The mediating role of psychological distress in the effect of positive psychological intervention on sleep quality among cancer patients undergoing radiotherapy: A randomized controlled trial

Purpose To evaluate the effects of positive psychological intervention (PPI) on sleep quality among cancer patients undergoing radiotherapy, and to investigate whether changes in psychological distress mediate the relationship between PPI and sleep quality specifically.Methods A total of 60 eligible patients were randomly assigned to two groups. The control group received usual care, and the intervention group received the PPI based on usual care. Sleep quality was assessed with the Pittsburgh Sleep Quality Index (PSQI) and psychological distress with the Distress Thermometer at three time points: pre-intervention (T0), immediate post-intervention (T1), and 4 wk post-intervention (T2).Results Significant differences were observed between the two groups in terms of sleep quality and psychological distress (p < 0.001). Compared with the control group, the intervention group showed significant and lager effect in improving sleep quality (d = 1.28, p < 0.001) and psychological distress (d = 0.82, p = 0.002) from T0 to T1. At T2, the intervention group maintained a large effect on sleep quality (d = 1.10, p < 0.001), while the effect on psychological distress (d = 0.78, p = 0.004) was significant, with moderate effect. The total effect of PPI on sleep quality encompasses a full mediating effect, with 52.2% of the PPI effects on sleep quality mediated by the reduction in psychological distress at T1, and 45% at T2.Conclusions A 4-week PPI exerts a significant effect on psychological distress and sleep quality in cancer patients undergoing radiotherapy. Meanwhile, psychological distress acts as a mediating variable in the improvement of sleep quality by PPI.