Recent research highlights the critical role of the gut microbiome in shaping antitumor immune responses elicited by radiotherapy. Modulations in microbiota composition affect tumor microenvironment dynamics and systemic immunity, potentially enhancing or limiting radiotherapy efficacy. This expanding field suggests microbiome-targeted strategies could augment cancer immunotherapy and radiotherapy synergism, paving the way for precision oncology approaches integrating microbial management alongside conventional treatments.