Method and device for IMAT using orthogonal double layer multi leaves collimators

A method for IMAT using orthogonal double layer multi leaves collimators, comprising:

• discretizing a rotating arc used for a radiotherapy into a plurality of equally spaced fields, the plurality of equally spaced fields having a fixed gantry angle;
• calculating field intensity matrices of the plurality of equally spaced fields by using a conjugate gradient method;
• through a double-layer grating static segmentation algorithm, calculating subfields of each of the plurality of equally spaced fields to obtain a first predetermined number of the subfields with the largest contribution;
• selecting two subfields with similar shapes from the first predetermined number of the subfields with the largest contribution, and distributing the two subfields to the rotating arc, and performing an interpolation to obtain discrete subfields;
• calculating a deposition matrix where the discrete subfields are located;
• calculating iteratively a shape and a weight of each discrete subfield;
• and
• using a Monte Carlo dose algorithm to calculate an intensity-modulated dose distribution.