Recent advances in cellular targeting strategies, such as cellspecific antibodies or small peptides, have increased interest in radionuclides as agents for cancer therapy. Two antibodytargeted radiophamaceuticals have recently been approved by the United States Food and Drug Administration using b À -emitting radionuclides ( 90 Y and 131 I). [1,2] One of the limitations of b À -emitting radiotherapeutics, such as 90 Y and 131 I, is their unsuitability for the treatment of small clusters of cancer cells (e.g. micrometastatic cancers or single-cell leukemias) because the path length of b À particle penetration is hundreds of cell diameters, resulting in damage to healthy bystander tissue. [3,4] In contrast, a-particles ( 4 He 2 + ) have much higher linear energy transfer (LET) values and are therefore more lethal over much shorter path lengths, on the order of a few cell diameters. It is estimated that a single a-decay that penetrates the cell nucleus can kill the cell, in contrast to thousands of b À -decays that are required to accomplish cell death. [5] Several a-emitting radionuclides have garnered special attention in recent years as radiotherapeutic agents. The four most-studied a-emitting radionuclides for radiotherapeutic applications are 211 At (t1 = 2 = 7.2 h), 212 Bi (t1 = 2 = 1 h), 213 Bi (t1 = 2 = 46 min), and 225 Ac(t1 = 2 = 10 d). [3] While the short half-life of 212 Bi and 213 Bi can pose significant logistical problems for synthesis, labeling, and delivery, some recent success has been reported with a 213 Bi-labeled myeloid leukemia antibody. [6] 225 Ac 3 + delivers a cascade of a-particles (four per 225 Ac 3 + ); however, the three daughter nuclei are extremely difficult to contain upon decay in vivo and can result in significant renal toxicity. [7] Thus, 211 At is currently an attractive candidate for the development of a-radionuclide therapy because its half-life is reasonable for targeted delivery, it has potential for treatment monitoring by singlephoton-emission-computed tomography (SPECT) imaging, [8] and because its daughter nucleus, 207 Bi (EC; t1 = 2 = 35 years)

0.5 N NaBH4 in 3 N NaOH (8.0 mL, aqueous) were added and the mixture stirred for 15 min. The mercury was allowed to settle, the solution was diluted with ether, and the combined ether extracts were dried and evaporated. The crude product was purified by column chromatography to give 2.585 g (71%) of 11c:

This investigation evaluated target fabrication and beam parameters for scale-up production of high specific activity (186)Re using deuteron irradiation of enriched (186)W via the (186)W(d,2n)(186)Re reaction. Thick W and WO3 targets were prepared, characterized and evaluated in deuteron irradiations. Full-thickness targets, as determined using SRIM, were prepared by uniaxially pressing powdered natural abundance W and WO3, or 96.86% enriched (186)W, into Al target supports. Alternatively, thick targets were prepared by pressing (186)W between two layers of graphite powder or by placing pre-sintered (1105°C, 12h) natural abundance WO3 pellets into an Al target support. Assessments of structural integrity were made on each target prepared. Prior to irradiation, material composition analyses were conducted using SEM, XRD, and Raman spectroscopy. Within a minimum of 24h post irradiation, gamma-ray spectroscopy was performed on all targets to assess production yields and radionuclidic byproducts. Problems were encountered with the structural integrity of some pressed W and WO3 pellets before and during irradiation, and target material characterization results could be correlated with the structural integrity of the pressed target pellets. Under the conditions studied, the findings suggest that all WO3 targets prepared and studied were unacceptable. By contrast, (186)W metal was found to be a viable target material for (186)Re production. Thick targets prepared with powdered (186)W pressed between layers of graphite provided a particularly robust target configuration.

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AbstractProduction of high specific activity