Aperture shape optimization in intensity-modulated radiation therapy planning

The gradient element of the aperture gradient map is utilized directly to generate the aperture shape without modulation. This process can be likened to choosing the direction of negative gradient descent for the generic aperture shape optimization. The negative gradient descent direction is more suitable under local conditions and has a slow convergence rate. To overcome these limitations, this study introduced conjugate gradients into aperture shape optimization based on gradient modulation. First, the aperture gradient map of the current beam was obtained for the proposed aperture shape optimization method, and the gradients of the aperture gradient map were modulated using conjugate gradients to form a modulated gradient map. The aperture shape was generated based on the modulated gradient map. The proposed optimization method does not change the optimal solution of the original optimization problem, but changes the iterative search direction when generating the aperture shape. The performance of the proposed method was verified using cases of head and neck cancer, and prostate cancer. The optimization results indicate that the proposed optimization method better protects the organs at risk and rapidly reduces the objective function value by ensuring a similar dose distribution to the planning target volume. Compared to the contrasting methods, the normal tissue complication probability obtained by the proposed optimization method decreased by up to 4.61%, and the optimization time of the proposed method decreased by 5.26% on average for ten cancer cases. The effectiveness and acceleration of the proposed method were verified through comparative experiments. According to the comparative experiments, the results indicate that the proposed optimization method is more suitable for clinical applications. It is feasible for the aperture shape optimization involving the proposed method.