Clinical and Treatment Factors associated with Lymphopenia after Palliative Radiation Therapy in Cancer Patients

Conventionally fractionated radiation therapy (RT) is associated with treatment-induced lymphopenia and reduced survival. The impact of shorter-course palliative RT on lymphopenia remains unclear. We evaluated the relationship between characteristics of common palliative RT regimens and lymphopenia in a large institutional cohort.

We retrospectively identified patients treated with palliative RT over 12 years. Patients with available absolute lymphocyte counts (ALC) before and after RT were included. Lymphopenia was graded per CTCAE criteria. A paired t-test was used to compare pre- and post-treatment absolute lymphocyte count (ALC). Univariable and multivariable logistic regression was used to determine the effect of palliative RT dose/fractionation on the likelihood of inducing lymphopenia.

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. There was a significant decline in absolute lymphocyte counts (ALC) following palliative RT (p<0.01). The magnitude of ALC decline varied by fractionation. Median change in ALC was -0.27, -0.49, and -0.66 for patients receiving 8 Gy in 1 fraction (Fx), 20 Gy in 5 Fx, and 30 Gy in 10 Fx, respectively (p<0.01). Treatment site (bone/spine vs. other sites) was not significantly associated with differences in ALC change (p=0.09). In the multivariable analyses, subjects who received 5 Fx (OR=1.85; 95% CI: 1.41 - 2.44) or 10 Fx (OR=3.12; 95% CI: 2.19 - 4.43) were approximately 2 and 3 times, respectively, more likely to develop lymphopenia as compared to those who received 1 Fx.