Primary radiotherapy for localized orbital MALT lymphoma

Purpose:To define the natural history, prognosis, and radiocurability of localized orbital extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT).

Methods and materials:Clinical records and pathologic material of 40 patients treated with local radiotherapy for localized orbital lymphoma were reviewed. Treatment consisted of 30-40 Gy in 1.8-2-Gy fractions (mean 34 Gy) of irradiation using 9-20-MeV electrons for conjunctival lesions, or 6-MV photons with complex treatment planning for retrobulbar lesions. The lens was routinely shielded with the use of a suspended eye bar.

Results:Upon pathologic review, 31 cases of orbital MALT lymphoma were identified. With the median follow-up of 5.9 years (range 9 months-0.3 years), the actuarial 10-year overall survival was 73%. Local control was 100%. Five distant failures resulted in a projected 10-year freedom from relapse of 71%. Most of the failures were extranodal in sites where MALT lymphoma has previously been shown to arise. No difference in outcome was observed among patients treated to less than or equal to 34 Gy vs. those treated to higher radiation doses. Two patients experienced clinically significant retinal damage after doses > or = Gy.

Conclusion:In this study, localized orbital MALT lymphoma was well controlled with radiotherapy. Even following relapse, patients with orbital MALT lymphoma exhibited an indolent course. Relapse occurred predominantly in extranodal mucosal sites, implying a possible homing mechanism for MALT lymphoma cells. Given the excellent local control rates, our current treatment recommendation is to use a radiation dose of 30-30.6 Gy in 1.5-.8-Gy fractions to minimize risk of late toxicity.