title: Pilot study of the delivery of microcollimated pars plana external beam radiation in porcine eyes.
abstract: OBJECTIVE
  To investigate the effects of a novel stereotactic radiosurgical system for pars plana delivery of microcollimated x-rays to the retina and determine the retinal radiological dose response and toxicity threshold in a pig model.
  
  
  METHODS
  The x-rays were delivered through the pars plana to the maculae of Yucatan miniswine to verify the targeting and safety of a cornea-scleral, stabilized, office-based delivery system. Twelve eyes were randomized to receive 0, 16, 24, 42, 60, or 90 Gy in a single dose to the retina. Eye examinations, fundus photography, fluorescein angiography, and spectral-domain optical coherence tomography were obtained at days 7, 30, 60, and 90. Indocyanine green angiography was done at day 90.
  
  
  RESULTS
  Through day 90 interim analysis, no abnormalities of external structures were noted. A small cortical lens opacity was noted in the 60-Gy group. Fundus evaluation revealed no abnormalities at 16 or 24 Gy. Beginning at day 30, circular pale retinal lesions with sharp margins were noted in the maculae of the eyes that received 42, 60, and 90 Gy. Higher-dose lesions showed late staining on fluorescein angiography, choroidal hypoperfusion on indocyanine green angiography, and defined photoreceptor loss and retinal thinning on spectral-domain optical coherence tomography.
  
  
  CONCLUSIONS
  Transscleral stereotactic radiation dosing of porcine eyes demonstrates no apparent clinical abnormalities in doses less than 24 Gy. Doses of 42 Gy or higher led to focal choroidal and retinal damage within the target area.
  
  
  CONCLUSIONS
  Radiation can induce small-blood vessel closure and thereby has therapeutic potential in neovascular diseases such as age-related macular degeneration.
authors.affiliation: Cole Eye Institute, Cleveland Clinic Foundation, Cleveland, Ohio, USA.
authors.forename: Mark R
authors.initials: MR
authors.lastname: Barakat
authors.forename: Mark
authors.initials: M
authors.lastname: Shusterman
authors.forename: Darius
authors.initials: D
authors.lastname: Moshfeghi
authors.forename: Ronald
authors.initials: R
authors.lastname: Danis
authors.forename: Michael
authors.initials: M
authors.lastname: Gertner
authors.forename: Rishi P
authors.initials: RP
authors.lastname: Singh
mesh_terms: D000818:Animals; D004396:Coloring Agents; D004307:Dose-Response Relationship, Radiation; D005451:Fluorescein Angiography; D007208:Indocyanine Green; D010865:Pilot Projects; D011829:Radiation Dosage; D011833:Radiation Injuries, Experimental / Q000175:diagnosis*; D011879:Radiotherapy Dosage; D012160:Retina / Q000473:pathology / Q000528:radiation effects*; D013552:Swine; D013556:Swine, Miniature; D041623:Tomography, Optical Coherence; D014965:X-Rays
chemical_list: D004396:Coloring Agents; D007208:Indocyanine Green