3638 - Very Low-dose Radiation Therapy for Intrathoracic Mucosa-Associated Lymphoid Tissue Lymphoma: A Single Institution Experience

Purpose/Objective(s):

Intrathoracic mucosa-associated lymphoid tissue (MALT) lymphoma is a rare, indolent malignancy for which the optimal treatment approach is not well defined. Here, we report a single-center analysis of 9 patients with localized intrathoracic (MALT) lymphoma treated with very low-dose radiation (VLDRT).

Materials/Methods:

We screened patients with marginal zone lymphoma treated at a single institution from 2018 through 2024. Patients with intrathoracic MALT treated with VLDRT (4 Gy) for which follow up imaging was available were included for analysis. Patients underwent CT simulation according to standard departmental procedures. All patients were treated with involved-site radiation therapy limited to the lesion only. The gross tumor volume (GTV) comprised the CT abnormality during inspiratory breath hold and the PTV comprised a 0.5 cm expansion on the GTV. We used the RECIL 2017 criteria to measure response to radiation therapy as documented on follow up CT or PET following radiation. Local recurrence was defined as reappearance of disease within the PTV. Regional and distant recurrence were defined as radiographically confirmed recurrence within the thorax and in extra-thoracic sites, respectively. Patients were censored at the last follow-up visit documented in the medical record.

Results:

We identified 9 patients with pulmonary MALT treated with VLDRT. The median age at diagnosis was 67 (range 50-77 years) and females predominated (n=6, 67%). One patient had a remote history of combined mantle cell and diffuse large B cell lymphoma treated with 6 cycles of R-CHOP prior to pulmonary MALT diagnosis. One patient received 4 cycles of rituximab prior to radiation. All patients except for one with active breast cancer had no evidence of disease from any second malignancy at the time of radiation treatment. Most patients had a single lesion (n=8, 89%). Median MALT-IPI score was 0.5 and median MZL-IPI score was 1. Median maximum tumor dimension was 3.1 cm and median SUV on PET was 5.4. Median follow up was 16.5 months (range 6.0-70.4 months). Of 10 treated lesions we observed a 100% response rate with all 10 exhibiting a complete response (CR). The majority (8 patients) of responses were achieved within 3-6 months following radiation, with 1 patient achieving a CR 18 months following radiation. There were no local treatment failures or grade 3-4 toxicity noted. Regional recurrence occurred in 2 patients and distant recurrence occurred in 3 patients. Following radiation, 1 patient received 2 years of rituximab therapy. At time of last known follow up, 8 patients were alive, and 1 patient was deceased with cause of death likely attributed to out of field disease progression.

Conclusion:

Our institutional experience indicates that VLDRT offers outstanding local control and serves as an effective treatment option for intrathoracic MALT lymphoma.