Activity standardization of 60Co and 106Ru/106Rh by means of the TDCR method and the importance of the beta spectrum.

Atomic and nuclear data represent an important input for the accuracy of primary activity measurements based on liquid scintillation. In particular, the reliability of ß-spectrum computation has been investigated for several years through experimental and theoretical studies providing solid evidence for the need to consider the atomic effects. In the present study, the activity standardization of two ß-emitting radionuclides (60Co, 106Ru/106Rh) was carried out by means of the 4πß-γ coincidence and Triple-to-Double Coincidence Ratio (TDCR) methods. The comparison between the activity concentrations given by both primary techniques presents new evidence that a better agreement is obtained when the exchange and screening effects are included in the ß-spectra implemented in the model of light emission for TDCR measurements. A new development of a stochastic model based on Geant4 simulations for TDCR calculations is also presented.

Measurement of the absolute gamma-ray emission intensities from the decay of 147Nd.

The 2011 Decay Data Evaluation Project (DDEP) evaluation for 147Nd includes recommended absolute emission intensities for the two main gamma-rays at 91.105 (2) keV and 531.016 (22) keV of 0.284 (18) and 0.127 (9) respectively, i.e. with uncertainties of 6.3% and 7.1%. These large uncertainties stem from inconsistencies in the published data and are unfit for modern purposes, since the production of 147Nd is used as an important neutron flux dosimeter. The LNE-LNHB has undertaken new absolute gamma-ray emission intensity measurements. The results of these measurements will be presented, along with a full uncertainty budget, and their effect on the recommended data uncertainties will be discussed.

Spectral unmixing applied to fast identification of γ-emitting radionuclides using NaI(Tl) detectors.

Spectral unmixing was investigated for fast spectroscopic identification in γ-emitter mixtures at low-statistics in the case of measurements performed to prevent illegal nuclear material trafficking or for in situ environmental analysis following a radiological or nuclear accident. For that purpose, a multiplicative update algorithm based on full-spectrum analysis was tested in the case of a 3″x3″ NaI(Tl) detector. Automatic decision-making was addressed using Monte Carlo calculations of decision thresholds and detection limits. The first results obtained with a portable instrument equipped with a 3″x3″ NaI(Tl) detector designed for the control of food samples by non-expert users following a radiological or nuclear accident, are also presented.

Sparse spectral unmixing for activity estimation in γ-RAY spectrometry applied to environmental measurements.

This paper presents a sparse spectral unmixing algorithm for activity estimation of radionuclides in γ-ray spectrometry. The spectral unmixing method aims to decompose a measured spectrum into spectral signatures of radionuclides, which is sensitive to the choice of the spectral signatures. The sparsity of the solution is imposed to identify the active radionuclides. Experimental results on simulated and real spectra show that the proposed method yields significant improvement for estimating radioactivity at low statistics.

Nuclide++: A C++ module to include DDEP recommended radioactive decay Data in Geant4.

This article describes the Nuclide++ module developed at LNE-LNHB to simulate the decay schemes related to single or multiple radionuclides, by randomly selecting decay pathways. Written in C++, with respect of the Geant4 coding style, this module can be used transparently in Geant4-based simulation applications as an alternative to the existing Radioactive Decay Module (RDM). Nuclide++ takes advantage of the DDEP recommended data, accurate ß-emitting spectra calculation and detailed description of the atomic rearrangement. This module can be useful in many applications, especially those involving radioactive sources. The reliability of the module was verified through comparisons with a while chosen radionuclides.

Activity measurements and determination of nuclear decay data of 166Ho in the MRTDosimetry project.

Holmium-166 is a high-energy ß--emitter radionuclide (~ 1.8 MeV) with a short half-life (~26.8h) that offers great potential as an alternative to 90Y for the treatment of liver cancer based on radioembolization. The possibility of quantitative Single Photon Emission Computed Tomography (SPECT) imaging of the main γ-ray emission at 80.6 keV, in addition to strong paramagnetic properties suitable for Magnetic Resonance Imaging (MRI), complement this therapeutic potential. The present paper describes the measurements carried out in three European radionuclide metrology laboratories for primary standardization of 166Ho and new determinations of X- and γ-ray photon-emission intensities in the framework of the European EMPIR project MRTDosimetry. New half-life measurements were also performed.

Prognostic factors for parotid metastasis of cutaneous squamous cell carcinoma of the head and neck.

BACKGROUND: Cutaneous squamous cell carcinoma (CSCC) develops on the head in 80% of cases. Parotid metastasis (PM) is rare, but treatment, which associates surgery and radiation therapy, is heavy and prognosis poor. MATERIAL AND METHODS: All cases of parotidectomy for PM of CSCC of the head and neck between 2005 and 2015 were studied retrospectively. Epidemiologic, oncologic and therapeutic data were analyzed. Overall and specific survival were calculated following Kaplan-Meier. Log-rank and Cox models were used to identify prognostic factors for PM. OBJECTIVES: The principal study objective was to identify factors for survival in PM from CSCC of the head and neck. RESULTS: Thirty-five patients were included. Mean time to onset of PM was 13months. Overall 1-, 2- and 5-year survival was respectively 70, 66 and 59%. Independent prognostic factors comprised immunodepression, age at treatment, positive CSCC margins, macroscopic facial nerve involvement, and metastatic cervical adenopathies. CONCLUSION: The study confirmed an association of several independent prognostic factors at the stage of parotid lymph-node metastasis, related to patient, primary CSCC and PM. Complete primary resection is essential to reduce the risk of PM. Intensified radiologic and clinical surveillance should enable early diagnosis.

Results of an international comparison of activity measurements of 68Ge.

An international key comparison, identifier CCRI(II)-K2.Ge-68, has been performed. The National Institute of Standards and Technology (NIST) served as the pilot laboratory, distributing aliquots of a 68Ge/68Ga solution. Results for the activity concentration, CA, of 68Ge at a reference date of 12h00 UTC 14 November 2014 were submitted by 17 laboratories, encompassing many variants of coincidence methods and liquid-scintillation counting methods. The first use of 4π(Cherenkov)ß-γ coincidence and anticoincidence methods in an international comparison is reported. One participant reported results by secondary methods only. Two results, both utilizing pure liquid-scintillation methods, were identified as outliers. Evaluation using the Power-Moderated Mean method results in a proposed Comparison Reference Value (CRV) of 621.7(11)kBqg-1, based on 14 results. The degrees of equivalence and their associated uncertainties are evaluated for each participant. Several participants submitted 3.6mL ampoules to the BIPM to link the comparison to the International Reference System (SIR) which may lead to the evaluation of a Key Comparison Reference Value and associated degrees of equivalence.

Standardization of 68Ge/68Ga using the 4πß-γ coincidence method based on Cherenkov counting.

In the framework of an international BIPM comparison (Bureau International des Poids et Mesures), the activity standardization of 68Ge in a solution of 68Ge/68Ga in equilibrium provided by NIST was carried out at LNHB. This exercise was organized to meet the growing interest in 68Ga as a radiopharmaceutical in nuclear medicine services (e.g. as a surrogate of 18F for PET imaging). Due to the volatility of germanium, the activity standardization of 68Ge was investigated at LNHB by means of 4πß-γ coincidence counting based on Cherenkov measurements. This technique was applied to take advantage of the Cherenkov threshold (~ 260keV in aqueous solutions) in order to prevent counting from electron-capture events associated with 68Ge disintegrations. Cherenkov counting was performed using glass and polyethylene vials and the resulting activity concentrations were compared with 4πß-γ coincidence measurements based on liquid scintillation. The efficiency-extrapolation curve obtained with Cherenkov measurements in glass vials was compared to Monte Carlo simulations based on the Geant4 code.

A general dead-time correction method based on live-time stamping. Application to the measurement of short-lived radionuclides.

Dead-time correction formulae are established in the general case of superimposed non-homogeneous Poisson processes. Based on the same principles as conventional live-timed counting, this method exploits the additional information made available using digital signal processing systems, and especially the possibility to store the time stamps of live-time intervals. No approximation needs to be made to obtain those formulae. Estimates of the variances of corrected rates are also presented. This method is applied to the activity measurement of short-lived radionuclides.

A radionuclide calibrator based on Cherenkov counting for activity measurements of high-energy pure ߯-emitters.

Due to their stability and reproducibility, re-entrant pressurized ionization chambers (also called radionuclide calibrators) are widely used for activity measurements in nuclear medicine services as well as in national metrology institutes to maintain reference standards. Generally, these secondary instruments yield accurate activity measurements for γ-emitting radionuclides. Ionization chambers are easy to use and thus well-adapted to guarantee the metrological traceability between national metrology institutes and end-users. However, the reproducibility of calibration factors can be significantly impaired when measuring high-energy pure ߯-emitters such as radiopharmaceuticals based on 90Y. This is because the bremsstrahlung emission contributing to the instrument response is strongly dependent on the geometry of the components surrounding the radioactive solution. The present article describes a new design based on pulse counting to address this problem. It takes advantage of Cherenkov emission resulting from Compton scattering in transparent materials. The interest of Cherenkov counting is to obtain a low-sensitivity detector that enables direct measurements of high-activity solutions (at least up to 10 GBq for 90Y-microspheres in aqueous suspensions used in nuclear medicine). A simple design based on a geometry close to an ionization chamber used at LNHB (Vinten 671 type) is described. The feasibility in terms of detection efficiencies (lower than 10-4 for 90Y solutions) of the new radionuclide calibrator is investigated by Monte Carlo calculations using the Geant4 code.

Investigation of the response variability of ionization chambers for the standard transfer of SIR-Spheres(®).

The present paper addresses the calibration of well-type ionization chambers (ICs) used at LNE-LNHB as standard transfer instruments to calibrate hospitals in the case of SIR-Spheres(®)(90)Y resin microspheres (Sirtex, Australia). Developed for interventional oncology, this radiopharmaceutical is directly injected in the liver for cancer treatment via a selective internal radiation therapy. The present work was carried out in the framework of the European project "Metrology for molecular radiotherapy" (MetroMRT). As commonly performed in radionuclide metrology for radiopharmaceuticals, the objective is to ensure the metrological traceability of SIR-Spheres(®) to hospitals. Preceding studies were focused on primary measurements of SIR-Spheres(®) based on the TDCR (Triple to Double Coincidence Ratio) method, applied after the dissolution of the (90)Y-labeled resin microspheres. As (90)Y is a high-energy ß(-)-emitter, the IC response strongly depends on the transport of electrons in the radioactive solution and surroundings (vial, chamber liners and materials). The variability of the IC-response due to the geometry dependence is investigated by means of measurements and Monte Carlo simulations in the case of a Vinten IC. The aim of the present study was also to propose a reliable uncertainty for ICs calibrations for the standard transfer of SIR-Spheres(®) to hospitals.

Real-time radionuclide identification in γ-emitter mixtures based on spiking neural network.

Portal radiation monitors dedicated to the prevention of illegal traffic of nuclear materials at international borders need to deliver as fast as possible a radionuclide identification of a potential radiological threat. Spectrometry techniques applied to identify the radionuclides contributing to γ-emitter mixtures are usually performed using off-line spectrum analysis. As an alternative to these usual methods, a real-time processing based on an artificial neural network and Bayes' rule is proposed for fast radionuclide identification. The validation of this real-time approach was carried out using γ-emitter spectra ((241)Am, (133)Ba, (207)Bi, (60)Co, (137)Cs) obtained with a high-efficiency well-type NaI(Tl). The first tests showed that the proposed algorithm enables a fast identification of each γ-emitting radionuclide using the information given by the whole spectrum. Based on an iterative process, the on-line analysis only needs low-statistics spectra without energy calibration to identify the nature of a radiological threat.

Calculation of extrapolation curves in the 4π(LS)ß-γ coincidence technique with the Monte Carlo code Geant4.

At LNE-LNHB, a liquid scintillation (LS) detection setup designed for Triple to Double Coincidence Ratio (TDCR) measurements is also used in the ß-channel of a 4π(LS)ß-γ coincidence system. This LS counter based on 3 photomultipliers was first modeled using the Monte Carlo code Geant4 to enable the simulation of optical photons produced by scintillation and Cerenkov effects. This stochastic modeling was especially designed for the calculation of double and triple coincidences between photomultipliers in TDCR measurements. In the present paper, this TDCR-Geant4 model is extended to 4π(LS)ß-γ coincidence counting to enable the simulation of the efficiency-extrapolation technique by the addition of a γ-channel. This simulation tool aims at the prediction of systematic biases in activity determination due to eventual non-linearity of efficiency-extrapolation curves. First results are described in the case of the standardization (59)Fe. The variation of the γ-efficiency in the ß-channel due to the Cerenkov emission is investigated in the case of the activity measurements of (54)Mn. The problem of the non-linearity between ß-efficiencies is featured in the case of the efficiency tracing technique for the activity measurements of (14)C using (60)Co as a tracer.

Primary standardization of SIR-Spheres based on the dissolution of the (90)Y-labeled resin microspheres.

The project "Metrology for molecular radiotherapy" is a collaborative European project initiated to bring together expertize in ionizing radiation metrology and nuclear medicine research. This project deals with the development of personalized dosimetry to individual patients who are undergoing molecular radiotherapy (also known as targeted radionuclide therapy). The general aim is to provide a metrological traceability to primary standards for individual dosimetry in the case of molecular radiotherapy. In particular, one objective is the standardization of (90)Y-labeled resin microspheres SIR-Spheres (Sirtex, Sydney, Australia) used for the treatment of liver cancer by radioembolization. The present paper describes the primary measurements carried out using the Triple to Double Coincidence Ratio (TDCR) method applied after the complete dissolution of the SIR-Spheres in the Sirtex vial. A method for the dissolution was developed to optimize the homogeneity of the solution to enable the primary measurements based on Cherenkov and liquid scintillation counting. A comprehensive description of the protocol implemented for the microsphere dissolution is reported. First calibration factors obtained with the reference ionization chambers at LNE-LNHB are also given.

First TDCR measurements at low energies using a miniature x-ray tube.

Developed for radionuclide standardization using liquid scintillation, the Triple to Double Coincidence Ratio (TDCR) method is applied using coincidence counting obtained with a specific three-photomultiplier system. For activity determination, a statistical model of light emission is classically used to establish a relation between the detection efficiency and the experimental TDCR value. At LNE-LNHB, a stochastic approach of the TDCR modeling was developed using the Monte Carlo code Geant4. The interest of this TDCR-Geant4 model is the possibility to simulate the propagation of optical photons from their creation in the scintillation vial to the production of photoelectrons in photomultipliers. As an alternative to the use of radionuclide sources, first TDCR measurements are presented using a miniature x-ray tube closely coupled to the scintillation vial. The objective of this new set-up was to enable low-energy depositions (lower than 20 keV) in liquid scintillator in order to study the influence of both time and geometrical dependence between PMTs already observed with radioactive sources. As for the statistical TDCR model, the non-linearity of light emission is implemented in the TDCR-Geant4 model using the Birks formula which depends on the kB factor and the scintillation yield. Measurements performed with the x-ray tube are extended to the assessment of these parameters and they are tested afterwards in the TDCR-Geant4 model for activity measurements of (3)H.

Digital pulse processing and optimization of the front-end electronics for nuclear instrumentation.

This article describes an algorithm developed for the digital processing of signals provided by a high-efficiency well-type NaI(Tl) detector used to apply the 4πγ technique. In order to achieve a low-energy threshold, a new front-end electronics has been specifically designed to optimize the coupling to an analog-to-digital converter (14 bit, 125 MHz) connected to a digital development kit produced by Altera(®). The digital pulse processing is based on an IIR (Infinite Impulse Response) approximation of the Gaussian filter (and its derivatives) that can be applied to the real-time processing of digitized signals. Based on measurements obtained with the photon emissions generated by an (241)Am source, the energy threshold is estimated to be equal to ~2 keV corresponding to the physical threshold of the NaI(Tl) detector. An algorithm developed for a Silicon Drift Detector used for low-energy x-ray spectrometry is also described. In that case, the digital pulse processing is specifically designed for signals provided by a reset-type preamplifier ((55)Fe source).

Results of an international comparison for the activity measurement of 177Lu.

An international Key Comparison of (177)Lu has recently been carried out. Twelve laboratories performed assays for radioactivity content on aliquots of a common master solution of (177)Lu, leading to eleven results submitted for entry into the Key Comparison Database of the Mutual Recognition Arrangement. A proposed Comparison Reference Value (CRV) was calculated to be 3.288(4)MBq/g using all eleven results. Degrees of equivalence and their uncertainties were calculated for each laboratory based on the CRV. Most of the values reported by the participating laboratories were within 0.6% of the CRV.

Overview of a FPGA-based nuclear instrumentation dedicated to primary activity measurements.

In National Metrology Institutes like LNE-LNHB, renewal and improvement of the instrumentation is an important task. Nowadays, the current trend is to adopt digital boards, which present numerous advantages over the standard electronics. The feasibility of an on-line fulfillment of nuclear-instrumentation functionalities using a commercial FPGA-based (Field-Programmable Gate Array) board has been validated in the case of TDCR primary measurements (Triple to Double Coincidence Ratio method based on liquid scintillation). The new applications presented in this paper have been included to allow either an on-line processing of the information or a raw-data acquisition for an off-line treatment. Developed as a complementary tool for TDCR counting, a time-to-digital converter specifically designed for this technique has been added. In addition, the description is given of a spectrometry channel based on the connection between conventional shaping amplifiers and the analog-to-digital converter (ADC) input available on the same digital board. First results are presented in the case of α- and γ-counting related to, respectively, the defined solid angle and well-type NaI(Tl) primary activity techniques. The combination of two different channels (liquid scintillation and γ-spectrometry) implementing the live-time anticoincidence processing is also described for the application of the 4πß-γ coincidence method. The need for an optimized coupling between the analog chain and the ADC stage is emphasized. The straight processing of the signals delivered by the preamplifier connected to a HPGe detector is also presented along with the first development of digital filtering.

Application of TDCR-Geant4 modeling to standardization of 63Ni.

As an alternative to the classical TDCR model applied to liquid scintillation (LS) counting, a stochastic approach based on the Geant4 toolkit is presented for the simulation of light emission inside the dedicated three-photomultiplier detection system. To this end, the Geant4 modeling includes a comprehensive description of optical properties associated with each material constituting the optical chamber. The objective is to simulate the propagation of optical photons from their creation in the LS cocktail to the production of photoelectrons in the photomultipliers. First validated for the case of radionuclide standardization based on Cerenkov emission, the scintillation process has been added to a TDCR-Geant4 modeling using the Birks expression in order to account for the light-emission nonlinearity owing to ionization quenching. The scintillation yield of the commercial Ultima Gold LS cocktail has been determined from double-coincidence detection efficiencies obtained for (60)Co and (54)Mn with the 4π(LS)ß-γ coincidence method. In this paper, the stochastic TDCR modeling is applied for the case of the standardization of (63)Ni (pure ß(-)-emitter; E(max)=66.98 keV) and the activity concentration is compared with the result given by the classical model.