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Abstract #73319 Published in IGR 18-4

Proton therapy of iris melanoma with 50 CGE : Influence of target volume on clinical outcome

PURPOSE: The aim of this study was to evaluate local tumour control, incidence of radiation-induced glaucoma and associated interventions of sector-based and whole anterior segment proton beam therapy (PBT) for the treatment of iris melanoma. PATIENTS AND METHODS: We retrospectively analysed the data of 77 patients with iris melanoma who underwent PBT applied as 50 CGE in four daily fractions. Of the patients, 47 received PBT with a circular-shaped collimator and 30 with a conformal sector-shaped target volume. Local control, eye preservation and secondary glaucoma were evaluated. RESULTS: Median follow-up time was 54.9 months. Local tumour control was 100% in patients receiving whole anterior segment irradiation. Two patients developed pigment dispersion in the non-irradiated area after sector-based PBT and received whole anterior segment salvage PBT. The mean volume of ciliary body irradiated was 89.0% and 34.9% for whole anterior segment and lesion-based irradiation, respectively. At the end of follow-up, secondary glaucoma was found in 74.3% of the patients with whole anterior segment irradiation and in 19.2% with sector-based irradiation. Patients with sector-based PBT had a stable visual acuity of logMAR 0.1, while it declined from logMAR 0.1 to 0.4 after whole anterior segment irradiation. CONCLUSION: We found a significant reduction in radiation-induced secondary glaucoma and glaucoma-associated surgical interventions and stable visual acuity after sector-based irradiation compared with whole anterior segment irradiation. Sector-based irradiation revealed a higher risk for local recurrence, but selected patients with well-circumscribed iris melanoma benefit from applying a lesion-based target volume when treated with sector-based PBT.

Department of Ophthalmology, Charité University of Medicine, Berlin, Germany.

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