Evaluation of Iodine-125 Interstitial Brachytherapy Using Micro-Positron Emission Tomography/Computed Tomography with (18)F-Fluorodeoxyglucose in Hepatocellular Carcinoma HepG2 Xenografts

BACKGROUND: Iodine-125 interstitial brachytherapy ((125)I-IBT) is a promising treatment option for unresectable hepatocellular carcinoma (HCC). This study evaluated the usefulness of micro-positron emission tomography/computed tomography (micro-PET/CT) with (18)F-fluorodeoxyglucose ((18)F-FDG) in assessing response to (125)I-IBT in HCC HepG2 xenograft. MATERIAL/METHODS: Twelve mice with bilateral HepG2 xenografts were divided into 3 equal groups implanted with iodine-125 seeds into the left xenografts with a dose of 30, 50, and 80 Gy, respectively, and the right xenografts were used as internal controls. Before and 28 days after treatment, the (18)F-FDG micro-PET/CT was performed. The ratios of left to right xenografts of tumor volume (R(TV)), maximum standardized uptake value (R(SUVmax)), mean optical density of caspase-3 expression (R(MODcaspase-3)), and apoptosis index (R(AI)) were compared. RESULTS: The R(TV) means of the 50 and 80 Gy groups were significantly lower than in the 30 Gy group after treatment (P<0.01) and the R(TV) means after treatment were lower than baseline in the 50 and 80 Gy groups (P<0.05). The R(SUVmax) mean after treatment was lower than baseline in the 80 Gy group (P<0.05). The R(MODCaspase-3) and R(AI) means of the 80 Gy group were higher than in the 30 Gy group (P<0.05). The R(SUVmax) was correlated negatively to R(MODcaspase-3) (r=−0.624, P<0.05) and R(AI) (r=−0.651, P<0.05). CONCLUSIONS: This study suggest that (125)I-IBT inhibits tumor growth via upregulating caspase-3 expression and prompting apoptosis in HCC HepG2 xenografts. The (18)F-FDG micro-PET/CT may be a useful functional imaging modality to assess early response to (125)I-IBT in HCC HepG2 xenograft.