National Centre for Nuclear Research 1 article published in JoVE Cancer Research Immunofluorescence Imaging of DNA Damage and Repair Foci in Human Colon Cancer Cells Kamila Maliszewska-Olejniczak1, Agnieszka Dróżdż1, Martyna Waluś1, Michał Dorosz1, Michał A. Gryziński1 1Nuclear Facilities Operations Department, National Centre for Nuclear Research, Sołtana 7, 05-400 Otwock, Poland Radiation-induced DNA damage response activated by neutron mixed-beam used in boron neutron capture therapy (BNCT) has not been fully established. This protocol provides a step-by-step procedure to detect radiation-induced foci (RIF) of repair proteins by immunofluorescence staining in human colon cancer cell lines after irradiation with the neutron-mixed beam.