title: Estimation of the planning organ at risk volume for the lenses during radiation therapy for nasal cavity and paranasal sinus cancer.
abstract: BACKGROUND
  To establish the optimal planning risk volume (PRV) of the lenses for patients who are receiving radiotherapy to the nasal cavity and paranasal sinus (NCPSC).
  
  
  METHODS
  Geometrical uncertainties of the lenses were evaluated for a prospective group of patients (G1). Differences between planned and delivered maximum doses to the lenses were evaluated for every fraction. The relationship between dose differences and geometrical uncertainties were analysed to establish an optimal PRV for the lenses. Obtained results were verified in the second group (G2) of patients for whom calculated PRV was applied.
  
  
  RESULTS
  Data of 426 observations for 15 patients from G1 were investigated. The systematic and random errors equalled, respectively, 0.6 mm and 2.3 mm in the medio-lateral direction; 0.8 mm and 1.6 mm in the cranio-caudal direction; and 0.4 mm and 1.5 mm in the anterio-posterior direction. The clinical PRV for the lenses was established at 2 mm. Applied margin was evaluated for 10 patients from G2. The dose distribution in the planning target volume (PTV) for G1 and for G2 was comparable (P = 0.122), whereas the differences between planned and delivered doses in the lenses were significantly smaller for G2 (P = 0.013).
  
  
  CONCLUSIONS
  The study showed that for radiotherapy of NCPSC, the PRV for the lenses could be defined as 2 mm. This margin does not affect the dose distribution in the PTV and effectively reduces the differences between planned and delivered doses in the lenses.
authors.affiliation: Department of Electroradiology, University of Medical Sciences, Poznan, Poland.|Department of Medical Physics, Greater Poland Cancer Centre, Poznan, Poland.
authors.forename: Tomasz
authors.initials: T
authors.lastname: Piotrowski
authors.affiliation: Department of Medical Physics, Greater Poland Cancer Centre, Poznan, Poland.
authors.forename: Adam
authors.initials: A
authors.lastname: Ryczkowski
authors.affiliation: Department of Medical Physics, Greater Poland Cancer Centre, Poznan, Poland.
authors.forename: Marta
authors.initials: M
authors.lastname: Adamczyk
authors.affiliation: Department of Medical Physics, Greater Poland Cancer Centre, Poznan, Poland.
authors.forename: Agata
authors.initials: A
authors.lastname: Jodda
mesh_terms: D005131:Eye Injuries / Q000209:etiology / Q000517:prevention & control*; D006801:Humans; D007908:Lens, Crystalline / Q000293:injuries* / Q000528:radiation effects; D059351:Organ Sparing Treatments / Q000379:methods; D058958:Organs at Risk / Q000528:radiation effects*; D010255:Paranasal Sinus Neoplasms / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000209:etiology / Q000517:prevention & control*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D018570:Risk Assessment / Q000379:methods; D012680:Sensitivity and Specificity; D016896:Treatment Outcome; D047368:Tumor Burden
keywords: helical tomotherapy; image-guided radiation therapy; lenses; nasal cavity and paranasal sinus cancer; planning risk volume