4. USES OF 233U There are several potential uses for 233U and its decay products. Figure 4.1 summarizes the larger potential uses. By definition, only known uses of 233U are described herein. There is no assurance that all of the potentially significant uses of 233U have been identified. 4.1 MEDICAL APPLICATIONS 4.1.1 Use One potential large-scale use for 233U involves one of its decay products, bismuth-213 (213Bi) for cancer treatment (Table 4.1). Specifically of interest is the use of antitumor antibodies radiolabled with an alpha emitter (Knapp and Mirzadeh 1994; Geerlings 1993). In this therapy, the radioisotope, 213Bi, is attached to antibodies that, in turn, attach to cancer cells; the resulting alpha emissions kill these cells with high efficiency. Initial clinical trials using 213Bi on human patients at the Memorial Sloan-Kettering Cancer Center Hospital in New York City have been favorable. The goal of radiotherapy is to kill the cancer cells without killing healthy cells and the patient. The interest in 213Bi, as compared to other radioisotopes, is that its nuclear characteristics may maximize damage to cancer cells while minimizing damage to healthy cells. This characteristic allows higher concentrations of the radioisotope to more effectively kill cancer cells without killing the patient from radiation or causing excess radiation exposure to other persons. •
High local damage. Radiation therapy has long been used to treat cancer. Alpha emitters compared to other radiation sources (x-ray, gamma, beta, etc.) deposit most of their energy in a very small volume within a few cell diameters. The large local energy deposition provides a higher assurance that the specific cell is destroyed, not just damaged. It is estimated that only two 213Bi decays will kill a cancer cell.
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Auxiliary damage control. In most types of radiation therapy, the radiation is concentrated on cancer cells, but healthy cells also receive high radiation doses. For example, if x-rays are used, many of the x-rays will be absorbed into healthy cells. Because alpha damage is very localized, secondary damage is minimized. This outcome is particularly important in treatment of certain cancers (e.g., leukemia) and other diseases (e.g., meningitis) where single cells or small clusters of cells are the targets that are interdispersed among healthy cells. Conventional radiation therapy will kill large numbers of healthy cells and have the potential to harm the patient (Feinendegen 1996).
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Minimal long-term damage. Many alpha emitters could be used for medical applications. Unfortunately, most alpha emitters decay through many additional decays to a stable isotope. Each of these subsequent decays creates radiation damage beyond the cancerous cell that was destroyed. These longer-term effects can adversely impact the health of both patients and doctors by several mechanisms.
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