Long-Term Effects of Radiation on Lymphocytes and Risk of Opportunistic Infections

Objectives Lymphocytes are very sensitive to ionizing radiation. The long-term effects and the risk of permanent immune compromise are not well defined in spite of more than a century of therapeutic radiation. The contemporary analysis is made more difficult in that most patients also receive immunosuppressive chemotherapy. Methods Cohort-all patients that underwent a prostate biopsy from 2002 to 2007. Those (n=1118) with at least two blood counts, with one at a minimum of 10 years after biopsy, were included. We identified three groups: those that received no treatment (due to benign biopsy findings or active surveillance), those undergoing prostate cancer surgery, and those undergoing radiation therapy. Blood counts were collected and analyzed for differences with a median follow-up of 178 months. Also evaluated was the risk of opportunistic infections. Results The median granulocyte count gradually increased with time, with no difference between the groups. Overall, the median lymphocyte count decreased from baseline over time (with a slight rise at 20 years). For the no treatment and surgery groups, the lymphocyte counts declined, but due to the initial decline after radiation therapy, that group saw a slow improvement. By 20 years, there was no difference between the groups. Most patients’ counts remained in the normal range throughout. The risk of defined opportunistic infections was low (12%) with no difference between the groups. Conclusion Pelvic radiation has minimal lasting effects on lymphocyte and granulocyte counts. In addition, patients receiving radiation do not appear to be significantly immunocompromised.