According to an embodiment, a treatment system includes a plurality of first radiators, a plurality of detectors, a determiner, and a controller. Each of the first radiators irradiates a radioactive beam to a subject. Each of the detectors detects a radioactive beam transmitted through the subject and generates an image based on the detected radioactive beam. The determiner determines whether an object in the subject is included in a first region using a given image that is one of the images. The controller controls the first radiators so that, when the object is not included in the first region, a smaller amount of radioactive beams is irradiated per unit time than when the object is included in the first region.
