The Aperture Shape Optimization Based on Fuzzy Enhancement

The aperture shape optimization (ASO) is a critical step in the direct aperture optimization (DAO) method. During ASO, the gradient of objective function is calculated with respect to the beamlet weight. These gradient components are directly utilized to generate the new aperture shape. In this way, the beamlet of the large positive gradient value may be grouped into the generated aperture shape. The treatment quality may be deteriorated by adding this aperture into the treatment plan. In order to overcome this drawback, a novel method based on the fuzzy enhancement was proposed to generate the aperture shape. We apply the fuzzy enhancement method to enhance the gradient map that is composed of the gradients of objective function in a beam. The enhanced gradient map was then employed to form a network flow, which was solved to generate the new aperture shape. The optimal aperture shape was generated by removing the beamlet of the large positive gradient value from the new generated aperture shape. To verify the effectiveness, the proposed method was compared with the conventional column generation (CG) method on a prostate cancer case and on a head-and-neck cancer case. Experimental results demonstrate that the new algorithm has a better performance than the CG algorithm. The proposed method can further reduce the dose delivered to the critical structures, when the similar dose coverage is delivered on the targets.