Minutes of the 4th Radionuclide Calibrator Users' Forum
Held at the National Physical Laboratory, Teddington, on 31 January 2007
| Attendees: | John Keightley | NPL (Chairman) | |
| Eleanor Bakhshandeiar | NPL (Secretary) | ||
| Matthew Aldridge | University College London Hospital | ||
| Shona Anderson | Mount Vernon Hospital | ||
| Mark Aplin | Royal Sussex County Hospital | ||
| Mark Barnfield | St James's University Hospital | ||
| Katrina Cockburn | Castle Hill Hospital | ||
| Rita Coleman | Southern Scientific Ltd | ||
| Mark Ford | Southern Scientific Ltd | ||
| Ken Frost | Southern Scientific Ltd | ||
| Richard Gadd | University Hospital of North Staffordshire | ||
| Andrew Garton | Harley Street Cancer Centre | ||
| Brian Gilmore | Belvoir Park Hospital, Belfast | ||
| Christopher Green | Northwick Park Hospital | ||
| Kate Griffith | Nottingham City Hospital | ||
| Andrew Harris | Sheffield Teaching Hospitals NHS Foundation Trust | ||
| Richard Haynes | Southern Scientific Ltd | ||
| Ian Hufton | Royal Liverpool University Hospital | ||
| Andy Irwin | St George's Hospital | ||
| Joanne Kerry | Lincoln County Hospital | ||
| Desmond MacMahon | NPL | ||
| Maria Marouli | NPL | ||
| Chris Nottage | Essex Rivers Healthcare | ||
| Maria Maroulli | NPL | ||
| David Parry-Jones | Addenbrooke's Hospital | ||
| Rowena Paul | Hammersmith Hospital | ||
| Hilary Philips | NPL | ||
| Brenda Pratt | The Royal Marsden NHS Trust | ||
| Jonathan Price | St James's University Hospital | ||
| Jil Segerman | Royal Sussex County Hospital | ||
| William Thomson | City Hospital NHS Trust, Birmingham | ||
| Claire Trumper | Pharmaceutical Profiles | ||
| Wendy Waddington | The Middlesex Hospital | ||
| Henry Weatherburn | Parkside Onclology Clinic | ||
| Farnoosh Zananiri | Bristol General Hospital | ||
| Stanislav Stanev | NPL | ||
Apologies
- Mike Woods, IRMC, Teddington
- Alex Tarbuck, University Hospital of North Staffordshire
- Harold Stockdale, Royal Liverpool University Hospital
- Sandra Hoffmann, Southampton General Hospital
1 Chairman's Welcome, Introduction and Previous Minutes
- The chairman (John Keightley) welcomed the delegates to the fourth RCUF meeting and gave a brief summary of the terms of reference for the RCUF. He announced that the new NPL programme has been proposed to the DTI and is currently awaiting approval. He also mentioned a few of the recent developments, in particular, publication of the good practice guide for radionuclide calibrators, the 99mTc comparison exercise and the re-standardisation of 64Cu at NPL.
- The minutes from the previous RCUF meeting were approved without changes.
- John asked the delegates to fill in the LDR Brachytherapy questionnaire provided in the delegates pack as NPL are currently reviewing the service we provide for 125I Brachytherapy seeds. If you are interested in taking part please click on the link and complete the form: LDR Brachytherapy Questionnaire.
2 Calibration factors (for the Capintec) for 111In with Cu filters - Bill Thomson, City Hospital, Birmingham
Bill's presentation was a follow-up of a presentation to the previous RCUF meeting, in which he described the use of Cu filters in reducing the variation in Capintec calibrator response when dispensing 123I from vial to syringe. The main points from the current presentation relating to 111In follow:
- The nuclide 111In suffers from similar problem as 123I as it exhibits relatively abundant low energy photon emissions between 23 and 26 keV which readily penetrate the relatively thin-walled Capintec chambers.
- The transfer of solution from vial to syringe yielded a difference in his Capintec calibrator response of around 26%. The use of the 0.5mm Cu filter system reduced this discrepancy to around 2-3%, due to the preferential attenuation of the lower energy photon emissions.
- Bill discussed the means of determination of new 111In calibration factors (or dial-settings) for this revised geometry. This involved the comparison of empirical measurements with theoretical attenuation factors performed in MathCad, which showed rather good agreement. He would like to verify these results by some more rigorous Monte Carlo simulations.
- Bill recommended the continued use of such Cu filters for reducing the vial/syringe discrepancies, but some further revision of the recommended 111In dial setting may be required.
Discussions
- Following Bill's presentation, there was some discussion on the validity of the manufacturers quoted activity, as Bill found some significant differences when calculating the appropriate dial settings using these quoted activities values as the reference compared to those obtained using a Secondary Standard radionuclide calibrator.
- Chris Nottage said that he made similar measurements with a Capintec CRC-15R and found that without employing a Cu filter, the vial/ampoule response ratio was close to unity, whereas after the introduction of a Cu filter system, the difference increased significantly, which seems to contradict the results presented by Bill Thompson.
- John Keightley pointed out that previous NPL run inter-comparison exercises for 123I : (NPL Reports CIRM-38 (2000) and CIRA-17 (1996)) and 111In (CIRM-1 (1997)) showed that small variations in the thickness of the inner wall of calibrators of the same type could generate considerable differences in response for low energy gamma emitters. This may partly help to explain the contradictory results of Bill Thompson and Chris Nottage.
- Chris Nottage said he is considering the employment of unique dial settings for each of his Capintec calibrators for the nuclide 125I, due to the noticeable differences between his systems.
3 Production of 64Cu at St Thomas Hospital, London: What, Why and How? - Rowena Paul, St Thomas
Hospital
- The nuclide 64Cu exhibits a "triangular" decay scheme: (positron branch 18%, beta-minus branch 37% and electron capture branch 41%) with a short half-life (12.7 hours). It is easy to produce and has low toxicity.
- The positron-branch makes it a useful candidate for diagnostic imaging and the beta-minus branch along with the emission of Auger electrons following electron-capture decay makes it an attractive candidate for therapy.
- The use of 64Cu (when coordinated to a series of bis-thiosemicarbazone ligands) for imaging and potential therapeutic uses is being researched, particularly in relation to tumour hypoxia and blood flow. It is proposed that tumour hypoxia can be exploited for the selective delivery of therapeutic nuclides.
4 Calibration factors for 223Ra - Sue Hooper, Velindre Hospital
- 223Radium is an alpha emitting radionuclide, and was supplied by Algeta ASA in Norway in the form of an 227Ac generator. This radionulcide is currently used as a trial for painful bone metastases of palliation hormone refractory prostate cancer patients. Sue explained how she determined a calibration factor for this radionuclide using a Capintec CRC-15-Beta ionisation chamber system, and detailed some of the problems she faced in following the suppliers calibration instructions.
- Although there were no large-scale deviations between measurements made in the supplied vial and syringes (< 1%); such a transfer may influence the state of equilibrium between 223Ra and its progeny.
- John Keightley pointed out that maybe the 223Ra could be standardised by secondary means (maybe using alpha spectrometry and/or gamma spectroscopy). The primary standardisation could be rather difficult due to presence of the gaseous daughter 219Rn. · Desmond MacMahon mentioned that the half-life value has not been reviewed by the international project DDEP:
- John Keightley pointed out that maybe the 223Ra could be standardised by secondary means (maybe using alpha spectrometry and/or gamma spectroscopy). The primary standardisation could be rather difficult due to presence of the gaseous daughter 219Rn. · Desmond MacMahon mentioned that the half-life value has not been reviewed by the international project DDEP: http://www.nucleide.org/DDEP_WG/DDEPdata.htm
5 Development of a UK Primary standard for positron emitters in gas - Maria Marouli, NPL / University
of Surrey
- Maria's presentation was based on her PhD project carried out at NPL. She introduced a few radionuclides used for PET, emphasising the importance primary standards for positron emitters to ensure the accuracy of the measurements, particularly in airborne radioactivity measurements. She explained the methods used to measure and the detectors used.
- She explained how gaseous standards may be linked to liquid standards (for example 11C).
6 Type testing of the new Fidelis electrometer - Eleanor Bakhshandeiar, NPL
- Eleanor explained the differences and the characteristics of the new Fidelis and the older NPL-CRC radionuclide calibrators. She presented the results of the type testing of the new radionuclide calibrator system and the future tests that NPL is planning to carry out on this system.
- Bill pointed out that there is still a pronounced step on the linearity graph due to range switching and the software could correct this. Mark Ford replied that the software corrections have already been applied.
- For more information on the electrometer and the software of the new Fidelis radionuclide calibrator, please contact Richard Hayes or Mark Ford at Southern Scientific.
7 Non-linearity of Electrometers in Radionuclide Calibrators - John Keightley, NPL
- John presented some software written in LabVIEW 8.2 for the recording of timed readings from NPL-CRC (and Capintec CRC-15R) ionisation chamber systems.
- John gave a demonstration of the software, showing how the collected data is useful for examining the system linearity when used with a rapidly decaying source (such as 99mTc). The software has been tested at St James Hospital but has not yet passed the rather stringent NPL QA procedures, and requires a manual.
- Jill Segerman pointed out the cause of the non-linear region in lower currents could be due to the 99Mo breakthrough.
- John is looking for volunteers to test this software and give him feedback. The software may be rather easily modified to work with various other radionuclide calibrator systems, and will be made available to RCUF members free of charge.
- For more information, please contact John Keightley.
8 Comparison of 99m Tc measurements in UK Hospitals 2006 - Desmond MacMahon, NPL
- Desmond presented the results from the recent comparison exercise, which was carried out in October and December 2006. Overall, there were 211 measurements reported, with 96% of all results within 5% of the NPL value and 64% within 2%. Desmond detailed some problems that occurred with the reporting of results and explained how the NPL value for 99m Tc is validated.
- The 99mTc comparison report can be downloaded here.
Discussions
- It was suggested that the report be published in "Nuclear Medicine Communications"
Action 1: Look into publishing the 99m Tc comparison report in Nuclear Medicine Communications
Responsible: Desmond MacMahon, John Keightley, NPL
9 Post Calibration Exercise: Determination of the correct calibration number - Christopher Green,
Northwick Park Hospital
- Christopher presented his method for the determination of an accurate calibration factor and the means of checking accuracy of his dose calibrators. He detailed his preference for doing so in conjunction with NPL comparison exercises.
- Bill Thompson pointed out the problems of determining calibration factors for syringes, as it is highly dependent on the radionuclide. Vial - syringe differences of around 1% is not a major problem, but any bigger differences may create some problems. Christopher answered the way he determines the activity in a syringe is to dispense the activity from the vial into the syringe, topping up the original vial with carrier up to the original level and re-measuring. Any residual activity is left is subtracted from the original activity.
- Christopher replied to the John Keightley's question on why there was a change from P6 to 10R Schott vials, stating that there was a variation in the quality of the P6 vial's glass and that 10R Schott vials are more uniform.
10 Uncertainties - Desmond MacMahon, NPL
Desmond briefly discussed some recommended methods of dealing with uncertainties, and referred to several documents, some of which may be downloaded for free:
UKAS M3003: The Expression of Uncertainty and Confidence in Measurement
GPG 11: A Beginner's Guide to Uncertainty of Measurement
GPG 49: The Assessment of Uncertainty in Radiological Calibration and Testing
- The expression of the value of the result of a measurement is incomplete without a statement of its evaluated uncertainty. Two numbers are needed to quantify an uncertainty, the width of the margin and the confidence level. He also talked about the standard deviation, standard deviation of mean, type A uncertainty and type B uncertainty and the differences between the two.
- Desmond also pointed out the differences between a correction and an uncertainty: the first is known (and the correction will entail some contribution to the final uncertainty) whereas the latter is unknown.
- He gave an example where one of the 99m Tc intercomparison participants had reported a value for temperature coefficient on their result sheets which was directly applied to the result and used as an uncertainty.
Action 2: At the next RCUF meeting, about an hour is to be spent explaining the calculation of uncertainties for Radionuclide Calibrators
Responsible: John Keightley, NPL
11 The importance of the daily calibrator check with a long-lived sealed source - Christopher Green,
Northwick Park Hospital
- Christopher gave a presentation on the importance of routine checking of the chamber for demonstrating its stability using a long-lived radionuclide source and keeping a daily record, stating that this record should also include any adjustments made.
- One of the delegates asked if there are any problems with using a 137Cs source as a check source, as 226Ra (because of its complications with equilibrium of the progeny) is difficult to obtain.
- Majority of the delegates claimed to be using a 137Cs check source rather than a 226Ra check source.
- 57Co has similarly been used as a check source as it has similar energy emissions to 99mTc.
- Jil Segerman said that her 137Cs source is coming to the end of its 5 years recommended use and she is thinking of replacing this source.
- John Keightley said that NPL radioactivity group has been considering the use of 166mHo as a check source, but there are some issues with the half life of this nuclide which need addressing first (only one measurement of the half-life with a 15% uncertainty).
- John Keightley stated that the currently recommended half- life of 137Cs is 10976 ± 30 days (at a coverage factor k = 1).
12 Implementation of the calibrators good practice guide - Bill Thomson, City Hospital, Birmingham
The Good Practice Guide 93 is available as a free download.
- Bill talked about the characteristics of an Ionisation Chamber. Going through the different sections of the GPG, he emphasised that traceability is a major factor. He went through the QC procedures and issues such as environment, power connections, shielding etc. He also talked about the uncertainties referring to the documents mentioned by Desmond earlier. Bill emphasised that a written quality assurance system is required.
13 Discussion session: Implementation of the good practice guide - Richard Gadd, University Hospital
of North Staffordshire
- Richard asked the delegates how many of the delegates have seen the document and put its recommendations into practice. About 10% of the audience claimed to have read and are actually utilising the GPG.
- Richard asked how many people have traceability to NPL. A few delegates said that cost has been a problem. Some said their chambers are indirectly traceable to NPL. Richard explained that one chamber could be used as a reference chamber and directly traceable to NPL and other chambers could be calibrated against that reference chamber accordingly.
- Richard also said that the GPG recommends using at least two radionuclides annually to check the calibrator. But if the chamber is used for only one radionulcide it should be checked for that radionulcide annually.
- The licence agreement allows one source calibration every six months. However the delegates were not clear on what exactly the licence agreement entails.
- A few delegates expressed their interest in having more intercomparison exercises, as this is a cheaper option for the hospitals.
- Some complaints were voiced on the format of the GPG when ordered as a hard copy (B5).
- Brian Gilmore pointed out that it is difficult to calibrate his radionuclide calibrator for extremely short-lived radionuclides (like 18F) as it is located in Belfast. John Keightley said that in this case a secondary standard calibrator itself could be shipped as reported in the following article:
Woods, M.J. and Baker, M., "Establishing equivalence for activity standards of short-lived radionuclides using the NPL secondary standard radionuclide calibrator", Applied Radiation and Isotopes, 60, (2004), 499-504.
- Richard also went to explain the method of linearity test. He explained that the key is to find a linear area and obtain the half- life. Using the half- life the theoretical values are obtained and these values could be compared to the experimental values. The graph should be looked at as a whole for the entire range.
- Delegates were interested in the development of software that could analyse the linearity results.
- Richard asked how many people correct for the impurities and emphasised on the importance of making corrections for impurities.
- Richard pointed out that when using a shielding the calibrator should be re-calibrated as this could affect the calibration factors. Also background should be kept low.
Action 3: NPL to look into re-issuing printed versions of GPG-93 in a larger footprint
Responsible: Eleanor Bakhshandeiar, NPL
(This has been followed up with the NPL's knowledge transfer group and the community should now be able to order this guide either as a B5 or A4 format)
Action 4: To specify the exact details of the Licence agreements
Responsible: Steve Judge, NPL
(Steve will make a presentation at the next RCUF meeting)
Action 5: NPL will look into organising more intercomparison exercises
Responsible: John Keightley, Steven Judge, NPL
Action 6: To find out the acceptance level of Mo breakthrough in lower ranges of activity of 99mTc, when studying calibrator linearity
Responsible: John Keightley, NPL
Action 7: To develop software for the analysis of linearity data
Responsible: Eleanor Bakhshandeiar, NPL
(This has been looked at and the NPL internet metrology project covers this. This database is at its beta test stage and should be released very soon)
Action 8: As there was an interest from the community to have software to correct for impurities, NPL should look into this
Responsible: John Keightley, NPL
Any Other Business: Chairman
- John Keightley announced that an updated set of recommended nuclear data would be published in May. To receive this information please, contact Andy Pearce
- There have been some recently released documents which may be of interest to the RCUF members: (as free downloads):
IAEA Technical Reports Series 454
Quality Assurance for Radioactivity Measurement in Nuclear Medicine
http://www-pub.iaea.org/MTCD/publications/PDF/TRS454_web.pdfIAEA
Nuclear Medicine Resources Manual
http://www-pub.iaea.org/MTCD/publications/PDF/Pub1198_web.pdfThe LNHB has recently published a Good Practice Guide for nuclear medicine (in French):
http://www.nucleide.org/Publications/Guide_Acti_NT06-033.pdf
The next RCUF meeting is likely to be held on 12 December 2007. Members will be informed as soon as the date has been confirmed.
Eleanor Bakhshandeiar, Secretary, RCUF
John Keightley, Chairman
Radioactivity and Neutron Group
National Physical Laboratory
1st March 2007
Last Updated: 19 Dec 2011
Created: 24 May 2010