Radionuclidic impurity

The only radionuclidic impurity detected in the 1-122 is less than 0.1% radioxenons and other radioiodines, which neither interfere with scintigraphic imaging nor result in a high radiation exposure to the patient. Further improvement of the radioiodine contamination could be attained with an iodine trap between the storage reservoir and the growth chamber. The milking efficiency is about 40%. We consider this generator assembly to be a preliminary version that can be refined considerably. Further details may be obtained from Richards and Ku (8). 

Radionuclidic Purity Radionuclidic purity is defined as the fraction of the total radioactivity in the form of the desired radionuclide present in a radiopharmaceutical. Radionuclide impurities may arise from impurities in the target material or from fission of heavy elements in the reactor [2], In radionuclide generator systems, the appearance of the parent nuclide in the daughter nuclide product is a radionuclidic impurity. In a "Mo/"mTc generator, "Mo may be found in the "mTc eluate due to breakthrough of "Mo on the aluminum column. The presence of these extraneous radionuclides increases the radiation dose to the patient and may also obscure the scintigraphic image. 

Technetium-99m containing drugs are prohibited from sale if these contain a radionuclide impurity mentioned in the monograph for Sodium Pertechnetate Tc-99m injection. 

Samarium-153 has relatively high neutron capture cross-sections (with a thermal capture cross-section of 206 b and an epithermal capture cross-section of 3000 b), thus enabling production of high specific activity with minimal long lived radionuclidic impurities. The activities of various samarium targets obtained post-irradiation in PARR-I are given in Table 12.4. 

The activity yield of Ho is given in Table 12.5. As this table shows, the specific activity of Ho increases with an increase in the irradiation time from 1 to 48 h, whereas a decrease in specific activity is obtained with an increase in the amount of Ho from 10 to 40 mg for the same irradiation time (48 h). This decrease of radioactivity is the consequence of the self-shielding effect. The radionuclidic impurity of ""Ho (half-life 1200 a, ct = 3.5 b) was found to be less than 2 x 10 for 48 h of irradiation. 

The major contributions to the adsorbed dose are caused by the radionuclide impurities in the eluate. The dose from 195mAu is less than 1% of the total adsorbed dose. The activity accumulates mainly in the liver and in the kidneys. Transformation of the data from animal studies could be carried out using the effective dose equivalent He (equation 95) and also results from "mTc-pertechnetate used for first pass studies612. 

Mo is separated from other radionuclides generated by this process (Barnes and Boyd 1982). Strict limits for radionuclidic impurities are stated in the monograph on sodium pertechnetate [ Tc] injection solution (Council of Europe 2005 a). 

Radionuclidic impurities in the eluate are directly related to the production mode of parent Mo. In any case, Mo is the most important impurity. The limit of contamination with stated in the Ph. Eur. is 0.1% of the total eluate activity. With irradiation-produced molybdenum-99, other radionuclidic impurities are limited to 0.01% of the total radioactivity. Identified impurities include Sn-113, Au-198, Au-199, Cs-134, and Nb-92. 

On the other hand, fission-produced molybdenum-99 may contain a number of radionuclidic impurities (Briner and Harris 1974 Hammermaier et al. 1986). Limits of contamination are listed in Table 5.5 with reference to the radionuclide and type of radiation. 

Table 5.5. Limits of radionuclidic impurities in the eluate of fission Pharmacopeia)...

The primary eluate is allowed to decay for 5 days, so that the " Tc activity does not interfere with the measurement of trace amounts of radionuclidic impurities. 

Other radionuclidic impurities stated in the Ph. Eur. were also determined. 1-131 was detected in very small amounts Ru-103 was not detectable in most eluates. Generators from one manufacturer were an exception, showing 0.27 nCi/mCi of 1-131, and values between 0.012 and 0.069 nCi/mCi of Ru-103 (Hammermaier et al. 1986). 

Purity of generator eluate Ph. Eur.) Radionuclidic impurities in primary eluate Radiochemical purity ... 

A testing program is needed to confirm the reliability of the selected procedures, especially to achieve high chemical yield and a sufficient decontamination factor for every interfering radionuclide. The analyst must estimate the allowable concentrations of radionuclide impurities and matrix components below this concentration, interference in measuring the radionuclide of interest is not of concern. 

All certificates must contain information that identifies the physical, chemical, and radiological properties of the SRM. Physical properties include density and mass. Chemical properties identify composition such as chemical form, acidity, and salt content. Radiological properties are the name of the radionuclide, the decay scheme, half-life, daughter radionuclides, reference time for calculating decay, and radionuclide impurity amounts. The most important information is the radionuclide activity or concentration and the uncertainty of this value. Details must be provided about the technique used to determine activity and the basis for the uncertainty value. Technical information such as the production method also may be given on the certificate. 

The production of Tc has been studied in detail (for a review cf. Qaim 2000). An enriched MoOs target is irradiated with 15 MeV protons in a target assembly similar to that shown in O Fig. 39.1, and Tc formed via the Mo(p,n) reaction is separated via thermochromatography using moist air as carrier gas (cf. Rosch et al. 1994). Further purification of the product is done using an AI2O3 column. The major radionuclidic impurity is Tc (Ti/2 = 4.9 h) at a level of about 7%. The radionuclide Tc is available in quantities of 5 GBq and is utilized in quantification of new Tc SPECT agents. 

---