Risk of Radiation Pneumonitis after Post-lobectomy Thoracic Radiotherapy for Non-small-cell Lung Cancer

Introduction Patients who had lobectomy prior to thoracic radiotherapy may be more prone to developing radiation pneumonitis (RP) given their smaller remaining lung volume. There is no consensus on the normal lung dose constraints in this population. V20 ≤30% to 35% and mean lung dose (MLD) ≤20 Gy are common dose constraints used in definitive radiotherapy for lung cancer. We aimed to determine whether V20 ≤33% and mean MLD ≤20 Gy are safe constraints with an acceptable risk of RP in post-lobectomy patients. Methods The data of all patients who received post-lobectomy thoracic radiotherapy for non-small-cell lung cancer at a single centre in Hong Kong from 2011 to 2018 were analysed retrospectively. The endpoint was Common Terminology Criteria for Adverse Events (CTCAE) grade ≥3 RP. Statistical analysis was performed to investigate whether V10 and V20 of whole lung were predictive factors for RP. Results Fifty-five patients had been treated using the dose constraints of V20 ≤33% and MLD ≤20 Gy. Three patients developed grade 5 RP. No patients had grade 3 or 4 RP. There was no significant association between the V10, V20 and grade ≥3 RP. Conclusion Our data showed that the risk of grade ≥3 RP was 5.5% in post-lobectomy patients using dose constraints of V20 ≤33% and MLD ≤20 Gy. Further prospective studies are necessary to clarify the optimal dose constraints in this population.