Dysprosium-164 has a natural abundance of 28.2% and enriched material will have a purity of over 90%. for applications in interventional oncology. Both drugs as well as medical devices labelled with radioactive holmium are used for internal radiotherapy. ITK inhibitor 2 One of the treatment possibilities is direct intratumoural treatment, in which the radioactive compound is injected with a needle directly into the tumour. Numerous other applications have been developed, like patches for treatment of skin cancer and holmium labelled antibodies and peptides. The second major application that is currently clinically applied is selective internal radiation therapy (SIRT, also called radioembolization), a novel treatment option for liver malignancies. This review discusses medical drugs and medical devices based on the therapeutic radionuclide holmium-166. strong class=”kwd-title” Keywords: Holmium-166, Holmium, Lanthanide, Radiation therapy, SIRT, Microspheres, Chitosan, DOTMP Introduction Holmium is one of the 15 rare earth elements called lanthanides, a group of elements that has become an established source of radionuclides for nuclear diagnostic and therapeutic applications (Nayak and Lahiri 1999). Holmium-166 (166Ho) can be produced by two methods; neutron activation by (n, ) irradiation in a nuclear reactor (Nayak and Lahiri 1999; Nijsen et al. 1999) or by neutron activation of dysprosium-164 (164Dy) (Nijsen et al. 2007) (Fig. ?(Fig.1).1). Because holmium-165 (165Ho) has a natural abundance of 100% and a cross section ITK inhibitor 2 of 64 b (Foote Jr et al. 1953), it can be neutron activated in a relatively short neutron activation time resulting in 166Ho with a high purity of ITK inhibitor 2 the isotope (Nijsen et al. 1999). The only by-product is metastable holmium-166 (166mHo), approximately a factor 7??106 times less than 166Ho. 166mHo has a half-life of 1200?years and emits beta radiation and a number of gamma rays between 80 and 1563?keV (Nijsen et al. 2007; Hino et al. 2000; Bernardes 2001). The cross section of the 165Ho(n, )166Ho reaction is 64 b (Foote Jr et al. 1953) and the cross section of the 165Ho(n, )166mHo reaction is around 3.4 b for thermal neutrons (Nethaway and Missimer 1968). Open in a separate window Fig. 1 Diagrams of the production methods of (1) 166Ho and (2) 166Dy. Reactor neutron activated 165Ho will result in 166Ho with a high purity (1). The second method is via neutron activation of 164Dy by two neutrons. Dysprosium-164 has Rabbit Polyclonal to Myb a ITK inhibitor 2 natural abundance of 28.2% and enriched material will have a purity of over 90%. By capture of two neutrons, 164Dy will be converted into 166Dy which will decay into carrier-free 166Ho as the daughter radionuclide (166Dy/166Ho generator) (data were collected from the International Atomic Energy Agency Database: https://www-nds.iaea.org/) The other production option is via neutron activation of 164Dy by two neutrons following a (2n, ) reaction forming dysprosium-166 (166Dy). The cross section of 164Dy is extremely high (2650 b). A second neutron irradiation on this instable nuclide is necessary to result in 166Dy. The radionuclide 166Dy will decay with a half-life of 81.5?h into 166Ho, during which two beta particles up to 481?keV are emitted (Smith et al. 1995). The radionuclide 166Ho emits high-energy beta particles (1774.32?keV; yield 48.8% and 1854.9?keV; yield 49.9%) and gamma rays (80.57?keV; yield 6.7% and 1379.40?keV; yield 0.9% (only emissions are given with yield higher than 0.5%) and has a half-life of 26.8?h (Nijsen et al. 2007) (Fig. ?(Fig.1).1). The high energetic beta particles are responsible for the therapeutic effect and the gamma ray of 80.57?keV can be used for nuclear imaging purposes. Furthermore, 165Ho can be visualized by MRI because of its paramagnetic properties (Nijsen et al. 2004; Seevinck et al. 2007; Smits et al..