Accurate determination of 129I concentrations and 129I/137Cs ratios in spent nuclear resins by Accelerator Mass Spectrometry

Determining long-lived radionuclide concentrations in radioactive waste has fundamental implications for the long-term management of storage sites. This paper focuses on the measurement of low ¹²⁹I contents in ion exchange resins used for primary fluid purification in Pressurised Water Reactors (PWR). Iodine-129 concentrations were successfully determined using Accelerator Mass Spectrometry (AMS) following a chemical procedure which included (1) acid digestion of resin samples in HNO₃/HClO₄, (2) radioactive decontamination by selective iodine extraction using a new chromatographic resin (CL Resin), and (3) AgI precipitation. Measured ¹²⁹I concentrations ranged from 4 to 12 ng/g, i.e. from 0.03 to 0.08 Bq/g. The calculation of ¹²⁹I/¹³⁷Cs activity ratios used for routine waste management produced values in agreement with the few available data for PWR resin samples.     

核医学场所空气中131I浓度监测及工作人员内照射剂量评价探讨

目的 了解医疗机构¹³¹I治疗工作场所空气中¹³¹I核素的活度浓度水平，探讨通过空气采样方法估算工作人员内照射剂量的方法并分析其影响因素。方法 选取郑州市10家开展¹³¹I核素治疗的工作场所，采用空气采样方法采集¹³¹I治疗工作场所中放射性气溶胶，用高纯锗γ能谱仪进行γ放射性核素测定并推算工作场所空气中¹³¹I核素的活度浓度水平，根据测量结果和现场调查结果估算放射工作人员因¹³¹I核素吸入导致的内照射剂量。结果 19个分装间空气样品的¹³¹I活度浓度为0.087~570 Bq/m³，平均为（51.04±128.58）Bq/m³；11个病房空气样品的¹³¹I活度浓度为0.162~54.6 Bq/m³，平均为（7.97±15.89）Bq/m³。根据GBZ 129-2016《职业性内照射个人监测规范》推荐的典型工作时间估算，放射工作人员由于吸入¹³¹I核素导致的年待积有效剂量范围为2 μSv~10 mSv，平均为（0.61±1.80）mSv，年有效剂量均未超过国家标准所规定的剂量限值。结论 郑州市10家医疗机构核医学工作场所中¹³¹I核素活度浓度较高的样品多分布在甲状腺癌住院患者较多、核素操作量较大的三甲医院，由此导致的工作人员内照射剂量不容忽视。根据空气样品的测量结果估算内照射剂量带有很大不确定度，但空气采样方法可及时发现异常或事故情况下的放射性污染，为工作人员开展体外直接测量和内照射评价提供预警。     

云南芒市地区野生食用蘑菇中137Cs、40K含量及所致居民剂量估算

目的 检测可食用野生蘑菇中人工放射性核素¹³⁷Cs和天然放射性核素⁴⁰K的含量及分布特点,计算野生蘑菇中放射性核素水平及其所致剂量。方法 采集了产自云南省芒市的18类33份可食用野生蘑菇样品,用实验室低本底高纯锗（HPGe）γ谱仪分析了其中放射性核素¹³⁷Cs、⁴⁰K的含量。结果 33份样品中,仅1份样品¹³⁷Cs的含量在探测限之下,其余32份样品中均可检测出¹³⁷Cs,比活度范围值为0.45~339.58 Bq/kg（干重）,平均值25.47 Bq/kg（干重）。所有样品均检测出天然放射性核素⁴⁰K,核素比活度最小值和最大值分别为453.4、1 882.6 Bq/kg（干重）,平均值为815.1 Bq/kg（干重）。当去除只有1个样品数的蘑菇种类后,毛钉菇、美味牛肝菌、白牛肝菌、锈盖粉孢牛肝菌、香菇、茶褐牛肝菌6个种类蘑菇间¹³⁷Cs含量差异有统计学意义（F=21.13,P<0.05）,而⁴⁰K含量差异无统计学意义。结论 6类不同蘑菇中¹³⁷Cs含量不同,其中毛钉菇、香菇中人工放射性核素¹³⁷Cs含量相对较高。但食入此类蘑菇对成人所致待积有效剂量极其微小,不会影响健康。     

Targeting murine heart and brain: visualisation conditions for multi-pinhole SPECT with <Superscript>99m</Superscript>Tc- and <Superscript>123</Superscript>I-labelled probes

Purpose  The study serves to optimise conditions for multi-pinhole SPECT small animal imaging of ¹²³I- and ^99mTc-labelled radiopharmaceuticals with different distributions in murine heart and brain and to investigate detection and dose range thresholds for verification of differences in tracer uptake. Methods  A Triad 88/Trionix system with three 6-pinhole collimators was used for investigation of dose requirements for imaging of the dopamine D₂ receptor ligand [¹²³I]IBZM and the cerebral perfusion tracer [^99mTc]HMPAO (1.2–0.4 MBq/g body weight) in healthy mice. The fatty acid [¹²³I]IPPA (0.94 ± 0.05 MBq/g body weight) and the perfusion tracer [^99mTc]sestamibi (3.8 ± 0.45 MBq/g body weight) were applied to cardiomyopathic mice overexpressing the prostaglandin EP₃ receptor. Results  In vivo imaging and in vitro data revealed 45 kBq total cerebral uptake and 201 kBq cardiac uptake as thresholds for visualisation of striatal [¹²³I]IBZM and of cardiac [^99mTc]sestamibi using 100 and 150 s acquisition time, respectively. Alterations of maximal cerebral uptake of [¹²³I]IBZM by >20% (116 kBq) were verified with the prerequisite of 50% striatal of total uptake. The labelling with [^99mTc]sestamibi revealed a 30% lower uptake in cardiomyopathic hearts compared to wild types. [¹²³I]IPPA uptake could be visualised at activity doses of 0.8 MBq/g body weight. Conclusion  Multi-pinhole SPECT enables detection of alterations of the cerebral uptake of ¹²³I- and ^99mTc-labelled tracers in an appropriate dose range in murine models targeting physiological processes in brain and heart. The thresholds of detection for differences in the tracer uptake determined under the conditions of our experiments well reflect distinctions in molar activity and uptake characteristics of the tracers. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Comparison of two full automatic synthesis methods of 9-(4-[F]fluoro-3-hydroxymethylbutyl)guanine using different chemistry modules

We have developed synthesis methods for 9-(4-[¹⁸F]fluoro-3-hydroxymethylbutyl)guanine ([¹⁸F]FHBG) using two commercial automatic chemistry modules, Tracerlab MX and Explora RN, and compared radiochemical yields. Synthesis conditions and sequence programs were modified for two modules because both these modules have different mechanical structures, including heater type, vacuum system, reactor, and tubing size. Synthesis using the Tracerlab MX module showed a 21.0±3.8% yield of radiochemical, which was 98±0.9% pure; the total preparation time was 63.0±5.0 min including an HPLC purification step. In contrast, synthesis using the Explora RN module showed a 32.0±1.2% yield of radiochemical, which was 99.0±0.6% pure; the total preparation time was 38±2 min, using different HPLC purification conditions and without the HPLC solvent evaporation step.     

6家医院碘治疗场所工作人员甲状腺131I活度测量

目的调查碘治疗场所工作人员甲状腺131I活度水平及其主要影响因素。方法采用配额抽样的方法, 按照碘治疗场所医院的不同类型, 在山西省和山东省共选择6家开展碘治疗的医院, 采用直接测量法, 对76名碘治疗场所工作人员的甲状腺131I活度进行了测量, 并进行内照射剂量估算。结果共有5家医院的29人甲状腺131I活度高于仪器的探测限, 占全部被检测人员的38.16%, 其中最高值为2 468.45 Bq, 是1名负责手动分装放射性碘的医师。6家医院碘治疗场所工作人员甲状腺131I活度差异无统计学意义(P>0.05), 但手动分装131I的医院测量结果高于自动分装的医院, 差异有统计学意义(Z=1.75, P<0.01), 两家手动分装131I医院的12名碘治疗场所工作人员甲状腺测量结果全部高于探测限, 中位数分别为324.59 Bq和331.98 Bq, 4家使用自动分装仪的医院测量结果的中位数均低于探测限, 甲状腺131I检出率分别为32.61%、25.00%、10.00%和0。对于同一家医院, 参与分装131I的医生和保洁人员甲状腺131I活度高于不参与分装的医生, 差异有统...     

High-Dose 111In Induces G1 Cell Cycle Arrest and Cell Death in Rat Bone Marrow Mesenchymal Stem Cells

Purpose

This study was performed to evaluate the effect of ¹¹¹In-labeling on the cell growth, cycle and viability of bone marrow mesenchymal stem cells (BMSCs).

Methods

Rat BMSCs were labeled with various doses of ¹¹¹In (0.4–11.1 Bq/cell). The growth curve of ¹¹¹In-BMSCs was obtained up to 14th day of labeling. The cell cycle was evaluated by 5-bromo-2-deoxyuridine (BrdU) labeling or propidium iodide (PI) staining. Senescent cells were counted under a light microscope after staining with 5-bromo-4-chloro-3-indolyl-D-galactopyranoside. Flow cytometry was performed to measure apoptotic and necrotic fractions after staining with annexin V-FITC and PI.

Results

The growth of BMSCs labeled with higher doses of ¹¹¹In (4.4 or 11.1 Bq/cell) was significantly inhibited from the 3rd day of labeling. Flow cytometry revealed less BrdU-positive BMSCs at 11.1 Bq ¹¹¹In/cell during all measurement days and G1 arrest at 4.4 and 11.1 Bq ¹¹¹In/cell. Significant increases in apoptosis and necrosis were also observed at 4.4 (3.04%/1.35%) and 11.1 Bq ¹¹¹In/cell (9.07%/3.18%) on the 14th day (control = 1.60%/0.39%). However, no cellular senescence was visualized up to the 14th day.

Conclusion

A high dose of ¹¹¹In-labeling induced cell cycle arrest and death in BMSCs; therefore, it should be used with a careful dosimetry in case of applying it to humans.     

应对福岛核事故我国食品和饮用水的放射性监测

目的 汇总分析日本福岛核电站事故发生后我国沿海城市和主要内陆城市食品和饮用水放射性的抽样监测结果,评价是否对我国居民的健康造成影响.方法 根据国家标准方法,制定应对日本福岛核事故对我国食品和饮用水的监测方案,统一数据报送格式,对数据进行对比分析.结果 4月2日北京露天生长菠菜样品中,监测到极微量的人工放射性核素131I,此后在全国范围内10种露天生长的蔬菜中也检测出131I,最高值为菠菜样品3.1 Bq/kg,到5月初未再检测出.牛奶、海产品和饮用水样品中未检测到人工放射性核素.结论 监测到的蔬菜中131I来自日本福岛核电站事故释放,与此次事故期间欧洲一些国家食品中的的131I水平相一致,远低于1986年切尔诺贝利核电站事故时我国蔬菜中131I活度,其对公众所致吸收剂量极其微小,不会对我国境内公众造成影响.     

Dosimetric characterization of a newly designed encapsulated interstitial brachytherapy source of iodine-125—model LS-1 BrachyseedTM

A newly designed encapsulated ¹²⁵I source has been introduced (Model LS-1 BrachySeed^TM manufactured by DRAXIMAGE Inc.) for interstitial brachytherapy . In this source ¹²⁵I radionuclide is contained in two ceramic beads positioned at each end of a titanium capsule. The source contains a rod of Pt–Ir, which serves as a radiographic marker for source localization in the patient. Principle photon emissions are 27.4 and 31.0 keV X-rays and a 35.5 keV gamma-ray. The 22.2 and 25.5 keV silver X-rays produced by fluorescence of the silver dopant in the ceramic bead radioisotope carriers, are also emitted. In this work, the dosimetric characteristics of the ¹²⁵I source were measured with micro LiF TLD chips and dosimetry parameters were characterized based upon the American Association of Physicists in Medicine, Task Group, No. 43 formalism. The corrected 1999 National Institute of Standards and Technology standard for low energy interstitial brachytherapy sources was used to specify the air kerma strength of the sources used in this study. The dose rate constant of the sources was determined to be 1.02±0.07 cGyh⁻¹ U⁻¹. The radial dose function was measured and was found to be similar to that of the silver-based model 6711 ¹²⁵I source. However, the anisotropy function of the Model LS-1 BrachySeed^TM source is considerably better than that of model 6711 ¹²⁵I source, especially on the points along and close to the longitudinal axis of the source. The BrachySeed^TM model LS-1 provides more isotropic angular dose distribution in tissue than model 6711 ¹²⁵I source. The anisotropy constant for the model LS-1 source was determined to be 1.006, which is considerably better than the value of 0.93 for the model 6711 source.     

Preparation and bioevaluation of a Tc-labeled chlorambucil analog as a tumor targeting agent

Chlorambucil belongs to a group of nitrogen mustards which are used for the treatment of variety of cancers. Hence, a chlorambucil derivative has been radiolabeled with [^99mTc(CO)₃(H₂O)₃]⁺ core and its efficacy as a tumor targeting agent has been evaluated. Radiochemical yield of the complex was >98% as observed by HPLC. The in vitro studies in MCF-7 breast cancer cells showed about 30% inhibition of the radiolabeled complex in presence of the cold chlorambucil derivative. Biodistribution studies in Swiss mice bearing fibrosarcoma tumor showed an uptake of 3.2±0.3% ID/g at 3 h.p.i.     

2013—2017年宁德核电站周围食品中90Sr放射性水平调查

目的 了解宁德核电站运行后核电站周围监测点区域内放射性核素⁹⁰Sr放射性水平,并与其对照区域⁹⁰Sr放射性水平进行比较。方法 在宁德核电站周边30 km范围内的监测点区域及其对照点区域进行布点,采集食品样品,利用二-（2-乙基已基）磷酸脂萃取色层法对食品样品中⁹⁰Sr放射性水平进行分析。结果 本次调查共完成宁德核电站周围监测区域及对照区域的6大类,30个品种的食品样品中⁹⁰Sr放射性水平的分析。监测区域内,谷类薯类及杂豆类样品中⁹⁰Sr的放射性比活度范围为0.017~1.830 Bq/kg,蔬菜类样品为0.021~0.318 Bq/kg,水产品类样品为0.007~7.690 Bq/kg,畜禽肉类样品为0.009~0.184 Bq/kg。对照区域内,谷类薯类及杂豆类样品中⁹⁰Sr含量测量范围为0.017~0.700 Bq/kg,蔬菜类为0.034~0.677 Bq/kg,水产品类为0.038~3.360 Bq/kg,畜禽肉类为0.019~0.054 Bq/kg。结论 本次调查的食品中⁹⁰Sr放射性水平均远低于我国食品标准限值,食入所致的居民内照射剂量对公众剂量的贡献极低。     

Automated synthesis of n.c.a. [F]FDOPA via nucleophilic aromatic substitution with [F]fluoride

An improved, automated synthesis of [¹⁸F]FDOPA including four synthetic steps (fluorination, reductive iodination, alkylation and hydrolysis) is reported with each step optimized individually. In a home-made automatic synthesizer, 9064±3076 MBq of [¹⁸F]FDOPA were produced within 120 min from EOB (n=5). Radiochemical purity and enantiomeric excess were both 95%. Specific activity was ca. 50 GBq/μmol at EOS. This automatically operable synthesis is well suited for the multi-patient-dose routine production of n.c.a. [¹⁸F]FDOPA.     

化疗联合125I粒子治疗不能手术的肺上沟癌的疗效分析

目的 探讨应用放射治疗计划系统（TPS）在CT引导下经皮穿刺种植放射性¹²⁵I粒子近距离联合化疗治疗肺上沟癌的疗效分析。方法 回顾性分析2002年12月至2010年12月本院收治的影像及病理证实为肺上沟癌的患者36例,其中鳞癌26例,腺癌10例。粒子植入后1周行化疗,具体方案为第1、8天静脉给予1 000 mg/m²吉西他滨,第1天静脉给予顺铂75 mg/m²,连续4个周期。¹²⁵I粒子在化疗间期植入,中位粒子数43,处方剂量（prescribed dose,PD）120 Gy,粒子中位活度0.7 mCi （2.59×10⁷ Bq）,范围0.68~0.82 mCi （2.52×10⁷~3.03×10⁷ Bq）。患者中位随访时间48个月,观察生存率。结果 靶区瘤体周围处方剂量mPD （118.7±7.2）Gy,D₉₀（126±4.7）Gy,D₉₀> mPD。术后6个月胸部CT显示,完全缓解（CR）11例,占30.6%;部分缓解（PR）19例,占52.8%;疾病稳定（SD）5例,占13.9%;疾病进展（PD）1例,占2.8%;总有效率（CR＋PR）为83.4%,共30例。1、3、5年的局部控制率分别为92%、83%和67%,中位局部控制时间56.8个月。1、3、5年累计生存率分别为84.1%、56.7%和36.8%,中位生存期38个月。结论 化疗联合组织间近距离¹²⁵I粒子植入是一种微创有效的治疗肺上沟癌的方法。     

碘治疗工作人员甲状腺131I活度的测量与评价

目的 了解核医学科碘治疗工作人员甲状腺内¹³¹I的活度,并估算年待积有效剂量,分析碘治疗人员的内照射现状。方法 选择甲状腺内照射碘测量仪,对山东省6家医院进行调查并进行甲状腺¹³¹I活度测量,得出6家医院核医学科碘治疗工作人员甲状腺¹³¹I的检出率和活度值,进而计算摄入量和年待积有效剂量。结果 6家医院共有63名碘治疗工作人员接受测量,其中有52人甲状腺内检测到¹³¹I,检出率83%,测得¹³¹I活度大多低于200 Bq。估算的年待积有效剂量范围为0.23~7.78 mSv,其中有84.6％的人年待积有效剂量＜2 mSv。结论 核医学科碘治疗工作人员应进行常规内照射个人监测,各医院在辐射防护制度方面需进一步完善。     

甘肃陇东地区室内222Rn、220Rn浓度季节变化的调查分析

目的 研究我国传统住房室内222Rn、220Rn随季节变化的规律.方法 选择甘肃省陇东地区5种不同类型的传统建筑44间及普通砖瓦房5间.采用LD-P型222Rn-220Rn分辨累积探测器,按冬、春、夏、秋4个季节对室内222Rn、220Rn浓度进行测量.结果 室内222Rn浓度随季节变化而变化,不同种类房屋变化规律不同...     

Assessment of 18F-labeled mitochondrial complex I inhibitors as PET myocardial perfusion imaging agents in rats, rabbits, and primates

Purpose  Myocardial extractions of mitochondria complex I (MC-I) inhibitors were high and well correlated with flow. This study assessed the potential of MC-I inhibitors to be developed as myocardial perfusion imaging (MPI) agents. Methods  RP1003, RP1004, and RP1005 representing three classes of MC-I inhibitor were synthesized and radio-labeled with ¹⁸F. These agents were evaluated for IC₅₀ values, tissue biodistribution, and cardiac PET imaging. ¹⁸F-RP1004 was further examined for first-pass extraction and by imaging in non-human primates (NHP) and rats following coronary ligation. Results  RP1003, RP1004, and RP1005 exhibited high MC-I inhibitory activity with IC₅₀ of 3.7, 16.7, and 14.4 nM. Heart uptakes in rats (percent injected dose per gram tissue) at 15 and 60 min after injection were 3.52 ± 0.36 and 2.68 ± 0.20 for ¹⁸F-RP1003, 2.40 ± 0.21 and 2.67 ± 0.27 for ¹⁸F-RP1004, and 2.28 ± 0.12 and 1.81 ± 0.17 for ¹⁸F-RP1005. The heart to lung and liver uptake ratios were favorable for cardiac imaging with these agents. In isolated perfused rabbit hearts, the uptake of ¹⁸F-RP1004 increased from 0.74 ± 0.19 to 1.68 ± 0.39 mL/min/g at flow rates of 1.66 to 5.06 mL/min/g. These values were higher than or similar to that of ^99mTc-sestamibi. Cardiac imaging with these agents in rats and rabbits allowed visualization of the heart with minimal lung interference and rapid liver activity clearance. Imaging with ¹⁸F-RP1004 also showed clear myocardium and marked liver activity washout in the NHP and clear detection of the perfusion-deficit area associated with left coronary artery ligation in the rat. Conclusion  MC-I inhibitors have the potential to be a new class of MPI agent.     

2012—2020年杭州市区水中90Sr和137Cs放射性水平调查

目的调查分析杭州市区水中90Sr和137Cs放射性水平和来源。方法 2012—2020年, 选取杭州市区3个水质监测点:钱塘江水(杭州市重要饮用水源)、末梢水(居民直接饮用水)、西湖水(游客密集区域, 水体每月与钱塘江水交换1次), 分别在丰水期和枯水期采集水样并用放射化学法测定样品中90Sr和137Cs的活度浓度, 根据137Cs和90Sr活度浓度获得活度比(137Cs /90Sr)。结果 2012—2020年, 末梢水中90Sr和137Cs的活度浓度范围分别为(2.0±1.1)～(7.4±0.4)mBq/L, (0.45±0.06)～(7.1±0.6)mBq/L, 137Cs /90Sr活度比值范围为0.07 ～ 2.40;钱塘江水中90Sr和137Cs的活度浓度范围分别为(3.7±1.1)～(17.0±4.4)mBq/L, (0.28±0.01)～(15.0±4.5)mBq/L, 137Cs/90Sr活度比值范围为0.03 ～ 0.90;西湖水中90Sr和137Cs的活度浓度范围分别为(2.2±0.5)～(11.0±2.0)mBq/L, (0.32±0.04)～(7.9±1.9)...     

Evaluation of 64Cu-labeled DOTA-d-Phe1-Tyr3-octreotide (64Cu-DOTA-TOC) for imaging somatostatin receptor-expressing tumors

Objective  In-111 (¹¹¹In)-labeled octreotide has been clinically used for imaging somatostatin receptor-positive tumors, and radiolabeled octreotide analogs for positron emission tomography (PET) have been developed. Cu-64 (⁶⁴Cu; half-life, 12.7 h) is an attractive radionuclide for PET imaging and is produced with high specific activity using a small biomedical cyclotron. The aim of this study is to produce and fundamentally examine a ⁶⁴Cu-labeled octreotide analog, ⁶⁴Cu-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-d-Phe¹-Tyr³-octreotide (⁶⁴Cu-DOTA-TOC). Methods   ⁶⁴Cu produced using a biomedical cyclotron was reacted with DOTA-TOC for 30 min at 45°C. The stability of ⁶⁴Cu-DOTA-TOC was evaluated in vitro (incubated with serum) and in vivo (blood collected after administration) by HPLC analysis. Biodistribution studies were performed in normal mice by administration of mixed solution of ⁶⁴Cu-DOTA-TOC and ¹¹¹In-DOTA-TOC and somatostatin receptor-positive U87MG tumor-bearing mice by administration of ⁶⁴Cu-DOTA-TOC or ⁶⁴Cu-1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraacetic acid-octreotide (⁶⁴Cu-TETA-OC). The tumor was imaged using ⁶⁴Cu-DOTA-TOC, ⁶⁴Cu-TETA-OC, and FDG with an animal PET scanner. Results   ⁶⁴Cu-DOTA-TOC can be produced in amounts sufficient for clinical study with high radiochemical yield. ⁶⁴Cu-DOTA-TOC was stable in vitro, but time-dependent transchelation to protein was observed after injection into mice. In biodistribution studies, the radioactivity of ⁶⁴Cu was higher than that of ¹¹¹In in all organs except kidney. In tumor-bearing mice, ⁶⁴Cu-DOTA-TOC showed a high accumulation in the tumor, and the tumor-to-blood ratio reached as high as 8.81 ± 1.17 at 6 h after administration. ⁶⁴Cu-DOTA-TOC showed significantly higher accumulation in the tumor than ⁶⁴Cu-TETA-OC. ⁶⁴Cu-DOTA-TOC PET showed a very clear image of the tumor, which was comparable to that of ¹⁸F-FDG PET and very similar to that of ⁶⁴Cu-TETA-OC. Conclusions   ⁶⁴Cu-DOTA-TOC clearly imaged a somatostatin receptor-positive tumor and seemed to be a potential PET tracer in the clinical phase.     

Dose estimates for the local inhabitants from 210Po ingestion via dietary sources at a proposed uranium mining site in India

Abstract

Purpose: To study the distribution of ²¹⁰Po activity in food in Bagjata in East Singhbhum, India.

Materials and methods: ²¹⁰Po were analyzed in the food samples of plant origin such as cereals, pulses, fruits, vegetables and food of animal origin such fish, chicken, egg, etc., in and around Bagjata uranium mining area as a part of baseline study after acid digestion. The intake and ingestion dose of the radionuclide was estimated.

Results: The general range of ²¹⁰Po activity in all the dietary components ranged widely from <0.2–36 Bqkg^-1_fresh. In the food of plant origin, the minimum activity of ²¹⁰Po was estimated in vegetables while maximum in pulses. In food of animal origin, the observed minimum activity of ²¹⁰Po was in eggs and the maximum observed was in chicken samples. The intake of ²¹⁰Po considering all dietary components was found to be 464 Bq.Y^-1 while the ingestion dose was calculated to be 557 μSv.Y^-1, respectively. The estimated doses are reflecting the natural background dose via the route of ingestion, which is much below the 1 mSv limit set in the International Commission on Radiological Protection (ICRP) recommendations.

Conclusion: The study confirms that current levels of ²¹⁰Po do not pose a significant radiological risk to the local inhabitants.     

Effect of cyclosporin A administration on the biodistribution and multipinhole μSPECT imaging of [<Superscript>123</Superscript>I]R91150 in rodent brain

Purpose  P-glycoprotein (Pgp) is an efflux protein found amongst other locations in the blood–brain barrier. It is important to investigate the effect of Pgp modulation on clinically used brain tracers, because brain uptake of the tracer can be altered by blocking of the Pgp efflux transporter. The function of Pgp can be blocked with cyclosporin A. Methods  We investigated the effect of cyclosporin A administration on the biodistribution of [¹²³I]R91150 in rodents, and the effect of Pgp blocking on the quality of multipinhole μSPECT imaging with [¹²³I]R91150. The influence of increasing doses of cyclosporin A on the brain uptake of [¹²³I]R91150 was investigated in NMRI mice. A biodistribution study with [¹²³I]R91150 was performed in male Sprague-Dawley rats pretreated with cyclosporin A and not pretreated. Brain uptake of [¹²³I]R91150 after cyclosporin A injection was compared to the brain uptake in untreated animals, and a displacement study with ketanserin was performed in both groups. A multipinhole μSPECT brain imaging study was also performed using a Milabs U-SPECT-II camera in male Sprague-Dawley rats. To exclude the effect of possible metabolites, a metabolite study was also performed. Results  At the highest cyclosporin A dose (50 mg/kg), a sevenfold increase in brain radioactivity concentration was observed in NMRI mice. Also, a dose-response relationship was established between the dose of cyclosporin A and the brain uptake of [¹²³I]R91150 in mice. Compared to the control group, a five-fold increase in [¹²³I]R91150 radioactivity concentration was observed in the brain of Sprague-Dawley rats after cyclosporin A treatment (50 mg/kg). Radioactivity concentration in the frontal cortex increased from 0.24±0.0092 to 1.58±0.097% injected dose per gram of tissue after treatment with cyclosporin A (at the 1-h time-point). Blood radioactivity concentrations did not increase to the same extent. The cortical activity was displaced by administration of ketanserin. A metabolite study confirmed that there was no increased metabolism of [¹²³I]R91150 due to cyclosporin A. The visual quality of multipinhole μSPECT images with [¹²³I]R91150 in Sprague-Dawley rats improved markedly after cyclosporin A pretreatment. Conclusion  From the results obtained in the biodistribution studies, it can be concluded that [¹²³I]R91150 is a substrate for Pgp in rodents. A relationship between the administered dose of cyclosporin A and the increase in [¹²³I]R91150 brain radioactivity concentration was established. The overall quality of our multipinhole μSPECT images with [¹²³I]R91150 in rats improved markedly after pretreatment of the animals with cyclosporin A.