Patent ID: 7583775

Claim:
A concentrated irradiation type radiotherapy apparatus, comprising: a radiation source configured to generate radioactive rays in a beam direction for both treatment and imaging; a radiation detector configured to detect radioactive rays transmitted through a subject; a rotating mechanism configured to rotate the radiation source and the radiation detector about a rotating axis; a reconstruction unit configured to reconstruct image data based on an output of the radiation detector; and a collimator unit equipped in the radiation source and configured to form the radioactive rays according to a subject to be treated, the collimator unit including a plurality of collimator plates disposed along the rotating axis, each of said plurality of collimator plates having a face on a substantially common plane perpendicular to the beam direction and being individually movable in a length direction perpendicular to the beam direction around an aperture, each collimator plate of said plurality of collimator plates being in direct contact with at least one adjacent collimator plate adjacent in a width direction perpendicular to both the beam direction and the length direction, and a mechanism for selectively moving one or more of said plurality of collimator plates, wherein said plurality of collimator plates includes a plurality of central collimator plates, each central collimator plate of said plurality of central collimator plates having a first X-ray transmittivity along the beam direction, and a plurality of non-central collimator plates, each non-central collimator plate of said plurality of non-central collimator plates having a second X-ray transmittivity along the beam direction, the second X-ray transmittivity being lower than the first X-ray transmittivity, the plurality of non-central collimator plates sandwiching the plurality of central collimator plates, each of the plurality of central collimator plates and each of the plurality of non-central collimator plates having a substantially equal width in the width direction and substantially equal length in the length direction.