A Microdosimetric Analysis of Absorbed Dose to Tumor as a Function of Number of Microspheres per Unit Volume in Y-90 Radioembolization

作者：Pasciak Alexander S^*; Bourgeois Austin C; Bradley Yong C

来源：Journal of Nuclear Medicine, 2016, 57(7): 1020-1026.

DOI：10.2967/jnumed.115.163444

• yttrium-90
• Y-90
• radioembolization
• interventional oncology

Differences in maximum tolerable absorbed dose to normal liver between Y-90 radioembolization and external-beam radiation therapy have been explained by citing differences in absorbed-dose heterogeneity at the microscopic level. We investigated microscopic absorbed-dose heterogeneity in radioembolization as a function of the number of microspheres per unit volume in tumor. The goal was to determine what effect the number of microspheres may have, if any, on tumor control in Y-90 radioembolization. Methods: Y-90 PET/CT data were combined with microscopic probability-density functions describing microsphere clustering to provide realistic simulation using Monte Carlo modeling on both a macroscopic and a microscopic level. A complete microdosimetric analysis using 100-mu m voxels was performed on the basis of Y-90 PET/CT data from 19 tumors treated using radioembolization. Simulations were performed with average tumor microsphere-number densities from 200 to 70,000 spheres/mL. Monte Carlo simulations of each tumor and number density were repeated 20 times to establish SE. A 2-way balanced ANOVA was used to determine whether differences in microsphere-number density affected common tumor-dose metrics. Results: Decreasing the microsphere-number density resulted in a decrease in D-70, the minimum dose to 70% of the tumor. The slope of the dose-volume histogram also decreased with decreasing microsphere-number density in all tumors. Compared with a density of 50,000 spheres/mL, decreases in D-70 were statistically significant below 20,000 spheres/mL. However, these differences are unlikely to have clinical significance until the density decreases to below 5,000 spheres/mL. Although D-70 was decreased at a low microsphere-number density, one can compensate for decreases by an increase in the average tumor absorbed dose, that is, by increasing the radioembolization treatment dose. Conclusion: Differences in microsphere-number density may have an effect on microscopic tumor absorbed-dose inhomogeneity. These results begin to explain differences in treatment planning strategies between glass and resin radioembolization devices.

• 出版日期2016-7