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Objective To calculate the absorbed dose of 90Y TheraSphere in the pancreas and the surrounding sensitive organs after the administration in the treatment of pancreatic cancer through the establishment of an individual voxel model, and to provide technical support for the clinical application of 90Y TheraSphere in the treatment of pancreatic cancer. Methods An individualized voxel model was constructed in Geant4 software based on the CT images of the patient. 12 monoenergetic electron specific absorption fractions (SAFs) in the range of 0.01 to 1 MeV were calculated and validated against the ICRP data. The model and method were used to calculate the absorbed doses in the target organs under uniform and nonuniform distribution of 90Y microspheres in the pancreas. Results The relative errors between the SAF values calculated based on the individualized voxel model and the ICRP data after mass calibration were less than 3.89%. When 90Y was uniformly distributed in the pancreas, the absorbed dose in the pancreas was 4.69 × 10−7 Gy/Bq; the absorbed doses in the liver, kidneys, and spleen were 6.15 × 10−12, 6 × 10−12, and 1.65 × 10−11 Gy/Bq, respectively. When 90Y was distributed within the tumor, the absorbed dose in the tumor was 6.69 × 10−6 Gy/Bq and the absorbed dose in normal pancreas was 5.72 × 10−8 Gy/Bq. The fitted relationship between tumor volume V and administered activity A at the prescribed dose of 120 Gy was quadratic, with relatively low activity required for concentrated administration in the center of the tumor. Conclusion The Monte Carlo dose calculation method based on individual voxel model accurately predicted the absorbed doses in the surrounding sensitive organs (liver, kidneys, and spleen) when 90Y TheraSphere was used to treat pancreatic cancer. These results and the analysis of the factors affecting the drug delivery activity will provide data support for the clinical research of 90Y TheraSphere in pancreatic cancer.
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Objective To evaluate the effects of radioactive impurity nuclides in 90Y glass microsphere on therapeutic dose during radioembolization of pancreatic cancer. To provide a reference for correction of the dose calculated for individuals with different pancreatic tumors. Methods In this study, the radioactive impurity nuclide composition of 90Y glass microsphere samples was analyzed to determine the source term of Monte Carlo calculation. Then, according to the PET/CT medical imaging data of pancreatic cancer patients, the three-dimensional modeling software Solidworks 2020 was used to construct the real and personalized digital human digestive system model of pancreatic cancer patients at a resolution showing the vascular distribution in pancreas and tumor. Finally, the Monte Carlo program GATE 8.2 was used to simulate the three-dimensional radiation dose fields of radioactive impurity nuclides 91Y and 65Zn from 90Y glass microspheres in various tissues and organs. The three-dimensional dose fields were visualized to analyze the influence of radioactive impurity nuclides on therapeutic dose. Results The three-dimensional radiation dose fields of 91Y and 65Zn from 90Y glass microspheres demonstrated two dose extreme points. The maximum dose value of 91Y to tissue was 0.272 mGy and the maximum dose value of 65Zn to tissue was 9.34 μGy, with average statistical errors of less than 3.2%. Conclusion The impact of radioactive impurity nuclides 91Y and 65Zn in 90Y glass microsphere sample on therapeutic dose is minimal and can be neglected.
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Objective To evaluate the migration of plutonium aerosol caused by α recoil. Methods In this paper, the recoil deposition and Brownian motion of plutonium-containing nanoaerosols were simulated by Monte Carlo method. The recoil angle and the vertical first landing time of Brownian motion in the process of settling were sampled, and then the lateral displacements of Brownian motion were sampled to determine the final settling position of aerosol. Results For aerosols with particle sizes of 10-50 nm, the maximum migration distance of a single recoil settling was 1.39 μm. Brownian motion increased the migration capacity. Although there was a high likelihood that aerosols settled within 100 μm, there remained a slight probability of long-term suspension in the air. Conclusion The α recoil is one of the mechanisms of plutonium aerosol migration. An important mechanism for long-distance migration of nanoaerosols is that Brownian motion after recoil may cause them to suspend for a long time.
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Objective To investigate the effects of particle size, wind speed and dumping velocity on aerosol concentration distribution during powder dumping in a reprocessing plant. Methods CeO2 powder was selected as the substitute material of PuO2. FLUENT software was used to calculate the pouring process of CeO2 powder under different operation conditions. Then the aerosol concentration distribution under different dumping speeds was measured by particle size spectrometer to verify the accuracy of simulation results. Results The particles with small particle size are more likely to be separated from the mainstream area by the drag force of the surrounding gas, and the radius of the diffusion range also increases with the decrease of the particle size. 2) When the ventilation speed is less than 1 m/s, the dust lifting can be reduced and the concentration of dust particles in the chamber can be reduced to a certain extent. 3) In the process of powder dumping, the spoon is rotated anticlockwise at a speed of 100° in 2～3 s, and less dust aerosol is produced on the right side of the tray. Conclusion When operating the powder particles with smaller particle size, more attention should be paid to the monitoring of aerosol at different positions; the change of air inlet velocity makes the flow field in glove box more complex, and the volume fraction of dust particles is related to the size and location of vortex formed by airflow. The greater the wind speed, the greater the impact on the powder dumping process. The experimental results are basically consistent with the simulation results, and the results show that the lower the dumping speed, the smaller the aerosol concentration near the tray.