title: Optimization of extracranial stereotactic radiation therapy of small lung lesions using accurate dose calculation algorithms.
abstract: BACKGROUND
  The aim of this study was to compare and to validate different dose calculation algorithms for the use in radiation therapy of small lung lesions and to optimize the treatment planning using accurate dose calculation algorithms.
  
  
  METHODS
  A 9-field conformal treatment plan was generated on an inhomogeneous phantom with lung mimics and a soft tissue equivalent insert, mimicking a lung tumor. The dose distribution was calculated with the Pencil Beam and Collapsed Cone algorithms implemented in Masterplan (Nucletron) and the Monte Carlo system XVMC and validated using Gafchromic EBT films. Differences in dose distribution were evaluated. The plans were then optimized by adding segments to the outer shell of the target in order to increase the dose near the interface to the lung.
  
  
  RESULTS
  The Pencil Beam algorithm overestimated the dose by up to 15% compared to the measurements. Collapsed Cone and Monte Carlo predicted the dose more accurately with a maximum difference of -8% and -3% respectively compared to the film. Plan optimization by adding small segments to the peripheral parts of the target, creating a 2-step fluence modulation, allowed to increase target coverage and homogeneity as compared to the uncorrected 9 field plan.
  
  
  CONCLUSIONS
  The use of forward 2-step fluence modulation in radiotherapy of small lung lesions allows the improvement of tumor coverage and dose homogeneity as compared to non-modulated treatment plans and may thus help to increase the local tumor control probability. While the Collapsed Cone algorithm is closer to measurements than the Pencil Beam algorithm, both algorithms are limited at tissue/lung interfaces, leaving Monte-Carlo the most accurate algorithm for dose prediction.
authors.affiliation: Department of Radiation Oncology, Mannheim Medical Center, University of Heidelberg, Mannheim, Germany. bdobler@web.de
authors.forename: Barbara
authors.initials: B
authors.lastname: Dobler
authors.forename: Cornelia
authors.initials: C
authors.lastname: Walter
authors.forename: Antje
authors.initials: A
authors.lastname: Knopf
authors.forename: Daniella
authors.initials: D
authors.lastname: Fabri
authors.forename: Rainer
authors.initials: R
authors.lastname: Loeschel
authors.forename: Martin
authors.initials: M
authors.lastname: Polednik
authors.forename: Frank
authors.initials: F
authors.lastname: Schneider
authors.forename: Frederik
authors.initials: F
authors.lastname: Wenz
authors.forename: Frank
authors.initials: F
authors.lastname: Lohr
mesh_terms: D000465:Algorithms; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D009010:Monte Carlo Method; D009038:Motion; D019047:Phantoms, Imaging; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal / Q000379:methods*; D016896:Treatment Outcome