1. Department of Radiotherapy, Maria Skłodowska-Curie Memorial Cancer Centre, Warsaw, Poland;
2. Clinical Oncology Division of Department of Gastrointestinal Oncology, Maria Skłodowska-Curie Memorial Cancer Centre, Warsaw, Poland;
3. Department of Clinical Trials and Biostatistics Unit, Maria Skłodowska-Curie Memorial Cancer Centre, Warsaw, Poland