Patterns of CT lung injury and toxicity after stereotactic radiotherapy delivered with helical tomotherapy in early stage medically inoperable NSCLC

Objective: To evaluate toxicity and patterns of radiologic lung injury on CT images after hypofractionated imageguided stereotactic body radiotherapy (SBRT) delivered with helical tomotherapy (HT) in medically early stage inoperable non-small-cell lung cancer (NSCLC). Methods: 28 elderly patients (31 lesions) with compromised pulmonary reserve were deemed inoperable and enrolled to undergo SBRT. Patterns of lung injury based on CT appearance were assessed at baseline and during follow up. Acute (6 months or less) and late (more than 6 months) events were classified as radiation pneumonitis and radiation fibrosis (RF), respectively. Results: After a median follow-up of 12 months (range, 4-20 months), 31 and 25 lesions were examined for acute and late injuries, respectively. Among the former group, 25 (80.6%) patients showed no radiological changes. The CT appearance of RF revealed modified conventional, mass-like and scar-like patterns in three, four and three lesions, respectively. No evidence of late lung injury was demonstrated in 15 lesions. Five patients developed clinical pneumonitis (four patients, grade 2 and one patient, grade 3, respectively), and none of whom had CT findings at 3 months post-treatment. No instance of symptomatic RF was detected. The tumour response rate was 84% (complete response1partial response). Local control was 83% at 1 year. Conclusion: Our findings show that HT-SBRT can be considered an effective treatment with a mild toxicity profile in medically inoperable patients with early stage NSCLC. No specific pattern of lung injury was demonstrated. Advances in knowledge: Our study is among the few showing that HT-SBRT represents a safe and effective option in patients with early stage medically inoperable NSCLC, and that it is not associated with a specific pattern of lung injury.