Radioactive Iodine for the Treatment of Subclinical Thyrotoxicosis Grade 1 and 2: Outcome of up to 18-Year Follow Up.

Background: Subclinical thyrotoxicosis (SCT) is associated with significant morbidity and mortality, specifically increased risk of atrial fibrillation and cardiovascular death. The management is ill-defined due to the scarcity of randomised controlled studies. Some clinicians recommend radioiodine (RAI) treatment however its long-term outcome is unknown. Therefore, further data is needed to provide robust evidence-based guidelines. Methods: A prospective, single-protocol analysis of the outcome of SCT patients (Grade 1; 0.1-0.4 mIU/L and Grade 2; <0.1 mIU/L) treated with mean dose of 427 MBq of I131, followed up for up to 18 years. Thyroid function tests were measured at 4-6 weeks, 3-, 6-, and 12-months post-RAI, and annually thereafter. Cure was defined as achieving a euthyroid/hypothyroid state. Results: Seventy-eight patients with a median age of 68 years (range 36-84) and varying aetiology [55 toxic multinodular goitre (TMNG), 10 toxic nodule (TN) and 13 Graves' disease (GD)] were followed up for a median period of 7.5 years (range 1-18). The cure rate was 100%. The rates of hypothyroidism in TMNG, TN and GD were 23.6%, 30% and 38.5% respectively. The median time to hypothyroidism was 6 and 12 months in GD and TMNG/TN respectively. No differences in outcome between Grade 1 versus Grade 2 were observed. Conclusion: RAI using single mean dose of 427 MBq is effective and safe, irrespective of aetiology or grade of TSH suppression. GD patients become hypothyroid within the first year, whilst TMNG/TN for up to 9-years. Thus after 12 months of follow up, annual thyroid function monitoring is advised.

Papillary thyroid carcinoma in cervical lymph nodes with vanished thyroid gland after ablation of Graves' disease by radioactive iodine.

Primary thyroid carcinoma after thyroid ablation by radioactive iodine is rare. We present a very rare condition of lateral apparent papillary thyroid carcinoma eight years after receiving radioactive iodine for thyrotoxicosis, which led to complete anatomical and functional involution of the thyroid gland.

Predicting outcomes and complications following radioiodine therapy in Graves' thyrotoxicosis.

OBJECTIVE: Radioiodine (RAI) is an effective treatment for Graves' thyrotoxicosis but is associated with a failure rate of 15% and may be a risk factor for thyroid eye disease (TED) and weight gain. We sought to examine predictors of RAI failure, weight gain, TED and patient satisfaction. DESIGN: Retrospective cohort study. PATIENTS: A total of 655 episodes of RAI in Graves' thyrotoxicosis patients (2006-2015). MEASUREMENTS: Biochemical assessment, including TFTs and thyrotropin receptor antibodies (TRAb), clinical features (eg, TED, weight and thionamide use) and patient questionnaire. RESULTS: The treatment failure rate was 17%. Failure was greater with higher fT4 (P = 0.002) and higher TRAb (P = 0.004). Failure rate was 42.2% when TRAb >40 U/L. Median weight gain was 3.2 kg in those with normal fT4 prior to RAI and 5.8 kg when fT4 was elevated (P < 0.001). New TED developed in 7.6% but was not associated with post-RAI dysthyroidism. Treatment satisfaction was generally high (median response 8/10). CONCLUSIONS: Treatment failure after RAI occurs in predictable groups and this should be reflected in the information provided to patients. Weight gain is common and may not entirely be explained by a return to pre-thyrotoxic baseline. We were unable to detect any significant impact of post-RAI dysthyroidism on weight gain, TED or thyroid symptoms in this large cohort.

Bilateral Keratoconus Induced by Secondary Hypothyroidism After Radioactive Iodine Therapy.

PURPOSE: To present a case of new-onset, bilateral, rapidly progressive keratoconus induced by secondary hypothyroidism after radioactive iodine therapy during the sixth decade of life that was successfully treated with corneal cross-linking. METHODS: Case report and literature review. RESULTS: A 53-year-old woman with no ocular complaints but with a history of Graves' disease and thyrotoxicosis was treated with radioactive iodine therapy and oral levothyroxine for secondary acquired hypothyroidism 3 years prior. Initially, uncorrected distance visual acuity (UDVA) was 20/40 and corrected distance visual acuity (CDVA) was 20/25 in both eyes. Over the following 3 years, the patient developed worsening UDVA and CDVA, with increasing manifest astigmatism of greater than 7.00 diopters (D) in the right eye and 4.75 D in the left eye, with corneal thinning and focal steepening and was diagnosed as having bilateral progressive keratoconus. The patient underwent sequential corneal cross-linking with resultant postoperative CDVA of 20/20 and reduced maximum keratometry and manifest astigmatism in both eyes. The patient's thyroid levels were within normal limits throughout the clinical course. CONCLUSIONS: This case provides evidence of the relationship between keratoconus development and thyroid gland dysfunction. The pathophysiology of this relationship has yet to be completely elucidated, but elevated levels of thyroxine in the aqueous humor and tear film and thyroxine receptors in the cornea likely play a role. Screening topographies for patients with thyroid gland dysfunction may be of value for these higher risk patients. [J Refract Surg. 2018;34(5):351-353.].

Management of thyrotoxicosis in children and adolescents: 35 years' experience in 304 patients.

BACKGROUND: Diffuse toxic goiter accounts for about 15% of all childhood thyroid diseases. There is great controversy over the management of Graves' disease in children and adolescents. This article reports our experience in 304 children and juvenile patients with Graves' disease. METHODS: Between 1981 and 2015, 304 patients aged 5-19 years with diffuse toxic goiter were studied, of whom 296 patients were treated with antithyroid drugs (ATD) for 18 months. Patients with persistent or relapsed hyperthyroidism who refused ablative therapy with surgery or radioiodine were managed with continuous methimazole (MMI) treatment. RESULTS: In 304 patients (245 females and 59 males), the mean age was 15.6±2.6 years. After 18 months of ATD therapy, 37 remained in remission and of the 128 who relapsed, two, 29 and 97 patients chose surgery, continuous ATD and radioiodine therapy, respectively. Of the 136 patients who received radioiodine, 66.2% became hypothyroid. Twenty-nine patients received continuous ATD therapy for 5.7±2.4 years. The mean MMI dose was 4.6±12 mg daily, no serious complications occurred and all of them remained euthyroid during the follow-up. Less abnormal thyroid-stimulating hormone (TSH) values were observed in these patients, as compared to patients who were on a maintenance dose of levothyroxine after radioiodine induced hypothyroidism. CONCLUSIONS: Original treatment with ATD and subsequent radioiodine therapy remain the mainstay of treatment for juvenile hyperthyroidism. Continuous ATD administration may be considered as another treatment modality for hyperthyroidism.

Graves disease following radioiodine therapy for toxic adenoma: Clinical case report.

RATIONALE: There is a low risk of developing Graves disease (GD) with elevated thyrotropin receptor antibodies (TRAbs) in patients undergoing radioiodine therapy for toxic adenoma. PATIENT CONCERNS: An old female patient with a history of Hashimoto thyroiditis was referred to our department due to thyrotoxic symptoms. After the administration of radioiodine, a significant remission was achieved. However, after 4 months, she was referred to our department again due to recurrence of hyperthyroid symptoms. DIAGNOSES: Based on the results of laboratory test, thyroid scan and ultrasound examination, she was diagnosed as thyrotoxicosis induced by toxic adenoma at the first visit. However, 4 months later, she was diagnosed as Graves' disease at the second visit. INTERVENTIONS: She received radioiodine therapy two times with different doses of 15 mCi and 12 mCi. OUTCOMES: After the administration of 15 mCi radioiodine, her thyroid hormones and clinical symptoms showed significant improvement. However, 4 months later, she presented thyrotoxicosis again. After the second radioiodine therapy with a lower dose, her clinical symptoms moved towards normalization during regular follow up. LESSONS: Toxic adenoma and GD are considered as 2 distinct disease entities; however, radioiodine therapy for toxic adenoma may induce GD. We should learn to differentiate these 2 disorders prior to radioiodine therapy because of different treatment strategies and goals.

Muscle paralysis in thyrotoxicosis.

Thyrotoxic periodic paralysis (TPP) is a condition characterised by muscle paralysis due to hypokalaemia usually secondary to thyrotoxicosis. We report a case of a 31-year-old man with no known comorbidities who presented to a tertiary healthcare unit with a 1-month history of difficulty in breathing, palpitations, weight loss and hoarseness of voice. On examination, his thyroid gland was palpable and fine hand tremors were present. An initial provisional diagnosis of hyperthyroidism was made. Three months after initial presentation, the patient presented in emergency with severe muscle pain and inability to stand. Laboratory results revealed hypokalaemia. All the symptoms reverted over the next few hours on administration of intravenous potassium. A diagnosis of TTP was established. After initial presentation, the patient was treated with carbimazole and propranolol. Once he was euthyroid, radioactive iodine ablation therapy (15 mCi) was carried out as definitive therapy, after which the patient's symptoms resolved; he is currently doing fine on levothyroxine replacement and there has been no recurrence of muscle paralysis.

Clinical efficacy of radioiodine therapy in multinodular toxic goiter, applying an implemented dose calculation algorithm.

Radioiodine is a common therapeutic option for Multinodular Toxic Goiter (MTG). We evaluated an algorithm for personalized radioiodine activity calculation. Ninety-three (28 male, 65 female; 43-84 years) patients with MTG eligible for radioiodine treatment (131I-iodide) were studied. The quantity of 131I-iodide to be administered was estimated by Thyroid Volume Reduction (TVR) algorithm, developed for Graves' disease. It takes into account 131I uptake, its effective half-life (T1/2eff), thyroid volume, and its expected reduction during treatment. A comparison with the activity calculated by other dosimetric protocols and the "fixed" activity method was performed. 131I uptake was measured by external counting, thyroid volume by ultrasonography (US), thyroid stimulating hormone (TSH), and thyroid hormones by standard immunometric methods. In a follow-up of 6-120 months, remission of hyperthyroidism after a single 131I-iodide treatment was observed in 76 patients (64 euthyroid, 12 hypothyroid). The thyroid volume reduction observed by US after the treatment fairly correlated with what predicted by our model; T1/2eff was highly variable and critically affected dose calculation. The administered activities (median 526 MBq, range 156-625 MBq) were slightly lower than the "fixed" activities (600 MBq) and with respect to the other protocols' prescriptions (-15/38%); the median 131I activity administered to relapsed patients (605 MBq) was significantly greater (P=0.01) with respect to the dose administered to cured patients (471 MBq). Our study shows that an effective cure of MTG can be obtained with relatively low 131I activities and probably with a relatively low incidence of hypothyroidism, using TVR method.

Radioiodine therapy in patients with type II amiodarone-induced thyrotoxicosis.

INTRODUCTION: The treatment of amiodarone-induced thyrotoxicosis (AIT) still remains a clinical challenge, requiring the cooperation of both endocrinologists and cardiologists. Unfortunately, even today AIT is related to significantly increased mortality. OBJECTIVES: The aim of this study was to compare the efficacy of radioidine therapy for type II AIT in 2 groups of patients: with high or normal radioiodine uptake and treated by amiodarone (AM) in the past (AM- group) and with low radioiodine uptake and currently treated with AM (AM+ group). PATIENTS AND METHODS: The AM- group included 57 patients and the AM+ group, 49. All patients received iodine-131 at a dose of 22mCi~800. Patient data were collected for over 2 years. RESULTS: After radioiodine administration, serum thyroid-stimulating hormone levels in the AM- group and AM+ group were 0.0 ±0.0 and 0.0 ±0.0, respectively, at 1 month; 1.2 ±3.3 and 0.6 ±1.2, respectively, at 12 months; and 4.2 ±3.6 and 1.9 ±0.8, respectively, at 2 years. All differences between the groups were statistically significant (P <0.0001). Free triiodothyronine and thyroxine levels were significantly higher in the AM+ group compared with the AM- group. During follow-up, death occurred in 22 patients in the AM+ group and 6 patients in the AM- group. CONCLUSIONS: Radioiodine treatment is a safe and effective therapeutic modality for patients with type II AIT despite low radioiodine uptake, especially for patients with contraindications to other types of treatment (eg, thyroidectomy). Moreover, since thyrotoxicosis in patients with AIT is a significant risk factor for increased mortality, and since there are no alternative antiarrythmic treatments, radioiodine administration seems to be the only effective therapeutic modality.

Radioiodine therapy in benign thyroid disorders. Evaluation of French nuclear medicine practices.

OBJECTIVES: Radioiodine is currently used routinely in the treatment of hyperthyroidism including Graves' disease (GD), toxic multinodular goitre (TMNG) and toxic solitary nodule (TSN) but no consensus exists on the most appropriate way to prescribe iodine--fixed dose or calculated doses based on the gland size or turnover of (131)I. We carried out the first nationwide French survey assessing the current practices in radioiodine treatment of hyperthyroidism. MATERIAL AND METHODS: A questionnaire was sent to French nuclear medicine hospital units and cancer treatment centres (n=69) about their practices in 2012. RESULTS: Euthyroidism was considered the successful outcome for 33% of respondents, whereas hypothyroidism was the aim in 26% of cases. Fixed activities were the commonest therapeutic approach (60.0% of GD prescribed doses and 72.5% for TMNG and TSN), followed by calculated activities from Marinelli's formula (based on a single uptake value and thyroid volume). The fixed administered dose was chosen from between 1 to 3 levels of standard doses, depending on the patient characteristics. Factors influencing this choice were disease, with a median of 370 MBq for GD and 555 MBq for TSN and TMNG, thyroid volume (59%) and uptake (52%) with (131)I or (99m)Tc. Even physicians using fixed doses performed pretherapeutic thyroid scan (98%). CONCLUSION: This study shows that practices concerning the prescription of (131)I therapeutic doses are heterogeneous. But the current trend in France, as in Europe, is the administration of fixed doses. The study provides the baseline data for exploring the evolution of French clinical practices.

Decreased birth weight, length, and head circumference in children born by women years after treatment for hyperthyroidism.

CONTEXT: Whether hyperthyroidism influences the birth characteristics of children born several years after treatment is unknown. OBJECTIVE: The objective of the study was to compare birth characteristics in singleton newborns delivered by women previously treated for Graves' disease (GD), toxic nodular goiter (TNG), or nontoxic goiter (NTG). DESIGN: This was a nested case-control design within a national cohort registry study from 1950 through 2006. SETTING: The study was conducted at a university and a hospital center in collaboration. PATIENTS: The birth characteristics of newborns (n = 3421) delivered in a cohort of 43 633 women treated for GD or toxic nodular goiter by radioiodine or surgery (exposed group) at least 1 year prior to pregnancy were compared with newborns (n = 2914) of 45 655 mothers, previously operated for NTG (unexposed group). MAIN OUTCOME: The primary outcome was birth weight, length, and head circumference. The secondary outcome was malformations, gestational age, and type of hyperthyroidism. RESULTS: The birth weight of exposed children was 3431 ± 607 g (mean ± SD) compared with the unexposed, 3520 ± 641 g (P < .001). The cumulative odds ratio (OR) for lower birth weight was 1.29 [95% confidence interval (CI) 1.16-1.43]. The average birth length for the exposed children was 50.0 ± 2.7 cm compared with the unexposed of 50.4 cm ± 2.6 cm (P < .01) [cumulative OR 1.25 (95% CI 1.13-1.37)]. The head circumference was 34.5 ± 1.9 cm among exposed and 34.7 ± 1.8 cm, respectively (P < .001), with an OR of 1.24 (95% CI 1.13-1.35). No differences in birth characteristics were observed between children born after maternal GD or toxic nodular goiter. CONCLUSIONS: Previous GD or TNG may influence the birth characteristics several years after radioiodine or surgical treatment.

Laser ablation and 131-iodine: a 24-month pilot study of combined treatment for large toxic nodular goiter.

CONTEXT: It is normally recognized that the preferred treatment in large toxic thyroid nodules should be thyroidectomy. OBJECTIVE: The aim of the study was to assess the efficacy of combined laser ablation treatment (LAT) and radioiodine 131 (131I) treatment of large thyroid toxic nodules with respect to rapidity of control of local symptoms, of hyperthyroidism, and of reduction of administered 131I activity in patients at refusal or with contraindications to surgery. DESIGN AND SETTING: We conducted a pilot study at a single center specializing in thyroid care. PATIENTS: Fifteen patients were treated with LAT, followed by 131I (group A), and a series of matched consecutive patients were treated by 131I only (group B). INTERVENTION(S): Laser energy was delivered with an output power of 3 W (1800 J per fiber per treatment) through two 75-mm, 21-gauge spinal needles. Radioiodine activity was calculated to deliver 200 Gy to the hyperfunctioning nodule. MAIN OUTCOME MEASURE(S): Thyroid function, thyroid peroxidase antibody, thyroglobulin antibody, ultrasound, and local symptoms were measured at baseline and up to 24 months. RESULTS: Nodule volume reduction at 24 months was: 71.3 ± 13.4 vs 47.4 ± 5.5%, group A (LAT+131I) vs group B (131I), respectively; P < .001). In group A (LAT+131I), a reduction in radioiodine-administered activity was obtained (-21.1 ± 8.1%). Local symptom score demonstrated a more rapid reduction in group A (LAT+131I). In three cases, no 131I treatment was needed after LAT. CONCLUSIONS: In this pilot study, combined LAT/131I treatment induced faster and greater improvement of local and systemic symptoms compared to 131I only. This approach seems a possible alternative to thyroidectomy in patients at refusal of surgery.

Radioactive iodine for thyrotoxicosis in childhood and adolescence: treatment and outcomes.

OBJECTIVE: The aim of the present study was to evaluate the outcome of radioiodine treatment in thyrotoxicosis in childhood and adolescence. METHODS: This was a retrospective study of 27 patients (ages 7.2- 19.8 years) with a diagnosis of thyrotoxicosis who received iodine-131 (I-131) treatment from January 2007 to December 2011 in the Nuclear Medicine Division, Department of Radiology, Faculty of Medicine, Chiang Mai University. Gender, duration of antithyroid drug (ATD) treatment, 24-hour I-131 uptake, thyroid weight, total dose and number of treatments with I-131, and thyroid status at 6 months after treatment were recorded. RESULTS: The outcomes of 27 patients (85.2% female, 14.8% male) treated with radioactive iodine were analyzed to assess the effectiveness of therapy as related to dose and gland size. All children and adolescents received 150 µCi of I-131/g of thyroid tissue (n=27). Six 6 months after treatment, 44.5% of the patients were hyperthyroid, 14.8% were euthyroid, and 40.7% were hypothyroid. Of the 12 cases with hyperthyroidism, 2 cases needed a second dose of I-131 treatment, and they finally reached a hypothyroid state. The patients were classified into 2 groups according to treatment success (euthyroid and hypothyroid) and treatment failure (hyperthyroid). There were no significant differences in age, gender, duration of ATD treatment, 2- and 24-hour I-131 uptake, thyroid weight, and total I-131 dose between these two groups. CONCLUSIONS: Radioiodine treatment is safe and effective for thyrotoxicosis in childhood and adolescence. It is suitable as a good second-line therapy for patients with severe complications, those who show poor compliance, and those who fail to respond to ATD treatment.

Predictors of treatment failure, incipient hypothyroidism, and weight gain following radioiodine therapy for Graves' thyrotoxicosis.

BACKGROUND: Following radioiodine ((131)I) therapy, both late recognition of hypothyroidism and treatment failure may result in adverse outcomes. AIM: We sought to assess indicators of both incipient hypothyroidism and treatment failure following (131)I and determine factors predictive of weight gain. SUBJECTS AND METHODS: Retrospective study of 288 patients receiving (131)I for treatment of Graves' thyrotoxicosis. Primary outcome measures were thyroid status and weight change at 1 yr following (131)I. RESULTS: The treatment failure rate at 1 yr was 13.5%. Hypothyroidism developed in 80.9%, with 58.5% of patients having levels of free T4 (fT4) <6 pmol/l at diagnosis. Patients receiving thionamides before and after (131)I had significantly higher levels of treatment failure (23.3%) than those with no thionamide exposure (6.3%, p=0.003), but also had more active Graves' disease. Following (131)I, development of a detectable TSH or low-normal fT4 levels was not associated with recurrent thyrotoxicosis. Median weight gain was 5.3 kg, although patients with nadir fT4 levels <6 pmol/l gained an average 2 kg more than those with levels >6 pmol/l (p=0.05). The main predictor of weight gain was fT4 level immediately prior to treatment; those in the lowest tertile gained a median 3.1 kg whilst those in the highest tertile gained 7.4 kg (median difference 4.3 kg; 95% confidence interval: 2.5-6.2). CONCLUSIONS: Marked hypothyroidism following (131)I is common and often occurs early. Simple biochemical parameters may help identify incipient hypothyroidism and potentially limit excess weight gain. Treatment failure is common in patients with severe thyrotoxicosis and in such cases larger doses of (131)I may be warranted.

Amiodarone-induced thyrotoxicosis in a case of Eisenmenger's syndrome.

Eisenmenger's syndrome is a condition due to any congenital heart defect with an intracardiac left-to-right communication that leads to pulmonary hypertension with reversed right-to-left blood flow and secondary cyanosis. The main complications of Eisenmenger's syndrome are heart failure and arrhythmias. Amiodarone, the drug of choice for arrhythmia treatment in such patients, can cause a number of complications, including amiodarone induced thyrotoxicosis (AIT). Hereby, we present a 41-year-old patient with Eisenmenger's syndrome who developed AIT and was successfully treated with radioactive iodine therapy. The patient had an accompanying heart failure and had been treated with amiodarone due to chronic atrial fibrillation. Twenty months later he developed an AIT for which was treated with 814 MBq (22 mCi) radioactive iodine. Since 7 weeks later only a slight decline in thyroid hormones was observed, the patient was received a transient treatment with methimazole, which had to be withdrawn soon due to severe leucopenia. Because of the need to maintain amiodarone, a second ablative radioactive iodine dose was administered leading to complete clinical remission. In conclusion, this case demonstrates that even though amiodarone reduces iodine uptake to a very low level, the therapy with radioactive iodine can be still effective if it is given in a repeated dose to patients who require continuation of amiodarone.

Efficiency of radioactive I-131 therapy in geriatric patients with toxic nodular goiter.

BACKGROUND AND AIMS: The success of I-131 therapy in geriatric patients who were referred to an endocrinology clinic with toxic nodular goiter and who lived in iodine-deficiency regions was studied. MATERIALS AND METHODS: Patients older than 60 years who received I-131 therapy were included via retrospective data analyses. Fifty-nine patients between 60 and 82 years of age were enrolled in the study. The patients received an oral capsular form of I-131 (10-25 mCi) and were followed up for 1 year with clinical and laboratory results. Euthyroid or hypothyroid status at the end of the year after treatment was deemed to be a response to treatment. RESULTS: Of the 21 (36%) male and 38 (64%) female patients, 29 (49%) had a solitary toxic nodule and 30 (51%) had toxic multinodular goiter. Twenty-nine (49%) of the patients received propylthiouracil therapy. At the end of the year, 38 (64%) patients were euthyroid, 11 (19%) were hypothyroid, and 10 (17%) were thyrotoxic. Forty-nine (83%) patients who were euthyroid and hypothyroid were considered responders. CONCLUSION: Geriatric patients with toxic nodular goiter were shown to have a high response rate to I-131 therapy. Thus, we suggest that radioactive iodine treatment should be the first-line treatment in these patients.

Follow-up on thyroidal uptake after radioiodine therapy: how robust is the peri-therapeutic dosimetry?

Radioiodine therapy (RIT) for benign thyroid diseases in Germany requires the patient to stay in a nuclear medicine therapy ward for at least 48 hours and the dose to the thyroid to be computed from activity measurements performed during that stay. A major part of the total dose will be delivered after the patient's discharge from the hospital and thus has to be predicted through extrapolation with the effective half-life measured peri-therapeutically. We performed repeated thyroid uptake measurements on patients up to five months post therapy to investigate post-therapeutic changes in their effective half-lives and examine the dosimetric consequences. 12 patients (4 m, 8 f; age 36 - 76 y; 4 Graves' disease, 4 toxic adenoma, 3 toxic goitre, 1 non-toxic goitre) underwent late uptake measurements (1 - 7 meas., 13 - 154 d post administration, median 54 d, performed with thyroid probe resp. whole body counter at lower activities). Doses calculated from late measurements were compared to those predicted at discharge; half-lives calculated from the late measurement closest to the median delay (54 d) were compared to those determined at time of discharge. A cross-calibration between activity calibrator, thyroid probe, and whole body counter over an activity range from 52 MBq down to 45 Bq revealed linearity to within 6%, which was considered sufficient. In 9 out of 12 patients the achieved dose was within the range predicted at discharge. Averaged deviation between achieved and predicted dose was 3.1±2.2% (median 2.5%, range 0.7% - 7.2%). Averaged deviation between post- and peri-therapeutic half-lives was 5.1±3.9% (median 3.5%, range 1.3% - 12.5%). For n=5 patients discharged after 3 days, averaged deviations were greater (dose 4.0%, half-life 5.6%) than for those patients (n=7) who stayed in the hospital for a minimum of 4 days (dose 2.5%, half-life 4.8%). Excretion of iodine from the thyroid remains practically unchanged for at least two months after RIT. The dosimetric procedure implemented in our institution warrants a robust prediction of the post-therapeutic half-life and thus the actual achieved dose.

Dosimetry prior to I-131-therapy of benign thyroid disease.

The activity to be administered in I-131 therapy of benign thyroid disease is determined by the radiation absorbed dose necessary to cure the disease, the target mass, and the residence time of the I-131 in the target volume. Data from 73 patients with complete sets of uptake measurements 2, 6, 24, 48, and 96 (n=53) or 120 (n=20) hours after oral administration of 1 MBq I-131 were used to deduce residence times from subsets of 3, 2, or only 1 measurement for each individual. The values were compared to those obtained with the reference method, i.e. a fit of an uptake function based on a 2-compartment model to all 5 measurements, to quantify the errors introduced by the less demanding assessments. Deviations are less than 10% if the 2- compartment uptake function is fitted to only 3 values measured after 6, 24, and 96-120h. Use of 2, 24, and 96-120h data results in errors >20% in individual patients. The effective half-lives as determined from 2 measurements after 24 and 96-120h correlate well with those deduced from the reference method with larger deviations in individuals with slow iodine kinetics and late maximal uptake. Residence times determined from the 24h uptake, assuming linear increase during the first day, and the effective half-life limited to maximum 8days underestimate the actual values systematically in patients with long and short half-lives. These errors can be eliminated by a modification of the calculation method resulting in deviations less than 14% in all but one individual for this procedure. The accuracy of methods based on only one retention value increases with the time of measurement after the administration of I-131. While systematic errors up to a factor of two occur if the 24h uptake is used for the estimate, deviations are less than 18% for measurements after 120h. The results suggest that only one late uptake assessment warrants residence time estimates with an acceptable error. Given the high inherent uncertainties in the complete dosimetry procedure, additional measurements must be considered only if a high precision of the absorbed dose assessment is required e.g. for clinical trials.

¹³¹I treatment of toxic nodular goiter under combined thyrostatic-thyromimetic medication is at low risk of late hypothyroidism.

AIM: Treatment of toxic nodular goiter with ¹³¹I is a first-line therapy for hyperthyroidism. To avoid a thyrotoxic storm, ¹³¹I is usually administered after pretreatment with antithyroid drugs, with thyroid-stimulating hormone (TSH) increase and functional recruitment of inhibited normal tissue. Therefore, both autonomous nodule(s) and normal tissue are irradiated. This may be a reason for late hypothyroidism occurring in 15-25% of patients. This study aimed at assessing different pretreatment modalities with combined methymazole and triiodothyronine, achieving euthyroidism with suppressed TSH. METHODS: After diagnosis of autonomously functioning toxic nodule, patients were subjected to thyrostatic medication. Two months later, TSH was checked; if >0.5 mU/L triiodothyronine treatment was associated. After 2 more months, if the TSH level was suppressed, patients received ¹³¹I-therapy. A total of 149 patients were consecutively enrolled, 41 of whom with uninodular and 108 with multinodular goiter. They were evaluated at diagnosis, pretreatment, 3 and 6 months after therapy and at late follow-up (6.8+/-4.2 years; range: 1-22 years). RESULTS: Administered activity was calculated according to ¹³¹I uptake and gland weight. Methymazole was discontinued 6 days before treatment and T3 was maintained until administration of ¹³¹I-therapy. Euthyroidism was achieved in 88% of patients. At late follow-up, subclinical hypothyroidism was observed in 10 patients (6.7%) and overt hypothyroidism in 5 patients (3.3%). No pathological consequences or side effects of ¹³¹I-therapy were found during the 6.8+/-4.2 year follow-up period. CONCLUSION: Treatment of toxic nodular goiter with ¹³¹I-therapy, under combined thyrostatic-thyromimetic treatment is a simple, safe, well-tolerated, and effective procedure.