title: Evaluation of motion mitigation using abdominal compression in the clinical implementation of pencil beam scanning proton therapy of liver tumors.
abstract: OBJECTIVE
  To determine whether individual liver tumor patients can be safely treated with pencil beam scanning proton therapy. This study reports a planning preparation workflow that can be used for beam angle selection and the evaluation of the efficacy of abdominal compression (AC) to mitigate motion.
  
  
  METHODS
  Four-dimensional computed tomography scans (4DCT) with and without AC were available from 10 liver tumor patients with fluoroscopy-proven motion reduction by AC, previously treated using photons. For each scan, the motion amplitudes and the motion-induced variation of water-equivalent thickness (ΔWET) in each voxel of the target volume were evaluated during treatment plan preparation. Optimal proton beam angles were selected after volume analysis of the respective beam-specific planning target volume (BSPTV). M⊥80and ΔWET80derived from the 80th percentiles of perpendicular motion amplitude (M⊥) and ΔWET were compared with and without AC. Proton plans were created on the average CT to achieve target coverage similar to that of the conventional photon treatments. 4D dynamic dose calculation was performed postplan by synchronizing proton beam delivery timing patterns to the 4DCT phases to assess interplay and fractionation effects, and to determine motion criteria for subsequent patient treatment.
  
  
  RESULTS
  Selected coplanar beam angles ranged between 180° and 39°, primarily from right lateral (oblique) and posterior (oblique) directions. While AC produced a significant reduction in mean Liver-GTV dose, any reduction in mean heart dose was patient dependent and not significant. Similarly, AC resulted in reductions in M⊥, ΔWET, and BSPTV volumes and improved dose degradation (ΔD95and ΔD1) within the CTV. For small motion (M⊥80< 7 mm and ΔWET80< 5 mm), motion mitigation was not needed. For moderate motion (M⊥807-10 mm or ΔWET805-7 mm), AC produced a modest improvement. For large motion (M⊥80> 10 mm or ΔWET80> 7 mm), AC and/or some other form of mitigation strategies were required.
  
  
  CONCLUSIONS
  A workflow for screening patients' motion characteristics and optimizing beam angle selection was established for the pencil beam scanning proton therapy treatment of liver tumors. Abdominal compression was found to be useful at mitigation of moderate and large motion.
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Liyong
authors.initials: L
authors.lastname: Lin
authors.affiliation: Université catholique de Louvain, MIRO, IREC institute, Louvain-la-Neuve, Belgium.|Université catholique de Louvain, ICTEAM institute, Louvain-la-Neuve, Belgium.
authors.forename: Kevin
authors.initials: K
authors.lastname: Souris
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Minglei
authors.initials: M
authors.lastname: Kang
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Adam
authors.initials: A
authors.lastname: Glick
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Haibo
authors.initials: H
authors.lastname: Lin
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Sheng
authors.initials: S
authors.lastname: Huang
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, USA.|OncoRay - National Center for Radiation Research in Oncology, Medical Faculty and University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany.
authors.forename: Kristin
authors.initials: K
authors.lastname: Stützer
authors.affiliation: Ion Beam Applications SA, Louvain-la-Neuve, Belgium.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Janssens
authors.affiliation: Université catholique de Louvain, MIRO, IREC institute, Louvain-la-Neuve, Belgium.|Katholieke Universiteit Leuven, Department of Oncology, Leuven, Belgium.
authors.forename: Edmond
authors.initials: E
authors.lastname: Sterpin
authors.affiliation: Université catholique de Louvain, MIRO, IREC institute, Louvain-la-Neuve, Belgium.|Université catholique de Louvain, ICTEAM institute, Louvain-la-Neuve, Belgium.
authors.forename: John A
authors.initials: JA
authors.lastname: Lee
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Solberg
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: James E
authors.initials: JE
authors.lastname: McDonough
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Charles B
authors.initials: CB
authors.lastname: Simone
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Edgar
authors.initials: E
authors.lastname: Ben-Josef
mesh_terms: D000005:Abdomen; D019583:Dose Fractionation, Radiation; D005260:Female; D005471:Fluoroscopy; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000532:radiotherapy*; D008297:Male; D009068:Movement; D061766:Proton Therapy; D011880:Radiotherapy Planning, Computer-Assisted; D012119:Respiration
keywords: abdominal compression; liver tumor; motion; pencil beam scanning; proton therapy