Real-time quantitation of thyroidal radioiodine uptake in thyroid disease with monitoring by a collar detection device

Radioactive iodine (RAI) is safe and effective in most patients with hyperthyroidism but not all individuals are cured by the first dose, and most develop post-RAI hypothyroidism. Postoperative RAI therapy for remnant ablation is successful in 80–90% of thyroid cancer patients and sometimes induces remission of nonresectable cervical and/or distant metastatic disease but the effective tumor dose is usually not precisely known and must be moderated to avoid short- and long-term adverse effects on other tissues. The Collar Therapy Indicator (COTI) is a radiation detection device embedded in a cloth collar secured around the patient’s neck and connected to a recording and data transmission box. In previously published experience, the data can be collected at multiple time points, reflecting local cervical RAI exposure and correlating well with conventional methods. We evaluated the real-time uptake of RAI in patients with hyperthyroid Graves’ disease and thyroid cancer. We performed a pilot feasibility prospective study. Data were analyzed using R^© (version 4.0.3, The R Foundation for Statistical Computing, 2020), and Python (version 3.6, Matplotlib version 3.0.3). The COTI was able to provide a quantitative temporal pattern of uptake within the thyroid in persons with Graves’ disease and lateralized the remnant tissue in persons with thyroid cancer. The study has demonstrated that the portable collar radiation detection device outside of a healthcare facility is accurate and feasible for use after administration of RAI for diagnostic studies and therapy to provide a complete collection of fractional target radioactivity data compared to that traditionally acquired with clinic-based measurements at one or two time-points.

Clinical Trials Registration NCT03517579, DOR 5/7/2018.

A thermoluminescent method for the evaluation of the 131I effective half-life in the thyroid when treating Graves' disease

When planning treatment for Graves' disease with ¹³¹I, the effective half-life (T_eff) should be estimated individually as it depends on biological characteristics such as iodine uptake and excretion, which differ from an individual to another (Berg et al. 1996). All the methods to quantify T_eff described in the literature are quite complex and are difficult to be used in clinical routine. With the aim of optimizing this process, a simplified method is proposed here to evaluate T_eff of ¹³¹I during treatment of Graves' disease. The present study suggests improving the method of determining T_eff based on thermoluminescence dosimetry. This involves implementing a new method and includes reduction of TLD (Thermoluminescent Dosimeter) measurements. The proposed method was validated on patients with Graves' disease. The radiation dose delivered to the patients was determined using the MIRD (Medical Internal Radiation Dosimetry) formalism. The relative difference between T_eff obtained based on seven measurement intervals at [0-24 h, 24-48 h, 48-72 h, 72-96 h, 96-120 h, 120-144 h, 144-168 h] and based on three measurement intervals at [0-24 h, 72-96 h, 144-168 h] and [0-24 h, 120-144 h, 144-168 h] was 1.9% and 3.81%, respectively. Comparison of doses obtained based on a general T_eff and on a personalized T_eff gave a statistically significant difference with a correlation coefficient R²of 0.44. The T_eff obtained from just three measurements was found to be sufficiently accurate and easily applicable. The results obtained demonstrate the need to determine and use personalized T_eff values instead of using a fixed value of 7 days.

Radioiodine therapy of Graves' disease

Graves' disease (GD), the most common cause of hyperthyroidism, is an autoimmune disease directly caused by circulating autoantibodies that bind and activate the TSH receptor, inducing metabolic activation of the thyroid gland; this may be associated with important cardiac (atrial fibrillation) and ocular (ophthalmopathy) complications. Treating GD with real curative intent implies the full elimination of the functioning thyroid parenchyma using surgery or radioactive iodine therapy (RAI). RAI has been used in humans with hyperthyroidism since 1941, thanks to the pioneering work of a physician (Dr. Saul Hertz) and a physicist (Dr. Arthur Roberts). The rationale of RAI is based on the effect of radiation of ¹³¹I on target cells leading to DNA damage, both directly, through breakage of molecular bonds, and indirectly through the formation of free radicals. In particular, irradiation causes a broad spectrum of cellular damage due to the production of reactive oxygen species and lipid peroxidation of the plasma membrane. Thus, RAI-related cellular death takes place through both apoptosis and necrosis. The aim of this review was to summarize indications, efficacy, safety profile, and dosimetric aspects of RAI treatment in patients affected by GD.

Improving individualised dosimetry in radioiodine therapy for hyperthyroidism using population biokinetic modelling

The application of an individualised dosimetric procedure for radioiodine therapy requires the intensive use of resources in nuclear medicine facilities. In practice, the amount of data taken per patient is too limited to obtain an accurate estimate of the absorbed dose in the thyroid. The individualised absorbed dose estimates can be enhanced using statistical tools for population-based approaches. The aim of this work was to build a population biokinetic model of thyroid uptake and elimination of radioiodine using a nonlinear mixed-effects approach in patients with Graves' disease. Input data for the model development were taken from a dosimetric method based on ¹²³I imaging data. ¹²³I decay-corrected uptake values were estimated at 4, 24, and 96 h post-administration and for 58 patients. The root mean squared error (RMSE) for predicted ¹²³I uptake values by the fitted model was 4%. The root mean squared error of prediction (RMSEP) for out-of-sample ¹²³I uptake values, computed by a leave-one-out cross-validation, was 12%. We calculated ¹³¹I activity to administer from out-of-sample predicted ¹²³I uptake values and compared the result with that calculated from observed ¹²³I uptake values. RMSEP values for therapeutic activity revealed that there were measuring points with higher weight than others in the model. The mixed-effects approach can be used to enhance the accuracy of dosimetric calculations in therapies using ¹³¹I. Assessing the accuracy of the predictive model enables choosing among different time-sampling schedules of the radioiodine thyroid uptake curve. This methodology can also be applied in other areas of radiation dosimetry.

Comparing pre-therapeutic 124I and 131I uptake tests with intra-therapeutic 131I uptake in benign thyroid disorders

PURPOSE

¹²⁴I-PET/CT can be used for pre-therapeutic assessment of radioactive iodine uptake in benign thyroid disorders, however systematic comparisons with intra-therapeutic uptake are still lacking for these disorders. The goals of this study were to compare ¹²⁴I RAIU and conventional ¹³¹I RAIU tests with each other; to compare both tests with intra-therapeutic uptake (reference); and to verify the time course of radioactive iodine uptake at three time points (30, 102, and 336 h [14 days] post administration; p.a.).

METHODS

Thirteen patients with benign thyroid diseases underwent ¹³¹I RAIU test and ¹²⁴I RAIU test one after another before the intra-therapeutic ¹³¹I uptake (reference) was measured via short-range and long-range measurements. After correction for decay, relative uptake differences were calculated and subjected to the Bland-Altman method for the evaluation of levels of agreement.

RESULTS

Radioactive iodine uptake tests with ¹²⁴I-PET/CT and ¹³¹I probe did not show systematic deviations at any time point. Likewise, at 30 and 102 h p.a. there was no systematic discrepancy between pre-therapeutic and intra-therapeutic uptake levels. At 14 days p.a., however, both pre-therapeutic tests tended to overestimate the uptake compared to reference. Findings showed, for the first time with ¹²⁴I, that radioiodine therapy has some early radiobiological effects possibly limiting the accuracy of pre-therapeutic dosimetry.

CONCLUSIONS

¹²⁴I RAIU tests represent a feasible alternative to standard ¹³¹I RAIU tests. The additional benefits of ¹²⁴I-PET/CT (e.g., functional topography, inclusion of retrosternal areas, possibility to enable fusion imaging) may thus increase the scope of this technology in benign thyroid disorders.

Comparison of clinical outcome after a fixed dose versus dosimetry-based radioiodine treatment of Graves' disease: Results of a randomized controlled trial in Indian population

OBJECTIVE

Two approaches are used to treat Graves' disease with radioiodine ((131)I)-the fixed dose approach and the other based on dosimetry. A prospective study was performed to compare the results of these two approaches in a randomized patient population, as such study is lacking in the Indian population till date.

MATERIALS AND METHODS

Patients with Graves' disease were randomized into two groups: (1) Fixed dose group and the (2) Calculated dose group, each comprising of 20 patients. All the patients underwent detailed clinical and biochemical evaluation. Thyroid mass was determined by high resolution ultrasound machine with linear transducer of 7-11 MHz. Patients were given 185-370 kBq (5-10 uCi) of (131)I and 24 hr radioiodine uptake (RAIU) was calculated using thyroid uptake probe and thyroid phantom. Fixed dose group patients were administered 185MBq of (131)I. Calculated dose group patients were given (131)I as per the following formula: Calculated dose = [3700 kBq/g × estimated thyroid wt. (g)] ÷ 24 hr RAIU (%). Success of first dose of radioiodine was defined as clinically/biochemically euthyroid/hypothyroid status at the end of 3 months without the need for further therapy.

RESULTS

In the fixed dose group, eight patients were hyperthyroid, four were euthyroid, and eight were hypothyroid after the first dose at 3 months. Success rate of first dose was 60%. In calculated dose group, seven patients were hyperthyroid, eight were euthyroid, and five were hypothyroid. Success rate of first dose was 65%.

CONCLUSIONS

There is no statistically significant difference between the success rates of the two methods at 3 months. Hence, fixed dose approach may be used for treatment of Graves' disease as it is simple and convenient for the patient. Longer follow-up with higher number of patients should be done to confirm or contradict our findings.

Radioiodine therapy in benign thyroid diseases: effects, side effects, and factors affecting therapeutic outcome

Radioiodine ((131)I) therapy of benign thyroid diseases was introduced 70 yr ago, and the patients treated since then are probably numbered in the millions. Fifty to 90% of hyperthyroid patients are cured within 1 yr after (131)I therapy. With longer follow-up, permanent hypothyroidism seems inevitable in Graves' disease, whereas this risk is much lower when treating toxic nodular goiter. The side effect causing most concern is the potential induction of ophthalmopathy in predisposed individuals. The response to (131)I therapy is to some extent related to the radiation dose. However, calculation of an exact thyroid dose is error-prone due to imprecise measurement of the (131)I biokinetics, and the importance of internal dosimetric factors, such as the thyroid follicle size, is probably underestimated. Besides these obstacles, several potential confounders interfere with the efficacy of (131)I therapy, and they may even interact mutually and counteract each other. Numerous studies have evaluated the effect of (131)I therapy, but results have been conflicting due to differences in design, sample size, patient selection, and dose calculation. It seems clear that no single factor reliably predicts the outcome from (131)I therapy. The individual radiosensitivity, still poorly defined and impossible to quantify, may be a major determinant of the outcome from (131)I therapy. Above all, the impact of (131)I therapy relies on the iodine-concentrating ability of the thyroid gland. The thyroid (131)I uptake (or retention) can be stimulated in several ways, including dietary iodine restriction and use of lithium. In particular, recombinant human thyrotropin has gained interest because this compound significantly amplifies the effect of (131)I therapy in patients with nontoxic nodular goiter.

Accuracy and optimal timing of activity measurements in estimating the absorbed dose of radioiodine in the treatment of Graves' disease

Calculation of the therapeutic activity of radioiodine (131)I for individualized dosimetry in the treatment of Graves' disease requires an accurate estimate of the thyroid absorbed radiation dose based on a tracer activity administration of (131)I. Common approaches (Marinelli-Quimby formula, MIRD algorithm) use, respectively, the effective half-life of radioiodine in the thyroid and the time-integrated activity. Many physicians perform one, two, or at most three tracer dose activity measurements at various times and calculate the required therapeutic activity by ad hoc methods. In this paper, we study the accuracy of estimates of four 'target variables': time-integrated activity coefficient, time of maximum activity, maximum activity, and effective half-life in the gland. Clinical data from 41 patients who underwent (131)I therapy for Graves' disease at the University Hospital in Pisa, Italy, are used for analysis. The radioiodine kinetics are described using a nonlinear mixed-effects model. The distributions of the target variables in the patient population are characterized. Using minimum root mean squared error as the criterion, optimal 1-, 2-, and 3-point sampling schedules are determined for estimation of the target variables, and probabilistic bounds are given for the errors under the optimal times. An algorithm is developed for computing the optimal 1-, 2-, and 3-point sampling schedules for the target variables. This algorithm is implemented in a freely available software tool. Taking into consideration (131)I effective half-life in the thyroid and measurement noise, the optimal 1-point time for time-integrated activity coefficient is a measurement 1 week following the tracer dose. Additional measurements give only a slight improvement in accuracy.