Background: Lymphocytes as a marker of immune function are essential to the immune response. Sternum and vertebra bone marrow (BM) exposed to radiation may affect lymphocytes during radiotherapy (RT) for esophageal carcinoma (EC). We analyzed the relationship among peripheral blood lymphocytes, exposed sternum and vertebra body BM, and overall survival (OS) to find BM dosimetric parameters of lymphopenia during chemoradiotherapy (CRT) for patients with esophageal squamous cell carcinoma (ESCC).
Methods: We examined 476 ESCC patients from January 2012 to January 2015, all of whom received concurrent or sequential CRT. Absolute lymphocyte counts (ALC) during RT of each patient were collected from the routine workup at the following RT times: pretreatment ALC (ALC0), at 1–5, 6–10, 11–15, 16–20, and 21–25, and more than 26 sessions (called ALC1–6, respectively). The sternum and vertebral body BM were delineated in accordance with uniform standards, and the irradiated volumes were calculated by dose-volume histograms (DVH). The Kaplan–Meier method and Cox proportional hazards regression were used to analyze the survival of the patients. Comparisons of DVH were performed using the Mann–Whitney U test or two-sample t-test where appropriate.
Results: A relative volume of sternum BM irradiated by more than 20 Gy could clearly affect the peripheral blood lymphocytes. The V20 of sternum BM and V50 of vertebra body BM were related to the OS of the patients, and the level of ALC2(at 6–10 times of RT) could predict the patients’ outcomes. The Cox regression analyses showed that the 218 patients with ALC2 ≥ 0.8×109/L had a significantly longer OS (47.0 vs. 30.9, p<0.0001) than the 258 patients with ALC2 < 0.8×109/L.
Conclusion: In patients with ESCC, the relative volume of sternum BM irradiated by more than 20 Gy was associated with lymphocyte. The V20 of the sternum BM and the V50 of the vertebra body BM were related to the OS of the patients. The level of ALC2 is a significant prognostic factor in esophageal carcinoma patients.