Production of High-Purity 52gMn from natV Targets with Alpha Beams at Cyclotrons

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 Mn^{2 +} 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 Mn^{2 +} , thus reducing its toxicity. Recently, the reaction n a t $^{nat}$ V(α,x)^52g Mn has been proposed as a possible alternative to the standard n a t $^{nat}$ 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 n a t $^{nat}$ 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 [ x x $^{xx}$ 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 x x $^{xx}$ 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 n a t $^{nat}$ V(α,x)^52g Mn leads to higher yield and higher purity, resulting in more favorable radiation dosimetry for patients.

CONCLUSIONS

Both n a t $^{nat}$ V(α,x) and n a t $^{nat}$ Cr(p,x) production routes provide clinically acceptable ^52g MnCl₂ for PET imaging. However, the n a t $^{nat}$ V(α,x)^52g Mn reaction provides a DI systematically lower than the one obtainable with n a t $^{nat}$ Cr(p,x)^52g Mn and a longer time window in which it can be used clinically (RNP ≥ 99%).

A new route to produce 52gMn with high purity for MultiModal Imaging

The 52gMn radionuclide is suitable for the innovative MultiModal Imaging technique, and in particular for a PET/MRI scan, due to its physical properties. The standard cyclotron-based production of 52gMn relies on the nuclear reaction NatCr(p,x)52gMn, but we have investigated theoretically the possibility of an alternative and competitive route, the reaction NatV(α,x)52gMn, which has not been considered for this purpose so far. By using the nuclear reaction code TALYS, we found some discrepancies between the theoretical calculations of the cross sections and the corresponding experimental data. Therefore we tuned the parameters governing the nuclear level densities in the microscopic models implemented in TALYS, thus improving the agreement with the data. Then, by studying the cross sections for 52gMn and its contaminants, we have identified an optimal energy window for the production of high purity 52gMn, around 40 MeV. We have also calculated the time evolution of the number of nuclei of the different Mn isotopes, for an irradiation in this energy window, finding that this route is expected to lead to a higher yield and Radionuclidic Purity with respect to the standard reaction with NatCr. The study suggests the reaction NatV(α,x)52gMn as a promising alternative route for the production of 52gMn.

Theoretical study of 47Sc production for theranostic applications using proton beams on enriched titanium targets

Recently, scandium-47 has attracted attention in the scientific community thanks to its promising features, making it suitable for targeted radiotherapy and theranostic applications, also in combination with the β+ emitters 43Sc/44Sc. However, in view of possible pre-clinical and clinical studies, finding efficient production routes is still a current research topic. In this work we investigate 47Sc cyclotron production using proton beams on enriched titanium targets. The analysis of the cross sections and yields of both 47Sc (T1/2 = 3.35 d) and its main contaminant 46Sc (T1/2 = 83.79 d) has been performed with the nuclear reaction code Talys (v.1.95). The experimental data (scarce and relatively old) are compared with model calculations and some discrepancies emerge even after the tuning of parameters defining the nuclear level densities, involved in the compound nucleus formation. The 49Ti case allows a more precise cross sections reproduction, conversely the 50Ti case requires further theoretical investigations. Preliminary yields analysis has been carried out for both 47Sc and 46Sc.

Improvement of nuclear reaction modeling for the production of 47Sc on natural vanadium targets for medical applications

The proton-induced reaction on natural vanadium targets is studied for the production of the innovative theranostic radionuclide 47Sc as well as of its contaminants, mainly 46Sc. The theoretical excitation functions are calculated using the nuclear reaction code TALYS and are compared with the most recent experimental data. A better agreement between the theoretical curves and the data is achieved with an optimization of the nuclear level density parameters. The obtained improvements represent a useful and important result for accurate evaluations of yields and purities which are needed quantities for subsequent dosimetric studies, in view of the radiopharmaceutical applications of 47Sc. The optimization procedure is explained and shown for 47Sc and 46Sc, and also a comparison among the theoretical and experimental cumulatives is given (for the main contaminant) in addition to an estimation of the production yields for two irradiation conditions for both nuclides.