1. Measurement Technique A technique was developed for measuring the radioactive concentration of breast milk samples for Tc-99m labelled radiopharmaceuticals. It utilises equipment that can be commonly found in most Nuclear Medicine departments. Key to the accuracy of this technique is consistency in positioning and geometry. Initial Setup A ‘Standard’ sample of Tc-99m (approx. 5 MBq) in a 2 ml volume is prepared. This is placed in a flat bottomed cylindrical plastic tube and measured inside a radionuclide calibrator. The radionuclide calibrator should comply with the quality control requirements set out in Good Practice Guide No. 93 [3]. A NaI scintillation probe (Radhound SS404 Al Sodium Iodide Scintillation Probe), as commonly used by Nuclear Medicine departments for contamination monitoring, is then positioned on a workbench (Figure 1). The detector is secured and its position marked in such a manner that it can either not be moved or can be accurately repositioned when required. Dr Ewan Eadie Department of Nuclear Medicine, Ninewells Hospital and Medical School, Dundee, DD1 9SY Milk Metrology: A Simple Technique for Measuring the Radioactive Concentration of Breast Milk Secretion of radioactivity in breastmilk Following the administration of a radiopharmaceutical, mothers may be required to interrupt breast feeding in order to reduce the radiation dose to the child from excreted radioactivity. Interruption periods for a range of radiopharmaceuticals are specified in the ARSAC Notes for Guidance [1]. However the published data on feeding interruption is limited and there is wide variation in the reported excreted activities [2]. With appropriate measurement it may be possible to reduce the feeding interruption time. Measurement of radioactive concentration in breast milk is not routinely performed. This may be because of a lack of access to the equipment needed. The measurement technique described here should be accessible to all Nuclear Medicine departments. System Tests A number of tests were carried out to determine the uncertainties associated with this measurement technique. The largest of these are listed below. Comparison The results from this measurement technique were compared to a Multi-Channel Analyser (Ortec digiBase). Average difference = 1.0% Maximum difference = 3.7% Patient Sample To date, only a single patient sample has been measured. This is mainly due to logistical problems accessing the samples. The concentration of the patient sample was: Contamination monitor technique: 37.5 kBq ml -1 Multi-Channel Analyser: 37 kBq ml -1 The sample was taken four hours post administration of Tc-99m MAA. Had the infant been allowed to resume feeding after this sample they would have received an effective dose of 1.2 mSv, based on 140 ml feeds separated by four hours [1]. However as no further measurement was possible, the mother was advised a standard interruption to feeding of 12 hours. Conclusion Nuclear Medicine departments are encouraged by the ARSAC Notes for Guidance to measure the radioactive concentration of breast milk following the administration of a radiopharmaceutical. The technique described here can easily be employed by any Nuclear Medicine department. The uncertainty in the final result is acceptable, especially when put within the context of the assumptions made about ingested volume. Measurement has shown good agreement between this technique and a multi-channel analyser. Future Work Access to patient samples is a major obstacle in performing measurements on the radioactive content of breast milk. To tackle this I would like to design a system that could be employed on post- natal wards, allowing the midwives to carry out the measurement and determine when feeding can resume. Recent work by PHE suggests external radiation dose from close contact with mother would increase feeding interruption by 1 hour for Tc-99m MAA [4]. Linearity (25 – 400 counts s -1 )13% (Ave. difference) Repeatability (Long Term)6% (CoV) Variation between users5% (CoV) Repeatability (Short Term)4% (CoV) Repeatability (Daily)4% (CoV) Source Placement2% (CoV) Detector Placement1% (CoV) The ‘Standard’ sample is positioned at a distance of 30 cm from the front window of the NaI probe. The position of the ‘Standard’ is also marked for consistency. This is done by drawing round the bottom of the tube (Figure 1). The ‘Standard’ is left to decay until the concentration is approximately that expected from a breast milk sample (i.e. 50 kBq ml -1 ). Once decayed, an average of ten background measurements and ten ‘Standard’ measurements are performed. This provides a background corrected sensitivity calibration in counts per second per kBq (counts s -1 kBq -1 ). Breast Milk Measurement It is important that the breast milk sample is measured with precisely the same positioning and geometry as the ‘Standard’. Therefore 2 ml of the milk sample is withdrawn (or the volume is increased to 2 ml depending upon the supplied sample) and placed inside another flat bottomed cylindrical tube. The tube is placed within the pre-marked circle and ten measurements are taken. From these measurements the concentration of the breast milk sample in kBq ml -1 is calculated. Once the concentration is known it is possible to determine the effective dose to the infant. Figure 1: Photograph of measurement setup References [1] Notes for Guidance on the Clinical Administration of Radiopharmaceuticals and Use of Sealed Radioactive Sources. Administration of Radioactive Substances Advisory Committee. 2006 (revised 2014). [2] Stabin, M.G. and Breitz, H.B. Breast Milk Excretion of Radiopharmaceuticals: Mechanisms, Findings, and Radiation Dosimtery. J Nucl Med. 2000; 41: 863-873 [3] A National Measurement Good Practice Guide No.93: Protocol for Establishing and Maintaining the Calibration of Medical Radionuclide Calibrators and their Quality Control. National Physical Laboratory. 2006. [4] Fraser, L. and Evans, W. D. Calculation of interruption times for breastfeeding following the administration of radiopharmaceuticals to patients. Presented at BNMS Harrogate 2014.