Physical behaviors and dose calculations of alpha-emitter radionuclides (227Th, 213Bi, and 211At) and their daughter nuclei in targeted alpha therapy for breast tissue

Abstract

One of the promising radiotherapy approaches to overcoming the challenges of treating breast cancer is targeted alpha therapy (TAT). However, the applications of alpha-particle emitter radionuclides in TAT could conceivably be limited as a result of their high recoil energy, which can spread away, thus resulting in the cytotoxicity of neighboring cells. This study therefore investigates the behavior and dose–response of some selected radionuclides (227Th, 213Bi, and 211At), as well as their daughter nuclei, in use in the TAT of breast tumors. The ASTAR, Stopping and Range of Ions in Matter (SRIM), and Convolution Approximation for Swift Particles (CasP) codes were used as simulating tools in determining the ion behaviors and dose response of the alpha particle emitted from the selected radionuclide (together with their daughter nuclei). The range of 213Bi in breast tissue was found to be less than that of its daughter (213Po) by 37 µm. Similarly, the range of 211At was found to be greater than its daughter nuclei (211Po) by 21 µm. For 227Th, its range was found to be greater than its daughter nuclei (223Ra) by 4 µm, while it was less than the range of its other daughter nuclei, 219Rn, 215Po, and 211Bi by 11, 19, and 8 µm, respectively. Apart from 223Ra, the Bragg peak of the energy loss of the daughter nuclei occurred at a greater depth relative to their parent radionuclide. The damage (total number of displacements per ion) induced by 213Bi in breast tissue was found to be less than that of its daughter (213Po) by 14, while that of 211At was found to be less than its daughter nuclei (211Po) by 9. The damage induced by 227Th was found to be greater than its daughter nuclei (223Ra) by 2, while it was less than the other daughter nuclei, 219Rn, 215Po, and 211Bi by 11, 19, and 8 µm, respectively. Except for 223Ra, due to their higher energy relative to their parent radionuclide, the alpha particle of the daughter nuclei induced more damage to the breast tissue than their parent radionuclides. In all cases, the alpha-dose of the daughter radionuclide was found to be lower compared to their parent radionuclides. It is expected that the range and damage of daughter radionuclides, which were found to be higher than those of the parent radionuclides will offer readers and treatment planners a conceptual framework on the use of 227Th, 213Bi, and 211At radionuclides in TAT of breast tumor.