Abstract: Radioactive ¹²⁵I seeds (RIS) interstitial implantation brachytherapy has been a first-line treatment for early-stage cancer of the prostate gland. However, its poor accuracy and homogeneity has limited its indication and hampered its popularization for a long time. Intriguingly, scholars based in China introduced computed tomography (CT)-guided technology to improve the accuracy and homogeneity of RIS implantation and broadened the indications. Then, they creatively designed and introduced three-dimensional printing coplanar template (3D-PCT) and 3D printing noncoplanar template (3D-PNCT) into the practice of RIS implantation. Use of such templates makes RIS implantation more precise and efficacious and aids preoperative planning, real-time dose optimization, and postoperative planning. However, studies on the standard workflow for 3D-PT-assisted CT-guided RIS implantation have not been published. Therefore, the China Northern Radioactive Seeds Brachytherapy Group organized multidisciplinary experts to formulate the guideline for this emerging treatment modality. This guideline aims at standardizing 3D-PT-assisted CT-guided RIS implantation procedures and criteria for selecting treatment candidates and assessing outcomes and for preventing and managing postoperative complications.