Dosimetry of radiopharmaceuticals used in adult patients with suspected pulmonary embolism

The absorbed dose of radiopharmaceuticals is estimated in adults with suspected pulmonary embolism explored by ventilation/perfusion studies. For pulmonary ventilation studies 81mKr, 133Xe, 99mTc (Technegas)-aerosol and 99mTc (DTPA)-aerosol are used. For perfusion agents, 99mTc(MAA), 99mTc (MSA) (macroaggregates and albumin microspheres) are used. For the dose calculation, the MIRD methodology and the anthropomorphic representation of the biokinetic organs of Cristy-Eckerman are used. In ventilation/perfusion studies, the lowest dose absorbed by the lungs with suspected embolism is due to 81mKr/ 99mTc (MSA), and the highest dose is due to 99mTc (Technegas)/99mTc (MAA) calculated for activities of 150 MBq for perfusion agents and 40 MBq for ventilation agents.

STUDYING OF RADIATION SAFETY OF 188Re-LABELED MAA PREPARATION FOR TREATMENT OF RESISTANT SYNOVITIS

The article is written about studying of radiation safety of 188Re-labeled microspheres of albumin preparation (hand mode) for treatment of resistant synovitis. The study material was a radiopharmaceutical based on albumin microspheres 5 –10 µm with rhenium-188 for treatment of resistant synovitis. The studying has led to conclusion the number of radiopharmaceutical portions prepared by one operator should not exceed 70 times a year, which will ensure that the main limits of equivalent doses to hands and skin with a reserve factor of 2 (250 μSv/h) are not exceeded. Protective equipment should be used to reduce doses to hands, as the most critical to operator's body part irradiation.

The Pre-clinical Test’s Results of the Efficiency of the Radiopharmaceutical Preperation "DTPA-Microspheres of Albumin, 90Y"

Purpose: Development of technology for producing a radiopharmaceutical based on 90Y labeled modified human blood albumin microspheres, and the study of the functional suitability of this drug in experimental animals. Material and methods: The research team studied the following characteristics of the drug: the distribution and excretion of the drug after its intra-arterial administration; the mechanism of action of the drug in animals with model pathology; therapeutic efficacy of the drug in animals with a liver tumor model. The following physicochemical characteristics of the developed radiopharmaceutical were announced: modified with DTPA and labeled 90Y human blood albumin microspheres, particle size 25-40 microns, radiochemical impurities less than 5.0%, 90Sr radionuclide impurities less than 0.002%, the amount of chemical impurities (Na, Al, Ca, Fe, Cu, Zn, Cd, Pb) not more than 10 μg / GBq, volumetric activity up to 150 mCi / ml at the date of preparation. Sprague Dawley female rats were taken as experimental animals (body weight 220-260 g). Studies were conducted on a model pathology - hepatocellular carcinoma, which occurs in 85% of all malignant tumors of the human liver. Results: in 2018-2019, nine pilot batches of the radiopharmaceutical product satisfying the declared characteristics were developed. Stable inhibition of the growth of tumor lesions by 7.62% was noted. The quality of life in animals with orthotopic tumor foci of hepatocarcinoma treated was better than in animals not treated. Life expectancy in the group of animals treated with the drug was higher than in the group of animals that did not receive treatment by 7.1%. The distribution of the drug was characterized by pulmonary bypass, not exceeding 9% of the injected activity and minimal forwarding into the circulating blood. The radiopharmaceutical was firmly held at the injection site and remained almost unchanged throughout the study. Binding to the tumor site of the drug was characterized by retention of at least 78% of the introduced activity. Conclusion: Conducted preclinical studies of the pharmacokinetics of the drug show its potential suitability for the treatment of liver cancer by radionuclide embolization. According to the results of preclinical studies of the therapeutic effectiveness of the radiopharmaceutical, it should be considered effective for use.

Effect of administration route on the biodistribution of albumin microspheres labelled with Re-188

Nowadays the radiolabeled microspheres are established tools for radioembolization of primary and metastatic liver cancer. Human serum albumin microspheres (HSA) are unique carriers for selective and controlled radionuclide delivery to malignant tumors. Rhenium-188 (Re-188), which decays with beta particles (2.12 MeV (71.1%) and 1.965 MeV (25.6%) and gamma emission (155 keV (15.1%)) is one of the most available and promising generator-based radionuclide for cancer therapy. The purpose of this work was to study the biodistribution of microspheres based on hu-man serum albumin labeled with Re-188 (Re-188-HSA) in animals after different routes of admin-istration. The size of more than 95% of microspheres was 10-20 μm. The studies were carried out on outbred white mice and inbred C57BL/6 mice with transplanted Lewis adenocarcinoma after intravenous, intramuscular and intratumoral administration. After intravenous injection the high-est amount of Re-188-HSA in organs and tissues was observed: up to 311.3%/g in lungs, up to 74.30%/g in thyroid gland, up to 12.70%/g in liver, up to 0,81%/g in blood. After the intramuscular injection of 188Re-HSA, the concentration of 188Re-HSA in organs and tissues was significantly lower and did not exceed 1%/g, except for thyroid gland (1,10-17.80%/g). After intratumoral injec-tion the amount of Re-188-HSA in tumor varied from 16.7 to 26.8%/g, that was higher as compared with other organs and tissues. Thus, the routes of Re-188-HSA administration significantly affect its behavior in the body. The obtained results can be used to evaluate the Re-188-HSA potential for radionuclide tumor therapy after intravascular or intratumoral administration.