A method and apparatus for treating a tumor in a patient. In one embodiment, the method comprises the steps of: dosing the patient with a substituted tumor-specific agent and irradiating the tumor with energetic ions, the ions having sufficient energy to penetrate into the tumor and cause nuclear fusion reactions, but not to pass through the tumor. In one embodiment, the substituted tumor-specific agent incorporates deuterium. In this embodiment, the energetic ions are tritium nuclei. In this embodiment, the apparatus comprises a tritium ion source, an accelerator producing an ion beam, a scanning mechanism, and a plurality of neutron detectors positioned adjacent to the patient. The tritium ion beam is programmed to traverse the site of the tumor with tritium ions having energy sufficient to penetrate into the tumor and cause nuclear fusion reactions, but not pass through the tumor.
