Measurement of exhaled nitric oxide and serum surfactant protein D levels for monitoring radiation pneumonitis following thoracic radiotherapy

The present study aimed to examine the role of exhaled nitric oxide (eNO) and serum surfactant protein D (SP-D) level in the determination of radiation pneumonitis (RP) after thoracic radiotherapy (RT). The study included 34 treatments for 33 patients, including 16 three-dimensional conformal and 18 stereotactic body RT treatments. eNO levels were measured prior to RT, immediately subsequent to RT, every week during the RT course and at 1, 3, 6, 9 and 12 months following the treatment. The therapy reduced the eNO from 24.3±12.8 ppb prior to RT to 19.0±10.4 ppb immediately subsequent to RT (P=0.04). A total of 5 patients (14%) developed symptomatic RP of grade 2 or higher 3–5 months later, and exhibited an eNO elevation of 2.1±0.68-fold the minimum value, whereas the RP- group exhibited 1.4±0.6-fold elevation (P=0.02). The sensitivity of a cut-off of a 1.4-fold increase in the eNO ratio at the onset of RP was 100%; however, the specificity was 52%, and no predictive alterations to eNO levels were observed prior to the onset of RP. RT was associated with an elevated serum SP-D level at 3–6 months after RT. There was a statistically significant difference in the initial serum SP-D level between RP+ and RP- patients. In conclusion, obtaining the eNO ratio was a useful RP monitoring tool but did not predict RP occurrence in the present setting, whereas serum SP-D level may be a potential predictor for the detection of RP risk.