title: Impact of fractionation and number of fields on dose homogeneity for intra-fractionally moving lung tumors using scanned carbon ion treatment.
abstract: OBJECTIVE
  Scanned particle beam therapy may result in over and under dosages within the target volume. This study quantifies how CTV dose coverage improves with number of fractions and fields.
  
  
  METHODS
  Based on 4DCTs of nine lung tumor patients, treatment plans were optimized separately for four different fields using an ITV approach. 4D RBE-weighted dose distributions were calculated for varying motion parameters and fraction numbers. The total RBE-weighted dose was determined for one and four-field application per fraction. DVHs were analyzed for the tumor and interpreted based on statistical modeling.
  
  
  RESULTS
  Dose homogeneity within the CTV increased with the fraction number, but depends significantly on the tumor motion amplitude. For single-field schedules and amplitudes >6mm, the dose coverage indices (V95min=90.7% and V107max=0.4%) differed to the stationary case even after 40 fractions. Target coverage for a four-field approach followed a proposed model and homogeneous dose distributions could be achieved 6-times faster than single-field treatments.
  
  
  CONCLUSIONS
  Fractionated delivery improves dose homogeneity in scanned ion beam therapy of moving targets. The achievable homogeneity depends mainly on tumor volume and motion amplitude. The outcome of multiple-field irradiations can be predicted based on single-field results and accelerates the achievement of homogeneous dose distributions.
authors.affiliation: GSI - Helmholtz Centre for Heavy Ion Research, Department of Biophysics, Darmstadt, Germany; TH Mittelhessen, Department of Hospital and Medical Engineering, Environmental Technology and Biotechnology, Giessen, Germany; University Hospital Erlangen and Friedrich-Alexander-Universität Erlangen-Nürnberg, Radiation Oncology, Germany. Electronic address: jens.woelfelschneider@fau.de.
authors.forename: Jens
authors.initials: J
authors.lastname: Wölfelschneider
authors.affiliation: GSI - Helmholtz Centre for Heavy Ion Research, Department of Biophysics, Darmstadt, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Friedrich
authors.affiliation: GSI - Helmholtz Centre for Heavy Ion Research, Department of Biophysics, Darmstadt, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Lüchtenborg
authors.affiliation: TH Mittelhessen, Department of Hospital and Medical Engineering, Environmental Technology and Biotechnology, Giessen, Germany; University Hospital Giessen-Marburg, Department of Radiotherapy and Radiooncology, Germany.
authors.forename: Klemens
authors.initials: K
authors.lastname: Zink
authors.affiliation: GSI - Helmholtz Centre for Heavy Ion Research, Department of Biophysics, Darmstadt, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Scholz
authors.affiliation: The University of Texas MD Anderson Cancer Center, Department of Radiation Physics, Houston, United States.
authors.forename: Lei
authors.initials: L
authors.lastname: Dong
authors.affiliation: GSI - Helmholtz Centre for Heavy Ion Research, Department of Biophysics, Darmstadt, Germany; TU Darmstadt, Department of Condensed Matter Physics, Darmstadt, Germany.
authors.forename: Marco
authors.initials: M
authors.lastname: Durante
authors.affiliation: GSI - Helmholtz Centre for Heavy Ion Research, Department of Biophysics, Darmstadt, Germany; University Hospital Erlangen and Friedrich-Alexander-Universität Erlangen-Nürnberg, Radiation Oncology, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Bert
mesh_terms: D002244:Carbon / Q000627:therapeutic use; D002289:Carcinoma, Non-Small-Cell Lung / Q000473:pathology / Q000532:radiotherapy; D019583:Dose Fractionation, Radiation; D063193:Heavy Ion Radiotherapy / Q000379:methods*; D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D047368:Tumor Burden
chemical_list: D002244:Carbon
keywords: Fractionation; Moving tumors; Particle therapy; Treatment planning