ESTRO 2020 Abstract book

S151 ESTRO 2020

Results The median follow-up was 41 months. The median age was 74 years old. Two hundred and forty-five patients were treated according to the continuous regimen and 245 to the discontinuous regimen. The two groups were comparable in terms of the major potential confounding factors. The 3-year LC was 92% for the discontinuous treatment versus 84% for the continuous one (p = 0.0017) (Figure 1), with a Hazard Ratio (HR) of 0.48 (CI 95% 0.26- 0.89). The 3-year OS was 64% for the discontinuous treatment versus 52% for the continuous one (p = 0.0024) (Figure 2), HR of 0.66 (CI 95% 0.5-0.86). 216 patient pairs were identified with propensity score matching. Discontinuous treatment schedule was still associated with better overall survival with a HR of 0.64 (95% CI 0.48 – 0.85), p = 0.0029 and better local control with a HR of 0.39 (95% CI 0.19 – 0.79), p = 0.0089. In multivariate analysis, only the irradiation schedule and the number of fractions were correlated with LC. The irradiation schedule, age, WHO performance status and T stage were significantly correlated with OS. Less than 2% of acute or post- treatment grade 3 pulmonary toxicity was reported for both groups.

Conclusion National guideline for contouring the heart and cardiac substructures have been developed across relevant Danish multidisciplinary cancer groups where RT dose to the heart are of concern. The inter-observer contour overlap was best for the heart and chambers and decreased for smaller structures. The guideline and validating contours will be used to develop an automated segmentation atlas. PH-0278 Schedule of irradiation impacts the overall survival in case of SBRT for stage I NSCLC L. Duvergé 1 , P. Bondiau 2 , L. Claude 3 , F. Thillays 4 , S. Supiot 4 , I. Sidibe 4 , L. Vaugier 4 , J. Bellec 1 , C. Ricordel 5 , J. Doyen 2 , E. Chajon 1 , R. De Crevoisier 1 , J. Castelli 1 1 Centre Eugène Marquis, Radiotherapy, Rennes, France ; 2 Centre Antoine Lacassagne, Radiotherapy, Nice, France ; 3 Centre Léon Bérard, Radiotherapy, Lyon, France ; 4 Institut de Cancérologie de l'Ouest Centre René Gauducheau, Radiotherapy, Saint-Herblain, France ; 5 Centre Hospitalier Universitaire, Pneumology, Rennes, France Purpose or Objective In the context of stereotactic body radiotherapy (SBRT) for early stage non-small cell lung cancer (NSCLC), the objective of our study was to determine the impact on local control (LC) and overall survival (OS) of a continuous versus discontinuous schedule of radiotherapy. Material and Methods A total of 490 consecutive NSCLC stage I patients treated in 4 French radiation oncology centers between January 2008 and July 2018, were retrospectively analyzed. The prescribed dose ranged from 30 to 75 Gy in 3 to 10 fractions with a median biologically effective dose of 125 Gy (α/β = 10 Gy). Based on the ratio between the treatment duration (TD) and the number of fractions (n), patients were divided into two groups: continuous (TD < 2n) versus discontinuous (TD ≥ 2n) schedule. Local control, overall survival and toxicity were compared using Cox regression analyses. In order to limit any differences between the two groups at baseline, a 1:1 propensity score matching (nearest neighbor matching algorithm, caliper distance of 0.2) was performed.

Conclusion Our study is the first to show a positive impact of a discontinuous versus continuous schedule on overall survival as well as on local control for early stage NSCLC treated by SBRT, with similar low profile of toxicity. A multicenter randomized prospective study will be started in order to validate our results. PH-0279 Accelerated hypofractionated radiotherapy with concurrent chemotherapy for NSCLC: a phase I/II study K. Glinski 1 , J. Socha 2 , E. Wasilewska-Tesluk 1,3 , K. Komosinska 2 , L. Kepka 2 1 Independent Public Health Care Facility of the Ministry of the Interior and Warmian& Mazurian Oncology Centre, Radiotherapy, Olsztyn, Poland ; 2 Military Institute of Medicine, Radiotherapy, Warsaw, Poland ; 3 Warmian and Mazurian Medical University, Radiotherapy, Olsztyn, Poland