Session Item

Thoracic radiotherapy (RT) in patients with a locally advanced lung cancer is associated with a high rate of acute pulmonary toxicity, with a possible functional impact with a decrease of the carbon monoxide diffusion capacity (DLCO).  Volumetric Modulated Arc Therapy (VMAT) allows a higher conformation with an increase of the low dose volumes when compared to 3D-conformationnal radiotherapy.  The impact of VMAT has never been investigated prospectively. The aim of the study is to evaluate the decrease of DLCO at 3 months (3M) after a VMAT-based RT.

All patients treated with a curative intent for a locally advanced lung cancer were prospectively considered in a monocentric observational study. Patients with a history of thoracic surgery or radiotherapy were excluded. Clinical evaluation was performed at baseline, every week during RT, at the end of RT, at 1, 3 and 9 months after completion while DLCO was evaluated at baseline, 3 and 9 months post-RT. The primary endpoint was a > 20% decrease of DLCO at 3 months. Association between the DLCO decrease and usual clinical/dosimetric features was evaluated using the Receiver Operative Characteristics while comparison between paired samples was performed using the Wilcoxon test. A p < 0.05 was considered as statistically significant.

Between November 2018 and July 2021 and among the 39 included patients, 29 patients were analyzable. The mean DLCO at 3M after RT decreased by 12% (p=0,003). Age, mean dose to the homolateral lung (HL) and to both lungs (BL), V5% and V10%  to BL and HL, the V5% to the contralateral lung as well as the Clinical and Planning Target Volumes were significantly associated with the DLCO decrease. 

VMAT-based thoracic RT seems to be associated with a decrease of DLCO at 3 months. Among several clinical and dosimetric features, low dose volumes (V5% and V10%) were identified has predictive factors of a > 20% DLCO decrease.