PT  - JOURNAL ARTICLE
AU  - Renne, Amy
AU  - Kao, Chien-Min
AU  - Song, Jeongseog
AU  - Gott, Matt
AU  - Gampa, Ravishanker
AU  - Kankanamalage, Pavithra
AU  - Rotsch, David
AU  - Capote, Roberto
AU  - Chen, Chin-Tu
AU  - Nolen, Jerry
TI  - <strong>Assessment of Production Reactions to Achieve High Radiological Purity Tb-155</strong>
DP  - 2022 Aug 01
TA  - Journal of Nuclear Medicine
PG  - 2756--2756
VI  - 63
IP  - supplement 2
4099  - http://jnm.snmjournals.org/content/63/supplement_2/2756.short
4100  - http://jnm.snmjournals.org/content/63/supplement_2/2756.full
SO  - J Nucl Med2022 Aug 01; 63
AB  - 2756 Introduction: Terbium-155 (155Tb) is a novel Auger electron emitter with promising application in cancer therapy. It is also useful for simultaneous SPECT imaging[1]. In addition, a companion isotope, 152Tb, is a useful PET imaging[2] radionuclide, thus making a potentially important theranostic pair. A current issue is that a potentially high yield production of 155Tb using the reaction 156Gd(p,2n)155Tb[3] can have impurities from 154Tb and 156Tb via the (p,3n) and (p,n) reactions, as well as, production on the 155Gd and 157Gd components of the enriched 156Gd target. Hence, alternative high yield reactions induced by 3He and 6Li beams are being studied at the Argonne superconducting LINAC, ATLAS (Argonne Tandem Linear Accelerator System). The advantage of these reactions is that they both are predicted to have large cross sections to the isotope 155Dy which is located between stable (156Dy) and very long-lived 154Dy, as shown qualitatively in Figure 1. The PACE4[4]simulations of the impurity of 156Tb via the direct production is very small for both 3He and 6Li beams as shown in Table I.  Hence, radiologically very pure 155Tb may be produced as the daughter of 155Dy. A recent publication[5] by a group at the Kurchatov Institute demonstrated the feasibility of this concept.Methods: Various reactions for producing 155Tb are being simulated with available nuclear model codes EMPIRE[6], PACE4[4], and TALYS/TENDL[7]. It is expected that the reactions 156Gd(3He,4n)155Dy  155Tb and 153Eu(6Li,4n)155Dy  155Tb will yield high radiological purity while still having adequate production rates. The novelty of this production method lies in 155Dy's unique position between two essentially stable isotopes (154Dy and 156Dy) so that the impurities 154Tb and 156Tb are predicted to be minimal. Additionally, 155Dy decays via electron capture exclusively with the relatively short half-life of 9.9 hours, to the desired product 155Tb with half-life 5.3 days. Preliminary gamma decay spectra from the 3He and 6Li reactions have been measured and indicate the validity of these possible reactions. The model-dependent excitation functions for these possible production reactions will be presented. The corresponding target thicknesses that yield the best overall yields and 155Tb purity will be predicted based on these simulations. Plans are in progress to measure the yields, excitation functions, and radiological purity of 155Tb produced at ATLAS using the 3He and 6Li induced reactions. Thermal simulations of the beam heating of targets of the optimized thicknesses for the various beams will also be assessed. Target cooling concepts that could be used with high power beams for production of 155Tb are being developed. Results: Initial gamma spectra from 3He and 6Li beams on targets of 156Gd and 153Eu, respectively, have demonstrated the production of 155Tb.  By using the reaction 156Gd(3He,4n)155Dy  155Tb or the corresponding 6Li induced reaction of 153Eu(6Li,4n)155Dy  155Tb relatively high radiological purity of 155Tb is expected. And, as shown in [5] even higher purity is feasible via fast chemical separation of the 155Dy (half-life 10 hours) from the production targets.Conclusions: This work suggests that the production of research quantities of pure 155Tb using ATLAS is feasible. Hence, high purity 155Tb in quantities required for pre-clinical applications will support the studies required to demonstrate the therapeutic effectiveness of this promising new theranostic Auger-electron emitter. Bringing this work out of the simulation environment and into the laboratory experiments will provide the ever-growing world of Auger electron therapy with an easily producible, purity reliable, research isotope.