Influence of fractionated irradiation on neutrophilic granulocyte function

Background: A recent study has demonstrated that radiation therapy with single doses of up to 32 Gy has only a minor effect on neutrophilic granulocyte function. In clinical practice, by contrast, fractionated irradiation is applied. Therefore, the aim of the current study was to verify the influence of fractionated radiation therapy on granulocyte function. Material and Methods: Density gradient-purified granulocytes of voluntary healthy donors were used for all experiments. Granulocytes were kept in RPMI 1640 without fetal calf serum, incubated for 48 h and irradiated. Their function was assessed by measuring luminol-enhanced chemiluminescence after stimulation with phorbol myristate acid (PMA). ALL tests were performed at Least five times. Results: Relative changes (any reactive oxygen species [ROS] release before stimulation was defined as being equal to 100%) in ROS release increased after stimulation with PMA (mean+/-SD): 0 Gy: 785+/-462.6%; 2 Gy: 704.3+/-388.1%; 6 Gy: 1,360.3+/-710.5%; 12 Gy: 1,119.4+/-581.1%; 18 Gy: 1,087.4+/-622.4; 6 Gy (3x2 Gy): 279.4+/-201.1%; 12 Gy (6x2 Gy): 278.8+/-175.3%; 18 Gy (9x2 Gy): 84.2+/-41.5%. Comparing relative changes in ROS release after PMA stimulation, the differences between 0, 2, 6, 12, 18 Gy, and 6 Gy (3x2 Gy), 12 Gy (6x2 Gy), 18 Gy (9x2 Gy), and between 6 Gy (3x2 Gy), 12 Gy (6x2 Gy) and 18 Gy (9x2 Gy) proved to be significant (all p<0.005). Conclusion: The study shows, that clinically used fractionated irradiation has an impact on granulocyte function, but contrary to common assumption, it is not the total dose itself but rather the fractionation which influences granulocyte function. This could have a major clinical impact on radiation treatment schemes especially for benign diseases or anti-inflammatory treatment.