title: Comparison of planned dose distributions calculated by Monte Carlo and Ray-Trace algorithms for the treatment of lung tumors with cyberknife: a preliminary study in 33 patients.
abstract: OBJECTIVE
  To compare dose distributions calculated using the Monte Carlo algorithm (MC) and Ray-Trace algorithm (effective path length method, EPL) for CyberKnife treatments of lung tumors.
  
  
  METHODS
  An acceptable treatment plan is created using Multiplan 2.1 and MC dose calculation. Dose is prescribed to the isodose line encompassing 95% of the planning target volume (PTV) and this is the plan clinically delivered. For comparison, the Ray-Trace algorithm with heterogeneity correction (EPL) is used to recalculate the dose distribution for this plan using the same beams, beam directions, and monitor units (MUs).
  
  
  RESULTS
  The maximum doses calculated by the EPL to target PTV are uniformly larger than the MC plans by up to a factor of 1.63. Up to a factor of four larger maximum dose differences are observed for the critical structures in the chest. More beams traversing larger distances through low density lung are associated with larger differences, consistent with the fact that the EPL overestimates doses in low-density structures and this effect is more pronounced as collimator size decreases.
  
  
  CONCLUSIONS
  We establish that changing the treatment plan calculation algorithm from EPL to MC can produce large differences in target and critical organs' dose coverage. The observed discrepancies are larger for plans using smaller collimator sizes and have strong dependency on the anatomical relationship of target-critical structures.
authors.affiliation: Department of Radiation Oncology, Saint Francis Hospital and Medical Center, Hartford, CT 06105, USA. ewilcox@stfranciscare.org
authors.forename: Ellen E
authors.initials: EE
authors.lastname: Wilcox
authors.forename: George M
authors.initials: GM
authors.lastname: Daskalov
authors.forename: Holly
authors.initials: H
authors.lastname: Lincoln
authors.forename: Richard C
authors.initials: RC
authors.lastname: Shumway
authors.forename: Bruce M
authors.initials: BM
authors.lastname: Kaplan
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Colasanto
mesh_terms: D000465:Algorithms; D006801:Humans; D008168:Lung / Q000528:radiation effects; D008175:Lung Neoplasms / Q000473:pathology / Q000601:surgery*; D009010:Monte Carlo Method; D016634:Radiosurgery / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D047368:Tumor Burden