Radiation-related lymphopenia is associated with spleen irradiation dose during radiotherapy in patients with hepatocellular carcinoma

The decrease in peripheral blood lymphocytes induced by radiation lessens the antitumour effect of the immune response, which might cause immunosuppression. We aimed to investigate the correlation between the decrease in peripheral blood lymphocytes during radiotherapy (RT) and the spleen irradiation dose in patients with hepatocellular carcinoma (HCC). The subjects were 59 patients with HCC who had received RT from 2005 to 2014. The Min ALC (minimum value of absolute counts for peripheral blood lymphocytes) was collected from the routine workup for each patient prior to RT and weekly during RT. Spleen dose-volume variables, including the percentage of the organ volume receiving ≥ n Gy (V_n) and the mean spleen dose (MSD), were calculated using Eclipse treatment planning. Potential associations between dosimetric variables and the Min ALC were assessed by multiple linear regression analysis. Peripheral lymphocytes decreased during RT (P < 0.001). The Min ALC correlated with the MSD (P = 0.005), spleen V₅ (P = 0.001), spleen V₂₅ (P = 0.026) and spleen V₃₀ (P = 0.018). Controlling for the Karnofsky performance status (KPS), sex, age, Child-Pugh grade, total dose and tumour stage, a multiple linear regression model with bootstrap analysis of 1000 replicates showed that only the spleen V₅ was correlated with the decrease in the Min ALC (P < 0.05). According to the receiver-operating characteristic (ROC) curve analysis, the predictive cutoff values of the MSD, V₅, V₂₅ and V₃₀ of the spleen for the Min ALC were 227.72 cGy, 17.84, 0.98 and 0.42%, respectively (P = 0.002, P = 0.004, P = 0.007 and P = 0.002, respectively). Furthermore, an MSD ≥ 227.72 cGy (OR = 14.39; 95% CI, 12.18 to 16.60) and V₅ (OR = 7.99; 95% CI, 6.91 to 9.07) of the spleen significantly predicted the Min ALC. Higher spleen irradiation doses were significantly correlated with lower Min ALC during RT for HCC. V₅ should be limited in clinical practice. Maximum sparing for spleen irradiation during RT is recommended to preserve peripheral blood lymphocytes, which may decrease immunosuppression.