title: Four-dimensional patient dose reconstruction for scanned ion beam therapy of moving liver tumors.
abstract: OBJECTIVE
  Estimation of the actual delivered 4-dimensional (4D) dose in treatments of patients with mobile hepatocellular cancer with scanned carbon ion beam therapy.
  
  
  METHODS
  Six patients were treated with 4 fractions to a total relative biological effectiveness (RBE)-weighted dose of 40 Gy (RBE) using a single field. Respiratory motion was addressed by dedicated margins and abdominal compression (5 patients) or gating (1 patient). 4D treatment dose reconstructions based on the treatment records and the measured motion monitoring data were performed for the single-fraction dose and a total of 17 fractions. To assess the impact of uncertainties in the temporal correlation between motion trajectory and beam delivery sequence, 3 dose distributions for varying temporal correlation were calculated per fraction. For 3 patients, the total treatment dose was formed from the fractional distributions using all possible combinations. Clinical target volume (CTV) coverage was analyzed using the volumes receiving at least 95% (V95) and 107% (V107) of the planned doses.
  
  
  RESULTS
  4D dose reconstruction based on daily measured data is possible in a clinical setting. V95 and V107 values for the single fractions ranged between 72% and 100%, and 0% and 32%, respectively. The estimated total treatment dose to the CTV exhibited improved and more robust dose coverage (mean V95 > 87%, SD < 3%) and overdose (mean V107 < 4%, SD < 3%) with respect to the single-fraction dose for all analyzed patients.
  
  
  CONCLUSIONS
  A considerable impact of interplay effects on the single-fraction CTV dose was found for most of the analyzed patients. However, due to the fractionated treatment, dose heterogeneities were substantially reduced for the total treatment dose. 4D treatment dose reconstruction for scanned ion beam therapy is technically feasible and may evolve into a valuable tool for dose assessment.
authors.affiliation: GSI Helmholtzzentrum für Schwerionenforschung, Department of Biophysics, Darmstadt, Germany; TU Darmstadt, Darmstadt, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Richter
authors.affiliation: GSI Helmholtzzentrum für Schwerionenforschung, Department of Biophysics, Darmstadt, Germany.
authors.forename: Nami
authors.initials: N
authors.lastname: Saito
authors.affiliation: Heidelberg Ion-Beam Therapy Center, Department of Medical Physics, Heidelberg, Germany.
authors.forename: Naved
authors.initials: N
authors.lastname: Chaudhri
authors.affiliation: University Hospital of Heidelberg, Department of Radiation Oncology, Heidelberg, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Härtig
authors.affiliation: Heidelberg Ion-Beam Therapy Center, Department of Medical Physics, Heidelberg, Germany.
authors.forename: Malte
authors.initials: M
authors.lastname: Ellerbrock
authors.affiliation: Heidelberg Ion-Beam Therapy Center, Department of Medical Physics, Heidelberg, Germany; University Hospital of Heidelberg, Department of Radiation Oncology, Heidelberg, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Jäkel
authors.affiliation: University Hospital of Heidelberg, Department of Radiation Oncology, Heidelberg, Germany.
authors.forename: Stephanie E
authors.initials: SE
authors.lastname: Combs
authors.affiliation: University Hospital of Heidelberg, Department of Radiation Oncology, Heidelberg, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Habermehl
authors.affiliation: University Hospital of Heidelberg, Department of Radiation Oncology, Heidelberg, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Herfarth
authors.affiliation: GSI Helmholtzzentrum für Schwerionenforschung, Department of Biophysics, Darmstadt, Germany; TU Darmstadt, Darmstadt, Germany.
authors.forename: Marco
authors.initials: M
authors.lastname: Durante
authors.affiliation: GSI Helmholtzzentrum für Schwerionenforschung, Department of Biophysics, Darmstadt, Germany; University Clinic Erlangen and Friedrich-Alexander University Erlangen-Nürnberg, Department of Radiation Oncology, Erlangen, Germany. Electronic address: christoph.bert@uk-erlangen.de.
authors.forename: Christoph
authors.initials: C
authors.lastname: Bert
mesh_terms: D019583:Dose Fractionation, Radiation; D005240:Feasibility Studies; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D063193:Heavy Ion Radiotherapy / Q000379:methods*; D006801:Humans; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D009068:Movement; D058958:Organs at Risk / Q000000981:diagnostic imaging; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012119:Respiration; D035501:Uncertainty