Purpose: Risk of radiation pneumonia (RP) could not be effectively detected due to non-specific clinical symptoms in the early stage. The purpose of this investigation was to evaluate serum biomarkers of cytokines interleukin-6 (IL-6), C-reactive protein (CRP) and procalcitonin (PCT) for its early detection in patients with thoracic malignant tumors receiving radiotherapy.
Patients and methods: The clinical data of 105 patients with thoracic malignant tumors (lung cancer, esophageal carcinoma and mediastinal tumors) treated by radiotherapy were retrospectively analyzed. The patients were divided into RP group and non-RP group according to the Common Terminology Criteria for Adverse Events (CTCAE 5.0). The serum level of IL-6 was detected by chemiluminescence, and the level of CRP was measured by nephelometry during radiotherapy. The level of PCT, one of the specific indicators to distinguish infection and non-infectious etiologies, was also detected by chemiluminescence.
Results: Among 105 patients treated by radiotherapy, 28 developed RP, and the other 77 had no RP. There was no significant difference in the risk of RP between patients’ factors (age, sex, PS score, smoking, tumor type) and treatment factors (chemotherapy, V₅, GTV dose). However, chronic obstructive pulmonary disease (COPD), V₂₀ and mean lung dose (MLD) were significantly different between the two groups (χ ² = 4.131, 3.986, 7.830, P < 0.05). Furthermore, PCT levels were also found to have insignificant differences between RP group and non-RP group (P  > 0.05). However, there were significant differences between the groups in the levels of IL-6 and CRP (P  < 0.05). The IL-6 levels significantly increased earlier than that of conventional CT imaging when patients suffering from RP and peaked at 6 weeks during radiotherapy. CRP had a similar change as IL-6. Single cytokine and combination of IL-6 and CRP possessed a good ability to predict RP with the AUC of IL-6 of 0.89±0.04 (95% CI, 0.80–0.95, P<0.001), CRP of 0.87±0.05 (95% CI, 0.78–0.94, P<0.001), IL-6 + CRP of 0.92 ± 0.03 (95% CI, 0.83–0.97, P < 0.001), respectively.
Conclusion: The combined detection of serum IL-6, CRP and PCT may be an effectual method for early detection and clinical practice management of risk of RP.
Keywords: cancer, radiotherapy, radiation pneumonitis, interleukin-6, C-reactive protein, procalcitonin, biomarkers