High-dose thoracic radiation therapy for non-small cell lung cancer: a novel grading scale of radiation-induced lung injury for symptomatic radiation pneumonitis

BACKGROUND: Symptomatic radiation pneumonitis (RP) may be a serious complication after thoracic radiation therapy (RT) for non-small cell lung cancer (NSCLC). This prospective observational study sought to evaluate the utility of a novel radiation-induced lung injury (RILI) grading scale (RGS) for the prediction of RP.

MATERIALS AND METHODS: Data of 41 patients with NSCLC treated with thoracic RT of 60-66 Gy were analysed. CT scans were scheduled before RT, one month post-RT, and every three months thereafter for one year. Symptomatic RP was defined as Common Terminology Criteria for Adverse Events grade ≥ 2. RGS grading ranged from 0 to 3. The inter-observer variability of the RGS was assessed by four senior radiologists. CT scans performed 28 ± 10 days after RT were used to analyse the predictive value of the RGS. The change in the RGS severity was correlated to dosimetric parameters.

RESULTS: The CT obtained one month post-RT showed RILI in 36 (88%) of patients (RGS grade 0 [5 patients], 1 [25 patients], 2 [6 patients], and 3 [5 patients]). The inter-observer agreement of the RGS grading was high (Kendall's W coefficient of concordance = 0.80, p < 0.01). Patients with RGS grades 2-3 had a significantly higher risk for development of RP (relative risk (RR): 2.4, 95% CI 1.6-3.7, p < 0.01) and RP symptoms within 8 weeks after RT (RR: 4.8, 95% CI 1.3-17.6, p < 0.01) compared to RGS grades 0-1. The specificity and sensitivity of the RGS grades 2-3 in predicting symptomatic RP was 100% (95% CI 80.5-100%) and 45.4% (95% CI 24.4-67.8%), respectively. Increase in RGS severity correlated to mean lung dose and the percentage of the total lung volume receiving 5 Gy.

CONCLUSIONS: The RGS is a simple radiologic tool associated with symptomatic RP. A validation study is warranted.