Author: Srinivas Cheenu Kappadath, Benjamin P. Lopez, Armeen Mahvash 👨🔬
Affiliation: UT MD Anderson Cancer Center 🌍
Purpose: 90Y-radioembolization is utilized with curative intent. While single-compartment doses to the perfused volume for the complete pathologic necrosis (CPN) of tumors have been reported, the actual doses delivered to the tumor and at-risk margins that leads to CPN have hitherto not been estimated. We present an ablative voxel-dosimetry model that calculates the necessary dose to tumors and at-risk margins based on numerical mm-scale dose modeling and available clinical CPN evidence.
Methods: 3D-activity distributions (MBq/voxel) simulating spherical tumors were modeled in 121×121×121mm3 soft-tissue with 1mm3 voxels. 3D-dose distributions (Gy/voxel) were estimated by convolving 3D-activity with 3D-90Y-dose kernel (Gy/MBq) of 1mm3 voxels. Based on published LEGACY trial data the necessary, the single-compartment HCC tumor doses for CPN after radiation segmentectomy, mean tumor voxel-dose (CPNDmean), point-dose at tumor boundary (CPNDrim), and point-dose 2mm beyond the tumor boundary (CPND+2mm), to achieve CPN were calculated. Single-compartment dose prescriptions to achieve CPN were modeled for more general cases: diameters tumors, dt (cm) = 2,3,4,5,6,7; and tumor-to-normal-liver uptake ratios T:N = 1:1,2:1,3:1,4:1,5:1.
Results: The nominal scenario for CPN in the LEGACY trial was a single hyperperfused tumor (dt=2.5cm, T:N=3:1), treated to single-compartment segmental dose of 400Gy. The corresponding voxel-level doses necessary to achieve CPN were CPNDmean=1053Gy, CPNDrim=860Gy, and CPND+2mm=561Gy. The single-compartment segmental doses necessary to satisfy the CPN criteria, in terms of CPNDmean, CPNDrim, and CPND+2mm, were established for more general cases; they prescribed higher single-compartment segmental doses for CPN in smaller dt (<2.5cm) or lower T:N (<3:1).
Conclusion: The ablative voxel-dosimetry model that incorporated mm-scale dose modeling and available clinical CPN evidence showed that high voxel-doses (CPNDmean>1000Gy; CPNDrim>850Gy) were necessary to induce CPN. The nominal dose prescription of 400Gy need modification to achieve CPN in more general case scenarios.