Calculation of therapeutic activity of radioiodine in Graves’ disease by means of Marinelli’s formula, using technetium (99mTc) scintigraphy

Abstract

The therapeutic activity of 131I administered to patients with Graves’ disease can be calculated by means of Marinelli’s formula. The thyroidal iodine uptake (131IUmax) needed for the calculation is usually determined with the use of 131I. The purpose of the paper was to estimate 131IUmax on the basis of technetium uptake in the thyroid at 20 min (99mTcU20min). Eighty patients suffering from Graves’ disease were qualified for radioiodine therapy with measurement of fT4, fT3, thyroid-stimulating hormone and its receptor (TRAb). Prior to the treatment, all the patients were euthyroid. 131IUmax for each patient was determined according to the levels of 131I after 24 h (131IU24h), while effective half-life (T eff) according to the measurements of 131IU24h and 131I uptake after 48 h (131IU48h). Additionally, on the day before measuring 131IU24h, 99mTcU20min was calculated for each patient. It was demonstrated that there existed a correlation, with statistical significance at p < 0.05, between the following pairs of values: TRAb and 131IU24h, TRAb and 99mTcU20min, and 99mTcU20min and 131IU24h. The interdependence between 131IU24h and 99mTcU20min at the level of significance p < 0.05 is described by the following algorithms: 131IU24h = 17.72 × ln (99mTcU20min) + 30.485, if TRAb < 10 IU/ml, and 131IU24h = 18.03 × ln (99mTcU20min) + 38.726, if TRAb > 10 IU/ml. It is possible to predict thyroid iodine uptake 131IU24h in Graves’ disease on the basis of measuring the uptake of 99mTcU20min. This shortens the time necessary for diagnosis and enables the calculation of 131I activity using Marinelli’s formula.

Correlation between &lt;sup&gt;99m&lt;/sup&gt;TcO&lt;sub&gt;4&lt;/sub&gt;&lt;sup style=&quot;margin-left:-7px;&quot;&gt;-&lt;/sup&gt; Thyroid Scintigraphy and Blood Test in Primary Hyperthyroidism

“…A correlation coefficient of 0.88 has previously been reported for test values 20 minutes after 99m 4 TcO − and 24 hours after 131 I administration, indicating a strong positive correlation between the two [8]. Recently, the potential of 99m 4 TcO − in predicting 131 I uptake in 131 I therapy has also been reported [9]. In a study of the correlations between 99m 4 TcO − uptake and free T3, free T4, and TSH receptor antibody, the correlation coefficient was 0.593 (p < 0.01) with free T3, 0.334 (p < 0.01) with free T4, and 0.414 (p < 0.01) with TSH receptor antibody [7].…”

Influence of high tissue-absorbed dose on anti-thyroid antibodies in radioiodine therapy of Graves’ disease patients

“…The 131 I dose was calculated using the Marinelli formula and administered as a single oral dose in an outpatient setting. 12 The radioiodine dose used was calculated according to the following formula 13 According to the in-house protocol, EHL estimation was based on the difference in RAIU between 24 h and 48 h. The 131 I EHL in the thyroid is 6 days. To explain how EHL was established, we provide the following examples: if RAIU at 48 h and 24 h was 53% and 65%, respectively, the difference (53% and 65%) was 12%.…”

Empiric radioiodine for hyperthyroidism: Outcomes, prescribing patterns, and its place in the modern era of theranostics

“…10,11 However, assessment of thyroid activity by scintigraphy using technetium-99m (Tc-99m) pertechnetate has been challenging due to its different kinetics and imaging characteristics to I-131. 6,12 Our institution has I-131 theranostic expertise for metastatic differentiated thyroid cancer. To date we have not yet applied theranostics to I-131 treatment of hyperthyroidism, which has been prescribed empirically in line with American Thyroid Association (ATA) guidelines, 2 limited to a maximum of 15 mCi (555MBq) due to local outpatient regulatory requirements.…”