National Standards Laboratories Research Articles

EURAMET supplementary comparison of the personal dose equivalent quantity for photon radiation: EURAMET.RI(I)-S5

Comparison measurements among primary standard facilities are required to achieve quality assurance in the realization and transfer of the quantity of personal dose equivalent, Hp(10), for photon radiation by national standards laboratories. Although some bilateral comparisons for this quantity had already taken place, in May 2003 the Consultative Committee for Ionizing Radiation [CCRI(I)] decided that a EUROMET supplementary comparison would be appropriate and that primary standards laboratories from other Regional Metrology Organizations could participate. The first comparison of the radiation protection quantity Hp(10) with low energy x-rays started in January 2004 and was completed in December 2007. The comparison was piloted by the PTB as EUROMET project No. 738 known also as EUROMET.RI(I)-S5.The operation and results of the comparison are reported here. The transfer instrument consisted of a secondary standard ionization chamber and a complete electronic measuring device. The response of this transfer instrument in various photon reference fields (N-15 and 0°, N-20 and 45°, N-30 and 75°, N-60 and 0°, N-120 and 0°, radiation quality according to ISO 4037-1:1996 [1]) was compared.Measurements were made by participants in 17 countries: Austria, France, Czech Republic, Finland, Germany, Greece, Hungary, Norway, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland, the Netherlands, the United Kingdom and by one international organization. The results obtained by most of the participants are consistent with the stated uncertainties.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

SU-E-T-728: TG-51A: Part 1: An Alternative Secondary Standard for Medical Linear Accelerators Using Alanine Dosimeters

Purpose: To demonstrate the suitability of the use of alanine dosimeters as a supplement or alternative to TG51 as an acceptable secondary calibration method for high energy photons beams from a medical linear accelerator. Methods: Alanine dosimiters were irradiated at three radiation treatment facilities and compared to dose/mu determined by TG51 using ionization chambers calibrated at ADCL. The ionization chamber was positioned in a Scanditronix Wellhoffer water phantom with dimensions 42 cm × 36 cm × 36 cm and at a dept of 5.0 cm. The volume of the ionization chamber was 0.6 cc. A polystyrene holder containing two alanine dosimeters was placed at the same point. Each alanine dosimeter is cylindrical in shape with a diameter of 5 mm and a length of 3 mm (volume = 0.25 cc). Ten sets of alanine detectors (20) were irradiated to 20 Gy in sequential exposures. An independent ionization chamber was used to normalize the exposures for any variation in accelerator output for every measurement. For one beam energy the alanine detectors were returned to a national standards laboratory for conversion to dose based on the same primary standard used for ionization chambers. The remaining dosimeters was evaluated on a Bruker EMX EPR spectrometer at the Armed Forces Radiobiology Research Institute which is directly traceable to NIST based on calibrated alanine dosimeters. Results: The average normalized dose per mu for all data is within expected experimental uncertainty. The uncertainty of each measurement technique is believed to be approximately 2% and will be discussed in detail. Conclusion: Analysis of the intercomparison measurements establishes that the alanine dosimeters are a valid method to establish the dose per mu for a medical linear accelerator that is traceable to the primary standard at a national standards laboratory in the same manner as used in TG51.

TH‐C‐BRB‐07: Development of a Wall‐Less Fricke Dosimetry System for Megavoltage Photon and Electron Beams

Purpose: To develop a dosimetry system based on the Fricke (ferrous sulphate) dosimeter that can be used to determine absolute dose in regions of large dose gradients in megavoltage photon and electron beams. Method and Materials: Building on the techniques first used at the Swiss national standards laboratory METAS we have developed a system where Fricke solution can be irradiated in polyethylene bags rather than the usual glass vials. This approach means that there is no wall correction and the dosimeter size and shape can be tailored to each application. As a first test the Fricke system was used to determine the absorbed dose absolutely in low energy electron beams. The Fricke response was compared with the NRC primary standard water calorimeter and calibrated ionization chambers using the TG‐51 protocol. Measurements were made in 4 8 12 18 and 22 MeV beams and the delivered dose was in the range of 7 Gy to 50 Gy. Results: The accuracy and precision of the Fricke dosimetry is very dependent on solution preparation and contaminants which affect the readout. It was found that the contaminating effect of the polyethylene bag on the readout signal was small and could be accurately corrected by using unirradiated controls. The standard uncertainty in the sensitivity coefficient of the Fricke system was found to be 0.2% and the standard uncertainty in the determination of absorbed dose to water was estimated to be 0.6 %. Conclusion: The Fricke dosimeter system remains relevant to megavoltage dosimetry offering accuracy comparable with or better than other integrating systems. The dosimeter is insensitive to dose homogeneities and can be used to determine mean dose to arbitrary volumes. It therefore has applications in reference dosimetry for (TG‐51) non‐compliant beams as well as dose verification in IMRT.

TH‐C‐BRB‐03: On the Suitability of Using NanoDot for Measuring Dose Distributions Resulting from KV‐CBCT Acquisitions

Purpose: There is a growing need to determine radiation exposure and dose distributions resulting from an image‐guidance procedure. Although Monte Carlo simulations are capable to calculate the dose distributions experimental measurements remain the gold standards to validate the accuracy of calculations. This study investigated the suitability of nanoDot dosimeters for measuring accumulative dose at several locations simultaneously to determine 3D dose distributions resulting from a kilovoltage cone‐beam CT (kV‐CBCT) scan. Method and Materials: The nanoDot dosimeters read with a microStar reader by Landauer were used in the study. The system can be calibrated to measure dose from kilovoltage to megavoltage energy beams. The manufacturer provides a set of calibration dosimeters for 80 kVp x‐rays. The accuracy of the nanoDot dosimeters for absorbed dose measurements for kV‐CBCT scans was validated by using an ionization chamber in which the air‐kerma calibration factors were traceable to National Standards Laboratory. The relative dose distributions measured with nanoDot were compared with Monte Carlo calculated dose distributions in a PLASTIC WATER® LR phantom. Results: Seven nanoDot dosimeters were placed at different locations to determine dose distributions resulting from each kV‐CBCT scan protocol. There are five different kV‐CBCT scan protocols in the Varian OBI 1.4 system including Head Low‐dose Thorax Pelvis and Pelvis Spot Light with two different Bow‐tie filters. Both absolute and relative dose distributions were investigated. The dose values measured from 35 points generally agree with that of Monte Carlo calculations within 2–4%. Conclusion: The nanoDot dosimeters have been shown to be very suitable detectors for measuring 3D dose distributions resulting from kV‐CBCT scans due to its small size the ease of use good reproducibility and manageable photon energy dependence.Conflict of Interest: The microStar reader used in the research was provided by Landauer Inc. Glenwood IL

An automated cryogenic current comparator resistance ratio bridge for routine resistance measurements

A design of an automated cryogenic current comparator (CCC) resistance ratio bridge for routine measurements in a national metrology institute or standards laboratory is described. It employs a type II CCC for use in a low loss liquid helium storage vessel and can be continuously operated from the mains power via specialized isolated supplies. All parameters including the servo control loops are digitally controlled. Noise sources in the system are analysed using the Allan deviation and it is demonstrated that non-white noise sources can be eliminated by choosing an appropriate current reversal rate.

Spectral irradiance model for tungsten halogen lamps in 340–850 nm wavelength range

We have developed a physical model for the spectral irradiance of 1 kW tungsten halogen incandescent lamps for the wavelength range 340-850 nm. The model consists of the Planck's radiation law, published values for the emissivity of tungsten, and a residual spectral correction function taking into account unknown factors of the lamp. The correction function was determined by measuring the spectra of a 1000 W, quartz-halogen, tungsten coiled filament (FEL) lamp at different temperatures. The new model was tested with lamps of types FEL and 1000 W, 120 V quartz halogen (DXW). Comparisons with measurements of two national standards laboratories indicate that the model can account for the spectral irradiance values of lamps with an agreement better than 1% throughout the spectral region studied. We further demonstrate that the spectral irradiance of a lamp can be predicted with an expanded uncertainty of 2.6% if the color temperature and illuminance values for the lamp are known with expanded uncertainties of 20 K and 2%, respectively. In addition, it is suggested that the spectral irradiance may be derived from resistance measurements of the filament with lamp on and off.

OPTICAL RADIATION MEASUREMENTS AT CNAM-INM

The Institut National de Métrologie du Conservatoire National des Arts et Métiers (CNAM - INM), is the French national metrological laboratory in charge of realising the radiometric and photometric units. Cryogenic radiometers are recognised as the most accurate radiometric standards. Like most of the national standard laboratories world-wide, the CNAM-INM employs such an instrument as the basis for its optical radiation measurement scales. The photometric measurements are used to quantify the visual effect of radiation on the human eye. But, as eye is a very complicated organ and not the same for everybody, it is necessary to define a standard observer which is mainly described by the luminous efficiency function V(λ). The two major photometric quantities for which our laboratory is realising standards are the luminous intensity and the luminous. In this paper is presented a review of the realisation of the luminous intensity unit.

Determination of global positioning system (GPS) receiver clock errors: impact on positioning accuracy

Enhancing the positioning precision is the primary pursuit of global positioning system (GPS) users. To achieve this goal, most studies have focused on the relationship between GPS receiver clock errors and GPS positioning precision. This study utilizes undifferentiated phase data to calculate GPS clock errors and to compare with the frequency of cesium clock directly, to verify estimated clock errors by the method used in this paper. The frequency stability calculated from this paper (the indirect method) and measured from the National Standard Time and Frequency Laboratory (NSTFL) of Taiwan (the direct method) match to 1.5 × 10−12 (the value from this study was smaller than that from NSTFL), suggesting that the proposed technique has reached a certain level of quality. The built-in quartz clocks in the GPS receivers yield relative frequency offsets that are 3–4 orders higher than those of rubidium clocks. The frequency stability of the quartz clocks is on average two orders worse than that of the rubidium clock. Using the rubidium clock instead of the quartz clock, the horizontal and vertical positioning accuracies were improved by 26–78% (0.6–3.6 mm) and 20–34% (1.3–3.0 mm), respectively, for a short baseline. These improvements are 7–25% (0.3–1.7 mm) and 11% (1.7 mm) for a long baseline. Our experiments show that the frequency stability of the clock, rather than relative frequency offset, is the governing factor of positioning accuracy.

Clinical characterization of a proton beam continuous uniform scanning system with dose layer stacking

A proton beam delivery system on a gantry with continuous uniform scanning and dose layer stacking at the Midwest Proton Radiotherapy Institute has been commissioned and accepted for clinical use. This paper was motivated by a lack of guidance on the testing and characterization for clinical uniform scanning systems. As such, it describes how these tasks were performed with a uniform scanning beam delivery system. This paper reports the methods used and important dosimetric characteristics of radiation fields produced by the system. The commissioning data include the transverse and longitudinal dose distributions, penumbra, and absolute dose values. Using a 208 MeV cyclotron's proton beam, the system provides field sizes up to 20 and 30 cm in diameter for proton ranges in water up to 27 and 20 cm, respectively. The dose layer stacking method allows for the flexible construction of spread-out Bragg peaks with uniform modulation of up to 15 cm in water, at typical dose rates of 1-3 Gy/min. For measuring relative dose distributions, multielement ion chamber arrays, small-volume ion chambers, and radiographic films were employed. Measurements during the clinical commissioning of the system have shown that the lateral and longitudinal dose uniformity of 2.5% or better can be achieved for all clinically important field sizes and ranges. The measured transverse penumbra widths offer a slight improvement in comparison to those achieved with a double scattering beam spreading technique at the facility. Absolute dose measurements were done using calibrated ion chambers, thermoluminescent and alanine detectors. Dose intercomparisons conducted using various types of detectors traceable to a national standards laboratory indicate that the measured dosimetry data agree with each other within 5%.

Shortened Lifetime for Reference Radiations?

The half-lives of 137Cs and 252Cf are 30.2 and 2.65 y, respectively(1,2). They are two radionuclide-based reference sources recommended in ISO standards 4037-1 and 8529-1(1,2) for the calibration of personal dosemeters and area monitors. The half-lives of these sources may be well known, but their lifetimes as reference sources may be shorter than the aforementioned values. Radionuclide sources containing 137Cs are used for many purposes including radiation therapy, the sterilisation of foodstuffs and disposable medical products, the irradiation of blood to suppress graft versus host reactions in immune-suppressed patients, the irradiation of cell cultures and small animals in radiobiological research, to name a few applications. There are ∼5000 devices containing nearly 55 000 high-activity radiation sources in use in the United States, and many more worldwide. Needless to say, the US national standards laboratory, the National Institute of Standards and Technology (NIST), maintains 137Cs irradiators for the calibration of numerous dosimetric devices. The NIST uses these sources during participation in international comparison exercises.

Use of a targeted oncolytic poxvirus, JX-594, in patients with refractory primary or metastatic liver cancer: a phase I trial

JX-594 is a targeted oncolytic poxvirus designed to selectively replicate in and destroy cancer cells with cell-cycle abnormalities and epidermal growth factor receptor (EGFR)-ras pathway activation. Direct oncolysis plus granulocyte-macrophage colony-stimulating factor (GM-CSF) expression also stimulates shutdown of tumour vasculature and antitumoral immunity. We aimed to assess intratumoral injection of JX-594 in patients with refractory primary or metastatic liver cancer. Between Jan 4, 2006, and July 4, 2007, 14 patients with histologically confirmed refractory primary or metastatic liver tumours (up to 10.9 cm total diameter) that were amenable to image-guided intratumoral injections were enrolled into this non-comparative, open-label, phase I dose-escalation trial (standard 3x3 design; two to six patients for each dose with 12-18 estimated total patients). Patients received one of four doses of intratumoral JX-594 (10(8) plaque-forming units [pfu], 3x10(8) pfu, 10(9) pfu, or 3x10(9) pfu) every 3 weeks at Dong-A University Hospital (Busan, South Korea). Patients were monitored after treatment for at least 48 h in hospital and for at least 4 weeks as out-patients. Adverse event-monitoring according to the National Cancer Institute Common Toxicity Criteria (version 3) and standard laboratory toxicity grading for haematology, liver and renal function, coagulation studies, serum chemistry, and urinalysis were done. The primary aims were to ascertain the maximum-tolerated dose (MTD) and safety of JX-594 treatment. Data were also collected on pharmacokinetics, pharmacodynamics, and efficacy. Analysis was per protocol. This study is registered with ClinicalTrials.gov, number NCT00629759. Of 22 patients with liver tumours who were assessed for eligibility, eight patients did not meet inclusion criteria. Therefore, 14 patients, including those with hepatocellular, colorectal, melanoma, and lung cancer, were enrolled. Patients were heavily pretreated (5.6 previous treatments, SD 2.8, range 2.0-12.0) and had large tumours (7.0 cm diameter, SD 2.7, range 1.8-10.9). Patients received a mean of 3.4 (SD 2.2, range 1.0-8.0) cycles of JX-594. All patients were evaluable for toxicity. All patients experienced grade I-III flu-like symptoms, and four had transient grade I-III dose-related thrombocytopenia. Grade III hyperbilirubinaemia was dose-limiting in both patients at the highest dose; the MTD was therefore 1x10(9) pfu. JX-594 replication-dependent dissemination in blood was shown, with resultant infection of non-injected tumour sites. GM-CSF expression resulted in grade I-III increases in neutrophil counts in four of six patients at the MTD. Tumour responses were shown in injected and non-injected tumours. Ten patients were radiographically evaluable for objective responses; non-evaluable patients had contraindications to contrast medium (n=2) or no post-treatment scans (n=2). According to Response Evaluation Criteria in Solid Tumors (RECIST), three patients had partial response, six had stable disease, and one had progressive disease. Intratumoral injection of JX-594 into primary or metastatic liver tumours was generally well-tolerated. Direct hyperbilirubinaemia was the dose-limiting toxicity. Safety was acceptable in the context of JX-594 replication, GM-CSF expression, systemic dissemination, and JX-594 had anti-tumoral effects against several refractory carcinomas. Phase II trials are now underway.

Final report on international key comparison of liquid hydrocarbon flow facilities, CCM-FF-K2

This international key comparison was carried out in the field of liquid hydrocarbon flow. The intercomparison initially involved nine laboratories each designated as national standard calibration laboratories. The comparison was carried out using the BIPM guidelines for key comparisons and is included in the BIPM database to support the capability statements of the institutes as part of the MRA. The intercomparison was designated as being comparison CCM-FF-K2 by WGFF.The key comparison was carried out using light liquid hydrocarbon across a flow range 5 l/s to 30 l/s. Two meters, a Kral positive displacement meter and a turbine meter, were used in the intercomparison package; however, the primary comparison used the Kral positive displacement meter. Strouhal and Reynolds numbers were used as the key parameters to express the laboratories' (dynamic) measurement of volume and flowrate.Six laboratories finally provided results to allow the calculation of a KCRV (based on Strouhal number), and all six sets of results were consistent with the KCRV. The deviations from the KCRV using the Kral meter lay within a band of ±0.026%.Main text.To reach the main text of this Paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

SU‐FF‐T‐219: Evaluation of the Long‐Term Stability for the Cylindrical Ionization Chambers

Purpose: To analyze the long‐term stability of Farmer‐type cylindrical ionization chambers using the calibration factor provided by the KFDA (Korea Food and Drug Administration). KFDA is the national secondary standard laboratory (SSDL) in Korea and approve as a member of the IAEA SSDL network. Materials and Methods: The cylindrical ionization chambers used in this study include PTW 30001(30006), 30013, 30002, 30004, 23333, Capintec PR06C, NE 2571, Exradin #a12 and Wellhofer FC65G(IC70). The Nk and ND,W calibration factors for the cylindrical chambers were analyzed and the measured ND,W was compared with the calculated ND,W calibration factor. Results: The long‐term stability of PTW 30013(30006), Wellhofer FC65G(IC70) and NE 2571 varied within 0.2 %, meaning that they are more stable than other ionization chambers. This result is different from previous ones showing that the long term stability of ionization chambers with graphite wall material was superior to ionization chambers made of PMMA material. It turns out that almost the same levels of the stability of calibration factor were shown between PTW 30013(30006) ionization chamber made of PMMA wall material and Wellhofer FC65G(IC70) ionization chambers made of graphite material, and thus the former is shown to be superior from the aspect of long‐term safety, and PMMA wall material is firmer, more convenient to use, and it is more effective from the financial aspect. Therefore, it may be considered to be more appropriate to use for the regular dose measurements in comparison with graphite type ionization chamber. The measured ND,W calibration factor was approximately 1.0% higher than the calculated ND,W that was determined using the Nk calibration factor. Conclusion: The long‐term stability of the cylindrical chambers was evaluated using the Nk and ND,W calibration factor. It should help to improve clinical electron dosimetry in radiotherapy.

Progress in providing neutron standards at the UK National Physical Laboratory

The UK national standards laboratory, the National Physical Laboratory (NPL), provides an extensive range of facilities for measurements on neutron sources and neutron-sensitive devices. This paper describes recent improvements and extensions to the neutron standards. Correction factors used in source strength measurements have been improved, as have the scatter corrections used in monoenergetic and source-based irradiations. Characterisation of the thermal field facility has been improved by activation measurements. Experimental facilities developed recently include a system for measuring personal dosemeter responses at several energies simultaneously, and a neutron source tailored to simulate typical workplace fields.

International comparison EUROMET.RI(I)-S2 of extrapolation chamber measurements of the absorbed dose rate in tissue for beta radiation (EUROMET project No 739): Final report

For quality assurance in the realization and transfer by the national standard laboratories of the unit of the absorbed dose rate at 0.07 mm tissue depth for beta radiation, comparison measurements among the primary standard facilities are needed. Although some bilateral comparisons have taken place for this quantity, the CCRI decided in May 2003 that a EUROMET supplementary comparison would be appropriate if inclusive of primary standards laboratories of other regional metrology organizations. The operation and results of such a comparison are reported here. A flat ionization chamber and measurement system was used as the transfer instrument. A comparison was made of the calibration coefficients of this transfer instrument in various beta-particle laboratory reference fields (Pm-147, Kr-85, Tl-204 and Sr-90/Y-90) measured by each of the eight participants from France, Italy, Finland, Germany, Russian Federation, USA, Canada and Japan. The PTB was the pilot laboratory and the comparison ran from January 2004 until April 2007 under EUROMET project No 739 and EUROMET.RI(I)-S2. The results for most of the participants are consistent with the stated uncertainties although an extreme deviation is apparent for Pm-147 beta radiation for one participant.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by EUROMET, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Technical Report: UV and VUV Radiometry Programs at the Synchrotron Ultraviolet Radiation Facility (SURF III)

Synchrotron radiation was recognized as an important tool for radiometry shortly after the advent of dedicated storage rings as radiation sources more than four decades ago. [1] Initially, synchrotron radiation was conceived as a calculable primary standard for absolute calibration of radiation sources. With the explosion of synchrotron radiation facilities around the globe during the last several decades, synchrotron-radiation-based radiometry has been actively pursued among many national standard laboratories in countries including the U.S., Germany, the U.K., Japan, and Russia because of increasing demands from semiconductor photolithography, UV curing industry, medical diagnostics and treatments, and solar radiation monitoring. To date, the use of synchrotron radiation for radiometry is no longer limited to a primary radiation standard. Dispersed synchrotron radiation, although usually not calculable, provides radiation from IR to X-rays for radiometric characterization of detector response and material optical properties.

CCEM.RF-K20: Comparison of electrical field strength measurements

The comparison 'EUROMET-Project Nr 520', which started in April 1999 under the responsibility of the Swiss Federal Office of Metrology, was extended to a GT-RF comparison 'CCEM-RF-K.20' which officially started in September 2000, with more participants. The goal of this comparison was to assess the capability of each participating laboratory to measure electromagnetic field strength by calibrating a circulated field strength meter in the frequency range 10 MHz to 1 GHz. The comparison has been interrupted and further continued and ended finally in September 2004 when we received the measurements from all participants. This document presents the results of this comparison in the form of a Final Report.Despite the fact that the probe may have suffered instabilities during the five-year duration of this exercise, we consider that the results of all participants are consistent with the claimed uncertainty. The results support the equivalence of national standards laboratories for realization of field strength in the frequency range 10 MHz–1000 MHz.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Realization of the scale of high fiber optic power at three national standards laboratories

Nowadays the transmission powers in optical telecommunication networks are often hundreds of milliwatts. Such high power levels are known to cause several nonlinear effects, thus affecting data transfer. Therefore, accurate measurements of such high power levels are required. The general issues that are to be considered when one is realizing a scale for high fiber optic power are discussed. The scales of the national standards laboratories in Finland, Sweden, and Denmark are described, and the results of a trilateral comparison of these scales are presented. The power range of the comparison was 1-200 mW. The results show that the stated measurement uncertainties of the three laboratories (1.3%-2.9%, k = 2) are applicable over this power range.

Richard Guy Helmer

Richard Guy Helmer

Comparison of radioactivity measurements with radionuclide calibrators in the Republic of Korea

Recognizing the importance of comparisons of radionuclide calibrators in nuclear medicine and the need to provide access to activity standards that are traceable to the international measurement system, the Korea Food & Drug Administration (KFDA) as a national secondary standard dosimetry laboratory (SSDL), started a comparison program in 2002. The first two comparisons were conducted with 131I (71 participants) and 99mTc (72 participants). The results indicated that only 61% of reported activities for 131I and 65% for 99mTc were within ±5% of the correct value. These numbers increased to 84% for 131I and 83% for 99mTc when a ±10% limit was applied. Follow-up action on those calibrators with results outside the ±10% limits only produced a small improvement. There was also a marked difference in performance between the various calibrator types used. The results have shown that such comparisons are necessary to improve the quality of the measurements and to identify those radionuclide calibrators that are not functioning correctly.