Dosimetry of 131I labeled metuximab and transarterial chemoembolization for treatment of hepatocellular carcinoma

Objective: Metuximab is a specific monoclonal antibody F(ab') fragment targeted to the hepatocellular carcinoma (HCC) associated antigen of HAb18G/CD147. 131I labeled metuximab has shown to be effective response on HCC in phase I/II trails. To evaluate the feasibility of 131I-metuximab combined with transarterial chemoembolization (TACE) is the treatment of HCC, the authors estimated the radiation absorbed dose to organs. Methods: 131I-metuximab (27.75 MBq/kg) and the mixture of anticancer drug and Lipiodol with interval 20 min later were administered to 21 patients with HCC via a transfemoral catheter. The pharmacokinetic and dosimetric data were collected by means of venous blood samples, urine collections, and 4 or 5 γ-scintigraphies (SPECT) over 7 d. The total amount of activity in percent of injected activity (% ID) of main organ and the total body were calculated by regions of interest (ROI). The cumulated activities were determined from integration of the time-% ID curves using the SPSS 12.0 software. Absorbed doses to organ and red marrow were estimated according to the medical internal radiation dose (MIRD) formalism and blood-based marrow estimation with a red marrow-to-blood activity concentration ratio. The tumor- to-no tumor ratio was calculated as well. Results: A mean administered activity was 1.89 GBq per session (range 1.47-2.23 GBq). SPECT scans showed the significant accumulation of the radioconjugate in liver tumor and faint uptake in other organs until 14 d. Organ absorbed dose (n=12): the total absorbed dose to liver, spleen, thyroid, lungs, kidney and total-body was (3.19 ± 1.01), (3.65 ± 2.41), (3.61 ± 2.40), (0.97 ± 0.23), (0.96 ± 0.35) and (0.57 ± 1.55) Gy, with (0.55 ± 0.09) Gy to the red marrow (n=7), respectively. From 2.88 ± 1.11 to 1.64 ± 0.39 were observed in tumor-to-liver ratio at 3 h to 168 h. Conclusion: Internal absorbed dose estimation based on MIRD formalism is not only to establish re- liable dose-response relationships for target tissue and dose-toxicity relationships for normal tissue but also to improve treatment planning in individual patient. (authors)