Radiation dose rates of differentiated thyroid cancer patients after <Superscript>131</Superscript>I therapy

Postoperative ¹³¹I treatment for differentiated thyroid cancer (DTC) can create a radiation hazard for nearby persons. The present prospective study aimed to investigate radiation dose rates in ¹³¹I-treated DTC patients to provide references for radiation protection. A total of 141 ¹³¹I-treated DTC patients were enrolled, and grouped into a singular treatment (ST) group and a repeated treatment (RT) group. The radiation dose rate of ¹³¹I-treated patients was measured. The rate of achieving discharge compliance and restricted contact time were analyzed based on Chinese regulations. Multivariate logistic regression analysis was used to analyze the independent factors associated with the clearance of radioiodine. The rate of achieving discharge compliance (¹³¹I retention <?400 MBq) was 79.8 and 93.7% at day 2 (D2) for the ST and RT groups, respectively, and reached 100% at D7 and D4, respectively. The restricted contact time with ¹³¹I-treated patients at 0.5 m for medical staff, caregivers, family members, and the general public ranged from 4 to 7 days. Multivariate logistic regression analysis showed that the 24-h iodine uptake rate was the only significant factor associated with radioiodine clearance. For the radiation safety of ¹³¹I-treated DTC patients, the present results can provide radiometric data for radiation protection.     

The use of radioactive iodine in the treatment of Graves disease

Fifty patients with uncomplicated Graves' disease were treated with radioactive iodine (I(131)). Twenty-six patients who were followed for one year or longer are the basis of this report. Twenty-five are now euthyroid; only one is not completely well. The total dose of radioiodine administered varied from 0.5 to 10 millicuries. The average length of time necessary for return to a euthyroid state was from three to four months. Hypometabolism developed in three patients, and in one the signs and symptoms of myxedema developed. No other complications ensued. One patient who apparently relapsed had complete return to normal after further iodine administration. The determination of the uptake of radioactive iodine by the thyroid gland is a useful diagnostic procedure in differentiating conditions simulating hyperthyroidism.Following treatment with radioactive iodine, the thyroid gland becomes smaller, the uptake of iodine by the gland is reduced, and the level of organic iodine in the plasma becomes normal. In acute thyroiditis, in spite of a high basal metabolic rate, high content of organic iodine in the plasma and other evidences of "hyperthyroidism," the uptake of I(131) has been very low.     

Nicotinamide increases thyroid radiosensitivity by stimulating nitric oxide synthase expression and the generation of organic peroxides.

Differentiated thyroid cancer and hyperthyroidism are treated with radioiodine. However, when the radioisotope dose exceeds certain limits, the patient must be hospitalized to avoid contact with people that would otherwise be exposed to radiation. It would be desirable to obtain a similar therapeutic effect using lower radioiodine doses. Radiosensitizers can be utilized for this purpose. Nicotinamide (NA) increases thyroid radiosensitivity to 131I in both normal and goitrous glands. NA causes a significant increase in thyroid blood flow, which would increase tissue oxygenation and tissue damage via free radicals. Wistar rats were treated with either nicotinamide (NA), 131I or both. The expression of the three isoforms of nitric oxide synthase (NOS) in the thyroid (Western blot) and the activities of SOD, GPx, catalase and organic peroxides were determined. Treatment with NA or 131I increased the expression of eNOS and the generation of organic peroxides. When administered jointly, they showed a synergistic effect. No changes were observed in the other NOS isoforms or in the activities of catalase, glutathione peroxidase and superoxide dismutase. NA potentiates the effect of 131I by increasing eNOS, which would in turn stimulate NO production, increasing thyroid blood flow and tissue damage via organic peroxides.     

Traitement de l’hyperthyroïdie par l’iode 131 : à propos de 280 cas

We report through this work the experience of nuclear medicine department at Ibn-Sina hospital (Rabat), in the treatment of hyperthyroidism with iodine-131. We retrospectively studied a cohort of 280 patients with hyperthyroidism, from several regions of Morocco between January 2001 and January 2010. A clinical examination and a serum assessment of TSHus, FT4 and FT3 have been made at baseline and at 3, 6, 12 and 24 months after radioiodine therapy. The activity of iodine-131 administered ranged from 296 to 740 MBq and depended on the pathology being treated, age, thyroid volume, intensity of clinical and biological hyperthyroidism and socioeconomic situation. Radioiodine therapy has often been proposed as a treatment for second or third intention, 71 patients were initially treated with iodine-131, while 209 patients had received iodine-131 after failure of medical treatment and/or recurrence after surgical treatment. Graves’ disease was the most common etiology (60%), followed by toxic adenoma (20%), and multinodular toxic goiter (13%). The therapeutic efficacy of a single dose of radioiodine evaluated after a 6-months follow-up was 92% in Graves’ disease, 98% in toxic adenomas and 97% in toxic multinodular goiter. No acute complication was observed. Taking into account our socioeconomic context, radioiodine therapy remains the preferred treatment of hyperthyroidism in our country with good value vs. price and excellent tolerance.     

Discussion on radioactive iodine treatment of hyperthyroidism and the risk of induced cancer

Iodine-131 (¹³¹I, radioiodine) has been used for over eight decades for the treatment of Graves’ disease, either as initial therapy or following failure of thionamides, as well as for the treatment of autonomous thyroid nodules. ¹³¹I treatment is simple to administer, effective, and relatively inexpensive. Recently, there has been some turmoil after a study published in JAMA Internal Medicine reported an increased risk of cancer from ¹³¹I treatment. The impact was of short duration however, as the paper received severe criticisms from many nuclear medicine physicians as well as from endocrinologists. Here we explain why that paper's conclusions are doubtful. We also review the major data on the topic of ¹³¹I therapy of hyperthyroidism and the risk of cancer.     

A Case of Esophageal Stricture After Iodine 131 Ablation

ObjectiveTo report the first case of esophageal stricture as a complication of radioiodine (¹³¹I) ablation therapy.MethodsWe review the medical and surgical history of this patient and discuss various potential causes of the esophageal stricture.ResultsA 79-year-old woman presented with increasing dysphagia and weight loss of about 4.5 kg after recent ¹³¹I therapy for thyroid cancer remnant ablation. Her pertinent history included gastroesophageal reflux disease, an anterior midcervical esophageal web, and a distal esophageal stricture. She also had a history of radiation therapy to her chest for breast cancer about 28 years previously. On the day of ¹³¹I therapy, the 5.5-GBq ¹³¹I capsule lodged accidentally in her midcervical area for approximately 2.5 hours. The resulting radiation dose to the proximal esophagus was estimated to be 7.86 Gy from gamma radiation and possibly as high as several thousand grays from beta radiation. During this time, the esophagus had possible direct exposure to the sodium phosphate dibasic that was used as filler in the sodium iodide capsule. Because of the worsening dysphagia, an esophagogastroduodenoscopy was performed 4 weeks after the ¹³¹I therapy, which showed a new proximal esophageal stricture.ConclusionWe believe that the additional localized radiation and sodium phosphate exposure from the lodging of the ¹³¹I capsule may have contributed to the development of a proximal esophageal stricture. To our knowledge, such an occurrence has not previously been described in the medical literature. For prevention of such an occurrence, we recommend a careful swallowing evaluation of patients with any history of esophageal radiation exposure, dysphagia, or esophageal strictures before administration of ¹³¹I in capsule form. Alternative methods of ¹³¹I delivery, if available, should be considered. (Endocr Pract. 2012;18: e61-e64)     

THE USE OF RADIOACTIVE IODINE IN THE TREATMENT OF GRAVES' DISEASE

Fifty patients with uncomplicated Graves'' disease were treated with radioactive iodine (I₁₃₁). Twenty-six patients who were followed for one year or longer are the basis of this report. Twenty-five are now euthyroid; only one is not completely well.The total dose of radioiodine administered varied from 0.5 to 10 millicuries. The average length of time necessary for return to a euthyroid state was from three to four months.Hypometabolism developed in three patients, and in one the signs and symptoms of myxedema developed. No other complications ensued. One patient who apparently relapsed had complete return to normal after further iodine administration.The determination of the uptake of radioactive iodine by the thyroid gland is a useful diagnostic procedure in differentiating conditions simulating hyperthyroidism.Following treatment with radioactive iodine, the thyroid gland becomes smaller, the uptake of iodine by the gland is reduced, and the level of organic iodine in the plasma becomes normal.In acute thyroiditis, in spite of a high basal metabolic rate, high content of organic iodine in the plasma and other evidences of “hyperthyroidism,” the uptake of I₁₃₁ has been very low.     

Hyperthyroidism due to Coexistence of Graves’ Disease and Struma Ovarii

ObjectiveTo report an unusual case of persistent thyrotoxicosis after treatment of Graves’ disease, because of coexistence of struma ovarii.MethodsWe report the clinical history, imaging studies, laboratory and pathologic data, and treatment in a patient with persistent hyperthyroidism after surgical treatment of Graves’ disease. In addition, we discuss some aspects of the pathogenesis of hyperthyroidism due to functioning struma ovarii.ResultsA 42-year-old woman underwent near-total thyroidectomy for treatment of Graves’ disease. Post-operatively, hyperthyroidism was still present. Methimazole was administered again, and performance of a ¹³¹I whole-body scan demonstrated a focus of intense uptake in the pelvis. Pelvic ultrasonography revealed a mass (11 by 8 by 7.1 cm) arising from the right ovary, with both solid and cystic components. Abdominal surgical exploration was performed, and the final histologic diagnosis was struma ovarii. The symptoms of hyperthyroidism diminished, and 3 weeks postoperatively, the thyroid hormone levels were in the hypothyroid range.ConclusionIn patients with refractory hyperthyroidism after thyroid surgical treatment, radioiodine scanning should be performed to diagnose or exclude the functioning profile of ovarian masses. (Endocr Pract. 2007;13:274-276)     

Effect of methyl thiouracil on radioiodine thyroidal retention in rats

Summary Some goitrogens like methyl thiouracil (MTU) because of their thynamide grouping act as antithyroid drugs inhibiting the organification of iodide, but do not alter the iodide transport. Their administration to an intact animal, therefore, might alter the thyroidal iodine kinetics. Here an attempt has been made to study the effect of MTU on thyroidal iodine kinetics in rats as well as to find out whether any difference in kinetics could be detected between different radioiodines, viz.,¹³¹I,¹²⁵I, and¹²³I. Cumulated thyroidal activity which is a time integral of the activity has been taken as the parameter to represent the sum effect of thyroidal iodine kinetics over a specific time period of interest.From the in vivo thyroidal activity measurements, carried out over extended periods of time, the cumulated activity was calculated for both MTU treated and normal rats that received¹³¹I,¹²⁵I, or¹²³I at different times before the MTU start. Within a day of the start of the MTU there is a rapid loss of thyroidal iodine. The severity of the loss depended upon the time that elapsed between the start of the MTU schedule and the particular radioiodine administered. The absence of isotopic effect on the uptake as well as on the rate of uptake for the three different radioiodine isotopes studied has been brought out.Alexander von Humboldt Fellow, on leave from Institute of Nuclear Medicine and Allied Sciences, Delhi -7, India     

Early and Late Toxicity of Radioiodine Therapy: Detection and Management

ObjectiveTo review the early and late toxicity associated with radioiodine (¹³¹I) therapy, highlighting the need for early detection and, where possible, preventive measures.MethodsWe performed a literature search on MEDLINE using the terms radioiodine, ¹³¹I toxicity, complications, Graves disease, and thyroid cancer and chose the most relevant studies for this review. Where appropriate, we refer to our own published series of patients as well.ResultsUptake of ¹³¹I into the salivary glands, lacrimal glands, fetal thyroid, and adult thyroid accounts for the early toxic effects of radioiodine therapy. Delayed radiation effects to the gonads, bone marrow, and cell nuclei give rise to late complications. Toxicity may also arise from uptake into metastatic tumors located at vulnerable sites, including the spinal cord, brain, and lungs.ConclusionAlthough radioiodine therapy for benign and malignant thyroid disorders is usually well tolerated, clinicians involved in the management of thyroid disorders need to be aware of the potential toxicity of radioiodine and take all measures to reduce these effects to a minimum. (Endocr Pract. 2010;16:1064-1070)     

Dependency of the remnant 131I-NaI biokinetics on the administered activity in patients with differentiated thyroid cancer

PurposeTo study the dependency of the effective half-life on the administered activity and the correlation between the time-integrated activity and the remnant uptake at 2d and 7d in patients treated for DTC with 1.11 GBq, 3.7 GBq or 5.55 GBq of ¹³¹I-NaI.MethodsNinety-two patients undergoing total thyroidectomy and lymph node removal were included. If cancer had not spread to lymph nodes, patients received 1.11 GBq of ¹³¹I-NaI when the lesion maximal diameter was smaller than 4 cm, and 3.7 GBq for bigger sizes. If cancer had spread to lymph nodes patients received 5.55 GBq. There were 30, 49 and 13 patients respectively treated with 1.11 GBq(Group 1), 3.7 GBq(Group 2) and 5.55 GBq(Group 3). Two SPECT/CT scans were performed at 2d and 7d after radioiodine administration for each patient to determine the thyroid remnant activities and effective half-lives of the radioiodine.ResultsStatistical analysis showed significant differences (p < 0.05) in the effective half-life among patients treated with 1.11 GBq, 3.7 GBq and 5.55 GBq. A high positive correlation (ρ > 0.95) was found between the time-integrated activity and the remnant activity at 2d for the three groups of patients.ConclusionsThere were significant differences in the effective half-life of the radioiodine in remnants of patients treated with activities of 1.11 GBq, 3.7 GBq or 5.55 GBq. The high positive linear correlation found between the time-integrated activity and the remnant activity at 2d for the three groups of patients indicate that the time-integrated activity could be estimated from one time-point.     

Long-Term Outcomes of Radioiodine Therapy for Juvenile Graves Disease with Emphasis on Subsequently Detected Thyroid Nodules: A Single Institution Experience from Japan

Objective: To investigate the long-term outcomes of radioiodine therapy (RIT) for juvenile Graves disease (GD) and the ultrasonographic changes of the thyroid gland.Methods: All of 117 juvenile patients (25 males and 92 females, aged 10 to 18 &lsqb;median 16] years) who had undergone RIT for GD at our clinic between 1999 and 2018 were retrospectively reviewed. Each RIT session was delivered on an outpatient basis. The maximum ¹³¹I dose per treatment was 13.0 mCi, and the total ¹³¹I dose per patient was 3.6 to 29.8 mCi (median, 13.0 mCi). ¹³¹I administration was performed once in 89 patients, twice in 26, and three times in 2 patients. Ultrasonography of the thyroid gland was regularly performed after RIT. The duration of follow-up after the initial RIT ranged from 4 to 226 (median 95) months.Results: At the latest follow-up more than 12 months after RIT (n = 111), the patients' thyroid functions were overt hypothyroidism (91%), subclinical hypothyroidism (2%), normal (5%), or subclinical hyperthyroidism (2%). New thyroid nodules were detected in 9 patients, 4 to 17 years after initial RIT. Patients with newly detected thyroid nodules underwent RIT with lower doses of ¹³¹I and had larger residual thyroid volumes than those without nodules. None of the patients were diagnosed with thyroid cancer or other malignancies during the follow-up period.Conclusion: Over a median follow-up period of 95 months (range, 4 to 226 months), RIT was found to be effective and safe in juvenile GD. However, cumulative evidence from further studies is required to confirm the long-term safety of RIT for juvenile GD.Abbreviations: ATD = antithyroid drug; GD = Graves disease; KI = potassium iodide; LT4 = levothyroxine; MMI = methimazole; PTU = propylthiouracil; RAIU = radio-active iodine uptake; RIT = radioiodine therapy; ^99mTc = technetium-99m; TSH = thyrotropin     

Influence of the external and internal radioactive contamination of the body and the clothes on the results of the thyroidal 131I measurements conducted in Belarus after the Chernobyl accident—Part 2: Monte Carlo simulation of response of detectors near the thyroid

This paper describes the calculation of the response of the most common types of radiation detectors that were used within the first few weeks after the Chernobyl accident to determine the activity of ¹³¹I in the thyroids of Belarusian subjects of an epidemiologic study of thyroid cancer. The radiation detectors, which were placed against the necks of the subjects, measured the exposure rates due to the emission of gamma rays resulting from the radioactive decay of ¹³¹I in their thyroids. Because of the external and internal radioactive contamination of the monitored subjects, gamma radiation from many radionuclides in various locations contributed to the exposure rates recorded by the detectors. To estimate accurately the contribution from gamma rays emitted from various internal and external parts of the body, the calibration factors of the radiation detectors, expressed in kBq per µR h^− 1, were calculated, by means of Monte Carlo simulation, for external irradiation from unit activities of 17 radionuclides located on 19 parts of the body, as well as for internal irradiation from the same 17 radionuclides in the lungs, from caesium radionuclides distributed uniformly in the whole body, and from ¹³¹I in the thyroid. The calculations were performed for six body sizes, representative of the age range of the subjects. In a companion paper, the levels of external and internal contamination of the body were estimated for a variety of exposure conditions. The results presented in the two papers were combined to calculate the ¹³¹I activities in the thyroids of all 11,732 Belarusian study subjects of an epidemiologic study of thyroid cancer and, in turn, their thyroid doses.

     

Influence of initial large dose on subsequent uptake of therapeutic radioiodine in thyroid cancer patients

Fifty-two patients with differentiated thyroid cancer, following thyroidectomy were studied by administering a quantity of up to 5 mCi of [¹³¹I]sodium iodide. In most of these patients, radioiodine uptake values obtained with the subsequent therapeutic dose were markedly lower than those observed with the initial doses. This observation was verified in seven of the patients with differentiated thyroid cancer, by measuring the radioiodine uptake with a second dose of 4.5 mCi of [¹³¹I]sodium iodide. Calculations showed that the major etiology was probably therapeutic irradiation of the thyroid by the first dose.     

Evaluation of the cytogenetic effects of <Superscript>131</Superscript>I preceded by recombinant human thyrotropin (rhTSH) in peripheral lymphocytes of Wistar rats

The present study was carried out to investigate the cytogenetic effects of therapeutic exposure to radioiodine preceded by rhTSH in an animal model. Three groups of Wistar rats (n = 6) were used: one group was treated only with ¹³¹I (11.1 MBq/animal); the other two groups received rhTSH (1.2 μg/rat of either Thyrogen or rhTSH-IPEN, respectively) 24 h before administration of radioiodine. The percentage of lymphocytes with chromosome aberrations and the average number of aberrations and of dicentrics per cell were determined on blood samples collected 24 h, 7 and 30 days after administration of ¹³¹I. The data show that the treatment with radioiodine alone or associated with rhTSH resulted in a greater quantity of chromosome alterations in relation to basal values after 24 h, with a gradual decline after 7 and 30 days of treatment. An increase in chromosome alterations was also seen after rhTSH treatment alone. Neither of the treatments, i.e., with ¹³¹I alone or associated with hormone, resulted in an aneugenic effect or influenced the kinetics of cellular proliferation in rat blood lymphocytes. There was no significant difference between the cytogenetic effects of Thyrogen and rhTSH-IPEN treatment. These data suggest that the treatment with radioiodine, associated or not with rhTSH, affects to a limited extent a relatively small number of cells although the occurrence of late stochastic effects could not be discarded.     

Radioactive Iodine Therapy Without Recent Antithyroid Drug Pretreatment For Hyperthyroidism Complicated By Severe Hyperbilirubinemia Due To Hepatic Dysfunction: Experience Of A Chinese Medical Center

Objective: The objective of this work is to report our experience with ¹³¹I therapy without recent antithyroid drug (ATD) pretreatment for refractory severe hyperthyroidism complicated by hyperbilirubinemia due to hepatic dysfunction.Methods: Five patients with refractory severe hyperthyroidism were treated with ¹³¹I at 90 to 120 μCi/g-thyroid (total activity, 6.2 to 10.1 mCi). The patients previously had received ATD treatment from 2 months to 12 years and discontinued ATDs from 2 months to 4 years before ¹³¹I treatment due to treatment failure or severe jaundice. Prior to ¹³¹I therapy, the patients were asked to take a low-iodine diet and were treated with bisoprolol fumarate, digoxin, furosemide, S-adenosylmethionine, polyene phosphatidylcholine, and plasma exchange as supportive treatment for related clinical conditions. Four of the patients also received lithium carbonate in conjunction with their ¹³¹I treatment. The patients were followed for 4 to 9 years after ¹³¹I therapy.Results: After ¹³¹I treatment, jaundice disappeared completely within 3 to 4 months in all patients, and liver function tests returned to normal. Concurrent atrial fibrillation and heart failure, leukopenia and thrombocytopenia, or thrombocytopenia and left cardiac enlargement improved remarkably in 3 patients during the follow-up period. Three to 45 months after ¹³¹I treatment, hypothyroidism was noted in the patients and they were treated with L-thyroxine replacement therapy.Conclusion:¹³¹I therapy without recent ATD pretreatment for refractory severe hyperthyroidism complicated by serious jaundice appears to be safe and effective, with good long-term results. It may be the preferred therapy for such patients and should be used as early as possible.Abbreviations:ATD = antithyroid drugFT₄ = free thyroxinePTU = propylthiouracilRAIU = radioactive iodine uptakeTSH = thyroid-stimulating hormone     

Autoradiolysis of iodinated monoclonal antibody preparations

We investigated the effects of ionizing radiation on the immunointegrity of antibody fragments (Fab) because large amounts of high specific activity ¹³¹I may damage the proteins. We found that 1000 Gy of external ¹³⁷Cs γ radiation was sufficient to destroy 80–90% of the immunointegrity of the initial preparation. This effect was also produced by internally added [¹³¹I]NaI in a quantity sufficient to provide the same radiation absorbed dose. Since radioiodinated monoclonal antibodies labeled to high specific activity are being evaluated for radioimmunotherapy, the above observation is significant since high levels of internal radiation occur with therapeutic doses of ¹³¹I-labeled antibody. Human serum albumin in low concentration (2%) added to the iodinated antibody solutions was successful in preventing loss of immunoreactivity and can be used to protect and stabilize therapeutic quantities of radiolabeled monoclonal antibody preparations.     

Apport de l’iode 131 dans le traitement de la maladie de Basedow dans le service de médecine nucléaire de l’hôpital Ibn Sina de Rabat

One hundred and twenty-nine Grave's Basedow diseases in any gender and variable age patients, coming from several cities of Morocco, were randomized in a study of radio-iodine treatment who took place at the nuclear medicine department of Ibn Sina Hospital (Rabat, Morocco) during the period (from January 2001 to December 2008). The radio-iodine treatment was a first, second or third option and radio-iodine activities delivered varied (from 222 to 555 MBq 6 to 15 mCi) according to the age, the thyroid volume, the degree of hyperthyroidism and socio-economical situation. The high amounts of ¹³¹I were reserved especially to the patients who live far and whose socio-economic level is low with an aim of quickly obtaining an easily controllable state of hypothyroidism by a substitute treatment. The results showed that: (1) 57.36% of patients reverted to euthyroïdism (n = 74) with a patient having received two ¹³¹I cures. The second cure was justified by recurrence of hyperthyroidism after the first cure; (2) 34.88% passed in hypothyroidism (n = 45) with three patients having received two cures of ¹³¹I, the second cure was justified by recurrence of hyperthyroidism after the first cure in two patients and by the persistence of the hyperthyroidism after the first cure for the third patient. The average time of passage in hypothyroidism was 4.5 months; (3) 7.76% had remained in hyperthyroidism after the radioactive iodine treatment. Finally, 92.24% of our patients treated by radioactive iodine had passed in euthyroïdism or hypothyroidism against 7.76% whose hyperthyroidism had persisted or occurred.     

Low vs. high radioiodine activity to ablate the thyroid after thyroidectomy for cancer: a randomized study

Background

Radioactive iodine is commonly administered following thyroidectomy for differentiated thyroid carcinoma to ablate the thyroid remnant. The optimal administered activity of radioiodine is unknown.

Methodology/Principal Findings

Adult subjects (n = 160) diagnosed with papillary or follicular thyroid carcinoma were randomly allocated to receive either 1100 MBq (30 mCi) or 3700 MBq (100 mCi) activity of radioiodine (¹³¹I) following thyroidectomy. The study participants were prepared for ablation using thyroid hormone withdrawal. Ablation was considered successful when serum thyroglobulin concentration was less than 1 ng/mL and no uptake was present in ¹³¹I scan. Ablation was successful following one administration of radioiodine in 42 (52%; 95% CI, 41% to 63%) of the 81 evaluable study participants who received 1100 MBq, and in 43 (56%, 45% to 67%) of the 77 subjects who received 3700 MBq activity (P = .61). There was no difference between the groups in the numbers of repeat radioiodine treatments needed to complete ablation (P = .27). The higher activity was associated with more nausea and taste disturbances, and a longer stay in a radioprotected isolation unit. None of the participants died from thyroid cancer during a median follow up of 51 months; three subjects in the 3700 MBq group and none in the 1100 MBq group were diagnosed with distant metastases during follow-up. In a meta-analysis of four randomized studies that compared the 1100 and 3700 MBq activities, the 1100 MBq activity tended to be associated with a higher risk of unsuccessful ablation (relative risk 1.148, 95% CI 0.974 to 1.353, P =  .10).

Conclusions/Significance

The results provide no conclusive evidence that 3700 MBq activity is more effective for ablation of the thyroid remnant than 1100 MBq activity. The 3700 MBq activity is associated with more adverse effects.

Trial Registration

ClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT00115895","term_id":"NCT00115895"}}NCT00115895