Response-adapted ultralow-dose RT may improve indolent orbital B-cell lymphoma outcomes

Response-adapted radiation therapy (RT) shows promise in the treatment of indolent orbital B-cell lymphoma, conferring high local control rates while reducing radiation exposure, according to the results of a phase II nonrandomized controlled trial.

In the trial, 50 patients (median 63 years, 62 percent female) with stage I to IV indolent B-cell lymphoma of the ocular adnexa received ultralow-dose radiation therapy at 4 Gy in 2 fractions, with response evaluated at 3-month intervals. Those with persistent orbital lymphoma received an additional 20 Gy in 10 fractions to complete the response-adapted treatment.

Of the patients, 64 percent had mucosa-associated lymphoid tissue lymphoma, 24 percent had follicular lymphoma, and 12 percent had unclassifiable low-grade B-cell lymphoma. Most patients had stage I disease (62 percent) and had newly diagnosed disease (72 percent). The median follow-up time was 37.4 months.

The primary endpoint of 2-year local orbital control within the irradiated field occurred in 89.4 percent (95 percent confidence interval [CI], 81.0–98.7) of patients. The 2-year overall survival rate was 98.0 percent (95 percent CI, 94.1–100).

Complete response to response-adapted RT was documented in 45 patients (90.0 percent, 95 percent CI, 78.2–96.7), including 44 with a complete response following ultralow-dose radiation and one with a complete response following an additional 20 Gy. None of these patients experienced local recurrences.

In terms of safety, grade 3 or higher toxic effects did not occur in any of the patients.

Results for the subset of 22 patients with newly diagnosed, untreated stage I mucosa-associated lymphoid tissue lymphoma showed similar results. The 2-year local control rate was 90.7 percent (95 percent CI, 79.2–100), and the 2-year freedom from distant relapse rate was 95.2 percent (95 percent CI, 86.6–100).