Impact of introducing IMRT on curative intent radiotherapy and survival for lung cancer

Abstract

Purpose or Objective Lung cancer survival remains poor. The introduction of Intensity-modulated radiotherapy (IMRT) has allowed treatment of more complex tumours as it improves radiotherapy dose conformity and normal tissue sparing. However, implementation of IMRT for the curative-intent treatment of lung cancer has lagged behind that of other disease sites and there is limited evidence in the literature assessing the clinical impact of IMRT. In this study, we evaluated whether the introduction of IMRT has had an influence on the proportion of patients treated with curative-intent radiotherapy, and whether this has had an effect on patient survival. Materials and Methods Patients with lung cancer treated with thoracic radiotherapy at our institute between 2005-2020 were retrospectively identified and grouped into three time periods: A) 2005-2008 (pre-IMRT), B) 2009-2012 (some availability IMRT), and C) 2013-2020 (full access IMRT). Data on performance status (PS), stage, age, gross tumour volume (GTV), planning target volume (PTV) and survival were collected. The proportion of patients treated with a curative dose (>40Gy) between these periods was compared. Multivariable survival models were fitted to evaluate the hazard for patients treated in each time period, adjusting for PS, stage, age and tumour volume. Results 12,499 patients were included in the analysis (n=2675 (A), n=3127 (B), and n=6697 (C)). The proportion of stage patients treated with curative-intent radiotherapy increased between the 3 time periods, from 38.1% to 50.2% to 65.6% (p<0.001). When stage IV patients were excluded, this increased to 40.1% to 58.1% to 82.9% (p<0.001). This trend was seen across all PS and stages, and was still upheld when SABR patients were excluded from the analysis. The GTV increased across the time periods (median GTV 35.5 cm3 [16.8, 60.1], 41.7 cm3 [16.3, 85.8] and 47.6 cm3 [17.6, 112.1] for groups A, B and C excluding SABR patients respectively, p<0.01) although the PTV volume did not. Curative-intent patients treated during period C had a survival improvement compared to time period A when adjusting for clinical variables (all stages HR=0.725 (0.632-0.831), p<0.001; stage III patients HR=0.740 (0.600-0.913), p<0.005). Conclusion This real world, big data analysis has shown that the introduction of IMRT was associated with more patients receiving curative-intent radiotherapy across all PS and stages of disease. In addition it facilitated the treatment of larger tumours that historically would have been treated palliatively. Despite treating larger, more complex tumours with curative-intent, a survival benefit was seen for patients treated when full access to IMRT was available. We acknowledge that other contributing factors such as improvement in staging and systemic therapy may have also contributed to the improved survival.