A study by the Tsukuba group, Japan. This study retrospectively reviewed 69 patients with esophageal cancer treated with XRT (n=15) and PBT (n= 54) and concurrent chemotherapy. The study found that the absolute lymphocyte counts (ALC) were significantly higher in PBT group than the XRT group, and a similar trend was observed in the neutrophil-to-lymphocyte ratio (NLR). Dose-volume analysis revealed significant correlations between the volume of the thoracic bones irradiated by 5-50 Gy and the minimum ALCs and maximum NLR. This study suggested that PBT prevented the development of lymphopenia by reducing the irradiated volume of the thoracic bone.