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Single-Cell Dosimetric Simulation and Evaluation of Sb-119 for Use as Auger Emitting Nuclide in Targeted Radiotherapy

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S Graves

S Graves*, B Cox, N Weisse, S Hoffman, RJ Nickles, University of Wisconsin, Madison, WI

SU-E-J-187 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Auger electrons have strong potential for targeted radiotherapy applications because of their relatively short ranged dose profile. ¹¹⁹Sb in particular shows promise as a radioisotope for this application because of its electron emissions with energies near 20 keV. A stochastic characterization of ¹¹⁹Sb and comparison to other auger emitting nuclides has been made to demonstrate this advantage.

Methods: A Monte Carlo electron transport code has been written in Python to model the dose to a single cell for activity distributions within the cell membrane, cellular cytoplasm, and nuclear cytoplasm. A spherical geometry has been used, where energy is deposited in shells about the cell center. An extrapolated power fit has been used to model low-energy electron stopping powers under a continual slowing down approximation. S-values for dose to the nucleus were calculated from simulation results and were compared to previous analytic results (Thisgaard et. al., Med. Phys. 35, 2008). Finally, the results from this code were compared to other auger electron transport Monte Carlo codes for dosimetric verification.

Results: For a cell and nucleus of radius 8μm and 6μm respectively, calculated ¹¹⁹Sb S-values for activity distributions were 4.10E-4 Gy/(s Bq) in the cell membrane, 5.93E-4 Gy/(s Bq) in the cytoplasm, and 2.06E-3 Gy/(s Bq) within the nucleus. These values are within 13% of S-values calculated analytically. An explanation for this difference is the omission of CK electrons from this simulation. S-values calculated for ¹²³I compared with other auger electron transport codes typically agree within a 10% margin.

Conclusion: Simulated ¹¹⁹Sb dose distributions have been shown to agree with analytic calculations. The ability of Auger electrons to localize dose to a single cell may lead to a significant dose reduction in healthy tissue. With the development of proper production and chelation techniques, ¹¹⁹Sb shows promise as a radiotherapeutic nuclide.

Funding Support, Disclosures, and Conflict of Interest: This research was supported by the US Department of Energy: DE-FG02-12ER41882

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