RÉSUMÉ
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.