Prospective monitoring of lung function tests with CO and NO diffusion during high dose thoracic radiotherapy for lung cancer: The CONORT study

Aim/Background

Thoracic radiotherapy (RT) is a usual treatment for lung cancer, with little impact on lung volume (FEV1 and FCV). Pulmonary diffusion is appreciated by the CO (TLCO) and NO (azote monoxide) diffusion capacity (TLNO). Double assessment of NO and CO diffusing capacities, and capillary/membrane alterations, have not yet been analyzed after high dose RT. CONORT is an observational prospective monocentric study, to measure the evolution of these parameters under high dose thoracic RT (especially IMRT and SBRT), on a large cohort of patients (pts) with a long follow-up.

Methods

CONORT study was approved by the Lyon Sud-Est IV ethics committee, the database was declared to the national information registry authority. The study aimed to estimate a difference of 15% in diffusing capacity tests, with a 90% power and a 5% alpha risk. PFTs including double diffusion are performed by the same operator, using the same technic, before-, during-, at the end and after RT(3, 6, 12 months). All pts gave their consent. Results at PFTs were expressed in % of theoretical value (%th), and were compared using Student t test.

Results

Between February 2014 and May 2015, 92 consecutive pts have been analyzed: 71% male, mean age 69.5 years. RT technique was IMRT in 58%, SBRT in 36%, 3D conformal RT in 6%. Mean pretreatment FEV1 was 2.06L (78.9% of the standard), mean FCV was 3.17L (94.9%), mean TLCO was 16.5 (64.7%) mean TLNO was 72.7 (60.3%). FEV1 and FCV were stable during and after RT. However, mean TLCO decreased by 4.4% (P = 0.01) between first and fourth PFT, mean DLNO decreased by 4% (P = 0.001) between first and second PFT, mean VC (capillary lung volume) decreased by 6.24% between first and fourth PFT (P = 0.011), and DM (membrane diffusing capacity) decreased by 3.6% between first and second PFT (P = 0.001).

Conclusions

CONORT is the first study evaluating the potential impact of high dose thoracic RT on double measurement of lung diffusing capacity. Results showed that thoracic RT has little impact on lung volumes, but lung diffusion decreases, initially by membrane alteration, then by capillary alteration, with full recovery at 6 months. Mature results (1 year) will be presented.

Clinical trial identification

CPP sud est IV: ref L13-23

Disclosure

All authors have declared no conflicts of interest.