Low-activity (125)I implantation into VX(2) tumor rabbits and quantitative evaluation of the precise therapeutic effect

There is still controversy about quantitatively evaluating the therapeutic effect of radioactive low-activity iodine-125 seeds ((125)I seeds). In the present study, a paired VX(2) tumor model in a rabbit hind leg muscle was established, which is virus-induced anaplastic squamous cell carcinoma characterized by hypervascularity, rapid growth and easy propagation in the skeletal muscle. (125)I seeds with 0.4 and 0.7 mCi activity were implanted into the left and right legs, respectively, using a radiation treatment planning system under positron emission tomography (PET)/computed tomography (CT) guidance. PET/CT scans and hematoxylin and eosin staining were observed at 72 h and 2 and 4 weeks after implantation to assess the therapeutic effect. The results showed that the average tumor length and standard uptake value (SUV) decreased over time, and both (125)I seed groups achieved therapeutic effects at 4 weeks post-implantation. Quantitative evaluation of tumor inhibition rate, SUV variation and tumor marker ratio (Bcl-2/Bax) suggested that 0.7 mCi (125)I seeds were more suitable than 0.4 mCi seeds in a clinical setting.