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Purpose: Focal epiretinal radiation has emerged as a promising tool in the management of choroidal neovascularization associated with age-related macular degeneration. However, the dosages tested are not backed by cell culture studies used in the clinical setting empirically., Methods: Choroidal endothelial cells (RF6A) were maintained in a log scale and exposed to a single fraction of 2, 4, 8, and 12 cobalt gray-equivalent of proton radiation with an internal control. Cell viability was quantified using Vi-cell XR and neutral red assay at days 5, 9, and 12 after radiation. Mitochondrial viability using WST-1 and reactive oxygen species levels using dihydrorhodamine 123 were measured at similar intervals., Results: By using neutral red assay, on day 12, the percentages of viable cells compared with control were 100.1 ± 5.7%, 96.7 ± 23.3%, 27.6 ± 6.6%, and 19.5 ± 3% at radiation doses of 2, 4, 8, and 12 cobalt gray-equivalent, respectively (P < 0.001). Increase in reactive oxygen species levels correlated with the number of dead cells implicating reactive oxygen species as an intermediary molecule (r = 0.85-0.96)., Conclusion: Our study shows sensitivity of cultured choroidal endothelial cells to proton beam radiation at doses of 8 and 12 cobalt gray-equivalent in an in vitro model.

JC:------------ABSTRACT------------------------- P4 Osteoclastoma seen between 1965 and 1984 is presented. All patients received megavoltage therapy using Telecobalt. Tumour dose of 45 Gy to 55.3 Gy in 15 to 18 fractions had been delivered. All patients had quantitation of pre-treatment tumour volume and post-treatment response using a radiographic grid. CT scan measurements have complimented the grid quantitation in recent years. Follow through visits from 5 to 24 years post-treatment (mean follow up 9.2 years) have shown optimum tumor regression, bone recalcification and restitution of joint functions amongst these patients. No case of bone sarcoma has been detected. Our observations lead us to support megavoltage radiation therapy as the treatment of choice for accessible and inaccessible osteoclastoma.