Dosimetry study on Auger electron-emitting nuclear medicine radioisotopes in micrometer and nanometer scales using...

Dosimetry of Auger electron-emitting nuclear medicine radioisotopes on cellular and DNA scales is essential in order to assess the biological effects and damage of these radioisotopes to the DNA molecule. This study examined the effects of widely used radioisotopes in nuclear medicine and also two therapeutic radioisotopes in the scale of micrometer and nanometer.

In this paper, on cell scale (micrometer scale), the S-values for widely used Auger electron-emitting diagnostic radioisotopes ¹²³I, ¹²⁵I, ^99mTc, ⁶⁷Ga, ²⁰¹Tl and ¹¹¹In and two therapeutic radioisotopes of ¹³¹I and ²¹¹At in three different geometrical cell models (spherical, elliptical and cubic) were calculated using Geant4-DNA and the results were compared with the results of other simulation codes as well as the MIRD technique. On DNA scale (nanometer scale), the average number of DNA strand breaks (SSB and DSB) resulting from the direct and indirect effects was calculated for the specified radioisotope.

The results showed that in the cell scale, S-values of the diagnostic radioisotopes were mostly greater than the S-values of the therapeutic radioisotope ¹³¹I, but they were less those of ²¹¹At. On DNA scale, two different geometric models of DNA molecule were simulated and the results of these two models were compared with each other, as well as with the literature. The results showed that the geometric shape of sugar-phosphate groups has a significant effect on the break rates of DNA molecules.

Among the widely used diagnostic radioisotopes, ²⁰¹Tl and ¹²⁵I had the greatest effect on the rate of SSBs and DSBs, respectively, while the ¹³¹I therapeutic radioisotope almost had no effect and therapeutic radioisotope of ²¹¹At had a moderate effect on the number of breaks.