Effect of Radiation Treatment Volume Reduction on Lymphopenia in Patients Receiving Chemoradiotherapy for Glioblastoma

To evaluate whether reduction in glioblastoma radiation treatment volume can reduce risk of acute severe lymphopenia (ASL). A total of 210 patients with supratentorial/nonmetastatic glioblastoma were treated with radiation therapy (RT) plus temozolomide from 2007 to 2016 and had laboratory data on total lymphocyte counts. Before 2015, 164 patients were treated with standard-field RT (SFRT), and limited-field RT (LFRT) was implemented thereafter for 46 patients to reduce treatment volume. Total lymphocyte counts were evaluated at baseline, during RT, and at approximately week 12 from initiating RT. Acute severe lymphopenia was defined as any total lymphocyte count < 500 cells/μL within 3 months (by week 12) of initiating RT. Multivariate analysis for overall survival (OS) was performed with Cox regression and with logistic regression for ASL. Propensity score matching was performed to adjust for variability between cohorts. Acute severe lymphopenia, progression-free survival (PFS), and OS were compared using the Kaplan-Meier method. Limited-field RT patients had higher gross tumor volume than SFRT patients yet lower brain dose–volume parameters, including volume receiving 25 Gy (V25 Gy: 41% vs 53%, respectively, P