Therapy planning system for neutron capture therapy

The present therapy planning system for neutron capture therapy creates therapy plans for neutron capture therapy, in which a subject is irradiated with a neutron beam, wherein the system is provided with: an image-acquiring unit for acquiring an image of the subject; a body outline setting unit for setting a body outline of the subject on the basis of an image acquired by the image-acquiring unit; a vacancy region setting part that sets a portion inside the body outline set by the body outline setting unit and in which image pixel values are within a predetermined range as a vacancy region in which a vacancy is disposed; and a mucosa region setting unit that sets a portion inside the body outline and encompassing a first thickness outside of the surface of the vacancy region set by the vacancy region setting part as a mucosa region in which a mucosa is disposed.