Biological safety evaluation of ¹²⁵I-filled carbon nanotubes covered with metallic esophageal stent

Objective: To evaluate the biological safety of ¹²⁵I-filled carbon nanotubes covered with metallic esophageal stent with regard to the normal esophagus before clinical application. Methods: ¹²⁵I-filled carbon nanotubes covered with metallic esophageal stent was prepared.Eighteen of New Zealand rabbits were randomly divided into three groups with 6 rabbits in each group. Three groups of stents, non-radioactive, low radio-activity (3.7-5.6 MBq), and high activity (11.1-13.0 MBq) were placed in the midpiece of esophagus of rabbits. Esophagus opacification and three-dimensions DSA were performed at 0.5 h, 7, 14 and 30 d after insertion of the stents, respectively. The rabbits were killed at 30 d after insertion of the stents, and histologic examinations of the esophageal walls were performed. Results: In non-radioactive and low activity groups, 1 of 6 rabbits died of wound infection at 1 and 3 d after surgery due to pulmonary infection, respectively. All specimens were obtained from 16 rabbits. Microscopically, in all rabbits of low activity and high activity groups, there were membrana mucosa necrotic and swell and breakage of the muscle fiber in esophageal submucosa and muscularis, submucosal inflammation, which were more severe in high activity group.In low activity group, one esophagus ectal membrane was involved, however, esophageal perforation did not develop. In high activity group, 3 of 6 rabbits esophageal perforation had developed, in which one esophagus mediastinum fistula developed, without inflammation. In non-radioactive group, it was almost normal in mucosa layer, a small amount of inflammatory cells were found in submucosal layer, and part of muscle fibers was fractured and no pathological changes of necrosis was found. Conclusions: Radioactive ¹²⁵I carbon nanotubes covered metallic stent with low activity (3.7 -5.6 MBq) can be used as intraluminal palliative brachytherapy, which is safe and effective. (authors)