title: Simulation accuracy in radiotherapy for maxillary sinus tumors.
abstract: OBJECTIVE
  To evaluate the accuracy and clinical importance of beam positioning during simulation of radiation treatment for tumors in the maxillary sinus.
  
  
  METHODS
  Five patients were prepared as if they were to be treated for a maxillary sinus tumor. A three-beam computed tomography (CT) scan-based computer plan was made for each patient. The location of the central beam axis of each beam was measured, relative to bony anatomical structures. A simulation was performed using the bony references to position the radiation beams during simulation. After this, the simulation procedure was repeated by the use of a noninvasive external localization frame with a known accuracy and reproducibility within 2 mm margins.
  
  
  RESULTS
  When defining the clinical target volume as the known tumor with a 1 cm margin, three out of five patients would suffer a partial geographical miss throughout the entire radiation treatment due to erroneous beam positioning at the simulation stage when using bony structures as a guide for beam positioning. The influence of these errors is analyzed as normal tissue complication and tumor control probabilities.
  
  
  CONCLUSIONS
  When defining a planning target volume, one should consider a margin to correct for possible simulation errors. We advise the use of objective, external (and thus nonanatomical) landmarks as a reference during simulation to reduce this extra margin to a minimum. In case of simulation, using bony structures as a reference, an additional margin should be entered, depending on the simulation accuracy that can be obtained.
authors.affiliation: Department of Radiation Oncology, Dr. Daniel den Hoed Cancer Center, Rotterdam, The Netherlands.
authors.forename: C G
authors.initials: CG
authors.lastname: Niël
authors.forename: J P
authors.initials: JP
authors.lastname: van Santvoort
authors.forename: J R
authors.initials: JR
authors.lastname: van Sörnsen-de Koste
authors.forename: P J
authors.initials: PJ
authors.lastname: Nowak
authors.forename: P C
authors.initials: PC
authors.lastname: Levendag
mesh_terms: D006801:Humans; D007103:Immobilization; D008444:Maxillary Sinus Neoplasms / Q000532:radiotherapy*; D011879:Radiotherapy Dosage