It is intended to provide a dynamic tumor radiation treatment apparatus and program for detecting the position of a tumor with high accuracy without imposing a burden on the patient, continuously detecting a tumor with high detection efficiency, and effectively irradiating only a malignant tumor with radiation to reduce the radiation exposure dose. A computer functioning by a dynamic tumor radiation treatment program includes gamma ray detecting means 20 for detecting an annihilation gamma ray, displacement threshold storage means 32 for storing the threshold of counting rate, gamma ray counting rate computing means 41 for computing the counting rate according to the detection signal of an annihilation gamma ray, threshold comparing means 43 for comparing the counting rate of annihilation gamma rays acquired from the gamma ray counting rate computing means 41 with the threshold of the counting rate acquired from the displacement threshold storage means 32, tumor position judging means 44 for judging whether or not the tumor is displaced out of the radiation irradiation spot, and irradiation control means 45 for making a control to stop radiation irradiation or outputting a stop command signal.
