Held at the National Physical Laboratory, Teddington, 25 June 2008

         Chairman's Welcome, Introduction and Previous Minutes

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• The Chairman (John Keightley) welcomed the delegates to the fifth RCUF meeting and gave a brief summary of the terms of reference for the RCUF.
  
  
• The minutes from the fourth RCUF meeting were approved without changes.
  
  
  

1       New "in-house" NPL Electrometer System for Ionisation Chamber Measurements : John Sephton, NPL

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• NPL are in the process of updating their “in house” electrometer systems, based on a current sensitive amplifier design, with the voltage rise across a standard feedback capacitor monitored with time.
  
  
• All measurements are traceable to the NPL standards of time, capacitance, voltage and ultimately the becquerel, via the use of appropriate calibration factors in terms of current per unit activity.
  
  
• In John’s presentation, reference was made to the possibility of NPL providing a portable (and traceable) current source providing fixed currents over several decades, in order to provide a means of testing the behaviour of Radionuclide Calibrator electrometers. It was decided that such a scheme is not feasible for use with modern radionuclide calibrators, as access to the electrometer inputs requires dismantling the system.
  
  
• ACTION ITEM 1 : John Keightley, John Sephton, Piers de Lavison (NPL)
  
  
  • Look into altering the scope of the proposed NPL project for provision of a portable current source, and instead concentrate efforts on provision of means to quantify the degree of electrometer non-linearity.
    
    
    

2       Uncertainty Estimation: using example of NPL Ionisation Chamber:  John Keightley, NPL

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• At the 4th RCUF meeting, it was requested that NPL give some guidance on the assignment of uncertainties for measurements made with radionuclide calibrators.
  
  
• John presented a brief review of the most important elements of the ISO "Guide to the Expression of Uncertainty in Measurement" (GUM), and how they relate to measurements made with the NPL Secondary Standard Ionisation Chamber systems.
  
  
• John promised to provide a list of links of useful material on Measurement Uncertainty Evaluation:
  
  
• ACTION ITEM 2 : John Keightley (NPL)
  
  
  • Provide list of useful information on Measurement Uncertainty Evaluation.
    
    
  • Completed (below).
    
    
• Click on the following links for more information. All except for the first link (the GUM) are freely downloadable.
  
  
  • The ISO Guide to the Expression of Uncertainty in Measurement (GUM)
    
    
  • Supplement 1 to the GUM : Propagation of Distributions using a Monte Carlo Method
    
    
  • UKAS M3003 : The Expression of Uncertainty and Confidence in Measurement
    
    
  • A Beginner’s Guide to Uncertainty of Measurement : NPL GPG 11
    
    
  • The Assessment of Uncertainty in Radiological Calibration and Testing : NPL GPG 49
    
    
  • General Documents derived from the GUM (from the BIPM website)
    
    
  • Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results : NIST Technical Note 1297
    
    
  • Quantifying Uncertainty in Analytical Measurement : EURACHEM/CITAC Guide CG4
    
    
  • Guidelines on Assessment and Reporting of Compliance with Specification: ILAC-G8:1996
    
    
  • Expression of the Uncertainty of Measurement in Calibration: EA-4/02
    
    
  • EA Guidelines on the Expression of Uncertainty in Quantitative Testing: EA-4/16
    
    
  • An Approach to Combining Results from Multiple Methods Motivated by the ISO GUM: J. Res. Natl. Inst. Stand. Technol. 105, 571 (2000)
     

Useful books dealing with Measurement Uncertainty:

•  
  • An Introduction to Error Analysis: The Study of Uncertainties in Physical Measurements. John R Taylor. University Science Books, U/S. (1997)
    ISBN-10: 093570275X : ISBN-13: 978-0935702750
    
    
  • An Introduction to Uncertainty in Measurement: Using the GUM (Guide to the Expression of Uncertainty in Measurement). Cambridge University Press (2006)
    ISBN-10: 0521844282 : ISBN-13: 978-0521844284
    
    

3       Estimating Uncertainties Associated with Tc-99m Measurements: Ian Hufton, Royal Liverpool
         University Hospital

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• Ian discussed the assignment of uncertainties for measurements of Tc-99m based on the results of the 2006 comparison exercise.
  
  

4       Linearity of the Fidelis (Part 1): Mike Dubben, Southern Scientific Ltd

5       Linearity of the Fidelis (Part 2): Paul Hinton, Royal Surrey Hospital

These presentations are not available as downloads here at the request of the authors, as the results are to be published in the open literature. Contact Mike Dubben (miked@ssl.gb.com) for more information.

• Mike Dubben explained that at the "range-switching points" a marked jump in response is apparent as the actual current supplied by the current source (used in the setting of the various ranges) actually varies with load impedance.
  
  
• A simple regression routine can be implemented to correct for these non-linear effects, and Mike discussed the use of the Fidelis “Engineering Mode Wizard” to assist with this.
  
  
• Mike stated that new Fidelis systems will have these corrections applied and data on linearity will be supplied to the customer. Existing Fidelis customers will have the corrections applied at the next yearly calibration.
  
  
  Mike pointed out that this work has implications for all radionuclide calibrators that are set up using current generators.
  
  
• Paul Hinton discussed the “decaying source” linearity measurements made at the Royal Surrey Hospital.
  
  
• ACTION ITEM 3 : Mike Dubben (Southern Scientific Ltd)
  
  
  • Confirm that existing Fidelis customers as well as new customers will have the linearity corrections applied and the remaining degree of electrometer non-linearity quantified.

6       Linearity of Capintec CRC-15R Systems: Richard Fernandez, Guy's & St Thomas' Hospitals

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• Richard discussed the testing of electrometer linearity for the 15 Radionuclide Calibrator systems at Guy’s and St Thomas’ Hospitals. For 3 of the systems, he utilised the NPL software discussed in the next presentation. He suggested that due to issues of radio-pharmacy sterility, a wireless or Bluetooth data logging system would be advantageous. Another suggestion was to log the data to a PDA rather than a Notebook PC.
  
  
• ACTION ITEM 4 : John Keightley (NPL)
  
  
  • Look into the feasibility of provision of wireless interfacing to radionuclide calibrators, as well as provision of a PDA based system.

7       Release of NPL Data logging Software for NPL-CRC and CRC 15R Systems : John Keightley, NPL

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• John discussed the development of a software routine to collect data from NPL-CRC and CRC-15R radionuclide calibrator systems. This software is available for free download from the following link:
  
  
  • npl_crc_logger.zip
    
    
• Some notes on the installation of the software are available from the following link:
  
  
  • readme.pdf
    
    
• The users of this software will require a 9 pin “crossover” cable. John discussed the pin configurations required if one wishes to build their own cable, and gave some links to popular websites where such cables may be purchased for a reasonable fee.
  
  
• It is planned over the next year to extend the range of calibrators that the software may communicate with. As NPL does not have a stock of all radionuclide calibrators used in the Medical Physics community, this may require visits from NPL to various hospitals in order to test the communications routines.
  
  

8       NPL Service Level Agreements and NPL Programme Formulation : Piers de Lavison and Alan
         du Sautoy (NPL)

Click to view presentation of Piers de Lavison


Click to view presentation of Alan du Sautoy

9       Discussion Session

• Check Sources

Chris Nottage stated that for his Capintec system, the measurement of his (solid) Cs-137 check sources seems to take several minutes for the readings to stabilise, but that this does not occur for other nuclides. John Keightley found it difficult to explain why electrometer stability would be either nuclide or source-matrix dependent.

• ACTION ITEM 5 : Chris Nottage (Essex Rivers  Healthcare)
  
  
  • Supply RCUF members with further details on “settling times” for Cs-137 check source measurements.

The issue was also raised about the calibrator response as a function of distance from a wall.

• ACTION ITEM 6 : John Keightley (NPL)
  
  
  • Perform studies on NPL Secondary Standard chamber’s response as a function of distance from wall, particularly for measurements of Cs-137, and report back to RCUF members.
    
    
• Future Comparison Exercises

A discussion was held on the possibility of conducting an NPL run intercomparison exercise in late 2008 or early 2009. A unanimous decision was reached to hold a comparison exercise for the pure beta emitting nuclide Y-90. It was proposed that NPL aim to include suppliers of Y-90 in the intercomparison exercise and that they are invited to the next RCUF meeting. John Keightley will draft a questionnaire for the RCUF members on the format of the comparison (vial types etc).

During the discussion, it was decided that NPL should place a list of the previous NPL intercomparison exercises on the RCUF website.

• ACTION ITEM 7 : John Keightley (NPL)
  
  
  • Provide list of previous NPL intercomparison exercises, along with links to the associated downloadable reports.
    
    
  • Completed (below).

Nuclide	Year	Link to PDF of Report on NPL website
I-123	1996	http://publications.npl.co.uk/npl_web/pdf/cira17.pdf
Ga-67	1996	http://publications.npl.co.uk/npl_web/pdf/cira12.pdf
In-111	1997	http://publications.npl.co.uk/npl_web/pdf/cirm1.pdf
Ir-192	1999	http://publications.npl.co.uk/npl_web/pdf/cirm9.pdf
I-131	1999	http://publications.npl.co.uk/npl_web/pdf/cirm31.pdf
I-123	2000	http://publications.npl.co.uk/npl_web/pdf/CIRM38.pdf
Ir-192	2000	http://publications.npl.co.uk/npl_web/pdf/CIRM44.pdf
Tl-201	2001	http://publications.npl.co.uk/npl_web/pdf/CIRM47.pdf
Sr-89	2003	http://publications.npl.co.uk/npl_web/pdf/dql_rn12.pdf
Tc-99m	2006	http://publications.npl.co.uk/npl_web/pdf/dql_rn18.pdf

• I-131 capsules

Chris Nottage stated that he has noticed readings from his Fidelis radionuclide calibrator system for I-131 capsule measurements appear to show a degree of correlation with the orientation of the capsule with respect the to source holder. The magnitude of the effect appears to be a maximum of 0.3% change in the response. John Keightley said that NPL would investigate this when he next receives an I-131 capsule.

• ACTION ITEM 8 : John Keightley (NPL)
  
  
  • Study response of NPL Secondary Standard Calibrator to I-131 capsules as a function of Capsule orientation. Report back to the RCUF members at the next meeting.
    
    
• P-32 problems : Ian Hufton (Royal Liverpool University Hospital)

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Ian reported that a recent change in supplier of P-32 has seen his derived calibration factors (based on the suppliers certified value for activity concentration) shift by around 20% and one must certainly question the validity of the reported activity concentration. Sue Hooper confirmed noticing similar results. Further work is required to confirm these results. John Keightley said that NPL would be willing to pursue this matter further.

• ACTION ITEM 9 : John Keightley (NPL) and Sue Hooper (Velindre NHS Trust)
  
  
  • Instigate an investigation into the determination of the causes of such anomalous results for P-32 measurements. This would include some investigations into possible impurity levels of P-33 and S-35, but these measurements would take some weeks/months to complete, as they would be dependent on measured deviations for the expected decay curves from pure P-32.
    
    
• Syringes

It was brought to NPL’s attention that there appears to be some doubt on the validity of a certain syringe calibration factor published in NPL Report CIRM 56. Initial tests at NPL confirmed this discrepancy, and the report has been withdrawn pending further investigation. Since there appears to be no “standard” syringe used by all hospitals, it was proposed that the RCUF form a small working group to draft a protocol for the determination of syringe calibration factors and that NPL set up a web repository for the sharing of data and experiences from all hospitals.

• ACTION ITEM 10 : John Keightley (NPL)
  
  
  • Assign RCUF members to form a small working group to provide guidance on the derivation of calibration factors for syringe response, and provide a simple web-based means for RCUF members to "pool" syringe factors.
    
    
• NPL Recommended Nuclear Decay Data

At the 4th RCUF meeting, John Keightley promised to make available copies of the NPL Report IR 6 (January 2008) by Andy Pearce (andy.pearce@npl.co.uk)

This report is now available in printed form, or one can download the pdf from the NPL website:

http://publications.npl.co.uk/npl_web/pdf/ir6.pdf

10       Next RCUF Meeting

The next RCUF meeting is likely to be held early/mid 2009, shortly after the completion of the proposed Y-90 comparison exercise. Members will be informed as soon an appropriate date has been confirmed. It was requested that at this meeting a presentation is made by NPL on the how the calibration factors for the NPL Secondary Standard Radionuclide Calibrators are derived from Primary Standards of radioactivity, and that RCUF members be given a tour of the facilities at NPL.

• ACTION ITEM 11 : John Keightley (NPL)
  
  
  • Incorporate a lab tour and NPL presentation on the primary standardisation of radioactivity into the agenda for the next RCUF meeting.

John Keightley, Chairman (RCUF)
Radioactivity and Neutron Group,
National Physical Laboratory

11th August 2008