Nuclear excitation functions for medical isotope production: targeted radionuclide therapy via natIr(d,x)193mPt

TL;DR

The paper tackles the challenge of obtaining high-specific-activity 193mPt for Auger-electron therapy by exploring natIr(d,x) as a production route. It employs a stacked-target activation approach with 33 MeV deuterons to measure 43 cross sections across Ir, Fe, Ni, and Cu up to 33 MeV, including first measurements of several new channels and a refined deuteron energy-fluence determination via variance minimization. The results identify an 11–18 MeV production window for favorable 193mPt radiopurity and show substantial discrepancies among modern reaction-model codes, highlighting limitations in predictive capabilities and the need for updated monitor data and enriched targets. The findings have practical implications for planning high-specific-activity radiopharmaceutical production and motivate further experimental and modeling work to improve cross-section predictions and reaction mechanisms in deuteron-induced systems.

Abstract

193mPt is an Auger emitting radionuclide which may have therapeutic potential, particularly when labeled to the chemotherapeutic drug cisplatin. One challenge to broader explorations of its clinical potential is the need for production routes with high specific activity. As part of a larger campaign to address gaps in reaction data for emerging medical radionuclides, this work seeks to characterize the natIr(d,x) reactions as a potential production pathway for 193mPt. A stacked target irradiation, consisting of natural iridium, iron, nickel, and copper foils, was performed using a 33 MeV deuteron beam at the Lawrence Berkeley National Laboratory 88-Inch Cyclotron. This measurement, along with previous experimental data, suggests an energy window between 11 to 18 MeV to maximize the production and radiopurity of 193mPt. This experiment has yielded cross sections for 43 channels of deuteron-induced reactions from threshold to 30 MeV, including the first experimental results of natIr(d,x)188m1+g,190m1+gIr (cumulative), natNi(d,x)56,57,58m,58gCo (independent), natCu(d,x)61Co (cumulative) and natFe(d,x)53Fe, 48V (cumulative). The results were compared with literature data, the TENDL-2023 database, and default theoretical calculations from the TALYS-2.04, CoH-3.6.0, EMPIRE-3.2.3, and ALICE-2020 reaction modeling codes. This work presents another example of the lack of predictive capabilities for this set of modern nuclear-reaction modeling codes, and highlights the unsatisfactory modeling of experimental cross sections. Experimental data are important to improve the codes in general, and new experimental results can be used to improve the models. Finally, this measurement has revealed the need for an updated evaluation of the natCu(d,x)63Zn deuteron monitor reaction.

Figures (26)

• Figure 1: Each target material mounted on acrylic frames with a hollow center. Kapton tape is attached along the edges of the foils, outside of the beam strike area.
• Figure 2: Visualization of the NPAT-calculated deuteron energy spectrum for each of the 10 iridium foils. As the beam energy degrades, the distribution becomes progressively more skewed, and the full width half maximum (FWHM) becomes progressively larger.
• Figure 3: (a) Result of $\chi^2$ analysis used in the variance minimization technique to determine the required adjustment (“Optimized”) to stopping power within the deuteron energy spectrum calculations. These corrections (with the red and green lines denoting the average energy of the beam entering each of the two listed compartments) show marked improvement in monitor reaction agreement (“Optimized” calculations) over the “Default” calculations. (b) Monitor reaction beam currents following the “Optimized” stopping power adjustments.
• Figure 4: Excitation function for ^natIr(d,x)^193mPt, visibly peaking between approximately 11-13 MeV.
• Figure 5: Excitation function for ^natIr(d,x)^188Pt. The ^191Ir(d, 5n)^188Pt channel opens at approximately $E_d$=26 MeV.