Radiobiological effect induced by different activities of (125)I seed brachytherapy in a hepatocellular carcinoma model.

BACKGROUND Iodine 125 ((125)I) seed irradiation is an effective non-surgical treatment for unresectable hepatocellular carcinoma (HCC) patients. However, the safety and tolerability of (125)I seed sequential irradiation therapy remain unclear, there is no unified standard of brachytherapy radiation dose, and further study on the basic radiobiology of continuous rate irradiation is necessary. METHODS Forty Kunming-mice (KM-mice, China) were injected with suspensions of human hepatocellular carcinoma cells (H22) to create an animal model and mimic (125)I seed implantation. The survival rates of mice, curative effect, pathological impairments including apoptosis and necrosis were investigated. The mice were randomly divided into four groups, A, B, C and D. In group A, 0.78 mCi (125)I seeds were implanted into the tumor focus. In groups B and C, 0.58 mCi and 0.38 mCi (125)I seeds were inserted at the same location, respectively. Group D was a control group, without any treatment. After 28 days of therapy, the survival rates and the tumor size were measured, and pathological impairments was measured by light or electron microscopy. RESULTS The tumor volume inhibition rate was 68.21% ± 3.21%, 51.38% ± 4.96%, and 35.71% ± 2.79% after 0.78 mCi, 0.58 mCi, and 0.38 mCi (125)I seeds irradiation, respectively. However, radiation-related side effects were also observed in the high-dose group. Pathological results showed that radiation effect was closely associated with radiation dose, as the increase of radiation dose, an increase in apoptosis and necrosis was detected. Significant cellular impairments were noted by pathological analysis under electron microscopy. CONCLUSIONS Our results demonstrate that the Kunming-mouse is an ideal animal to study (125)I brachytherapy, and the curative effect was closely associated with radiation dose. High-dose of brachytherapy may effectively increase apoptosis and necrosis in liver cells in KM-mice. A dose of 0.58 mCi (125)I radioactive particles may be a safe, effective and minimally invasive therapeutic option for liver cancer.