Purpose : The aim of this study was to identify the effects of nutrition risk, physical activity, insomnia, anxiety, and depression on fatigue among breast cancer patients undergoing radiotherapy.

Methods: Methods: The participants of this study were 160 breast cancer patients at Y University Hospital in South Korea. The data were collected from September to November 2022. Data were analyzed using descriptive statistics, t-test, ANOVA, Mann-Whitney test, Kruskal-Wallis test, Bonferroni correction, Pearson''s correlation coefficients, and multiple regression with SPSS version 28.0.

Results: The mean scores of fatigue were 18.44±7.30 points, nutrition risk was 2.03±1.52 points, insomnia was 5.43±4.79 points, physical activity was 1366.49±1617.87 METs, vigorous physical activity was 305.50±896.78 METs, moderate physical activity was 218.25±543.73 METs, walking was 842.74±626.29 points, anxiety was 6.79±2.81 points, and depression was 8.17±3.36 points.
The general characteristics showed that there were differences in fatigue among pain (F=11.45, p=.003), duration of illness (t=-2.37, p=.019), and total radiation dose (t=-2.13, p=.035).
Fatigue showed a significant positive correlation with nutrition risk (r=.35, p<.001), insomnia (r=.35, p<.001), and anxiety (r=.47, p<.001), and a significant negative correlation with physical activity (r=-.20, p=.012).
Additionally, the influencing factors on fatigue in multiple regression analysis were nutrition risk (β=.28, p<.001), duration of illness (β=.19, p=.004), depression (β=.24, p=.005), total radiation dose (β=.18, p=.007), and physical activity (β=-.15, p=.032). These factors explained 43.0% of the total variance (F=11.85, p<.001).

Conclusion: The study suggests that reducing nutrition risk and depression in breast cancer patients during radiotherapy, and recommending physical activity, can help manage their fatigue. Therefore, a program that combines physical exercise with dietary support and psychological treatment needs to be provided.