Image-guided permanent I-125 seed implantation for refractory head-and-neck carcinoma in China: A comprehensive review of contemporary technical and clinical aspects

Permanent I-125 seed implantation is one of the most commonly used brachytherapy (BT) forms, potentially applicable to almost any solid tumor as a standalone anti-tumor therapy or in combination with external beam radiotherapy (EBRT). The main advantage of I-125 seed implantation BT is its ability to deliver a high radiation dose within target volumes while maintaining a sharp dose drop-off profile, thereby protecting adjacent normal tissue. The clinical use of I-125 seed implantation in China has significantly increased in the past decades due to the application of an image-guided BT treatment planning system with reverse optimization capabilities and 3D printing individual template (3D-PIT) assistance. Computed tomography-guided I-125 seed implantation became a widely common modality of BT and has been used in many clinical settings for a variety of refractory cancer in China since 2002. The application has been expanded significantly not only for prostate cancer as monotherapy but also in combination with EBRT for the salvage treatment for refractory/recurrent head-and-neck carcinoma (HNC). With the assistance of 3D-PIT, since 2015, the quality control of I-125 seed implantation has been significantly adapted with high precision and real-time dose optimization. This review aims to summarize the developments and status of 3D-PIT-based I-125 seed implantation BT for the treatment of refractory HNC and standardized workflow in China.