Biological halflife of iodine in adults with intact thyroid function and in athyreotic persons

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Canadian National Calibration Reference Centre for Bioassay and In Vivo Monitoring Human Monitoring Laboratory

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THESTUDY Purpose Update our knowledge of thyroid metabolism. Obtain new knowledge for hyperthyroid, hypothyroid and athyroid persons. Particpants Ottawa Civic Hospital. HML. Volunteers (patients) receiving diagnostic/metastatic survey doses of 131I. Protocol Repeat counts at HML. $25 per visit.

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KNOWNDATA ICRP78 MODEL Rest of Body Blood Thyroid 30% 0.83 d 70% 0.35 d 100% 80 d 20% 60 d 80% 15 d

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BIOLOGICALHALFLIFE - or, how is it obtained? The effective half life is related to: The radiological half life (8.04 d) The biological half life The 131I retention can give the biological half life l l l e r B = + l B Ln T = ( ) 2 1 2

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MEASUREMENTS Measurements began in March 1997 and ended in December 1999. Thyroid counts and wholebody counts PHA / MCS

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THESUBJECTS 39 9 0.07 Sv 3.3 Sv Activities given: Set 1: ~333 kBq Set 2: ~150 MBq Up to six counts per subject Composed of three groups

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TheGROUPS Hypothyroid - uptake 0% - 6%; 3 persons. T½ = 29.3 ± 8.8 (smean) Euthyroid - uptake 6% - 22%; 27 persons. T½ = 66.1 ± 6.3 (smean) Hyperthyroid - uptake >22%; 9 persons. T½ = 38.2 ± 8.6 (smean) Athyroid - uptake ~ 0% (1 - 12%); 9 persons. T½ = 1.0 ± 0.2 (smean) T½ = 18.4 ± 1.1 (smean)

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UPTAKES

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SET2RESULTS SPECIMEN PLOT ?e = 0.113 d-1 ?B = 0.026 d-1 T1/2 = 26.15 d

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SET4RESULTS SPECIMEN PLOT ?e = 0.121 d-1 ?B = 0.035 d-1 T1/2 = 19.74 d ?e = 0.806 d-1 ?B = 0.72 d-1 T1/2 = 0.96 d

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RESULTSUMMARY Sets 1 - 3

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RESULTSUMMARY Sets 1 - 3

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MORESULTSUMMARY Set 4

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MORESULTSUMMARY Uptake(%) =16.1 ± 1.2 (smean) Half Life (d) Set 2 66.1 ± 6.3 Rest of Body Blood Thyroid 30% 0.83 d 70% 0.35 d 80 d 60 d 15 d

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MORESULTSUMMARY Half Life (d) Set 2 66.1 ± 6.3 Set 4 1.0 ± 0.2 Set 4 18.4 ± 1.1 Uptake(%) =16.1 ± 1.2 (smean) Blood 100% 0.35 d

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RETENTION R t e e e e Ln T Ln T Ln T Ln T ( ) . . . . ( ) . ( ) . ( ) . ( ) . = + + + - æ è ç ö ø ÷ - æ è ç ö ø ÷ - æ è ç ö ø ÷ - æ è ç ö ø ÷ 0 669 0 2 0 13 0 0008 2 0 25 2 57 3 2 1 03 2 18 5 Bend occurs at < 5 days Includes radioactive decay

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RETENTION Bend occurs at < 10 days R t e e e e Ln T Ln T Ln T Ln T ( ) . . . . ( ) . ( ) . ( ) . ( ) . = + + + - æ è ç ö ø ÷ - æ è ç ö ø ÷ - æ è ç ö ø ÷ - æ è ç ö ø ÷ 0 869 0 2 0 13 0 0008 2 0 25 2 57 3 2 1 03 2 18 5 Includes radioactive decay

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Uptake is too high in model. T-test (value = 11.36, tcrit = 1.68, P < 0.001) Half-life may need lowering. T-test (value = 1.97, tcrit = 1.68, P =0.027) There are two other pathways. Probably salivary glands and “rest of body” Always use individual specific parameters for case studies. CONCLUSIONS WHAT THIS STUDY HAS FOUND:

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H D T E N E

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