Charged particle beam irradiation apparatus and method of irradiation with charged particle beam

A method of irradiation with a charged particle beam with a charged particle beam irradiation apparatus comprising:

• scanning magnetic field generating means comprising two electromagnets arranged in series along a direction of an incident axis of a charged particle beam and deflecting the charged particle beam in opposite directions,
• energy modulating means comprising a cylindrical member having a length and a distribution of wall thickness in a circumferential direction, means for rotating the cylindrical member around a rotation axis, and detecting means for detecting angle of rotation of the cylindrical member, the energy modulating means being disposed at a downstream side of the scanning magnetic field generating means so that the charged particle beam passes through the rotation axis,
• energy attenuating means for limiting energy of the charged particle beam, and
• means for rotating the scanning magnetic field generating means and the energy modulating means together around the incident axis of the charged particle beam, the method comprising irradiating a three-dimensional irradiation area by:
• approximating the three-dimensional irradiation area as a group of cylindrical columns arranged parallel to an incidence direction z of an incident charged particle beam wherein a coordinate Pi of the center of each cylindrical column in an XY direction is the beam irradiation position, a length .DELTA.zi of each cylindrical column is a scanning range in a beam propagating direction (a depth direction) at the beam irradiation position Pi, and the coordinate of the maximum depth of irradiation is zi;
• loading as previously prepared parameters Pi, .DELTA.zi and zi, and i=1, 2, . . . N for the irradiation area from a set table;
• determining an angle of rotation and a strength of a magnetic field of the scanning magnetic field generating means and an angle of rotation of the energy modulating means in response to each Pi;
• determining the maximum energy of the charged particle beam with the energy attenuating means in response to the maximum depth of irradiation zi;
• and
• determining an effective range of the angle of rotation based on data from the energy modulating means in response to the scanning range of depth .DELTA.zi (initial value i=1), and irradiating with the charged particle beam within the effective range.