title: Accurate estimation of dose distributions inside an eye irradiated with 106Ru plaques.
abstract: BACKGROUND
  Irradiation of intraocular tumors requires dedicated techniques, such as brachytherapy with (106)Ru plaques. The currently available treatment planning system relies on the assumption that the eye is a homogeneous water sphere and on simplified radiation transport physics. However, accurate dose distributions and their assessment demand better models for both the eye and the physics.
  
  
  METHODS
  The Monte Carlo code PENELOPE, conveniently adapted to simulate the beta decay of (106)Ru over (106)Rh into (106)Pd, was used to simulate radiation transport based on a computerized tomography scan of a patient's eye. A detailed geometrical description of two plaques (models CCA and CCB) from the manufacturer BEBIG was embedded in the computerized tomography scan.
  
  
  RESULTS
  The simulations were firstly validated by comparison with experimental results in a water phantom. Dose maps were computed for three plaque locations on the eyeball. From these maps, isodose curves and cumulative dose-volume histograms in the eye and for the structures at risk were assessed. For example, it was observed that a 4-mm anterior displacement with respect to a posterior placement of a CCA plaque for treating a posterior tumor would reduce from 40 to 0% the volume of the optic disc receiving more than 80 Gy. Such a small difference in anatomical position leads to a change in the dose that is crucial for side effects, especially with respect to visual acuity. The radiation oncologist has to bring these large changes in absorbed dose in the structures at risk to the attention of the surgeon, especially when the plaque has to be positioned close to relevant tissues.
  
  
  CONCLUSIONS
  The detailed geometry of an eye plaque  in computerized and segmented tomography of a realistic patient phantom was simulated accurately. Dose-volume histograms for relevant anatomical structures of the eye and the orbit were obtained with unprecedented accuracy. This represents an important step toward an optimized brachytherapy treatment of ocular tumors.
authors.affiliation: NCTeam, Strahlenklinik, Universitätsklinikum Essen, Hufelandstr. 55, 45122, Essen, Germany. lorenzo.brualla@uni-due.de
authors.forename: L
authors.initials: L
authors.lastname: Brualla
authors.forename: J
authors.initials: J
authors.lastname: Sempau
authors.forename: F J
authors.initials: FJ
authors.lastname: Zaragoza
authors.forename: A
authors.initials: A
authors.lastname: Wittig
authors.forename: W
authors.initials: W
authors.lastname: Sauerwein
mesh_terms: D000328:Adult; D001918:Brachytherapy / Q000379:methods*; D003198:Computer Simulation; D005123:Eye / Q000000981:diagnostic imaging / Q000528:radiation effects*; D005134:Eye Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011832:Radiation Injuries / Q000517:prevention & control; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012414:Rubidium Radioisotopes / Q000627:therapeutic use*; D014057:Tomography, X-Ray Computed; D014792:Visual Acuity / Q000528:radiation effects
chemical_list: D012414:Rubidium Radioisotopes