GATE/Geant4-based dosimetry for ex vivo in solution irradiation of blood with radionuclides

To establish a dose-response relationship between radiation-induced DNA damage and the corresponding absorbed doses in blood irradiated with radionuclides in solution under ex vivo conditions, the absorbed dose coefficient for 1 ml for 1 h internal ex vivo irradiation of peripheral blood (d_Blood) must be determined. d_Blood is specific for each radionuclide, and it depends on the irradiation geometry. Therefore, the aim of this study is to use the Monte Carlo radiation transport code GATE/Geant4 to calculate the mean absorbed dose rates for ex vivo irradiation of blood with several radionuclides used in Nuclear Medicine.

The Monte Carlo simulation reproduces the irradiation geometry of a blood sample of 7 ml mixed with 1 ml of a water equivalent radioactive solution in an 8 ml vial. The simulation was performed for ten different radionuclides: ¹⁸F, ⁶⁸Ga, ⁹⁰Y, ^99mTc, ¹²³I, ¹²⁴I, ¹³¹I, ¹⁷⁷Lu, ²²³Ra, and ²²⁵Ac. Two sets of simulations for each radionuclide were performed with 1x10⁹ histories. The first set was simulated with a mass density of 1.0525 g/cm³ of the blood plus water mixture. The second set of simulations was performed with a mass density of 1 g/cm³ for comparison with previous studies.

The values of d_Blood for ten radionuclides were calculated. The values range from 10.23 mGy∙ml∙MBq^-1 for ^99mTc to 15632.02 mGy∙ml∙MBq^-1 for ²²⁵Ac. The maximum relative change compared to previous studies was 13.0% for ¹²⁴I.

This study provides a comprehensive set of absorbed dose coefficients for 1 ml for 1 h internal ex vivo irradiation of peripheral blood in a special vial geometry and radionuclides typically used in Nuclear Medicine. Furthermore, the method proposed by this work can be easily adapted to a variety of internal irradiation conditions and serve as a reference for future studies.