Held at the Christie Hospital, Manchester, on 31 January 2002

Attendees:	Bill Thomson		City Hospital, Birmingham
	Jacqueline Roberts		Leeds General Infirmary
	Mark Barnfield		St James University Hospital
	Stuart Hesslewood		City Hospital, Birmingham
	Ian Belton		Cumberland Infirmary, Carlisle
	Susan Ryan		New Cross Hospital, Wolverhampton
	Joanne Kerry		Lincoln County Hospital
	Dudley Ibbett		Derbyshire Royal Infirmary, Derby
	Alex Hoffmann		Southampton General Hospital
	Wendy Johns		Hope Hospital, Salford
	Colin Jennings		Walsgrave Hospital, Coventry
	Phil Hillel		Royal Hallamshire Hospital, Sheffield
	Kate Griffith		Nottingham City Hospital
	Harold Stockdale		The Royal Liverpool University Hospitals
	Brian Gilmore		Belvoir Park Hospital, Belfast
	Richard Gadd		North Staffordshire Hospital, Stoke-on-Trent
	Alan Maxwell		Bradford Hospitals
	Stephen Jeans		Christie Hospital, Manchester
	Marge Rose		Christie Hospital, Manchester
	Susan Owens		Christie Hospital, Manchester
	Duncan White		Barnsley District General Hospital
	Sue Hooper		Velindre Hospital, Cardiff
	David Parry-Jones		Addenbrookes Hospital, Cambridge
	Janice Brown		Mount Vernon Hospital, London
	Susan Kelly		Western Infirmary, Glasgow
	Hugh Wilkins		West Cumberland Hospital, Cumbria
	Chris Carter		AEA Technology QSA
	Mike Woods		NPL (Chairman)
	Michaela Baker		NPL (Secretary)
	Dagmara Tyler		NPL

1.       BACKGROUND

The National Measurement System (NMS) is the UK's national infrastructure of laboratories that delivers world-class measurement science & technology, providing traceable and increasingly accurate standards of measurement for use in trade, industry, academia and government.

The NMS is funded by the UK DTI and is broken down into a number of technical programmes. The NMS Ionising Radiation Metrology Programme is one such programme that seeks to provide an effective and efficient national measurement infrastructure for ionising radiation, radioactivity and neutron measurements for three primary purposes:

• In order to enable UK companies, organisations and individuals to comply with the large and growing body of legislation related to ionising radiation such as IRR99 & IR(ME)R 2000.
• In order to improve quality of life by underpinning activities such as the medical use of ionising radiation and environmental monitoring.
• In order to provide commercial benefit by supporting competitiveness, quality assurance, good practice and innovation in significant industrial sectors such as power production, defence, healthcare supplies and instrumentation.

The Programme achieves these aims through the:

• maintenance and development of the UK primary standards for ionising radiation, radioactivity and neutron measurements.
• provision of these standards to the user communities through calibration, testing and measurement services, secondary standards, reference materials and reference data.
• provision of information, advice and training courses on measurement techniques and best practice.
• participation in the international measurement system in order to demonstrate the equivalence of UK standards with those of other nations, and so helping to reduce barriers to free trade and facilitating the exchange of scientific expertise.
• maintenance of awareness of the present and anticipated future metrological and knowledge transfer needs of the user communities by two-way communication between the suppliers and users of the NMS.

The majority of this work in the field of ionising radiations is conducted on behalf of the DTI by the Ionising Radiation (CIRM) at the National Physical Laboratory (NPL). One activity included in the present NMS programme for Ionising Radiation Metrology is the establishment and running of a Radionuclide Calibrator Users Forum. The aim of the Forum is to facilitate discussions and exchange of information between medical physicists regarding measurement and calibration issues associated with the use of radionuclide calibrators.

2.     INTRODUCTION

This inaugural meeting of the Forum was attended by 30 physicists, mainly from Medical Physics Departments located in the central and northern part of the UK, 3 NPL representatives and one from AEA Technology.

Mike Woods (NPL) described how the DTI NMSPU (NMS Policy Unit) formulates its measurement programmes in consultation with the relevant measurement communities and how NPL executes the individual projects that are agreed. These include R&D projects directed at resolving specific measurement problems, the maintenance and development of measurement and calibration services, the provision of advice and technology transfer activities such as user fora. Details of the ionising radiation metrology programme can be found on the DTI web site:

http://www.dti.gov.uk/nms/prog/old/ir.pdf

The purpose and the aims of the RCUF were presented, specifying that the role of NPL is primarily to facilitate this Forum and that membership is open to all users of radionuclide calibrators. The proposed Terms of Reference were accepted by all present and are detailed in Appendix 1.

The participants then introduced themselves, giving a very brief overview of their work, outlining any measurement and calibration problems associated with the type of radionuclide calibrators they use. From the suggestions made in this introductory session as well as those proposed prior to the meeting, a revised list of topics for discussions was agreed.

The main subjects chosen for discussions were:

• the accuracy of activity measurements for pure beta emitters using typical radionuclide calibrators, and in particular the beta chambers;
• radionuclides of interest for future UK comparisons;
• the effect of the newly introduced 10R Type 1+ Schott vials on the response of typical calibrators;
• the availability and accuracy of the NPL secondary standard calibrator and its range of calibration factors;
• how to improve the accuracy of ¹²³I activity measurements.

3.        PRESENTATIONS

Bill Thomson’s presentation was two-fold. First, the improvement in accuracy of ¹²³I measurements that can be obtained using copper inserts for typical radionuclide calibrators was described. The technique is based on the fact that a 0.5 mm copper insert significantly attenuates the low energy photons (X-rays) emitted by ¹²³I, which are the main cause of the large variations in the responses of ionisation chambers.

Discussions following this presentation highlighted the fact that, although the response of calibrators becomes more consistent and independent of variation in the thickness of the vials’ walls, the degree of overall attenuation depends also on the thickness of the inner walls of calibrators. For this reason each system needs to be individually recalibrated and new ¹²³I calibration factors derived for the specific copper insert being used. The second part of the presentation outlined a method of checking the elution efficiency of ⁸⁵Kr^m generators using a closed, but not pressurised, insert in radionuclide calibrators.

The second presentation was given by Michaela Baker (NPL) on previous and present NPL projects with direct relevance and applicability to the Medical Physics field. It provided a good opportunity to inform users about the calibration services available at NPL; about further calibration factors for the NPL secondary standard radionuclide calibrator and, in particular, for beta emitters and for AKR measurements of LDR brachytherapy ¹⁹²Ir wires and ¹²⁵I seeds, as well as the extended technology transfer programme.

4.       DISCUSSIONS AND AGREED ACTIONS

4.1    Next UK radionuclide calibrator intercomparison exercise to be for ³²P

Discussions revealed that the use of pure beta emitters such as ³²P, ⁸⁹Sr and ⁹⁰Y has increased recently and that the activity assay of these particular radionuclides, using the recommended factors for commercial calibrators, is a cause for concern. As the cost of the starting solution is often the main drawback to conducting such an intercomparison, ³²P was chosen for the next exercise. This will be organised jointly by NPL and AEA Technology QSA.

⁹⁰Y will be considered for the following intercomparison

4.2    Cost-sharing calibration exercise for ⁸⁹Sr

To overcome the high cost of conducting individual calibrations or an intercomparison exercise using individual samples for this radionuclide, it was agreed that one source should be circulated around various hospitals and lastly sent to NPL for calibration. Such a joint calibration is feasible because of the long half-life of ⁸⁹Sr. This will be coordinated by Alex Hoffmann from Southampton General Hospital and the individual results will be collated by NPL. It may be more convenient to circulate two sources: one around the hospitals in the South and another one covering the Northern part of UK, if the interest in such a calibration is high. Those interested should contact Alex on:

Tel: 02380 79 6628/6627, e-mail: Sandra.Hoffmann@suht.swest.nhs.uk

4.3    NPL to investigate the general performance of dedicated beta chambers

As some of the participants raised their concern about the operation and the accuracy of these systems, it was decided that NPL would initially ask users to specify all the problems they noticed. NPL would also contact Southern Scientific to find out more about the capabilities of these instruments and then decide what course of action to take.

4.4    Advertise future radionuclide calibrator intercomparison exercises in RAD magazine

Agreed.

4.5    10R Type 1+ Schott vials

NPL will derive new calibration factors for these vials, for the radionuclides commonly used in medical physics, with ⁸⁹Sr, ³²P and ⁹⁰Y as priorities. This will cover the NPL calibrator as well as some of the other, more commonly used calibrators. NPL will also check the specifications/dimensions of these vials and determine the variation in response between these containers, and check with Amersham the progress on the replacement programme.

4.6    Bill Thompson and NPL to publish a summary of “¹²³I measurements using a copper insert” paper in RAD magazine

Agreed.

4.7    ¹²³I recalibration exercise

Following the measurements problems highlighted by the previous 1996 and 2000 intercomparison exercises for this radionuclide, a follow-up recalibration exercise was suggested. This will be considered at the next meeting

4.8      Invite manufacturers and suppliers of radionuclide calibrators to the next meeting

It was generally agreed that it would be beneficial to have representatives of manufacturers and suppliers at these meeting, but that any presentations given by them should be on the basis of an invitation to address specific issues. These issues to be agreed following suggestions by members before the next meeting.

4.9      Build up an NPL database of hospital reported activity/NPL value, for NPL calibrations

In order to gain more information about the general performance as well as the long-term stability of the radionuclide calibrators used in hospitals, it was proposed that, when hospitals send solutions for calibration at NPL, they should be asked to report their measured activity and the type and serial number of calibrators used. This would allow NPL to create and maintain a database of reported activity/NPL true activity, for specific radionuclides, for individual calibrator types. Reporting of hospitals own measurements will be voluntary and any data will be kept anonymous. This information would enable NPL to identify problems with the performance of such calibrators and to verify the general accuracy of their recommended factors.

4.10  NPL to set up a RCUF web site on the NPL web site, which will include:

• Register of members of RCUF and users of Radionuclide Calibrators
  (for this, users would be asked to provide: departments/hospitals within an NHS trust, type of calibrators (serial number) and what they are used for, contact name – the information to be sent to Michaela Baker at NPL);
• Terms of Reference for RCUF;
• Meeting notes;
• Summary of all UK intercomparison exercises for activity measurements using radionuclide calibrators;
• International equivalence of NPL standards of activity and other NPL international links and activities;
• Presentations given at RCUF meetings;
• NPL nuclear data, including recommended half-lives for medical radionuclides;
• NPL radionuclide calibrator page, containing complete list of calibration factors available for these systems and possibly similar lists for other calibrators;
• Procedure for recalibration of individual hospital calibrators following NPL calibration and national comparison exercises.

Michaela Baker and Mike Woods