Purpose:The aim of this study was to explore the feasibility and clinical value of computed tomography (CT)-guided trans-sternal puncture to implant 125 I seeds to treat masses in the anterior or middle mediastinum.Material and methods: From September 2017 to December 2019, twenty patients with masses in the anterior or middle mediastinum were enrolled and treated with CT-guided trans-sternal 125 I seeds implantation. Dosimetry parameters were compared between post-operative and pre-operative plans. Satisfaction rate of 125 I seed distribution, complications, and local efficacy were evaluated.Results: A total of 22 lesions were treated with 125 I implantation in twenty patients, all procedures being successfully completed. The dosimetry parameters of the 20 patients immediately after surgery were as follows: mean D 90 = 134.30