ESTRO 2021 Abstract Book

S969

ESTRO 2021

Purpose or Objective The aim of this study was to investigate whether the integration of radiomic signatures based on the Gross Tumor Volume (GTV), but also on Clinical Target Volume (CTV) and Planning Target Volume (PTV) can be identified for predicting the response to adaptive therapies. Materials and Methods 130 patients with stage IIIA-IIIB NSCLC who underwent concomitant radiochemotherapy (RCT) were enrolled. The characteristics analyzed were extracted from the CT simulation images by performing manual contouring and defining 3D ROI of GTV, CTV and the PTV. Through the pyradiomics system we performed the segmentation of the different targets GTV, CTV and PTV, the calculation, the extraction of the features and the subsequent division into groups. For each segmentation and feature we performed the Wilcoxon Test and analyzed the comparison between GTV-CTV; GTV-PTV; CTV-PTV. Results The analysis carried out between the various segmentations showed a higher p-value average for the GTV-CTV group, while CTV-PTV group had a lower p-value average (Figure 1). A machine learning process allowed to identify for all three segmentations radiomic signatures correlated significantly to the early response to treatment. ROC curves obtained showed an AUC of 0.77, 0.71 and 0.74, respectively (Figure 2).

Conclusion These data support the hypothesis that a specific radiomic signature can be identified not only considering the CTV but also GTV and PTV, confirming the potential and feasibility of a radiomic approach in predicting the response in patients with stage III NSCLC. PO-1168 Moderately hypofractionated radiotherapy in non-small cell lung cancer I. Fajardo Paneque 1 , J.L. Tisaire Sánchez 1 , L. Díaz Gómez 1 , M.J. Macías Lozano 1 , J. Jaén Olasolo 1 1 Hospital de Jerez de la Frontera, Radiation Oncology, Jerez de la Frontera, Cádiz, Spain Purpose or Objective Moderately hypofractionated radiation therapy (MHypoRT) for non-small cell lung cancer (NSCLC) is being increasingly adopted due to its benefits in terms of comfort for the patients and cost saving for healthcare systems by reducing the number of visits to the hospital. This is of particular relevance in the context of COVID-19 world pandemic. In this study we analyze clinical results of NSCLC patients undergoing MHypoRT with or without chemotherapy (ChT). Materials and Methods Between August 2017 and February 2021, 61 consecutive NSCLC patients treated with MHypoRT in our center were prospectively registered. All patients were treated with Volumetric Modulated Arc Therapy (VMAT) and Image-Guided Radiotherapy (IGRT). Main objectives of the study were acute toxicity, late toxicity recorded 6 months after the end of Radiation Therapy (RT) according to CTCAE v4.0, and survival. Time periods were calculated from the start of RT until death or last visit. Survival curves are constructed according to Kaplan-Meier method and the differences between groups were compared using log-rank test. Results 61 patients (62 tumors) with a mean age of 67 years old entered the study. The majority (88.5%) were male. Patients and tumor characteristics are sumarized in table 1. 6 stage I/II patients unsuitable for surgery or Stereotactic Body Ablative Radiotherapy were treated, as well as 11 oligometastatic patients who achieved a good response after initial therapy.