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.