ESTRO 2021 Abstract Book

S184

ESTRO 2021

Results 425 patients were identified with complete blood parameter values. Higher pre-NLR, post-NLR and change in NLR plus lower post ALC were all independent predictors of worse survival. Receiver operator curve analysis found a pre-NLR >2.5 (OR 1.71, 95%CI 1.06-2.79, p< 0.05), a post-NLR >5.5 (OR 2.36, 95%CI 1.49-3.76, p< 0.001], a change in NLR >3.6 (OR 2.41, 95%CI 1.5-3.91, p<0.001) and a post-ALC <0.8 (OR 2.86, 95%CI 1.76- 4.69, p <0.001) optimally predicted poor overall survival on both univariate and multivariate analysis when adjusted for cofounding factors. None of the NLR/ALC parameters were independent predictors of disease recurrence.

Conclusion NLR and ALC, surrogate markers for systemic inflammation, have prognostic value in NSCLC patients treated with curative intent radiotherapy. These simple and readily available parameters may have a future role in risk stratification post treatment to inform the intensity of surveillance protocols. PH-0275 Estimating the casual effect of reducing dose to cardiac structures in lung cancer radiotherapy A. McWilliam 1 , A. Abravan 2 , K. Banfill 1 , G. Price 1 , C. Faivre-Finn 3 , M. van Herk 3 1 The University of Manchester, Division of cancer science, Manchester, United Kingdom; 2 The University of Manchester, Division of cancer Science, Manchester, United Kingdom; 3 The University of Manchester, Division of cancer sciences, Manchester, United Kingdom Purpose or Objective Excess radiation dose to cardiac sub-structures has been shown to be associated with early mortality and excess cardiac events in patients with lung cancer. Planning studies have demonstrated feasibility of sparing cardiac regions, with minimal detriment to other organ at risk doses or ITV coverage. This work aims to calculate the causal effect from radiation on these regions to estimate the population survival gain from sparing sensitive cardiac structures.

Materials and Methods The population attributable function (PAF) is calculated. This has a causal interpretation in that it estimates