The impact of lymphopenia during chemoradiotherapy using photons or protons on the clinical outcomes of esophageal cancer patients

We assessed the development of lymphopenia during concurrent chemoradiotherapy (CRT) using X-ray versus proton beams and the impact on survival in patients with esophageal cancer. Among patients with esophageal cancer who were administered concurrent CRT with a curative intent at our institute from 2014 to 2018, 69 (15 receiving X-ray radiotherapy (XRT) and 54 receiving proton beam therapy [PBT]) who underwent weekly blood testing during treatment were enrolled. The absolute lymphocyte counts (ALC) at 1, 5 and 6 weeks were significantly higher in the patients who received PBT than in those who received XRT (p = 0.002, p = 0.006 and p = 0.009, respectively), and a similar trend in the neutrophil-to-lymphocyte ratio (NLR) was observed (p = 0.003 at 5 weeks). The 2-year overall survival (OS) and progression-free survival (PFS) rates tended to be higher in the patients who maintained an ALC ≥200 compared with those who did not (p = 0.083 and p = 0.053, respectively), and similar trends were observed in the NLR (p = 0.061 and p = 0.038, respectively). Dose–volume analysis revealed significant correlations between volumes of the thoracic bones irradiated by 5–50 Gy and minimum ALCs and maximum NLR. These findings suggested that PBT prevented the development of lymphopenia during CRT by reducing the irradiated volume of the thoracic bone, and the maintained lymphocyte count is possibly one of the early predictors for survival in patients with esophageal cancer.