Radiation-Induced Lymphopenia and Its Impact on Survival in Patients with Brain Metastasis

Background: Differences in radiation-induced lymphopenia and prognosis between methods of radiotherapy (RT) for brain metastases remain unclear. Methods: In this retrospective analysis of patients who underwent whole-brain radiotherapy (WBRT) or stereotactic radiosurgery/radiotherapy (SRS/SRT) for brain metastases, baseline total lymphocyte count (TLC) data were obtained within 2 weeks before RT initiation. Follow-up TLC data were evaluated at 0–2, 2–4, and 4–8 weeks after RT completion. Persistent lymphopenia was defined as < 800/μL at any time point. Results: Overall, 138 RT courses in 128 patients were eligible (94 WBRT; 44 SRS/SRT). In the WBRT courses, the median baseline TLC was 1325/μL (IQR: 923–1799). Follow-up TLC decreased significantly to 946/μL (626–1316), 992/μL (675–1291), and 1075/μL (762–1435) (p < 0.001). SRS/SRT courses showed no significant TLC decrease. Multivariate analysis revealed female sex, prior RT, baseline TLC < 800/μL, and WBRT use were significantly associated with persistent lymphopenia. In the WBRT group, overall survival was significantly different between those with and without persistent lymphopenia (median, 2.6 and 6.1 months; p < 0.001). However, there was no significant difference in survival in the SRS/SRT group (p = 0.60). Conclusion: This study suggests SRS/SRT might be preferable for lymphocyte preservation in brain metastasis patients.