P2.17-21 A Post-Hoc Analysis of TROG 09.02 (CHISEL) Phase III Trial Investigating Pulmonary Function Changes After SABR and Conformal Radiation Therapy

Abstract

Listen

Translate article

The TROG 09.02 (CHISEL) trial compared conventional radiotherapy (CRT) administered over a period of four to six weeks with stereotactic ablative body radiotherapy (SABR).(1) Patients randomised to the SABR arm had superior freedom from local failure and longer overall survival.(1) The aim of this analysis was to assess differences in lung function and spirometry tests between SABR and CRT and describe longitudinal changes in respiratory function. We conducted a post-hoc analysis of all patients recruited to the CHISEL trial. During this trial patients underwent serial Respiratory Function Tests (RFT) including Forced Expiratory Volume in one second (FEV1), Diffusing capacity of the lungs for carbon monoxide (DLCO), Distance Walked in 6 minutes (SMWT) and Forced Vital Capacity (FVC). These were performed at baseline then 3-6 monthly post-treatment. Patients were assessed per treatment received. Linear regression models were used to compare FEV1, FVC and DLCO between SABR and CRT. Separate models at 3 and 12 months post-treatment were created to assess the two different processes impacting lung function post radiation therapy (acute pneumonitis and chronic fibrosis). Linear regression models were used to assess the association of baseline PFT Measures with decline in respiratory function at 3 and 12 months. Between December 2009 and June 2015, 101 patients were treated in 11 centres in Australia and New Zealand. 34 patients were treated with CRT and 63 with SABR. On regression analysis at 3 months there was no evidence of a difference between arms in the change from baseline in absolute values of FEV1 (beta 0.037, 95% CI [-0.063, 0.14], p=0.47), DLCO (beta -0.5, 95% CI [-1.4, 0.37], p=0.26) nor forced VC (beta 0.024, 95% CI [-0.17, 0.22], p=0.81). At 12 months there were no differences observed in change from baseline of FEV1 (beta0.031, 95% CI [-0.12, 0.18], p=0.69), DLCO (beta -0.43, 95% CI [-1.7, 0.84], p=0.51) nor forced VC (beta 0.047, 95% CI [-0.28, 0.18], p=0.69) between arms.There was no evidence of a difference in the change from baseline in SMWT (m) between two arms at 3 months (beta 35.9, 95% CI [-10, 82.3], p=0.13).Patients in both arms demonstrated similar deterioration in all RFT parameters with time. Despite the considerably higher biologically effective doses delivered to the tumour in SABR there was no difference in decline in respiratory function observed between the two groups. This is likely due to the higher integral dose, steep dose gradients and reduced margins possible with SABR relative to CRT.