Experimental excitation functions of Pd-103 production by deuteron irradiations

Brachytherapy was developed to treat prostate cancer 50 years ago. It consists in the implantation of Ti or SS seeds containing suitable radionuclides: nowadays only three radionuclides are available for use in low dose rate – LDR – prostate brachytherapy: I-125 (T1/2 = 59.4 d, mean photon energy emitted: 21 keV), Pd-103 (T1/2 = 17 d, mean photon energy emitted: 27 keV), and Cs-131 (T1/2 = 9.7 d, mean photon energy emitted: 29 keV). Pd-103 is an effective alternative to I-125 for high grade, rapidly growing cancer because of its faster dose rate that also raise thanks to possible differences in external tissue complications. With the rapid development of nanoscience and nanothecnology, it starts to become feasible the possibility to substitute the implantation of the seeds of millimetric dimension with the injection in the affected tissue of radioactive NPs. While for the seeds already in use the specific activity is practically unimportant, the nanomedicine approach, involving the synthesis of nanoparticles as nano-seeds or as drug carriers, requires that high Specific Activities – As – have to be achieved. Nowadays Pd-103 is mainly produced in nuclear reactors via 102Pd(n,) reaction with a very low AS or by accelerator in no-carrier added form – NCA – exclusively by the irradiation of rhodium metal targets with 18 MeV protons via Rh-103(p,n)Pd-103 reaction. We have studied the possibility to produce it by deuteron beams irradiation, which is more attractive and presents some advantages in respect to proton irradiation. A new data set of excitation functions for Rh-103(d,2n)Pd-103 nuclear reaction was measured and compared with the only other two studies reported in literature. The experimental results are compared with the curves of theoretical nuclear model calculations EMPIRE 3.2.2 and TENDEL-2015. The thin-target yields have been plotted as a function of their average energy into the targets and were fitted with the best mathematical functions. By integration of these functions the calculated Thick-Target Yields were obtained, in order to find the optimized couple of irradiation energy and energy loss inside the thick target to maximize the production of the radionuclide of interest. The best incident energy for the production of 103Pd with the highest AS and the related radionuclidic purity obtainable with this method will be discussed in detail.