname: Eccles
authors.affiliation: CRUK/MRC Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford, United Kingdom ; Department of Radiation Oncology, University of Freiburg, Freiburg im Breisgau, Germany.
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Brunner
keywords: Stent; cone-beam CT; image-guided radiotherapy; pancreatic cancer; position change