Reduction In Clonogenic Survival Of Sodium-Iodide Symporter (Nis)-Positive Cells Following Intracellular Uptake Of Tc-99m Versus Re-188

Purpose: Cellular radionuclide uptake increases the heterogeneity of absorbed dose to biological structures. Dose increase depends on uptake yield and emission characteristics of radioisotopes. We used an in vitro model to compare the impact of cellular uptake of Re-188-perrhenate and Tc-99m-pertechnetate on cellular survival.Materials and methods: Rat thyroid PC Cl3 cells in culture were incubated with Re-188 or Tc-99m in the presence or absence of perchlorate for 1 hour. Clonogenic cell survival was measured by colony formation. In addition, intracellular radionuclide uptake was quantified.Results: Dose effect curves were established for Re-188 and Tc-99m for various extra-and intracellular distributions of the radioactivity. In the presence of perchlorate, no uptake of radionuclides was detected and Re-188 reduced cell survival more efficiently than Tc-99m. A(37), the activity that is necessary to yield 37% cell survival was 14 MBq/ml for Re-188 and 480 MBq/ml for Tc-99m. In the absence of perchlorate, both radionuclides showed similar uptakes; however, A(37) was reduced by 30% for the beta-emitter and by 95% for Tc-99m. The dose D-37 that yields 37% cell survival was between 2.3 and 2.8 Gy for both radionuclides.Conclusions: Uptake of Re-188 and Tc-99m decreased cell survival. Intracellular Tc-99m yielded a dose increase that was higher compared to Re-188 due to emitted Auger and internal conversion-electrons. Up to 5 Gy there was no difference in radiotoxicity of Re-188 and Tc-99m. At doses higher than 5 Gy intracellular Tc-99m became less radiotoxic than Re-188, probably due to a non-uniform lognormal radionuclide uptake.