This study explored the dynamic symptom network during radiotherapy in patients with esophageal cancer using the CLPN. Our findings revealed symptom predictive ability and interactions between symptoms at two adjacent time points, emphasizing the need for early and precise symptom interventions.
Distress had the strongest predictive power during T0→T1. Distress at T0 predicted multiple changes in symptoms at T1. Of these, anxiety had the strongest predictive ability. Cancer-related distress is a psychologically, socially, and spiritually multifactorial unpleasant experience that interferes with an individual's ability to cope effectively with illness and treatment. However, it is a relatively mild, normal expression of negative psychological emotions 26. Anxiety disorders are an extension of the distress continuum, which begins with normal feelings of common psychological brittleness, sadness, and fear and can lead to the emergence of psychiatric disorder symptoms when induced by risk factors or under chronic stress. Anxiety differs from distress in that it is excessive, unfounded, and often illogical fears and worries 26. Once the distress progresses to anxiety or depression, the patient is exposed to increased safety risks, such as suicidal and self-injurious behaviors 27, and fewer effective interventions, even requiring medication for severe anxiety disorders. The fact that distress predicts anxiety may be related to the patient's psychological fragility, fear of radiotherapy, and experience of physiological symptoms such as fatigue and pain during radiotherapy, which exacerbates distress symptoms. Radiotherapy exacerbates anxiety and depressive symptoms in patients 28,29. The majority of the participants in this study were clinically advanced, and almost all of them experienced varying degrees of distress at baseline. Notably, clinically advanced and psychologically vulnerable patients with cancer experience anxiety symptoms immediately after treatment 30. Considering the high prevalence of anxiety and depression at T1 and the patient safety risks that may result, the use of distress at baseline as an early target for symptomatic intervention and the provision of psychosocial support to patients as early as possible are essential for preventing the onset of serious psychiatric disorders.
In addition, distress at T0 predicted symptoms such as disturbed sleep and fatigue, consistent with the findings of several studies 24,27 that negative emotions exacerbate disturbed sleep and lead to physical fatigue. Therefore, addressing the symptoms of distress in patients with esophageal cancer at baseline can have a positive effect on preventing the development of anxiety disorders, disturbed sleep, fatigue, and depression during radiation therapy.
During T0→T1, anxiety and depression had higher in-EI. They were susceptible to other symptoms at T0, indicating that they could be used as mid-radiotherapy outcome indicators to assess the effectiveness of symptomatic interventions at T0. As previously described, anxiety and depression act as extensions of a continuum of distress, and the assessment of and intervention for psychological symptoms in patients before radiotherapy are key to preventing them from developing psychiatric disorders during radiotherapy.
During the T1→T2 period, distress remained the highest out-EI symptom, but unlike the T0→T1 period, distress in T1 predominantly predicted loss of appetite and sadness in T2. This result was consistent with the findings of Shang et al. 24. Patients' psychological symptoms worsen in the middle stage of radiotherapy, and psychological stress can activate the gut-brain axis to affect the normal functioning of the gastrointestinal tract by inhibiting the vagus nerve from sending signals, which in turn leads to symptoms such as bloating, nausea, and loss of appetite 31–33.
The onset of depression at T1 predicted anxiety and disturbed sleep at T2, and the onset of depression at T1 was influenced by distress at T0. Disturbed sleep at T2, the symptom with the highest in-EI, could be prevented by managing symptoms of distress at baseline, thus alleviating disturbed sleep. Loss of appetite, the second-highest in-EI, was affected by psychological symptoms and dysphagia at T1. In patients with esophageal cancer, the radiation site is often located in the chest, which may lead to swelling of the throat and esophagus and consequently dysphagia, and the exacerbation of this symptom is cumulative with the duration of radiotherapy. The patient may experience symptoms after 1 week of radiotherapy and continue until 2 weeks after the end of radiotherapy 34. However, some studies have shown that radiotherapy for esophageal cancer can alleviate dysphagia symptoms, which may depend on the cause of the symptoms; if dysphagia is due to tumor compression of the esophagus or pharynx, radiotherapy can alleviate these symptoms 35.
Dry mouth has the highest mediator centrality during T0→T1, and they assume a vital role in a dynamic network that transmits symptom changes and connects symptoms at different time points, and intervention in these symptoms is a critical way to prevent the occurrence of other symptoms. The severity and incidence of dry mouth were significantly higher at T1 than at T0, which is consistent with the study of Pinna et al. 36. Patients with esophageal cancer can experience dry mouth after radiotherapy because the radiation produced by radiotherapy spreads to a certain extent to the surrounding tissues; therefore, even though the main site of radiotherapy is the esophagus, salivary glands in the adjacent oral tissues may also be involved 36, and the occurrence of dry mouth symptoms can widely affect the changes in other symptoms in the T1 stage.
In the T1→T2 phase, drowsiness was considered the symptom with the strongest bridging effect. The symptoms are affected by multiple symptoms from mid-radiotherapy to 1 month after the end of radiotherapy, and they also influence the development of multiple symptoms. Notably, dry mouth predicts drowsiness, which may be because dry mouth causes patients to wake up frequently or fail to reach the deep sleep stage, often making them feel tired or sleepy during the day. Drowsiness affects multiple psychological symptoms in patients' T2 stage, such as distress and depression, and also affects appetite, so focusing on the sleepy symptoms in T1→T2 is warranted.