title: Comparison of Acuros (AXB) and Anisotropic Analytical Algorithm (AAA) for dose calculation in treatment of oesophageal cancer: effects on modelling tumour control probability.
abstract: OBJECTIVE
  To investigate systematic changes in dose arising when treatment plans optimised using the Anisotropic Analytical Algorithm (AAA) are recalculated using Acuros XB (AXB) in patients treated with definitive chemoradiotherapy (dCRT) for locally advanced oesophageal cancers.
  
  
  BACKGROUND
  We have compared treatment plans created using AAA with those recalculated using AXB. Although the Anisotropic Analytical Algorithm (AAA) is currently more widely used in clinical routine, Acuros XB (AXB) has been shown to more accurately calculate the dose distribution, particularly in heterogeneous regions. Studies to predict clinical outcome should be based on modelling the dose delivered to the patient as accurately as possible.
  
  
  METHODS
  CT datasets from ten patients were selected for this retrospective study. VMAT (Volumetric modulated arc therapy) plans with 2 arcs, collimator rotation ± 5-10° and dose prescription 50 Gy / 25 fractions were created using Varian Eclipse (v10.0). The initial dose calculation was performed with AAA, and AXB plans were created by re-calculating the dose distribution using the same number of monitor units (MU) and multileaf collimator (MLC) files as the original plan. The difference in calculated dose to organs at risk (OAR) was compared using dose-volume histogram (DVH) statistics and p values were calculated using the Wilcoxon signed rank test. The potential clinical effect of dosimetric differences in the gross tumour volume (GTV) was evaluated using three different TCP models from the literature.
  
  
  RESULTS
  PTV Median dose was apparently 0.9 Gy lower (range: 0.5 Gy - 1.3 Gy; p < 0.05) for VMAT AAA plans re-calculated with AXB and GTV mean dose was reduced by on average 1.0 Gy (0.3 Gy -1.5 Gy; p < 0.05). An apparent difference in TCP of between 1.2% and 3.1% was found depending on the choice of TCP model. OAR mean dose was lower in the AXB recalculated plan than the AAA plan (on average, dose reduction: lung 1.7%, heart 2.4%). Similar trends were seen for CRT plans.
  
  
  CONCLUSIONS
  Differences in dose distribution are observed with VMAT and CRT plans recalculated with AXB particularly within soft tissue at the tumour/lung interface, where AXB has been shown to more accurately represent the true dose distribution. AAA apparently overestimates dose, particularly the PTV median dose and GTV mean dose, which could result in a difference in TCP model parameters that reaches clinical significance.
authors.affiliation: Oxford Cancer Centre, Oxford University Hospitals, Oxford, OX3 7LE, UK. sriram.padmanaban@ouh.nhs.uk.
authors.forename: Sriram
authors.initials: S
authors.lastname: Padmanaban
authors.affiliation: CRUK/MRC Oxford Institute for Radiation Oncology, Gray Laboratories, University of Oxford, Oxford, OX3 7DQ, UK. samantha.warren@oncology.ox.ac.uk.
authors.forename: Samantha
authors.initials: S
authors.lastname: Warren
authors.affiliation: Oxford Cancer Centre, Oxford University Hospitals, Oxford, OX3 7LE, UK. Anthony.Walsh@health.wa.gov.au.
authors.forename: Anthony
authors.initials: A
authors.lastname: Walsh
authors.affiliation: CRUK/MRC Oxford Institute for Radiation Oncology, Gray Laboratories, University of Oxford, Oxford, OX3 7DQ, UK. mike.partridge@oncology.ox.ac.uk.
authors.forename: Mike
authors.initials: M
authors.lastname: Partridge
authors.affiliation: CRUK/MRC Oxford Institute for Radiation Oncology, Gray Laboratories, University of Oxford, Oxford, OX3 7DQ, UK. maria.hawkins@oncology.ox.ac.uk.
authors.forename: Maria A
authors.initials: MA
authors.lastname: Hawkins
mesh_terms: D000465:Algorithms; D004938:Esophageal Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D006801:Humans; D058958:Organs at Risk / Q000000981:diagnostic imaging / Q000528:radiation effects; D011336:Probability; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage / Q000592:standards; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed