Generator-produced alpha-emitters

Abstract

This review briefly describes the nuclear characteristics and production parameters for 7.2-h 211At, 60.6-min 212Bil 45.6-min 213Bi, 1 1 d 233Ra, and 20-h 255Fm. These a-emitting radioisotopes are the subject of current interest for a-partide-mediated radioimmunotherapy. IntroductionAlpha particles are of considerable interest for radioimmunotherapy applications. Due to their short range in tissue (a few cell diameters), and high linear-energy-transfer (LET), a-particles are especially suited for targeting micrometatases and single tumor cells such as leukemia and other blood-borne diseases (Bloomer et a/., 1984, Ruegg, et a/., 1990, Huneke, et a/., 1992, Junghans, et a/., 1993, Hartmann, et a/., 1994, Kennel and Mirzadeh, 1997, Scheinberg, 1997. The list of potential radionuclides for these applications includes only five a-emitting radioisotopes, namely 211At (tIQ = 7.2 h), 212Bi (t1,2 = 60.6 m), 213Bi (tlQ = 45.6 m), 233Ra ( t l M = 11 d), and 255Fm (tln = 20 h). A list of the generator-produced a-emitters and the corresponding references are given in 1 DISCLAIMERPortions of this document may be illegible in electronic imRge products. Images are produced from the best available original document. 21'Rn(14.6 h) + *"At(7.2 h). Astatine-211 can be produced through the decay of 14.6 h 211Rn. The 21'Rn, in turn, is produced through a number of nuclear reactions which are summarized in Table 3. The corresponding references are also given in this table. These reactions include spallation of Th with high energy protons having a cross-section of 0.7 mb at 28 GeV protons or by photo-spallation of Th with a cross-section of 0.13 mb at a photon energy of 300 MeV. The production of 2'1Rn by the 209BitLi14n]211Rn reaction, with a amax = 0.7 b at E , = 54 MeV and yield of -2 pCi/nA at '/z saturation, has also been reported. By far, the predominant nuclear reaction for the production of 211Atl however, is not through a generator system but by direct activation of 209Bi with 28 MeV u particles, The maximum of the excitation function for this reaction is -1 b at E , = 29MeV. In order to minimize the production of radiocontaminant 210Po, the a-particle should exit the Bi target at E , = 20 MeV, limiting the Bi thickness to only 100 pg.cm-*. The typical yield is -1.5 mCi/pA at half saturation (-3.5 hours of irradiation). Since there are only a few cyclotrons in the U.S. capable of accelerating a-particles to -28 MeV, the required energy for the production of 211At via the 209Bi[a,2n] reaction, the availability of 211At is also very limited. There are a number of procedures reported for extracting 21'At from an irradiated Bi target, and a recent review of the subject is available (Ruth et al, 1988). The dry distillation method is the most convenient approach and it has been described in detail elsewhere (Lambrecht and Mirzadeh, 1985).224Raf3.7 d) -* 212Pbf10.6 h) .--* 2'2Bi(60.6 minl. Bismuth-212 is available from the 224Ra/212Bigenerator system, where 224Ra is the daughter of 1.9-y =%I . Th-228 is the second member of the 232Th ...

Actinium-225 in Targeted Alpha-Particle Therapeutic Applications

“…The element was discovered by Debierne in 1899 and Giesel in 1902 [9]. Actinium occurs naturally in association with uranium radionuclides and 225 Ac can be obtained either from the decay of 233 U or from the neutron transmutation of 226 Ra by successive n,γ capture decay reactions via 227 Ac, 228 Th to 229 Th [10–12]. Currently, there are two sources of 225 Ac that have been used in clinical trials: (1) the U.S. Department of Energy, Oak Ridge National Laboratory (ORNL) in Oak Ridge, TN, United States of America and (2) the Institute for Transuranium Elements in Karlsruhe, Germany.…”

The Development of the α-Particle Emitting Radionuclides 212Bi and 213Bi, and Their Decay Chain Related Radionuclides, for Therapeutic Applications

“…It has been estimated that ∼12 g or 93 GBq (2.5 Ci) of 229 Th might be extracted from this stockpile. 27 However, the 233 U stock also contains 232 U which produces a mixture of 228 Th and 229 Th. As mentioned previously, 229 Th may also be produced by successive neutron capture of 226 Ra in high flux reactors such as at HFIR at ORNL.…”

“…The use and development of the R-emitter 211 At as applied to radiopharmaceutical development and other R-particle emitters have been reviewed elsewhere. [26][27][28] …”

The development and use of radionuclide generators in nuclear medicine -- recent advances and future perspectives

“…Because of the extremely localized deposition of high energy from alpha particles, the possibility of using alpha-emitting radioisotopes for cancer therapy is of great interest [27]. In particular, those alpha-emitters which have the appropriate radionuclide properties and are available from generator systems are of prime interest because of availability and expected cost effectiveness.…”