Response-adapted ultra-low-dose radiation therapy (ULD RT) is effective and results in negligible toxicity in patients with orbital indolent B-cell lymphoma (BCL), according to research presented at the 2022 ASTRO Annual Meeting.

Historically, RT doses of 30-50 Gy have been used in patients with orbital indolent BCL, explained study presenter Chelsea C. Pinnix, MD, PhD, of the University of Texas MD Anderson Cancer Center in Houston.  

This treatment approach can provide excellent local control but can result in substantial toxicity, she said. “Even with moderate doses of 24-25 Gy, ocular side effects are common, including cataract and dry eye,” Dr Pinnix added.


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Dr Pinnix and colleagues conducted a phase 2 study (ClinicalTrials.gov Identifier: NCT02494700) to determine if ULD RT can maintain disease control but reduce orbital morbidity in this patient population. 

The study included 50 evaluable patients with stage I-IV orbital indolent BCL. The median age at baseline was 63 years (range, 29-88), and 62% were women. Most patients (64%) had MALT lymphoma, 24% had follicular lymphoma, and 12% had low-grade BCL. A majority of patients (72%) had newly diagnosed disease, and 62% had stage I disease. 

Patients received RT at 4 Gy in 2 fractions. They were assessed at 3-month intervals for response. Patients with a complete response (CR) to ULD RT were observed. Patients with stable or progressive disease after ULD RT were offered an additional 20 Gy of RT. Patients with a minimal or partial response at 1 year could receive an additional 20 Gy as well.

At a median follow-up of 37.5 months, 90% of patients had a CR to adapted ULD RT. Of the 45 patients with a CR, 44 responded to ULD RT alone, and 1 was treated with 20 Gy for persistent disease. There were 6 patients who were eligible for an additional 20 Gy. 

The 2-year local control rate was 89.4%. There were 5 local control events, but there were no local recurrences in the 45 patients who achieved a CR.

The 2-year overall survival rate was 98%. There were no known deaths due to lymphoma. The 3 deaths were due to metastatic breast cancer, dementia, and unknown reasons.

Dr Pinnix noted that 10 patients received systemic therapy after ULD RT, 3 of them before the first response assessment for RT. Of the 7 patients who received systemic therapy after the first assessment, 6 had a CR at that assessment. 

Toxicity after ULD RT was limited, Dr Pinnix said. There were 3 patients (6%) who experienced grade 1 dry eye. One patient had cataract removal from both eyes for known cataracts 7 months after RT.

Dr Pinnix and colleagues also evaluated ULD RT in a retrospective cohort of 55 patients, and results were similar to those in the prospective cohort. 

“There are several benefits to this approach, including the decreased toxicity, the convenience for our patients, the decreased cost of therapy,” Dr Pinnix said. “Patients that require systemic therapy for extra-orbital disease can quickly pursue it after completion of this treatment.” 

Dr Pinnix noted, however, that additional research is needed, and additional follow-up is required to confirm durable local control.

Disclosures: One study author declared affiliations with biotech, pharmaceutical,

and/or device companies. Please see the original reference for a full list of disclosures.

Reference

Pinnix CC, Dabaja B, Gunther JR, et al. Response adapted ultra low dose radiation therapy for the definitive management of orbital indolent B-cell lymphoma. ASTRO 2022. October 23-26, 2022. Abstract 3.