Der Einfluß physiologischer und pharmakologischer Iodmengen auf den I-Uptake der Schilddrüse – Eine Modellrechnung

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Summary Aim: Graves' hyperthyroidism and antithyroid drugs empty the intrathyroid stores of hormones and iodine. The consequence is rapid 131I turnover and impending failure of radioiodine therapy. Can administration of additional inactive iodide improve 131I kinetics? Patients, methods: Fifteen consecutive patients, in whom the 48 h post-therapeutically calculated thyroid dose was between 150 and 249 Gy due to an unexpectedly short half-life, received 3 × 200 μg inactive potassium-iodide (127I) daily for 3 days (Group A), while 17 consecutive patients with a thyroid dose of ≥ 250 Gy (Group B) served as the non-iodide group. 48 hours after 131I administration (M1) and 4 or 5 days later (M2) the following parameters were compared: effective 131I half-life, thyroid dose, total T3, total T4, 131I-activity in the T3- and T4-RIAs. Results: In Group A, the effective 131I half-life M1 before iodine (3.81 ± 0.93 days) was significantly (p <0.01) shorter than the effective 131I half-life M2 (4.65 ± 0.79 days). Effective 131I half-life M1 correlated with the benefit from inactive 127I (r = –0.79): Administration of 127I was beneficial in patients with an effective 131I half-life M1 of <3 or 4 days. Patients from Group A with high initial specific 131I activity of T3 and T4 showed lower specific 131I activity after addition of inactive iodine compared with patients from the same group with a lower initial specific 131I activity of T3 and T4 and compared with the patient group B who was given no additional inactive iodide. This correlation was mathematically described and reflected in the flatter gradient in Group A (y = 0.5195x + 0.8727 for 131I T3 and y = 1.0827x – 0.4444 for 131I T4) and steeper gradient for Group B (y = 0.6998x + 0.5417 for 131I T3 and y = 1.3191x – 0.2901 for 131I T4). Radioiodine therapy was successful in all 15 patients from Group A. Conclusion: The administration of 600 μg inactive iodide for three days during radioiodine therapy in patients with Graves' hyperthyroidism and an unexpectedly short half-life of <3 or 4 days was a safe and effective alternative to the administration of a second radioiodine capsule

Section: Discussionmentioning

confidence: 87%

“…fective 131 Ihalf-life during radioiodine therapyh as at heoretical ande mpirical basis, namelyo ur previouslyp ublished model of iodine kinetics (27,28) andf irstc linical study (24).…”

Section: Gabevon Zusätzlicheminakti-vemiodidbei Derradioiodtherapiedementioning

confidence: 99%

Administration of additional inactive iodide during radioiodine therapy for Graves' disease

Dietlein¹,

Moka²,

Reinholz³

et al. 2007

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“…Das mit der Nahrung zugeführte Iodid wird sowohl von der Schilddrüse aufgenommen als auch über die Nieren ausgeschieden (7,(13)(14)(15)17). Unter Vernachlässigung der thyroidalen Iodausscheidung ergibt sich der theoretisch maximal mögliche prozentuale Iod-Uptake der Schilddrüse aus der Iodid-Clearance (IC) von Schilddrüse (SD) und Nieren:…”

Section: Patienten Material Methoden Theoretische Grundlagenunclassified

“…Dies trägt zu der systematisch niedriger errechneten integralen Iodspeicherung bei Verwendung des 24-Stunden-Uptakes auch mit Zugrundelegung der tatsächlichen effektiven Halbwertszeit der thyroidalen Iodausscheidung bei. Darüber hinaus stellt die Beschreibung des abfallenden Schen-kels der Iodspeicherkurve als monoexponentielle Funktion eine deutliche Vereinfachung dar, da Iodaufnahme und -abgabe simultan erfolgen und der abfallende Kurvenanteil nur dann einem monoexponentiellen Verlauf folgen würde, wenn zum Zeitpunkt des Speichermaximums die Aufnahme des Radioiods in die Schilddrüse bereits abgeschlossen wäre (2,11,14,15). Die tatsächliche Halbwertszeit der Iodausscheidung lässt sich durch alleinige Analyse des abfallenden Kurvenschenkels nicht ermitteln und wird somit in der Regel unterschätzt.…”

Section: Diskussionunclassified

Concept and validation of a simple model of the intrathyroidal iodine kinetics

Bormuth¹,

Braun²,

Zimny³

et al. 2004

Summary Aim of this study is the introduction and validation of a simple model of the intrathyroidal iodine kinetics, designed for optimizing radioiodine therapy planning and dose measurement in a routine clinical setting. Methods: The new model defines the intrathyroidal iodine kinetics as balance of the thyroidal iodine intake and -excretion, characterized by the two exponential equations At = A0 * (1-exp(-λ1t)) and At = A0 * (exp(-λ2t) -1), respectively. A0 describes the theoretically maximum iodine uptake when the thyroidal iodine excretion is ignored, λ1 and λ2 represent the constants characterizing the iodine intake and excretion, respectively. The thyroidal iodine content at the time t equals the sum of both functions, which is At = A0 * (exp(-λ2t)-exp(-λ1t)). In 25 patients with autonomous goiter / nodules (n = 18), Graves’ disease (n = 5), or endemic euthyroid goiter (n = 2), the iodine uptake in the thyroid during the radioiodine therapy as fraction of the applied activity was determined daily, with the remaining body covered by a lead shield. On average, 7.2 measurements were performed per patient (minimum 4, maximum 13). With these uptake values, individual regression curves were fitted using the above equation, and the difference between the actual measurements and the corresponding values of the regression curves was determined. Results: The average deviation of the 179 uptake values from the calculated points of the respective regression curves was only 1.4%. There was no significant difference between the three disease groups. The distribution of the relative deviations during the individual courses was constant, systematic errors were not detected. Conclusion: Our results suggest that the intrathyroidal iodine kinetics can be precisely described with the model At = A0 * (exp(-λ2t)-exp(-λ1t)). With only three measurements, the trend of the curve can be calculated, which allows to determine the total radioiodine storage in the thyroid.

“…Sowohl der Uptake als auch die Halbwertszeit sind u. a. von der lodversorgung des Patienten abhängig (22). In dieser Arbeit wurde ein lodstoffwechselmodell verwendet, welches das Verhalten radioaktiven lods im Körper hinreichend richtig beschreiben soll (25,26). Auch sollte überprüft werden, inwieweit durch verschiedene Mengen stabilen lods der Uptake und damit die Exposition der Schilddrüse bei unbeabsichtigter Zufuhr von 1-131 verringert werden kann.…”

Section: Zusammenfassungunclassified

Influence of stable iodine on the uptake of the thyroid – model vs. experiment

Weber¹,

Wellner²,

Voth³

et al. 2001

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Summary Aim: The influence of physiological and pharmacological amounts of iodine on the uptake of radioiodine in the thyroid was examined in a 4-compartment model. This model allows equations to be derived describing the distribution of tracer iodine as a function of time. The aim of the study was to compare the predictions of the model with experimental data. Methods: Five euthyroid persons received stable iodine (200 μg, 10 mg). 1-123-uptake into the thyroid was measured with the Nal (Tl)-detector of a body counter under physiological conditions and after application of each dose of additional iodine. Actual measurements and predicted values were compared, taking into account the individual iodine supply as estimated from the thyroid uptake under physiological conditions and data from the literature. Results: Thyroid iodine uptake decreased from 80% under physiological conditions to 50% in individuals with very low iodine supply (15 μg/d) (n = 2). The uptake calculated from the model was 36%. Iodine uptake into the thyroid did not decrease in individuals with typical iodine supply, i.e. for Cologne 65-85 μg/d (n = 3). After application of 10 mg of stable iodine, uptake into the thyroid decreased in all individuals to about 5%, in accordance with the model calculations. Conclusion: Comparison of theoretical predictions with the measured values demonstrated that the model tested is well suited for describing the time course of iodine distribution and uptake within the body. It can now be used to study aspects of iodine metabolism relevant to the pharmacological administration of iodine which cannot be investigated experimentally in humans for ethical and technical reasons.