Post-treatment lymphocytopaenia, integral body dose and overall survival in lung cancer patients treated with radical radiotherapy

Introduction Post-treatment lymphocytopaenia is a recognized complication of thoracic radiotherapy likely due to irradiation of a large volume of circulatory blood. We hypothesize that post-treatment absolute lymphocyte count (ALC) is associated with integral body dose and overall survival (OS) in lung cancer patients treated with radical radiotherapy. Materials and methods Data on clinicopathological variables, dosimetric parameters, and pre and post-treatment blood counts were collected retrospectively in 217 lung cancer patients (131 with non-small cell lung cancer and 86 with small cell lung cancer) treated with radical radiotherapy. Induction chemotherapy followed by radiotherapy and concurrent chemoradiotherapy were delivered in 89 (42%) and 99 (47%) patients respectively. Multiple stepwise regression analysis was performed separately for ALC and absolute neutrophil count (ANC) to derive a model for prediction of post-treatment count and multivariate analysis was performed for OS using a Cox regression model. Results There was a significant decline in post-treatment counts for both ANC and ALC (p < 0.001). Multiple stepwise linear regression analysis confirmed pre-treatment ALC, body integral dose and use of concurrent chemotherapy as significant predictors of post-treatment ALC (R2 = 0.33, F(4,212) = 26.6 p < 0.001). Pre-treatment ANC, integral heart dose and number of fractions were significant predictors of post-treatment ANC (R2 = 0.18, F(3,213) = 16.38 p < 0.001). Low post-treatment ALC, high pre-treatment ANC, high planning target volume integral dose and lower number of fractions were predictive of inferior OS. Conclusions There is a negative correlation between integral body dose and post-treatment ALC which is an adverse prognostic factor in lung cancer patients treated with radical radiotherapy.