The innovative 52g Mn for positron emission tomography (PET) imaging: Production cross section modeling and dosimetric evaluation

Background: Manganese is a paramagnetic element suitable for magnetic resonance imaging (MRI) of neuronal function. However, high concentrations of Mn2 + can be neurotoxic. 52g Mn may be a valid alternative as positron emission tomography (PET) imaging agent, to obtain information similar to that delivered by MRI but using trace levels of Mn2 + , thus reducing its toxicity. Recently, the reaction nat$^{nat}$ V(α,x)52g Mn has been proposed as a possible alternative to the standard nat$^{nat}$ Cr(p,x)52g Mn one, but improvements in the modeling were needed to better compare the two production routes. Purpose: This work focuses on the development of precise simulations and models to compare the 52g Mn production from both reactions in terms of amount of activity and radionuclidic purity (RNP), as well as in terms of dose increase (DI) due to the co-produced radioactive contaminants, versus pure 52g MnCl2 . Methods: The nuclear code Talys has been employed to optimize the nat$^{nat}$ V(α,x)52g Mn cross section by tuning the parameters of the microscopic level densities. Thick-target yields have been calculated from the expression of the rates as energy convolution of cross sections and stopping powers, and finally integrating the time evolution of the relevant decay chains. Dosimetric assessments of [ xx$^{xx}$ Mn]Cl2 have been accomplished with OLINDA software 2.2.0 using female and male adult phantoms and biodistribution data for 52g MnCl2 in normal mice. At the end, the yield of xx$^{xx}$ Mn radioisotopes estimated for the two production routes have been combined with the dosimetric results, to assess the DI at different times after the end of the irradiation. Results: Good agreement was obtained between cross-section calculations and measurements. The comparison of the two reaction channels suggests that nat$^{nat}$ V(α,x)52g Mn leads to higher yield and higher purity, resulting in more favorable radiation dosimetry for patients. Conclusions: Both nat$^{nat}$ V(α,x) and nat$^{nat}$ Cr(p,x) production routes provide clinically acceptable 52g MnCl2 for PET imaging. However, the nat$^{nat}$ V(α,x)52g Mn reaction provides a DI systematically lower than the one obtainable with nat$^{nat}$ Cr(p,x)52g Mn and a longer time window in which it can be used clinically (RNP ≥ 99%).