Patent Number: 
Section: abstract

The objective is to obtain a bolus, with which there can be formed an irradiation field that is accurately suited to the depth-direction shape of an irradiation subject, and a particle beam therapy system. An irradiation orbit of a particle beam is defined by a first slant with respect to a first axis that starts from a first reference point, that is perpendicular to a beam axis, and that includes the first reference point and by a second slant with respect to a second axis that is perpendicular to the beam axis and the first axis; the shape of a bolus is set in such a way that the path length, of a particle beam, within the bolus in each of the irradiation orbits defined for combinations within a predetermined range among combinations of the first slant and the second slant, compensates the path length from a body surface to a to-be-irradiated portion.