<p>How to design lightweight radiation shielding structures is a key scientific challenge in fields such as nuclear energy and deep space exploration. Due to functional requirements, these shielding structures are often partially open, making classical design approaches difficult to apply directly to complex configurations. Machine learning-based design methods, while capable of handling complex geometries, often suffer from excessive design freedom, leading to high training costs. Therefore, developing efficient methods for lightweight shielding structure design is of critical importance. In this work, a topology optimization method is proposed for the first time to achieve the lightweight design of a gamma-ray shielding structure. The method employs an analytical model of radiation attenuation based on the law of energy flux conservation and the exponential decay law. We demonstrate the effectiveness and universality of the method through the optimization design for various opening shapes and multiple volume constraints for 2D and 3D cases, using the best shielding performance as the optimization goal. Results indicate that, typically, folding the opening channel once is sufficient to achieve optimal shielding effectiveness. The optimized structure is scalable, allowing for the direct transfer of optimized structures to engineering components.</p>