title: Accuracy of out-of-field dose calculation of tomotherapy and cyberknife treatment planning systems: a dosimetric study.
abstract: OBJECTIVE
  Late toxicities such as second cancer induction become more important as treatment outcome improves. Often the dose distribution calculated with a commercial treatment planning system (TPS) is used to estimate radiation carcinogenesis for the radiotherapy patient. However, for locations beyond the treatment field borders, the accuracy is not well known. The aim of this study was to perform detailed out-of-field-measurements for a typical radiotherapy treatment plan administered with a Cyberknife and a Tomotherapy machine and to compare the measurements to the predictions of the TPS.
  
  
  METHODS
  Individually calibrated thermoluminescent dosimeters were used to measure absorbed dose in an anthropomorphic phantom at 184 locations. The measured dose distributions from 6 MV intensity-modulated treatment beams for CyberKnife and TomoTherapy machines were compared to the dose calculations from the TPS.
  
  
  RESULTS
  The TPS are underestimating the dose far away from the target volume. Quantitatively the Cyberknife underestimates the dose at 40 cm from the PTV border by a factor of 60, the Tomotherapy TPS by a factor of two. If a 50% dose uncertainty is accepted, the Cyberknife TPS can predict doses down to approximately 10 mGy/treatment Gy, the Tomotherapy-TPS down to 0.75 mGy/treatment Gy. The Cyberknife TPS can then be used up to 10 cm from the PTV border the Tomotherapy up to 35 cm.
  
  
  CONCLUSIONS
  We determined that the Cyberknife and Tomotherapy TPS underestimate substantially the doses far away from the treated volume. It is recommended not to use out-of-field doses from the Cyberknife TPS for applications like modeling of second cancer induction. The Tomotherapy TPS can be used up to 35 cm from the PTV border (for a 390 cm(3) large PTV).
authors.affiliation: Faculty of Science, Universtiy of Zurich, Zurich, Switzerland; Radiotherapy Hirslanden, Hirslanden Medical Center, Aarau, Switzerland. Electronic address: uwe.schneider@uzh.ch.
authors.forename: Uwe
authors.initials: U
authors.lastname: Schneider
authors.affiliation: Radiotherapy Hirslanden, Hirslanden Medical Center, Aarau, Switzerland.
authors.forename: Roger A
authors.initials: RA
authors.lastname: Hälg
authors.affiliation: Radiotherapy Hirslanden, Hirslanden Medical Center, Aarau, Switzerland.
authors.forename: Matthias
authors.initials: M
authors.lastname: Hartmann
authors.affiliation: Radiotherapy Hirslanden, Hirslanden Medical Center, Aarau, Switzerland.
authors.forename: Andreas
authors.initials: A
authors.lastname: Mack
authors.affiliation: Radiotherapy Hirslanden, Hirslanden Medical Center, Aarau, Switzerland.
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Storelli
authors.affiliation: University Institute for Radiation Physics, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland.
authors.forename: Andreas
authors.initials: A
authors.lastname: Joosten
authors.affiliation: University Institute for Radiation Physics, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland.
authors.forename: Raphaël
authors.initials: R
authors.lastname: Möckli
authors.affiliation: Radiotherapy Hirslanden, Hirslanden Medical Center, Aarau, Switzerland.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Besserer
mesh_terms: D000293:Adolescent; D006801:Humans; D008297:Male; D058958:Organs at Risk / Q000528:radiation effects*; D011471:Prostatic Neoplasms / Q000628:therapy*; D016634:Radiosurgery / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D015203:Reproducibility of Results; D012208:Rhabdomyosarcoma / Q000628:therapy*; D012680:Sensitivity and Specificity; D013819:Thermoluminescent Dosimetry / Q000379:methods*
keywords: Bestrahlungsplanungssystem; Dosisberechnung; Out-of-field-dose; Zweittumorinzidenz; dose calculation; periphere Dosis; second cancer induction; treatment planning system