Fan beam modulator for ion beams providing continuous intensity modulation

摘要

An intensity modulator for controlling the intensity of ions, such as protons, controllably block a portion of sub-areas of an area beam to control the average intensity within that sub-area. A fan beam is then created by a focusing process that reforms the area beam while blurring intensity variations in each sub-area to a corresponding beamlet in the fan beam of uniform intensity.

主权项

1. A method of modulating ions comprising:
(a) generating an area beam of ions directed along an axis and having a longitudinal and latitudinal extent in cross-section and divided into latitudinally adjacent beamlets of ions; (b) occluding the area beam with a set of latitudinally arrayed ion-blocking shutters each having a latitudinal width substantially equal to a latitudinal width of a beamlet, the ion-blocking shutters controllably extended to different longitudinal distances at the cross-section according to a desired intensity of a beamlet of ions to block only a controllable portion of the longitudinal extent of the beamlet and to pass without blocking a remaining portion of the beamlet so that the intensity of the beamlet is substantially nonuniform in a longitudinal direction, some of the different longitudinal distances at the cross-section being less than a length of the longitudinal extent of the area beam; wherein an average intensity of the beamlet is defined by a portion of the beamlet occluded by a given shutter; and (c) refocussing the occluded area beam with a lens system to collapsing the area beam and beamlets in the longitudinal direction to form a fan beam directable toward a patient for radiation therapy to provide a substantially uniform longitudinal intensity in each collapsed beamlet.