A radiotherapy system comprising: an irradiation apparatus for irradiating an irradiated subject being a cancer patient to form an irradiated site, comprising a radiation generating device, a beam shaping assembly, and a collimator, wherein the radiation generating device is capable of generating radiation, the beam shaping assembly is capable of adjusting beam quality of the radiation generated by the radiation generating device and includes a beam exit, the collimator is capable of concentrating radiation passing through the beam shaping assembly; and a medical image-based radiation shielding device of the irradiation apparatus, comprising: a medical image scanning means for scanning an irradiated site of the irradiated subject and outputting medical image voxel data; a data processing and three-dimensional modeling means for establishing a three-dimensional phantom tissue model according to the medical image voxel data and establishing a three-dimensional shield model; a shield located between the irradiation apparatus and the irradiated site, and wherein the shield is located between the collimator or beam exit and the irradiated site, wherein the shield is formed by printing the three-dimensional shield model data input to a 3D printer, characterized in that the radiotherapy system is a boron neutron capture therapy system; the radiation generating device is a neutron generating device comprising an accelerator and a target, wherein the accelerator accelerates charged particles to interact with the target to generate neutrons; the data processing and three-dimensional modeling means is provided to establish the three-dimensional shield model according to the three-dimensional phantom tissue model, combined with data information of the irradiation apparatus and positional relationship between the irradiation apparatus and the irradiated site; and the shield is configured to shield normal tissues of the cancer patient from radiation generated by the irradiation apparatus. an irradiation apparatus for irradiating an irradiated subject being a cancer patient to form an irradiated site, comprising a radiation generating device, a beam shaping assembly, and a collimator, wherein the radiation generating device is capable of generating radiation, the beam shaping assembly is capable of adjusting beam quality of the radiation generated by the radiation generating device and includes a beam exit, the collimator is capable of concentrating radiation passing through the beam shaping assembly; and a medical image-based radiation shielding device of the irradiation apparatus, comprising: a medical image scanning means for scanning an irradiated site of the irradiated subject and outputting medical image voxel data; a data processing and three-dimensional modeling means for establishing a three-dimensional phantom tissue model according to the medical image voxel data and establishing a three-dimensional shield model; a shield located between the irradiation apparatus and the irradiated site, and wherein the shield is located between the collimator or beam exit and the irradiated site, wherein the shield is formed by printing the three-dimensional shield model data input to a 3D printer, characterized in that the radiotherapy system is a boron neutron capture therapy system; the radiation generating device is a neutron generating device comprising an accelerator and a target, wherein the accelerator accelerates charged particles to interact with the target to generate neutrons; the data processing and three-dimensional modeling means is provided to establish the three-dimensional shield model according to the three-dimensional phantom tissue model, combined with data information of the irradiation apparatus and positional relationship between the irradiation apparatus and the irradiated site; and the shield is configured to shield normal tissues of the cancer patient from radiation generated by the irradiation apparatus. a medical image scanning means for scanning an irradiated site of the irradiated subject and outputting medical image voxel data; a data processing and three-dimensional modeling means for establishing a three-dimensional phantom tissue model according to the medical image voxel data and establishing a three-dimensional shield model; a shield located between the irradiation apparatus and the irradiated site, and wherein the shield is located between the collimator or beam exit and the irradiated site, wherein the shield is formed by printing the three-dimensional shield model data input to a 3D printer, characterized in that the radiotherapy system is a boron neutron capture therapy system; the radiation generating device is a neutron generating device comprising an accelerator and a target, wherein the accelerator accelerates charged particles to interact with the target to generate neutrons; the data processing and three-dimensional modeling means is provided to establish the three-dimensional shield model according to the three-dimensional phantom tissue model, combined with data information of the irradiation apparatus and positional relationship between the irradiation apparatus and the irradiated site; and the shield is configured to shield normal tissues of the cancer patient from radiation generated by the irradiation apparatus.