Background: Diffuse and multifocal patterns of conjunctival melanoma may not be treatable with standard eye-sparing methods. The purpose of this study was to evaluate the usefulness of proton beam radiation therapy as an alternative to exenteration.
Methods: Twenty patients with extended conjunctival melanoma were treated by proton beam irradiation. Most cases were T3 tumours which were not accessible to brachytherapy due to their extension, localisation with fornical or caruncular involvement. Only 2 patients had a tumour limited to the bulbar conjunctiva. Both were recurrent tumours with multiple lesions. Sixteen cases were recurrences after various pre-treatments. The area of the conjunctiva which was suspected to have microscopic disease was treated by 31 Gy in 6 fractions. The "high risk" areas with a clinically detectable tumour (primary target volume) were treated by an additional boost using a smaller beam size and applying 2 fractions up to 45 Gy. An individually shaped compensator was brought into the beam to modify the range of the protons so that the eye was irradiated only at a depth of 2 mm.
Results: The mean follow-up time was 38.1+/-26.6 months (median 34 months). Recurrent disease occurred in 6 cases (30%); 2 of them outside the irradiated volume, 3 within the target volume treated by 31 Gy, and just one in the primary target volume treated by 45 Gy. An exenteration followed only in two patients (10%). 6 patients (30%) suffered from metastatic disease and 4 (20%) of them have died by now. During follow up we found no statistically significant association between the occurrence of local recurrence after proton radiotherapy and the development of metastases. Best corrected visual acuity remained stable in 12 cases (60%); in 14 patients the best corrected visual acuity was 0.25 or better. A sicca-syndrome developed in 19/20 patients. However, only 10/20 patients used artificial tears more than 5x/d. A focal cataract developed in 7 patients (35%). There was eyelash loss in the area of irradiated eyelids. In 4 cases a limbal stem cell deficiency occurred with the consequence of corneal vascularisation.
Conclusions: Proton radiotherapy may serve as an alternative to exenteration in case of T3 and diffuse T1 or T2 conjunctival melanomas.