The distribution of 188Re in the body of patients and the values of individual absorbed doses at intra-arterial radioembolization with radiopharmaceutical «MSA, 20—40μm, 188Re»

Intra-arterial radioembolization (RE) with radiopharmaceuticals based on microspheres labeled with beta-emitting radionuclides is one of the most promising methods of inoperable liver cancer treatment. Phase 1 and 2 of clinical trials of a domestic radiopharmaceutical based on albumin microspheres with a diameter of 20—40 μm, labeled with rhenium-188 («MSA 20—40 μm, 188Re») has already been completed. Objective. To study the distribution of radiopharmaceutical «MSA 20—40 μm, 188Re» in the body of patients after radioembolization, to determine the individual absorbed doses of tumor lesions and risk organs of patients, and the local radiation doses of personnel. Material and methods. Radiopharmaceutical «MSA 20—40 μm, 188Re» with activities ranged from 3.1 MBq to 6.5 MBq was used for intra-arterial RE in 50 patients (18 females and 32 males) with primary liver cancer (C22.0, C22.1, C22.2, C22.9) and metastatic liver cancer (C18.0, C18.6, C18.7, C19.0, C20.0, C97). Scintigraphy and SPECT/CT of the whole body were performed at 1, 24, 48, and 72 h after RE. Radiometry of urine samples, which was taken for 48 h after RE, was carried out. The calculation of absorbed doses was performed according to recommendations of Medical Internal Radiation Dose (MIRD). To measure local radiation doses of medical personnel luminescent microdosimeters were used. Results. The urinary excretion of 188Re in patients of Phase I of clinical trials was on averaged 22.8%, decreasing to 13.6% after updating of radiopharmaceutical synthesis technology. A small (3.4%-13.4%) pulmonary shunt was observed in all patients. Absorbed doses in tumor lesions ranged from 4.6 Gy to 68.5 Gy, depending on administered activities and lesions volume. The values of individual radiation doses in critical organs of patients were significantly lower than the commonly applied dose constraints in radiotherapy. No personnel dose limits were exceeded in accordance with Radiation safety standards-99/2009. Conclusion. High stability of «MSA 20—40 μm, 188Re» during radioembolization procedure ensures the delivery of significantly higher absorbed doses in tumor foci as compared with risk organs of patients with inoperable liver cancer.