British Journal of Radiology 75 (2002),464-466 © 2002 The British Institute of Radiology
Breast milk activity during early lactation following maternal 99Tcm macroaggregated albumin lung perfusion scan
E McCauley, MSc
and
A Mackie, PhD
Regional Medical Physics Department, University Hospital of North Durham, North Road, Durham DH1 5TW, UK
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Abstract
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A breast feeding infant may receive a radiation dose from ingestion of breast milk following the administration of a radiopharmaceutical to the mother. The Administration of Radioactive Substances Advisory Committee recommendation to interrupt breast feeding may not necessarily apply in the period of early lactation when colostrum is being produced. Following a lung scan using 99Tcm macroaggregated albumin (MAA) on a patient approximately 15 h post partum, radioactivity within breast milk was measured. Milk was expressed approximately every 4 h during the day and samples were counted. The sample radioactivity concentration peaked at 15 h and decayed monoexponentially (half clearance time was approximately 4.8 h). The estimated effective dose to the infant from ingestion alone, had breast feeding not been interrupted, was approximately 0.02 mSv. These data suggest that interruption to breast feeding may not be necessary following administration of up to the diagnostic reference level of 99Tcm MAA during early lactation.
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Introduction
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When a nursing mother undergoes a nuclear medicine investigation a proportion of the administered radiopharmaceutical may be secreted in breast milk, giving a radiation dose to a breastfed child. In the UK the Ionising Radiation (Medical Exposure) Regulations 2000 [1] require special attention be paid to justification of nuclear medicine procedures for breast feeding females. The Medical and Dental Guidance Notes [2] suggest conducting a risk assessment, employing a dose constraint of 1 mSv to the baby. The Administration of Radioactive Substances Advisory Committee (ARSAC) notes for guidance include recommended interruption times for breast feeding to reduce the radiation dose to the infant to less than 1 mSv from ingested radioactivity [3]. However, ARSAC advise not to use these interruption times in the period of early lactation when colostrum is being produced. Colostrum is secreted in the first few days after birth, providing easily digestible, concentrated nutrition in a small volume. After 3–4 days, mature milk is produced in increasing quantities with the contribution from colostrum gradually declining. Data for radioactivity secreted within colostrum are sparse. Peak radioactive concentration of colostrum, or its time to decline, have been reported to occur both earlier [4] and much later [5] than for mature milk. Temporal variation in concentration can be expected between patients, radiopharmaceuticals and with administration time post-partum. Therefore measurements of radioactivity are required on serial samples of early breast milk in order to estimate any breast feeding interruption period necessary for individual patients.
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Materials and method
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A 26-year-old female was referred for a lung scan for the investigation of pulmonary embolism. The procedure was performed approximately 15 h post-partum. The patient received 133Xenon for the ventilation study and 86 MBq of 99Tcm macroaggregated albumin (MAA) (Pulmocis®; CIS, High Wycombe, UK) for the perfusion study. The absence of significant quantities of free 99Tcm pertechnetate in the 99Tcm MAA was confirmed (labelling efficiency 98.8%).
Milk was expressed as completely as possible, using an electric pump, at intervals of approximately 4 h during the day only. The radioactivity concentration of each sample was determined using a gamma counter of known counting efficiency, applying a decay correction to take account of time since expression. The spectrum of several samples was examined to confirm the absence of contaminating radionuclides.
The radioactivity concentration of the breast milk samples was plotted against time following 99Tcm MAA administration to the mother. A monoexponential curve was fitted to the data after the peak activity concentration had been reached, to determine the decay constant. The exponential clearance model, plus the estimated radioactivity ingested by the feeding infant at times prior to peak activity concentration, was used to estimate the total radioactivity ingested [6]. The effective dose to the feeding infant was calculated using a weight adjusted effective dose per unit activity of 99Tcm of 0.35 mSv MBq-1 [6].
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Results
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The radioactivity concentration of breast milk is shown in Table 1
, together with time since administration. The radioactive concentration increased initially, reaching a peak at approximately 15 h, and decreasing approximately monoexponentially (decay constant=0.144 h-1) thereafter. This equates to a half clearance time of approximately 4.8 h in this patient.
Using worst case assumptions in the exponential clearance model for the volumes of milk ingested at 4-hourly intervals (142 ml per feed) [5], the total ingested activity for uninterrupted feeding in this case would have been 52 kBq of 99Tcm pertechnetate. This represents just 0.06% of administered radioactivity. The effective dose to the infant from ingested radioactivity would be 0.02 mSv in this case.
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Discussion
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The 15 h delay to reach peak sample radioactivity concentration in this patient is in agreement with published data. Heaton [7] demonstrated a plateau in the radioactivity concentration within colostrum between 2 h and 6 h following administration of 99Tcm MAA in a single patient, without significant decrease until 20 h. Mountford and Coakley [5] reported that colostrum radioactivity concentration rose between 5 h and 7 h in one patient. Similarly, the half clearance time of approximately 4.8 h is in agreement with Heaton [7], a mean value of 4.3 h reported for 20 patients receiving 99Tcm MAA [5], and 4.2 h in a cohort of 33 patients [6]. Although there is agreement that temporal variation of breast milk radioactivity concentration occurs, our patient secreted only 0.06% of the administered dose. This is lower than any previously reported value [5, 8]; minimum value 0.3% (mean 2.4%) for 20 patients receiving 99Tcm MAA [5]. This difference may be owing to variation in circulating pertechnetate levels in plasma caused by variability in the breakdown rate of 99Tcm MAA in the capillary bed, and individual differences in the percentage of pertechnetate secreted in breast milk, which may be related to breast milk maturity.
The ARSAC recommended interruption time for breast feeding for mature milk is 12 h after the administration of up to 80 MBq of 99Tcm MAA. For this patient there would have been no need to interrupt breast feeding at all, since worst case assumptions resulted in an estimated effective dose of 0.02 mSv to the infant. In practice, volumes of colostrum expressed during the first 24–48 h post-partum are likely to be significantly below the assumed 850 ml day-1. In this case the volume of early samples was only a few millilitres, increasing to less than 50 ml by 40 h (55 h post-partum). The expression of small volume samples is not expected to significantly affect the result since evidence suggests that radioactivity concentration is independent of volume of milk secreted [4]. These data emphasize the need to make direct measurement of expressed samples on an individual patient basis, unless mature milk is being produced. To keep infant dose within the 1 mSv constraint [2], the contribution from external irradiation must also be taken into account. This "cuddle dose" can be estimated from published data, using worst case assumptions, as 0.1 mSv [9, 10].
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Conclusion
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These data support current ARSAC advice to determine any interruption period to breast feeding on an individual basis during early lactation. Interruption may not be necessary to ensure an infant dose of less than 1 mSv following the administration of up to the diagnostic reference level of 99Tcm MAA during early lactation. However, the absence of a significant body of data during colostrum production, variability between patients, radiopharmaceuticals and time post-partum necessitates individual risk assessment. Even if dose estimates indicate no need to interrupt feeding, the mother should be advised to express and discard the first feed, consistent with the "as low as reasonably practicable" principle, as recommended by ARSAC.
Received for publication September 18, 2001.
Revision received January 24, 2002.
Accepted for publication January 29, 2002.
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References
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Department of Health. The Ionising Radiation (Medical Exposure) Regulations 2000, Statutory Instrument No. 1059. London: HMSO, 2000.
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Draft Medical and Dental Guidance Notes. A good practice guide to implement ionising radiation protection in the clinical environment. London: Department of Health, 2000.
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Administration of Radioactive Substances Advisory Committee. Notes for guidance on the clinical administration of radiopharmaceuticals and use of sealed radioactive sources. London: Department of Health, 1998.
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Rubow S, Klopper J, Wasserman H, Baard B, van Niekerk M. The excretion of radiopharmaceuticals in human breast milk: additional data and dosimetry. Eur J Nucl Med 1994;21:144–53.[Medline]
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Mountford PJ, Coakley AJ. A review of the secretion of radioactivity in breast milk: data, quantitative analysis and recommendations. Nuc Med Commun 1989;10:15–27.
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Mountford PJ, Lazarus CR, Edwards S. Chapter 8: Radiopharmaceuticals. In: Bennett PN, editor. Drugs and human lactation (2nd edn). Amsterdam, The Netherlands: Elsevier Science, 1996:609–77.
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Heaton B. The build up of technetium in breast milk following the administration of 99Tc(m)O4 labelled macroaggregated albumin. Br J Radiol 1979;52:149–50.[Abstract/Free Full Text]
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Rose MR, Prescott MC, Herman KJ. Excretion of Iodine-123-hippuran, technetium-99m-red blood cells and technetium-99m-macroaggregated albumin into breast milk. J Nucl Med 1990;31:978–84.[Abstract/Free Full Text]
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Mountford PJ. Risk assessment of the nuclear medicine patient. BJR 1997;70:671–84.[Medline]
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Mountford PJ, O'Docherty MJ, Forge NI. Radiation dose rates from adult patients undergoing nuclear medicine investigations. Nucl Med Commun 1991;12:767–77.[Medline]
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Abstract
Introduction
