Theoretical basis for long-term measurements of equilibrium factors using LR 115 detectors

In this paper, we propose a method to determine the equilibrium factor using a bare LR 115 detector. The partial sensitivities ρ_i of the LR 115 detector to ²²²Rn and its alpha-emitting short-lived progeny, ²¹⁸Po and ²¹⁴Po, were investigated. We first determined the distributions of lengths of major and minor axes of the perforated alpha tracks in the LR 115 detector produced by ²²²Rn, ²¹⁸Po and ²¹⁴Po through Monte Carlo simulations. The track parameters were calculated using a track development model with a published V function, by assuming a removed active layer of 6.54 μm. The distributions determined for different alpha emitters were found to completely overlap with one another. This implied equality of partial sensitivities for radon and its progeny, which was also confirmed through analytical considerations. Equality of partial sensitivities makes possible convenient measurements of the proxy equilibrium factor F_p, which is defined in the present work as (F₁+F₃) and is equal to the ratio between the sum of concentrations of the two alpha emitting radon progeny (²¹⁸Po+²¹⁴Po) to the concentration of radon gas (²²²Rn). In particular, we have found F_p=(ρ/ρ_itC₀)−1, where ρ (track/m²) is the total track density on the detector, ρ_i=0.288×10⁻² m, t is the exposure time and C₀ (Bq/m³) is the concentration of ²²²Rn. If C₀ is known (e.g. from a separate measurement), we can obtain F_p. The proxy equilibrium factor F_p is also found to be well correlated with the equilibrium factor between radon gas and its progeny through the Jacobi room model. This leads to a novel method for long-term determination of the equilibrium factor.     

Direct gamma-spectrometric measurement of the Ra 186.2 keV line for detecting U/Ra disequilibrium in determining the environmental dose rate for the luminescence dating of sediments

In the age determination of sediments according to the luminescence method, it is important to know whether there was secular equilibrium in the Th and U decay series during accumulation of the environmental radiation dose in geological times. This can be investigated via gamma-ray spectrometry, whereby—in the ²³⁸U series—²¹⁴Pb and ²¹⁴Bi are considered as the indicators for ²²⁶Ra-mobility, and ²¹⁰Pb as the indicator for ²²⁶Rn-emanation. In the present work, the direct measurement of ²²⁶Ra—which can give extra information on the interpretation of the radioactive equilibrium—is investigated as to its precision and accuracy. Since there is a serious spectral interference on its 186.2 keV gamma-line (by ²³⁵U at 185.7 keV), various correction procedures were outlined and their performance was checked via the analysis of (certified) reference materials, leading to the recommendation of a “method of choice”.     

A liquid-scintillation-based primary standardization of Pb

A new radioactivity solution standard of ²¹⁰Pb has been developed and will be disseminated by the National Institute of Standards and Technology (NIST) as standard reference material (SRM) 4337. This new ²¹⁰Pb solution standard is contained in a 5 mL flame-sealed borosilicate glass ampoule, consists of (5.133±0.002) g of a nominal 1 mol L⁻¹ nitric acid solution, has a density of (1.028±0.002) g mL⁻¹ at 20 °C, has carrier ion concentrations of about 11 μg Pb²⁺ and 21 μg Bi³⁺ per gram of solution, and is certified to contain a massic activity (9.037±0.22) kBq g⁻¹ as of the reference time 1200 EST, 15 June 2006. All of the uncertainties cited above correspond to standard uncertainties multiplied by a coverage factor k=2. The standardization for the ²¹⁰Pb content of the solution was based on 4πβ liquid scintillation (LS) measurements using CIEMAT/NIST ³H-standard efficiency tracing (CNET). Confirmatory determinations were also performed by high-resolution HPGe γ-ray spectrometry, by 2π spectrometry with a Si surface barrier detector of separated ²¹⁰Po, and by 4πβ(LS)–γ(NaI) anticoincidence counting.     

Sensitivity of LR115 detector in diffusion chamber to Rn in the presence of Rn

Determination has been made of the sensitivity of LR115 type 2-track detectors (in units of m) to ²²²Rn, measured in the presence of ²²⁰Rn. Measurements have been made by means of a widely used diffusion chamber while Monte Carlo simulations have also been conducted. The experimentally derived sensitivities for ²²²Rn and ²²⁰Rn were found to be 0.470±0.022 and 0.486±0.042 m, respectively. For Monte Carlo simulations, the sensitivities to ²²²Rn gas were found to range from 0.618×10^–2 m (assuming that all ²¹⁸Po progeny decay before deposition onto the internal walls of the diffusion chamber) to 0.405×10^–2 m (assuming that all ²¹⁸Po progeny are deposited on the internal walls of the same containment vessel before decaying). The sensitivity to ²²⁰Rn gas of 0.465×10^–2 m found from Monte Carlo simulations agrees to within uncertainty with experimental findings. The experimentally derived sensitivity value for ²²²Rn indicates that 30% of the ²¹⁸Po progeny decay before deposition onto the internal walls of the diffusion chamber.     

Liquid-scintillation-based anticoincidence counting of Co-60 and Pb-210

The method of liquid-scintillation-based 4πβ–γ anticoincidence counting was employed to assay the radioactivity concentration of acid solutions containing radionuclides ⁶⁰Co and ²¹⁰Pb (in equilibrium with its daughters). The limiting factors on the accuracy for such activity measurements and suggestions for minimizing such factors are reported.     

Dependency of the [18F]fluoromisonidazole uptake on oxygen delivery and tissue oxygenation in the porcine liver

We have previously shown that the accumulation of fluorine-18-labeled fluoromisonidazole ([¹⁸F]FMISO) is inversely correlated to tissue oxygenation, allowing the quantification of porcine liver tissue hypoxia in vivo. We determined the activity from administered [¹⁸F]FMISO in relation to the hepatic oxygen availability and the partial pressure of oxygen in tissue (tPO₂) to define a critical oxygen delivery on a regional basis. [¹⁸F]FMISO was injected 2 h after onset of regional liver hypoxia due to arterial occlusion of branches of the hepatic artery in 10 domestic pigs. During the experimental procedure the fractional concentration of inspired oxygen (FiO₂) was set to 0.67 in group A ( N=5) and to 0.21 in group B ( N=5) animals. Immediately before sacrifice, the tPO₂ was determined in normal flow and flow-impaired liver segments. The standardized uptake values (SUV) for [¹⁸F]FMISO was calculated from 659 single tissue samples obtained 3 h after injection of approximately 10 MBq/kg body weight [¹⁸F]FMISO and was compared with the regional total hepatic oxygen delivery (DO₂) calculated from the regional arterial and portal venous flow (based on ¹⁴¹Ce- and ^99mTc-microspheres measurements) and the oxygen content of the arterial and portal venous blood. In 121 tPO₂-measured liver tissue samples, the mean DO₂ was significantly decreased in occluded liver tissue samples [group A: 0.063 (0.044–0.089); group B: 0.046 (0.032–0.066)] compared to normal flow segments [group A: 0.177 (0.124–0.252); group B: 0.179 (0.128–0.25) mL·min⁻¹·g⁻¹; geometric mean (95% confidence limits); p < 0.01 in group A and p < 0.001 in group B]. The tPO₂ of occluded segments [group A: 5.1 (3.2–8.1); group B: 3.9 (2.4–6.2) mm Hg] was significantly decreased compared to normal flow segments [group A: 20.2 (12.6–32.5); group B: 22.4 (14.3–35.2) mm Hg; p < 0.01 in group A and p < 0.001 in group B]. Three hours after [¹⁸F]FMISO administration, the mean [¹⁸F]FMISO SUV determined in tPO₂-measured occluded segments was significantly higher [group A: 4.08 (3.12–5.34), group B: 5.43 (4.14–7.13)] compared to normal liver tissue [group A: 1.57 (1.2–2.06), group B: 1.5 (1.16–1.93); p < 0.001 for both groups]. The [¹⁸F]FMISO SUV allowed prediction of the tPO₂ with satisfying accuracy in hypoxic regions using the exponential regression curve { [¹⁸F]FMISO=1.05+6.7^{(−0.117 tPO₂}); r²=0.75;p < 0.001}. In addition, regardless of ventilation conditions, a significant exponential relationship between the DO₂ and the [¹⁸F]FMISO SUV was found ( r²=0.39,p < 0.001). Our results suggest that the reduction of the oxygen delivery below the critical range of 0.1–0.11 mL·min⁻¹·g⁻¹ regularly causes liver tissue hypoxia. The severity of hypoxia is reflected by the [¹⁸F]FMISO accumulation and allows the in vivo estimation of the tPO₂ in hypoxic regions.     

Biodistribution of 225Ra citrate in mice: retention of daughter radioisotopes in bone

Alpha-particle-emitting radionuclides have potential for therapy of localized disease due to their high linear energy transformation and short pathlengths. Radiometals that home naturally to bone can be exploited for this purpose, and ²²³Ra (t_1/2=11.4 days) recently has been studied for therapy of bone tumors in mice and rats. Actinium-225 (t_1/2=10 days) is also an attractive radioisotope for endoradiotherapy. In a single decay of a ²²⁵Ac nucleus and its subsequent decay daughters, over 27 MeV (90% of total energy) is released by sequential emission of four particles, ranging in energy from 5.7 to 8.4 MeV. Although Ac³⁺ does not home naturally to bone, its parent radioisotope ²²⁵Ra (β⁻, t_1/2=15 days) can be used as an in vivo source for ²²⁵Ac. Thus, injection of ²²⁵Ra takes advantage of the bone-homing properties of radium coupled with the significant amount of energy released from the ²²⁵Ac decay chain. Our data confirm that a large fraction of radium citrate injected intravenously into mice localizes rapidly in bone. Injected doses per gram (ID/g) for ²²⁵Ra range from 25% in skull to about 10% in sternum. Once deposited, the ²²⁵Ra remains in the bone with a biological half life of >40 days. Furthermore, >95% of the daughter radioisotope, ²²⁵Ac, is retained in the bone. However, a significant fraction of one of the daughter radioisotopes, ²¹³Bi, is found in kidney. The biodistribution data indicate that ²²⁵Ra injection should be a powerful agent for killing cells associated with bone; however, the toxicity of this radioisotope which is similar to that of other emitters limits the dose that can be tolerated.     

Comparison of outdoor activity size distributions of Rn and Rn progeny

Inhalation of ²²²Rn and ²²⁰Rn progeny from the domestic environment contributes the greatest fraction of the natural radiation exposure to the public. Dosimetric models are most often used in the assessment of human lung doses due to inhaled radioactivity because of the difficulty in making direct measurements. These models require information about the parameters of activity size distributions of thoron and radon progeny. The present study presents measured data on the attached and unattached activity size distributions of thoron and radon progeny in outdoor air in El-Minia, Egypt. The attached fraction was collected using a low-pressure Berner cascade impactor technique. A screen diffusion battery was used for collecting the unattached fraction. Most of the attached activities for ²²²Rn and ²²⁰Rn progeny were associated with aerosol particles of the accumulation mode. The activity size distribution of thoron progeny was found to be shifted to slightly smaller particle size compared to radon progeny.     

Preparation of in-house reference soil sample containing high levels of naturally occurring radioactive materials from the oil industry

An in-house reference soil sample containing high levels of naturally occurring radioactive materials collected from contaminated areas in the Syrian oilfields has been prepared as a part of the quality assurance program in AECS. Homogeneity of the sample has been examined using three methods, viz. particle size distribution of the sample matrix, total alpha/beta counting and gamma spectrometry. In conjunction with Dixon and Grubb tests as statistical tools, ten random samples from the original sample were used for this investigation. Reference values for the three radium isotopes (²²⁴Ra, ²²⁶Ra, ²²⁸Ra) were determined using gamma spectrometry equipped with HPGe detectors having high relative efficiencies of 80%, while the reference value of ²¹⁰Pb in the sample was determined using radiochemical separation and counting of its daughter ²¹⁰Po by alpha spectrometry. ANOVA analysis was used to estimate the uncertainties due to measurement and inhomogeneity of the sample; uncertainty due to inhomogeneity was found to be around 2.6 times the measurement uncertainty.     

Preparation of high specific activity (86)Y using a small biomedical cyclotron

⁸⁶Y is an attractive PET radionuclide due to its intermediate half-life. ⁸⁶Y was produced via the ⁸⁶Sr(p,n)⁸⁶Y nuclear reaction. Enriched SrCO₃ or SrO was irradiated with 2-6 μA of beam current for <4 h on a CS-15 cyclotron. It was shown that the SrO target could withstand at least 6 μA of beam current, a significant improvement over a maximum of 2 μA on the SrCO₃ target. Average yields of 4.5 mCi/μA·h were achieved with SrO, which represent 71% of the theoretical yield, compared to 2.3 mCi/μA·h with SrCO₃. The radioisotopic contaminants were ^86mY (220%), ⁸⁷Y (0.27%), ^87mY (0.43%) and ⁸⁸Y (0.024%). ⁸⁶Y was isolated in an electrochemical cell consisting of three Pt electrodes. The solution was electrolyzed at 2000 mA (40 min) using two Pt plate electrodes. A second electrolysis (230 mA for 20 min) was performed using one Pt plate and a Pt wire. On average, 97.1% of the ⁸⁶Y was recollected on the Pt wire after a second electrolysis. The ⁸⁶Y was collected from the Pt wire using 2.8 M HNO₃/EtOH (3:1). After evaporation, ⁸⁶Y was reconstituted in 100 μl of 0.1 M HCl. Target materials were recovered as SrCO₃ and then converted to SrO by thermal decomposition at 1150°C. Specific activity of ⁸⁶Y was determined to be 29±19 mCi/μg via titration of ⁸⁶Y(OAc)₃ with DOTA or DTPA. We have established techniques for the routine, economical production of high purity, high specific activity ⁸⁶Y on a small biomedical cyclotron that are translatable to other institutions.     

Processing of reactor-produced W for fabrication of clinical scale alumina-based W/Re generators

The traditional technique for processing of reactor-irradiated ¹⁸⁶W-enriched tungsten oxide (WO₃) targets involves formation of ¹⁸⁸W-sodium tungstate solutions by target dissolution in 0.1 M NaOH. Following long irradiations (> 21 days) in the ORNL High Flux Isotope Reactor (HFIR) the ¹⁸⁶WO₃ targets contain a NaOH-insoluble ¹⁸⁸W-labeled black solid (approx. 30–50% of total activity) which decreases the yield and specific activity of the processed ¹⁸⁸W (e.g. 5–6 mCi/mg ¹⁸⁶W for a 79-day irradiation). The black material is postulated to represent a “tungsten blue” insoluble polymeric form of tungsten oxide, which we have now found to dissolve in 0.1 M NaOH containing 5% sodium hypochlorite solution. Complete dissolution results in a significant increase in the yield and specific activity of sodium ¹⁸⁸W-tungstate. As an alternative approach, irradiated ¹⁸⁶W-enriched metal targets dissolve in sodium hydroxide solution by cautious addition of < 30% hydrogen peroxide. Sodium ¹⁸⁸W-tungstate solutions prepared from processing of such metal targets show no evidence of residual black insoluble material. Specific activity values for completely dissolved HFIR-irradiated ¹⁸⁶W targets have increased to 10 mCi/mg (43.5 days) and 12.9 mCi/mg (49.2 days). Large clinical scale (> 1 Ci) generators prepared from hypochlorite-processed ¹⁸⁶W oxide or peroxide-processed ¹⁸⁶W metal targets exhibit the expected ¹⁸⁸Re high yield and low ¹⁸⁸W breakthrough.     

Evaluation of novel cationic 99mTc(I)-tricarbonyl complexes as potential radiotracers for myocardial perfusion imaging

This report describes the evaluation of three cationic ^99mTc(I)–tricarbonyl complexes — [^99mTc(CO)₃(L)]⁺ (L=N-methoxyethyl-N,N-bis[2-(bis(3-ethoxypropyl)phosphino)ethyl]amine (ME-PNP), N-[15-crown-5)-2-yl]-N,N-bis[2-(bis(3-ethoxypropyl)phosphino)ethyl]amine (15C5-PNP) and N-[18-crown-6)-2-yl]-N,N-bis[2-(bis(3-ethoxypropyl)phosphino)ethyl]amine (18C6-PNP)) — as potential radiotracers for myocardial perfusion imaging. Biodistribution, imaging and metabolism studies were performed using Sprague–Dawley rats. It was found that bisphosphine ligands have a significant impact on the biodistribution characteristics and clearance kinetics of their cationic ^99mTc(I)–tricarbonyl complexes. Among the three radiotracers evaluated in this study, [^99mTc(CO)₃(15C5-PNP)]⁺ has a very high initial heart uptake and is retained in the rat myocardium for >2 h. It also shows rapid clearance from the liver and lungs. The heart/liver ratio of [^99mTc(CO)₃(15C5-PNP)]⁺ is 2.5 times better than that of ^99mTc-sestamibi at 30 min postinjection. [^99mTc(CO)₃(15C5-PNP)]⁺ is almost identical to ^99mTcN-DBODC5 with respect to heart uptake, heart/lung ratio and heart/liver ratio. Results from metabolism studies show that there is no significant metabolism for [^99mTc(CO)₃(15C5-PNP)]⁺ in the urine, but it does show a small metabolite peak (<10%) in the radio high-performance liquid chromatography chromatogram of the feces sample at 120 min postinjection. Results planar imaging studies demonstrate that [^99mTc(CO)₃(15C5-PNP)]⁺ has a much better liver clearance profile than ^99mTc-sestamibi and might give clinically useful images of the heart as early as 30 min postinjection. [^99mTc(CO)₃(15C5-PNP)]⁺ is a very promising candidate for more preclinical evaluations in various animal models.     

8例组织细胞坏死性淋巴结炎18F-FDG PET/CT表现及临床分析

目的 分析组织细胞坏死性淋巴结炎（HNL）病人的 ¹⁸F-脱氧葡萄糖（FDG）PET/CT表现及临床资料,提高对该病认识水平。 方法 回顾性分析8例经病理证实的HNL病人的 ¹⁸F-FDG PET/CT资料,其中男4例、女4例,中位年龄26.5岁。分析HNL在 ¹⁸F-FDG PET/CT成像上所示的受累淋巴结分布、形态、密度及摄取,并采用Pearson相关分析来确定淋巴结的 ¹⁸F-FDG最大标准化摄取值（SUV_max）与其长径、短径之间的相关性。 结果 8例HNL病人 ¹⁸F-FDG PET/CT成像均有多部位淋巴结受累,位于颈部8例（6例双侧、2例单侧）,腋窝7例（5例双侧、2例单侧）,肺门及纵隔4例,腹部4例,盆腔3例及腹股沟区2例（均为双侧）。受累淋巴结大都呈椭圆形,无融合,密度较均匀,无钙化及液化坏死。受累淋巴结SUV_max为12.86±5.70,长径为（1.41±0.42） cm,短径为（0.84±0.26） cm,CT值为（44.77±9.59） HU。其中短径<1 cm的淋巴结约占63.4%,SUV_max为11.21±5.80。受累淋巴结SUV_max与长径呈低度正相关（r=0.349,P=0.025）,与短径呈中度正相关（r=0.504,P=0.001）。 结论 ¹⁸F-FDG PET/CT成像在HNL诊断、鉴别诊断及淋巴结活检定位中发挥重要作用。     

Design and synthesis of Ac radioimmunopharmaceuticals

The alpha-particle-emitting radionuclides ²¹³Bi, ²¹¹At, ²²⁴Ra are under investigation for the treatment of leukemias, gliomas, and ankylosing spondylitis, respectively. ²¹³Bi and ²¹¹At were attached to monoclonal antibodies and used as targeted immunotherapeutic agents while unconjugated ²²⁴Ra chloride selectively seeks bone. ²²⁵Ac possesses favorable physical properties for radioimmunotherapy (10 d half-life and 4 net alpha particles), but has a history of unfavorable radiolabeling chemistry and poor metal-chelate stability. We selected functionalized derivatives of DOTA as the most promising to pursue from out of a group of potential ²²⁵Ac chelate compounds. A two-step synthetic process employing either MeO–DOTA–NCS or 2B–DOTA–NCS as the chelating moiety was developed to attach ²²⁵Ac to monoclonal antibodies. This method was tested using several different IgG systems. The chelation reaction yield in the first step was 93±8% radiochemically pure (n=26). The second step yielded ²²⁵Ac–DOTA–IgG constructs that were 95±5% radiochemically pure (n=27) and the mean percent immunoreactivity ranged from 25% to 81%, depending on the antibody used. This process has yielded several potential novel targeted ²²⁵Ac-labeled immunotherapeutic agents that may now be evaluated in appropriate model systems and ultimately in humans.     

Half-life measurements of Rb by liquid scintillation counting

The specific activity of natural ⁸⁷Rb was measured by means of 4πβ liquid scintillation counting in a two-photomultiplier-tube spectrometer. ³H-efficiency tracing was used together with the CIEMAT/NIST method to obtain the detection efficiency. For this purpose a new parameterization of the shape factor for the third forbidden non-unique β-transition was performed. The hygroscopic behaviour of the salts used for sample preparation was studied. The half-life of ⁸⁷Rb was found to be T_1/2=4.967(32)×10¹⁰ y.     

Excitation functions of Se(d,xn)Br reactions: Comparative evaluation of possible routes for the production of Br at a small cyclotron

Excitation functions were measured for the first time for ⁷⁴Se(d,n)⁷⁵Br and ⁷⁴Se(d,2n)^74mBr reactions from threshold to 23 MeV. Use was made of the stacked-foil technique, and thin samples were prepared by electrolytic deposition of 31.4% enriched ⁷⁴Se on Al-backing. Differential and integral yields of ^74mBr and ⁷⁵Br were calculated from the measured excitation functions. The optimum energy range for the production of ⁷⁵Br via the ⁷⁴Se(d,n)-process was found to be E_d = 12 → 8 MeV, with ⁷⁵Br-yield amounting to 509 MBq (13.75 mCi)/μAh and the ^74mBr impurity to 78Kr(p,)⁷⁵Br and ⁷⁴Se(d,n)⁷⁵Br, suggested for the production of ⁷⁵Br at a small cyclotron is given. The (d,n) reaction gives higher yield than the (p,) process and is preferable at cyclotrons with E_d 10 MeV. In general, at a small cyclotron the achievable batch yields of ⁷⁵Br via both the processes are limited.     

Development of an automated system for the quick production of N-labeled compounds with high specific activity using anhydrous [N]NH3

An automated system was developed to synthesize ¹³N-labeled compounds with high specific activity using anhydrous [¹³N]NH₃ as a synthetic precursor. This system enabled (1) production of an aqueous solution of [¹³N]NH₃, (2) concentration and desiccation of the [¹³N]NH₃ solution, (3) reaction of anhydrous [¹³N]NH₃ with substrate, (4) purification and formulation.

By the use of this system, [¹³N]p-nitrophenyl carbamate ([¹³N]NPC) ready for i.v. injection could be obtained in 5.1±0.1 min at the yield of 3.5±0.4 GBq, specific activity 460±55 GBq/μmol, and radiochemical purity >99% (n=3) by irradiating a 10 mM ethanol solution with 18 MeV protons at 17 μA for 25 min. With special precautions, [¹³N]NPC could be obtained at the extremely high specific activity of 1800±200 GBq/μmol.     

Experimental studies and nuclear model calculations on proton-induced reactions on Se, Se and Se with particular reference to the production of the medically interesting radionuclides Br and Br

Excitation functions of the reactions ^natSe(p,x)^75,76,77,82Br, ⁷⁶Se(p,xn)^75,76Br, ⁷⁶Se(p,x)⁷⁵Se and ⁷⁷Se(p,xn)^76,77Br were measured from their respective thresholds up to 40 MeV, with particular emphasis on data for the production of the medically important radionuclides ⁷⁶Br and ⁷⁷Br. The conventional stacked-foil technique was used. The samples were prepared by a sedimentation process. Irradiations were performed using the compact cyclotron CV 28 and the injector of COSY, both at the Research Centre Jülich. In order to validate the data, nuclear model calculations were performed using the code ALICE-IPPE which is based on the preequilibrium-evaporation model. Good agreement was found between the experimental and theoretical data, except in the high-energy region where the calculated data were somewhat higher. All the measured excitation curves were compared with the data available in the literature. From the experimental data the theoretical yields of all the investigated radionuclides were calculated and plotted as a function of proton energy. The calculated yield of ⁷⁷Br from the ^natSe(p,x)⁷⁷Br process over the energy range E_p=25→15 is 72.7 MBq/μA h and from the ⁷⁷Se(p,n)⁷⁷Br reaction over E_p=15→6 MeV it is 86.2 MBq/μA h. The yield of ⁷⁶Br from the ⁷⁶Se(p,n)⁷⁶Br reaction for E_p=15→8 is 360.1 MBq/μA h and from the ⁷⁷Se(p,2n)⁷⁶Br reaction for E_p=28→18 MeV it is 879.2 MBq/μA h. The radionuclidic impurity levels are discussed.     

Purification and activity standardisation of a Ho solution

As part of a project to use the long-lived (T_1/2=1200a) ^166mHo as reference source in its reference ionisation chamber, IRA standardised a commercially acquired solution of this nuclide using the 4πβ–γ coincidence and 4πγ (NaI) methods. The ^166mHo solution supplied by Isotope Product Laboratories was measured to have about 5% Europium impurities (3% ¹⁵⁴Eu, 0.94% ¹⁵²Eu and 0.9% ¹⁵⁵Eu). Holmium had therefore to be separated from europium, and this was carried out by means of ion-exchange chromatography. The holmium fractions were collected without europium contamination: 162 h long HPGe gamma measurements indicated no europium impurity (detection limits of 0.01% for ¹⁵²Eu and ¹⁵⁴Eu, and 0.03% for ¹⁵⁵Eu). The primary measurement of the purified ^166mHo solution with the 4π (PC) β–γ coincidence technique was carried out at three gamma energy settings: a window around the 184.4 keV peak and gamma thresholds at 121.8 and 637.3 keV. The results show very good self-consistency, and the activity concentration of the solution was evaluated to be 45.640±0.098 kBq/g (0.21% with k=1). The activity concentration of this solution was also measured by integral counting with a well-type 5″×5″ NaI(Tl) detector and efficiencies computed by Monte Carlo simulations using the GEANT code. These measurements were mutually consistent, while the resulting weighted average of the 4π NaI(Tl) method was found to agree within 0.15% with the result of the 4πβ–γ coincidence technique. An ampoule of this solution and the measured value of the concentration were submitted to the BIPM as a contribution to the Système International de Référence.     

Preparation and evaluation of para-[At]astatobenzoyl labeled anti-renal cell carcinoma antibody A6H F(ab′)2. In vivo distribution comparison with para-[I]iodobenzoyl labeled A6H F(ab′)2

A preliminary investigation of an ²¹¹At labeled anti-renal cell carcinoma antibody fragment, A6H F(ab′)₂, was conducted. In the investigation, A6H F(ab′)₂ was labeled by conjugation with N-succinimidyl p-[²¹¹At]astatobenzoate, and the in vivo biodistribution was evaluated in athymic mice bearing TK-82 renal cell carcinoma xenografts. As a control, p-[¹²⁵I]iodobenzoyl labeled A6H F(ab′)₂ was coinjected with the astatinated F(ab′)₂. The data obtained demonstrated that the two radiolabels (²¹¹At and ¹²⁵I) had quite similar distributions, providing evidence that the ²¹¹At remained attached to the A6H F(ab′)₂ in vivo. Further, the astatinated antibody attained a 2:1 tumor-to-blood ratio, and greater than 35:1 tumor-to-muscle ratio, at 4 h post-injection, suggesting that this antibody conjugate could be used to evaluate treatment of metastatic renal cell carcinoma in a mouse model.