Low-activity I-125 implantation into VX2 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 (I-125 seeds). In the present study, a paired VX2 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. I-125 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 I-125 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 I-125 seeds were more suitable than 0.4 mCi seeds in a clinical setting.