Radiotherapy Strategies for Use in Combined Treatment of Small-cell Lung Cancer

The purpose of this study is to evaluate the efficacy of radiotherapy as part of the combined treatment approach for patients diagnosed with histopathologically confirmed small cell lung cancer (SCLC) in the advanced stage of extensive disease (ED) who are undergoing chemo-immunotherapy. The planned study aims to assess the impact of incorporating consolidative radiotherapy into the treatment strategy, focusing on residual changes following chemo-immunotherapy (during immunotherapy) and its effect on progression-free survival. This research experiment will be conducted as a randomized multi-center study, comprising the following treatment arms: * Arm I: Continuation of standard of care - PDL1/PD1 immunotherapy (durvalumab or atezolozumab) after chemo-immunotherapy based on platinum compounds; * Arm II: Standard of care, followed by consolidating radiotherapy of the chest area and possibly metastases (if indicated) in doses and for palliative indications (total dose of 30 Gy in 10 daily doses of 3 Gy each); * Arm III: Standard of care, followed by consolidating radiotherapy in the radical/ablative doses (total dose of 45 Gy delivered in 15 daily fractions of 3 Gy for the chest area, and total dose of 24 Gy in single fractions of 8 Gy administered every 2-3 days for the metastatic lesions) of the chest area and all metastatic lesions. Additionally, as part of routine weekly blood collections, an extra volume of 10 ml of blood will be collected. This additional blood sample will be obtained before starting radiotherapy, during each week of radiotherapy (maximum three collections), and at the time of disease progression (one collection), resulting in a total of five extra samples. The collected blood will be prepared, stored and used for circulating tumor DNA (ctDNA) testing, according to the protocol. The ctDNA analysis data will be utilized as a potential marker to determine the time to progression and assess the benefits derived from the administered radiotherapy.