Assessing the Spleen as an Organ at Risk in Radiation Therapy and Its Relationship With Radiation-Induced Lymphopenia: A Retrospective Study and Literature Review

PURPOSE: We conducted a systematic review and a retrospective study to investigate the relationship between spleen irradiation and lymphocyte toxicity. METHODS AND MATERIALS: Forty-six patients diagnosed with locally advanced gastric, esophageal, and pancreatic cancer who underwent radiation therapy were included in this study. The spleen was contoured for each patient. Volumes that received 5 up to 40 Gy (5 Gy increments), minimum, mean, and maximum dose were considered along with lymphocyte count to determine toxicity. Comprehensive and systematic literature searches were performed using PubMed, SCOPUS, Cochrane Central Databases, and Google Scholar. RESULTS: Literature review on spleen unintended irradiation and lymphocyte toxicity resulted in 408 patients from 5 studies. In our study, univariate and multivariate linear regressions found an association between V15 (chemotherapy as controlling factor) and nadir lymphocyte count (P = .04) and between D(MAX) and nadir lymphocyte count (P = .046). An increase of 1 Gy in mean splenic dose was associated with a 1% decrease in absolute lymphocyte count at nadir. CONCLUSIONS: Although there is no consensus regarding lymphopenia spleen dose volume threshold, all studies found that higher splenic dose increases the risk of lymphopenia. Our study's results suggest that spleen unintentional V15 and maximum dose irradiation were associated with lymphopenia during chemoradiation therapy.