Author: Lior Arazi, Gil'ad N. Cohen, Antonio L. Damato, Irene P. Zhang π¨βπ¬
Affiliation: Unit of Nuclear Engineering, Faculty of Engineering Sciences, Ben-Gurion University of the Negev, NYU Grossman School of Medicine, Memorial Sloan Kettering Cancer Center π
Purpose: Diffusing alpha-emitters Radiation Therapy (βAlpha DaRTβ) is a promising new radiation therapy modality for treating bulky tumors. The dose delivered by Alpha-DaRT sources is dependent on the diffusion properties of the surrounding tumor tissue, which are inhomogeneous on the length scale of millimeters. We study the effect of spatial inhomogeneity in the diffusion lengths of key alpha-emitters involved in Alpha DaRT on the resulting alpha-particle dose.
Methods: We performed 2D FEM-based dose calculations in the midplane of a triangular arrangement of Alpha-DaRT sources, which is the current clinically recommended arrangement. The calculation domain was divided into a randomly generated Voronoi pattern with an average cell size of 1 mm2. Diffusion lengths LRn and LPb, for 220Rn and 212Pb, respectively, were assigned to cells randomly from normal distributions with means ΞΌRn = 0.4 mm and ΞΌPb = 0.3 mm, respectively, and standard deviations equal to 10% of the mean. Uncertainty in the alpha dose at the center of the triangle, which has been calculated to be the point of lowest dose assuming uniform diffusion lengths, is quantified by repeatedly generating Voronoi patterns with LRn inhomogeneity and fixed LPb and vice versa.
Results: A 10% standard deviation in LRn (LPb) produced a 10% (2%) standard deviation in the dose at the triangle center over 60 repeated calculations. Inhomogeneity in LRn is more likely to produce a central dose higher than would be calculated for uniform diffusion lengths, while inhomogeneity in LPb is more likely to produce a lower central dose.
Conclusion: These results suggest that spatial inhomogeneity in the diffusion lengths of 220Rn and 212Pb introduces uncertainty in the lowest dose delivered by a given source arrangement. Further study of diffusion property uncertainties for Alpha-DaRT treatment will be necessary for improvements in dosimetry practice.