Compositions and methods for the radiological and immunotherapeutic treatment of cancer are provided. Metallic nanoparticles conjugated with an immunoadjuvant are dispersed within a biodegradable polymer matrix that can be implanted in a patient and released gradually. The implant may be configured as, or be a component of, brachytherapy spacers and applicators, or radiotherapy fiducial markers. The composition may be combined with marginless radiotherapy, allowing for lower doses of radiation and enhancing the immune response against cancer, including at non-irradiated sites.
