Impact of Palliative Radiation on Lymphopenia in Cancer Patients

Summary: Conventionally fractionated radiation therapy regimens have been shown to induce lymphopenia in cancer patients. Whether the same effect is seen with shorter courses of palliative radiation has not been well studied. Herein, we sought to analyze the effect of palliative RT on rates of lymphopenia among a large cohort of patients treated within our health system. Using the Oncora database, we retrospectively identified all patients within our health system who were treated with a palliative dose of RT in the last 10 years who had information on lymphocyte counts before and after palliative RT. Lymphopenia was defined according to CTCAE guidelines. Palliative RT was defined as 8 Gray (Gy) in one fraction (Fx) or 20 Gy in 5 Fx or 30 Gy in 10 Fx. We used a paired t-test to compare the absolute lymphocyte counts for patients pre- and post- palliative RT and used p=0.05 as a cutoff for statistical significance. We conducted a univariable regression model to determine the effect of palliative radiation dose/fractionation on the likelihood of inducing lymphopenia. Odds ratios were used to compare the three fractionation schemas to each other. Out of the 2002 patients who received palliative radiation, 877 had lymphopenia prior to treatment. Of the remaining 1125, 748 developed lymphopenia following palliative RT (p < 0.001). There was a significant difference between the pre- and post-treatment absolute lymphocyte count (ALC) values (diff = -0.60; 95% confidence interval for the mean difference: [-0.70, -0.51], p < 0.001) with a concomittant correlation between receipt of palliative RT and incidence of lymphopenia (37.4% of patients developing lymphopenia, p < 0.001). Furthermore, increasing the number of fractions of palliative RT was associated with increased rates of lymphopenia. The odds ratios (OR) for each fractionation indicate that subjects who received 5 Fx (OR=1.92; 95% CI: 1.46 - 2.52) or 10 Fx (OR=3.21; 95% CI: 2.27 - 4.53) were approximately 2 and 3 times, respectively, more likely to develop lymphopenia as compared to those who received 1 Fx. Palliative RT can induce lymphopenia in cancer patients. In patients with existing lymphopenia prior to treatment, RT can worsen the grade of lymphopenia. Increasing the number of fractions of palliative RT increases the risk of developing lymphopenia. Treating physicians should attempt to minimize the number of palliative RT fractions to minimize lymphopenia risk. Joshua J. Kim, BS (Presenting Author) - Northwell Health; Meredith Akerman, MS (Co-Author) - Northwell Health; David Lindsay, MD PhD (Co-Author) - Oncora Medical; Joe Herman, MD (Co-Author) - Histosonics, Inc.; Leila Tchelebi, MD (Co-Author) - Northwell Health