“Big Boom” Radiation Treatment (RT) of 4 Gy Single Fraction: Is It an Acceptable Alternative to “Boom Boom” Radiation Treatment 2 Gyx2 Fractions for Non-Hodgkin Lymphomas (NHL)?

Abstract

RT plays an important role in the treatment of NHL. Early in the COVID-19 pandemic, in order to decrease patient and staff exposure to potential infection, the International Lymphoma Radiation Oncology Group [ILROG] published emergency guidelines to support hypofractionation across multiple dose regimens. For NHL, ILROG recommended substitution of the familiar 2 Gy x2 regimen with a 4 Gy x1 alternative. This preliminary report describes our center's experience with a regimen of a single dose of 4 Gy ("Big Boom").We present our initial findings of patients treated with 4 Gy x1 between March 30, 2020 through November 30, 2020 (n = 40 lesions; 36 patients). We utilized Lugano PET criteria and clinical assessments to determine patient outcomes. Outcomes included initial clinical/radiographic response and acute toxicities. Patients were treated with either a definitive (curative) or a palliative intent (to relieve symptoms and not necessarily to achieve long-term disease control).Table 1 summarizes the patient and treatment characteristics. 29 patients (72%) were treated with a definitive intent, and 11 (28%) with a palliative intent. Median time to initial assessment for all sites was 2.2 months (range: 0.6-4.4), with overall median follow up time of 3.8 months (range: 1.0-7.3). The overall initial response rate was 85% for all sites, with 59% achieving complete response (CR) and 26% achieving a partial response (PR) (n = 39 lesion sites; 35 patients - 1 patient deceased shortly after RT [unrelated to radiation]). 4 initial partial response/no response (PR/NR) sites later became CR with either additional full dose RT (2 Gyx12) or no other treatments. The median follow-up time for those 4 lesions sites was 4.2 months (range: 2.3-9.2). 9 patients reported grade 1 toxicity, and none had grade 2+ toxicity.Given the initial high response rate and the ease of using a "one and done" treatment method, we propose that the early response rates of using a 4 Gyx1 regimen are similar to that of 4 Gy in 2 fractions. Longer term follow-up is required to confirm the durability of these results. As we continue to accrue and evaluate, data will be updated at the time of the meeting and potentially joined with other centers participating in the comprehensive ILROG-COVID guidelines research effort.