title: A novel lateral disequilibrium inclusive (LDI) pencil-beam based dose calculation algorithm: evaluation in inhomogeneous phantoms and comparison with Monte Carlo calculations.
abstract: OBJECTIVE
  Pencil-beam (PB) based dose calculation for treatment planning is limited by inaccuracies in regions of tissue inhomogeneities, particularly in situations with lateral electron disequilibrium as is present at tissue/lung interfaces. To overcome these limitations, a new "lateral disequilibrium inclusive" (LDI) PB based calculation algorithm was introduced. In this study, the authors evaluated the accuracy of the new model by film and ionization chamber measurements and Monte Carlo simulations.
  
  
  METHODS
  To validate the performance of the new LDI algorithm implemented in Corvus 09, eight test plans were generated on inhomogeneous thorax and pelvis phantoms. In addition, three plans were calculated with a simple effective path length (EPL) algorithm on the inhomogeneous thorax phantom. To simulate homogeneous tissues, four test plans were evaluated in homogeneous phantoms (homogeneous dose calculation).
  
  
  RESULTS
  The mean pixel pass rates and standard deviations of the gamma 4%/4 mm test for the film measurements were (96 +/- 3)% for the plans calculated with LDI, (70 +/- 5)% for the plans calculated with EPL, and (99 +/- 1)% for the homogeneous plans. Ionization chamber measurements and Monte Carlo simulations confirmed the high accuracy of the new algorithm (dose deviations < or = 4%; gamma 3%/3 mm > or = 96%).
  
  
  CONCLUSIONS
  LDI represents an accurate and fast dose calculation algorithm for treatment planning.
authors.affiliation: Department of Radiation Oncology, Mannheim Medical Centre, University of Heidelberg, 68167 Mannheim, Germany. hansjoerg.wertz@umm.de
authors.forename: Hansjoerg
authors.initials: H
authors.lastname: Wertz
authors.forename: Lennart
authors.initials: L
authors.lastname: Jahnke
authors.forename: Frank
authors.initials: F
authors.lastname: Schneider
authors.forename: Martin
authors.initials: M
authors.lastname: Polednik
authors.forename: Jens
authors.initials: J
authors.lastname: Fleckenstein
authors.forename: Frank
authors.initials: F
authors.lastname: Lohr
authors.forename: Frederik
authors.initials: F
authors.lastname: Wenz
mesh_terms: D000465:Algorithms; D006801:Humans; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011874:Radiometry / Q000295:instrumentation*; D011880:Radiotherapy Planning, Computer-Assisted; D012984:Software