Single-Agent Rituximab and Ultra-Low-Dose Adaptive Radiotherapy for the Treatment of Indolent B-cell Non-Hodgkin Lymphomas (iNHL)

Katherine Lake^*Meredith JacksonSamantha BrocklehurstSean AllAkshat M PatelXingzhe LiNeil B DesaiElif YilmazHeather WolfeMohammad FaizanHsiao-Ching LiFarrukh AwanMargaret M KozakPraveen Ramakrishnan GeethakumariKiran Kumar^*

• University of Texas Southwestern Medical Center, Dallas, United States

For indolent B-cell non-Hodgkin lymphomas (iNHL), ultra-low-dose radiation therapy (ULDRT) with 4 Gy has demonstrated durable local control (70%), though distal relapses may occur. Concurrent systemic chemotherapy with radiation therapy (RT) extends progression free survival (PFS) but is often avoided due to toxicity. We hypothesize that the combination of adaptive ULDRT, with repeat treatment as needed, and single-agent rituximab results in excellent local and systemic control with minimal toxicity. We conducted an IRB approved retrospective review of patients with iNHL (n=26) who were treated with both ULDRT and rituximab (4 weekly doses of 375 mg/m 2 ), either concurrently, or within a short interval (median 16 days), at our institution from 2017-2024. Treatment response and disease control (local and distant) were measured by PET/CT. Overall survival (OS) and PFS were analyzed using the Kaplan-Meier method. CTCAE v4 was used to record acute and long-term toxicities. Overall response rate (ORR) at first follow up was 28/31 (90%), of which 19 sites (61%) achieved complete response (CR) and 9 (29%) partial response (PR). One (3%) patient had stable disease (SD). In our cohort, the 2-year in-field, out-of-field, and overall PFS were 91%, 78%, and 78%, respectively, and OS was 92%. No patient had disease transformation. The combination of rituximab and ULDRT demonstrates sustained local and distant disease control with minimal side effects in iNHL.