Occupational Radiation Exposure and Changes in Thyroid Hormones in a Cohort of Chinese Medical Radiation Workers.

OBJECTIVE: This study aimed to evaluate the association between occupational radiation exposure and changes in thyroid hormone levels among medical radiation workers. METHODS: This retrospective cohort study included 2,946 radiation workers from 20 Guangzhou hospitals. Data on general characteristics, participant radiation dosimetry, and thyroid function test results [thyroid-stimulating hormone (TSH), triiodothyronine (T3), and thyroid hormone (T4)] were extracted from dosimetry and medical records. The generalized estimating equation was used to evaluate the trend of changes in thyroid hormone levels over time and was adjusted for age, gender, and occupation. RESULTS: The average annual effective dose was very low and showed a general downward trend. During the follow-up period, changes in T3 and T4 levels among radiation workers were -0.015 [95% confidence interval ( CI) -0.018 to -0.012] nmol/L per year and -2.294 (95% CI -2.426 to -2.162) nmol/L per year, respectively. Thyroid hormone levels were significantly different between males and females. T3 levels in the group of upper quartile of dose were significantly higher than in the lower quartile group ( P = 0.006). No significant decreased trend in thyroid hormone levels was observed with increasing average effective doses. CONCLUSION: Thyroid hormone secretion might be affected even in low-dose radiation exposure environments.

Assessment of the systemic effects of low-level laser therapy (LLLT) on thyroid hormone function in a rabbit model.

The aim of this study was to assess the effects of low-level laser therapy (LLLT) applied to a dental extraction socket on thyroid gland function in a rabbit model, based on serum triiodothyronine and thyroxine levels. Sixteen male New Zealand rabbits were randomly distributed into two groups: a control group (non-irradiated animals) and an experimental group (irradiated animals: one irradiation point in the extraction socket of the lower incisor). Animals in the experimental group were irradiated with an aluminium gallium arsenide diode laser (AlGaAs; wavelength 830 nm, 40 mW, CW laser), for 13 days, every 48 h, at a dose of 6 J/cm(2) per session, resulting in a total dose of 42 J/cm(2). Serum triiodothyronine and thyroxine levels were measured in both groups before extraction and on the last day of observation (day 15). There were no statistically significant differences between the groups in pre- and post-irradiation triiodothyronine and thyroxine values. With the irradiation protocol used in this study, LLLT did not affect thyroid function in rabbits as assessed by circulating serum triiodothyronine and thyroxine levels.

Thyroid remnant dose: 124I-PET/CT dosimetric comparison of rhTSH versus thyroid hormone withholding before radioiodine remnant ablation in differentiated thyroid cancer.

AIM: Recombinant human thyroid-stimulating hormone (rhTSH) recently was approved as an alternative to thyroid hormone withholding (THW) to elevate TSH for thyroid remnant ablation in differentiated thyroid carcinoma patients. High ablation success rates are reported with diverse rhTSH-aided (131)I activities. Improved renal function causes approximately 50% faster radioiodine clearance under euthyroidism versus hypothyroidism. Knowledge of comparative remnant radioiodine kinetics, particularly the remnant radiation dose in Gy/GBq of administered (131)I activity (RDpA), could assist in choosing rhTSH-aided ablative activities. MATERIAL AND METHODS: To compare the RDpA, determined through (124)I-positron emission tomography/computed tomography (PET/CT), under the two stimulation methods, we retrospectively divided into two groups 55 consecutive totally-thyroidectomized, radioiodine-naïve patients. The rhTSH group (n=16) received (124)I on thyroid hormone, 24 h after two consecutive daily intramuscular injections of rhTSH, 0.9 mg. The THW group (n=39) received (124)I after weeks-long THW, when serum TSH first measured > or = 25 mIU/L. We performed PET investigations 4 h, 24 h, 48 h, 72 h and 96 h and PET/CT 25 h after (124)I administration. RESULTS: Median stimulated serum thyroglobulin was 15 times higher (p=0.023) and M1 disease almost twice as prevalent (p=0.05) in rhTSH versus THW patients. Mean+/-standard deviation RDpA was statistically equivalent between the groups: rhTSH, 461+/-600 Gy/GBq, THW, 302+/-329 Gy/GBq, two-sided p=0.258. CONCLUSIONS: rhTSH or THW deliver statistically equivalent radiation doses to thyroid remnant and may be chosen based on safety, quality-of-life, convenience and pharmacoeconomic factors. Institutional fixed radioiodine activities formulated for use with THW need not be adjusted for rhTSH-aided ablation.

Thyroid function in children treated for acute lymphoblastic leukemia.

To determine the late effects of treatment on thyroid function in children who survive acute lymphoblastic leukemia, we assessed plasma levels of thyroid hormones in 24 children (15 girls and 9 boys) who had received combination of chemotherapy along with 18-24 Gy of irradiation to the cranium. The children were aged between 1 and 10.5 years (mean 3.1) at diagnosis and thyroid status was investigated between 1.3 and 13 years (mean 6.8) after completion of therapy. Six children showed a low peak of plasma thyroid stimulating hormone (TSH), after stimulation with thyrotrophin-releasing hormone (TRH). Three children showed a low basal plasma TSH concentration. Serum levels of thyroxine (T4, fT4) and triiodothyronine (T3, fT3) were normal in all patients. The frequency of thyroid hypofunction (low peak response of TSH to TRH) was more common in children receiving 24 compared to 18 Gy cranial irradiation (50% vs 14%; odds ratio = 7) and those who had completed therapy more than 5 years ago (31.3% vs 12.5%, odds ratio 3.18) although no significant association could be found (95% IC: 0.27-65.8 and 0.24-90 respectively). Because of the low mean age at diagnosis of our population no significant association could be found between children younger than 3 years of age at diagnosis and thyroid hypofunction (odds ratio = 0.14; 95% IC: 0.01-1.48). We conclude that treatment for acute lymphoblastic leukemia including cranial irradiation may lead to TRH/TSH dysfunction and therefore long term survivors should be followed for a long period after completion of therapy.

Changes in lipid peroxide levels and the activity of reactive oxygen scavenging systems in thyroid tissue after exposure to radioactive iodine in rats.

Exposure to ionizing radiation causes radiolysis of water in tissues leading to generation of reactive oxygen species (ROS), which are known to affect the antioxidant defense systems and induce lipid peroxidation (LP). Use of radioactive iodine (131I) for diagnosis and therapy of thyroid disorders may also generate ROS in the thyroid. Early (24 and 48 hours) and late (18 days) effects of subablation doses of 131I (370/555/1110 kBq) on the antioxidant defense and LP in the thyroid tissues have been studied. LP was elevated in all 131I treated groups by 10% to 41%. Although there was no change in catalase (CAT), the superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities showed evidence of change from 48 hours onwards--SOD decreased by 32% to 56% and GPx increased by 15% to 43%. Nonprotein thiols (reduced glutathione, GSH) showed an elevation of 16% at 24 hours, but later declined by 15% by day 18 after 370 KBq of 131I. Thus, the increase in LP observed may be due to beta irradiation induced ROS by 131I. The parallel decrease in SOD could be due to inactivation by ROS. The increase in GPx may be a consequence of induction due to elevated LP and/or ROS, which may be inadequate to lower the LP. In spite of elevated LP, the thyroid function appears to be normal.

Pattern of recovery of the hypothalamic-pituitary-thyroid axis following radioactive iodine therapy in patients with Graves' disease.

PURPOSE: To characterize the time course of recovery of the hypothalamic-pituitary-thyroid (HPT) axis by determining the frequency, onset, duration, and clinical attributes of the central hypothyroid phase following 131I therapy for Graves' disease and to examine whether the central hypothyroid phase is due to direct pituitary thyrotroph suppression or to hypothalamic thyrotropin-releasing hormone (TRH) deficiency. PATIENTS AND METHODS: Twenty-one hyperthyroid patients with Graves' disease evaluated at a university endocrine clinic and treated with radioactive iodine were prospectively studied. Serial thyroid function levels (serum thyroxine [T4], free thyroxine [free T4], triiodothyronine [T3], and thyroid-stimulating hormone [TSH]) were measured and TRH stimulation tests were performed at 2 to 4 week intervals for all subjects following 131I treatment. None of the patients was treated with thionamides after receiving 131I therapy. RESULTS: Nineteen (90%) of the patients with Graves' disease experienced a transient central hypothyroid phase defined as the presence of a suppressed or inappropriately normal TSH level despite a low free T4 level following 131I treatment. This phase occurred a mean of 62.8 +/- 5.1 days following 131I treatment, persisted for an average of 24.7 +/- 2.4 days, and was not predictive of eventual treatment outcome. All patients had concordantly low T4 and T3 levels during this period and exhibited a blunted TSH response to TRH compared to 29 euthyroid control subjects, suggesting primary feedback suppression at the level of the pituitary thyrotrophs. The suppressed thyrotrophs required a minimum of 2 weeks to recover once patients became hypothyroid. The length of preexisting hyperthyroidism, basal free T4 elevation, and administered dose of 131I failed to predict the duration of the central hypothyroid phase, although a higher dose of 131I was associated with an earlier onset of central hypothyroidism (r = -.51, P < 0.05). CONCLUSIONS: Clinicians should be aware of the delay in the recovery of the HPT axis that occurs in the majority of patients with Graves' disease treated with 131I and is manifested by a transient central hypothyroid phase. The blunted TSH response to TRH stimulation during this period suggests that suppression occurs primarily at the level of the pituitary thyrotrophs. The use of sensitive TSH measurements alone to monitor these patients during this period is not helpful and may be misleading.

[The sanatorium-health resort treatment of children with thyroid hyperplasia]. / Sanatorno-kurortnoe lechenie detei s giperplaziei shchitovidnoi zhelezy.

A favourable effect of sanatorium treatment on the key body functions was found in children with thyroid hyperplasia consequent to environmental pollution due to Chernobyl accident. It is emphasized that balneofactors in the above children should be used in sparing regimens.

[The effect of environmental factors on the concentration of tumor markers in the blood serum and on the indices characterizing thyroid function]. / Vliianie nekotorykh faktorov okruzhaiushchwei sredy na kontsentratsiiu v syvorotke krovi opukholevykh markerov i pokazateli, kharakterizuiushchie sostoianie shchitovidnoi zhelezy.

Combined versus separate exposure of male organism to cesium-137 and chemical agents results in a more pronounced hyperferritinemia in the former case. In female chemists the ferritin level is dependent to a considerable extent on the menstrual cycle showing a tendency for the iron-containing protein level to decrease because of the action of a number of chemical agents. The rise of the level of cancer embryonic antigen is more readily seen in persons with high levels of cesium-137. Concentrations of carbohydrate antigen (CA-125) and mucin-like antigen are appreciably higher in female chemists incorporating cesium-137, and in those within the 30-km radius of the ChNPP. The level of thyroglobulin was raised in the chemists having a background incorporation of cesium, the liquidators of the aftermaths, and particularly in those happened to be in the 30-km zone. Each of the unfavourable factors taken separately (chemical agent or cesium-137) had lesser effect on the degree of elevation of TG content and hormone-forming function of the thyroid gland. An additional information has been obtained concerning the risk groups, which, however, serves as an indirect measure of carcinogenic effect various environmental factors exert on the organism.