Endocrine Abstracts (2006) 11 P863

Effects of increment of endogenous TSH levels on the effective half-life time of 131I and iodine uptake by thyroid remnants in patients after thyroidectomy

M Knapska-Kucharska, J Makarewicz, L Oszukowska, Z Adamczewski & A Lewinski


Departament of Nuclear Medicine and Oncological Endocrinology, Chair and Department of Endocrinology and Metabolic Diseases, Medical University of Lodz, Lodz, Poland.


The effectiveness of thyroid remnants ablation with 131I after thyroidectomy for differentiated thyroid carcinoma (DTC) depends mainly on absorbed radiation dose, which is proportional to 131I uptake (Tup) and its effective half-life time (EHL) in the remnants.

Aim: Assessment of endogenous TSH level increment effects on EHL of 131I and Tup in thyroid remnants after surgery for DTC.

Material: Twenty-one patients were studied (20 women, 1 man), the age: 30–79 years (mean: 48 y.): 10 patients with tumour - pT1a, 1 patient - pT1b, 6 - pT2, 4 with pT4 (UICC 1997).

Methods: Diagnostic doses of 4 MBq 131I were orally administered to each patient 10, 20 and 30 days after thyroidectomy and Tup was measured 2 h, 4 h, 24 h, 48 h and 240 h after the administration. TSH level was determined before each 131I administration. EHL and the products of Tup and EHL were calculated. The differences between TSH, Tup, EHL and Tup*EHL were assessed at each time-point (paired Wilcoxon test).

Results:

Median at dayDifference between days (p)
10203010 vs 2010 vs 3020 vs 30
TSH (μIU/ml)6.729.053.2<0.00010.000040.00004
Tup (%)3.23.44.80.0330.0630.420
EHL (days)4.04.63.60.0300.1200.013
Tup*EHL12.915.69.90.0060.920.17

Conclusions: Between the 10th and the 20th day after surgery the rise of TSH was accompanied by a rise of both Tup and Tup*EHL while no further increment of Tup or Tup*EHL was observed between the 20th and the 30th day. EHL did not change significantly during the study period. 2. No improvement of dosimetric parameters (EHL, Tup) was noted during the long (30 days) vs the short (20 days) TSH stimulation.

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