title: Monte Carlo dosimetry of the eye plaque design used at the St. Erik Eye Hospital for (125)I brachytherapy.
abstract: OBJECTIVE
  At St. Erik Eye Hospital in Stockholm, Sweden, ocular tumors of apical height above 6 mm are treated with brachytherapy, using iodine-125 seeds attached to a gold alloy plaque while the treatment planning is performed assuming homogeneous water surroundings. The aim of this work was to investigate the dose-modifying effects of the plaque and the seed fixating silicone rubber glue.
  
  
  METHODS
  The impact of the gold plaque and silicone rubber glue was studied with the Monte Carlo N-particle transport code, version 5.
  
  
  RESULTS
  For the 2 cm most proximal to the plaque surface along the plaque's central axis, the eyeball received 104.6-93.0% of the dose in all-water conditions.
  
  
  CONCLUSIONS
  The 0.3 mm thick layer of silicone rubber glue, used for seed fixation, attenuates photons little enough to allow characteristic X-rays from the gold alloy plaque to reach the eyeball. Close to the plaque, the dose rates were higher with the plaque and glue present, than in homogeneous water conditions. This is in contrast to what has been reported for more commonly used eye plaques, demonstrating the importance of investigating the dosimetry of individual treatment systems.
authors.affiliation: Division of Radiological Sciences, Department of Medical and Health Sciences, Linköping University, Linköping, Sweden; Department of Medical Physics, Karolinska University Hospital, Stockholm, Sweden. Electronic address: mattias.karlsson@liu.se.
authors.forename: Mattias
authors.initials: M
authors.lastname: Karlsson
authors.affiliation: Department of Medical Physics, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: Josef
authors.initials: J
authors.lastname: Nilsson
authors.affiliation: Department of Medical Physics, Karolinska University Hospital, Stockholm, Sweden; Department of Oncology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Marie
authors.initials: M
authors.lastname: Lundell
authors.affiliation: Swedish Radiation Safety Authority, Stockholm, Sweden; Department of Medical and Health Sciences and Center for Medical Image Science and Visualization, Linköping University, Linköping, Sweden.
authors.forename: Asa
authors.initials: A
authors.lastname: Carlsson Tedgren
mesh_terms: D001918:Brachytherapy / Q000295:instrumentation / Q000379:methods*; D005134:Eye Neoplasms / Q000532:radiotherapy*; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008545:Melanoma / Q000532:radiotherapy*; D009010:Monte Carlo Method; D010165:Palladium / Q000627:therapeutic use; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*
chemical_list: D007457:Iodine Radioisotopes; D010165:Palladium
keywords: (125)I; Brachytherapy; Dosimetry; Eye plaque; Monte Carlo simulations; Ocular melanoma