Radioiodine therapy in Graves' disease patients with large diffuse goiters treated with or without carbimazole at the time of radioiodine therapy

Nomogram construction and evaluation for predicting non-remission after a single radioactive iodine therapy for Graves' hyperthyroidism: a retrospective cohort study

Background

Radioactive iodine (RAI) therapy is a widely used treatment for Graves' Hyperthyroidism (GH). However, various factors can impact the non-remission rate of GH after single RAI therapy. This study aimed to develop an online dynamic nomogram to assist physicians in providing personalized therapy for GH.

Methods

Data from 454 GH patients who received RAI therapy were retrospectively reviewed and included in the present study. The univariate and multivariate analysis were conducted to investigate and identify independent influencing factors. The nomogram was developed based on the training cohort to explore non-remission rates. Finally, the reliability and accuracy of the constructed nomogram model were verified in the validation cohort via the calibration, receiver operating characteristic (ROC) curve, and decision curve analysis (DCA).

Results

24-hours radioactive iodine uptake (RAIU24h), effective half-life (Teff), total iodine dose (TID) and iodine dose per gram of thyroid tissue (IDPG) were independent predictors. The nomogram had a high C-index 0.922 (95% CI: 0.892-0.953), for predicting non-remission. The calibration curves demonstrated excellent consistency between the predicted and the actual probability of non-remission. ROC analysis showed that the AUC of the nomogram model and the four independent factors in the training cohort were 0.922, 0.673, 0.760, 0.761, and 0.786, respectively. The optimal cutoff value for the total nomogram scores was determined to be 155. A total score of ≥155 indicates a higher likelihood of non-remission after a single RAI therapy for GH, whereas a score below 155 suggests a greater likelihood of remission. Additionally, the DCA curve indicated that this nomogram had good clinical utility in predicting non-remission.

Conclusion

An online nomogram was constructed with good predictive performance, which can be used as a practical approach to predict and assist physicians in making personalized therapy decisions for GH patients.

Long-term carbimazole pretreatment reduces the efficacy of radioiodine therapy

INTRODUCTION

Data from several studies suggest that pretreatment with antithyroid drugs (ATD) before (131)I increases the risk of treatment failure. This effect has been demonstrated more consistently with propylthiouracil than with carbimazole (CMZ) or methimazole (MMI). Men with Graves' disease (GD) have a lower rate of remission with (131)I compared to women and the impact of long-term ATD pretreatment on the success of (131)I is unknown. The objective of our study was to compare the efficacy of fixed doses of radioiodine between patients with and without long-term CMZ pretreatment.

MATERIALS AND METHODS

We performed a retrospective study on 335 male patients with GD treated with (131)I from 1998 to 2008. 148 patients had been pretreated with CMZ, and the remaining 187 patients received (131)I without pretreatment. We compared the success rate of a single dose of (131)I, between patients with and without long-term CMZ pretreatment.

RESULTS

The success rate of a single dose of (131)I was significantly higher in patients without pretreatment than in patients who were pretreated with CMZ (91.4% vs. 82.3%, P = 0.01). The rate of hypothyroidism in the first 6 months after (131)I therapy was significantly higher in patients without pretreatment (55.1% vs. 44.6%, P = 0.05). There was also a trend for higher cumulative rate of hypothyroidism at last follow-up in nonpretreated patients (78.1% vs. 69.7%).

CONCLUSION

Male patients with Graves' hyperthyroidism pretreated with CMZ have lower efficacy with 131I therapy compared to nonpretreated patients. CMZ pretreatment given for a prolonged period reduces the efficacy of (131)I therapy.

Protective effect of an antithyroid compound against γ-radiation-induced damage in human colon cancer cells

We have previously reported the radioprotective effect of propylthiouracil (PTU) on thyroid cells. The aim of the present study was to analyze whether tumor cells and normal cells demonstrate the same response to PTU. Human colon carcinoma cells were irradiated with γ-irradiation with or without PTU. We evaluated the clonogenic survival, intracellular reactive oxygen species levels, catalase, superoxide dismutase and glutathione peroxidase activities, and apoptosis by nuclear cell morphology and caspase-3 activity assays. Cyclic AMP (cAMP) levels were measured by radioimmunoassay. PTU treatment increased surviving cell fraction at 2 Gy (SF2) from 56.9 ± 3.6 in controls to 75.0 ± 3.5 (p < 0.05) and diminished radiation-induced apoptosis. In addition, we observed that the level of antioxidant enzymes' activity was increased in cells treated with PTU. Moreover, pretreatment with PTU increased intracellular levels of cAMP. Forskolin (p < 0.01) and dibutyryl cAMP (p < 0.05) mimicked the effect of PTU on SF2. Co-treatment with H89, an inhibitor of protein kinase A, abolished the radioprotective effect of PTU. PTU reduces the toxicity of ionizing radiation by increasing cAMP levels and also possibly through a reduction in apoptosis levels and in radiation-induced oxidative stress damage. We therefore conclude that PTU protects both normal and cancer cells during exposure to radiation in conditions mimicking the radiotherapy.

Increasing the radioiodine dose does not improve cure rates in severe graves' hyperthyroidism: a clinical trial with historical control

Objective. It is generally accepted that higher doses of radioiodine (¹³¹I) improve cure rates in Graves' disease (GD). In this trial we sought to evaluate whether very high ¹³¹I doses increase the efficacy of treatment in severe GD. Design. Clinical trial with historical control. Patients with GD and a goiter ≥48 mL were eligible for the study. The patients in the contemporaneous intervention cohort were treated with 250 μCi of ¹³¹I/mL thyroid tissue, corrected by 24-RAIU values (Group 1; n = 15). A subgroup of patients with GD and a goiter ≥48 mL who were treated with 200 μCi of ¹³¹I/mL/24-RAIU in a previously published randomized controlled trial served as a historical control group (Group 2; n = 15). The primary outcome evaluated was the one-year cure rate. Results. There were no significant baseline differences regarding age, gender, body mass index, smoking status, pretreatment with methimazole, thyroid volume, or thyroid hormone levels of the two treatment groups. The cumulative 12-month cure rate for the patients in Group 1 was 66.6%, a figure similar to the 12-month cure rate observed in Group 2 (60.0%; P = 0.99). Conclusions. Our results suggest that increasing the ¹³¹I dose does not improve cure rates in severe GD. This trial is registered with ClinicalTrials.gov NCT01039818.

Protection against radiation-induced damage of 6-propyl-2-thiouracil (PTU) in thyroid cells

Many epidemiologic studies have shown that the exposure to high external radiation doses increases thyroid neoplastic frequency, especially when given during childhood or adolescence. The use of radioprotective drugs may decrease the damage caused by radiation therapy and therefore could be useful to prevent the development of thyroid tumors. The aim of this study was to investigate the possible application of 6-propyl-2-thiouracil (PTU) as a radioprotector in the thyroid gland. Rat thyroid epithelial cells (FRTL-5) were exposed to different doses of γ irradiation with or without the addition of PTU, methimazole (MMI), reduced glutathione (GSH) and perchlorate (KClO4). Radiation response was analyzed by clonogenic survival assay. Cyclic AMP (cAMP) levels were measured by radioimmunoassay (RIA). Apoptosis was quantified by nuclear cell morphology and caspase 3 activity assays. Intracellular reactive oxygen species (ROS) levels were measured using the fluorescent dye 2',7'-dichlorofluorescein-diacetate. Catalase, superoxide dismutase and glutathione peroxidase activities were also determined. Pretreatment with PTU, MMI and GSH prior to irradiation significantly increased the surviving cell fraction (SF) at 2 Gy (P < 0.05), while no effect was observed with KClO4. An increase in extracellular levels of cAMP was found only in PTU treated cells in a dose and time-dependent manner. Cells incubated with agents that stimulate cAMP (forskolin and dibutyril cAMP) mimicked the effect of PTU on SF. Moreover, pretreatment with the inhibitor of protein kinase A, H-89, abolished the radioprotective effect of PTU. PTU treatment diminished radiation-induced apoptosis and protected cells against radiation-induced ROS elevation and suppression of the antioxidant enzyme's activity. PTU was found to radioprotect normal thyroid cells through cAMP elevation and reduction in both apoptosis and radiation-induced oxidative stress damage.

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.

Radioprotection of thyroid cells mediated by methimazole

PURPOSE

The radioprotective effect of antithyroid drugs on radioiodine treatment is a controversial issue. However, it is of clinical relevance whether antithyroid medication has to be interrupted for therapy and when antithyroid medication can be continued after radioiodine treatment. We investigated DNA damage caused by internal or external radiation using thyroid cells (sodium iodine symporter [NIS] positive).

MATERIALS AND METHODS

Adherent thyroid cells were irradiated following incubation with the mediators methimazole and perchlorate using either X-ray tube or Re-188-perrhenate. DNA damage was quantified by OTM (Olive's tail moment) of the alkaline comet assay.

RESULTS

Following external irradiation of 15 Gy OTM was 4.3 ± 4.2 compared to 0.5 ± 1.4 in controls. DNA damage was reduced by methimazole to 70%. Incubation with Re-188 showed effects depending on presence of the mediators. Non-irradiated controls had a mean OTM < 1, internal irradiation increased OTM to 25.5 ± 9.1 in cells without mediators. OTM decreased to 60% after pre-incubation with methimazole and to 15% with perchlorate. Re-188 uptake was modified by both perchlorate and, to a lesser extent, methimazole.

CONCLUSIONS

Methimazole was shown to have a radioprotective effect not only by its scavenger capacity but also by interaction with NIS. Perchlorate acted by competitive inhibition of NIS mediated Re-188 uptake.

Different strategies to overcome the effect of carbimazole on high- and low-dose radioiodine therapy: results from continuous dose-effect models

BACKGROUND

Until now, it remains elusive which strategy - antithyroid drug withdrawal or increased radioiodine target doses - should be preferred to avoid the detrimental effect of antithyroid drugs in high- and low-dose radioiodine therapy, respectively.

METHODS

We explored the effects of carbimazole on the 1-year post-radioiodine success and hypothyroidism rates by continuous dose-effect models, whereas success was defined as elimination of hyperthyroidism. Euthyroidism rates with and without carbimazole were calculated by numerical integration of the area between success and hypothyroidism curves. Target dose amplification factors for equal chance of success with and without carbimazole were calculated using logistic regression.

RESULTS

Two hundred and twenty-eight patients were included in this study. Radioiodine target doses between 33 and 839 Gy were applied. Overall, the euthyroidism rates were 16.5% and 64.8%, while the hypothyroidism rates were 37.6% and 14.8% in Graves' disease and toxic nodular goitre, respectively. The success rate with simultaneous carbimazole (median dose 15 mg day(-1); range 2.5-60 mg day(-1)) was reduced over the entire target dose range in Graves' disease and toxic nodular goitre. The areas between curves for euthyroidism without and with simultaneous carbimazole were 127 and 43 Gy in Graves' disease and 178 and 128 Gy in toxic nodular goitre. The estimated radioiodine target dose amplification factor was 5.5 for Graves' disease and 3.0 for toxic nodular goitre.

CONCLUSIONS

Simultaneous carbimazole reduces the euthyroidism rate, the aim of low-dose radioiodine therapy, over the entire target dose range in both Graves' disease and toxic nodular goitre. Therefore, antithyroid drug discontinuation should be preferred in low-dose radioiodine therapy. Conversely, escalation of the target dose should be preferred in high-dose radioiodine therapy.

Thyroid echogenicity predicts outcome of radioiodine therapy in patients with Graves' disease

CONTEXT

Despite accounting for variations in gland size and iodine kinetics, the success of radioiodine therapy in patients with Graves' disease remains moderately common and unpredictable.

OBJECTIVES

We hypothesized that hypoechogenic glands, with large, densely packed cells, are more radiosensitive than normoechogenic glands, in which much radiation is wasted on more abundant colloid. We evaluated this hypothesis in a cohort of patients with Graves' disease.

DESIGN

This was a prospective trial of patients recruited during 4 yr and followed up 1 yr after radioiodine therapy.

SETTING

This trial was held in a university hospital-outpatient clinic.

PATIENTS

A total of 177 consecutive patients with first presentation of Graves' disease (28 males), 23-76 yr old, who relapsed after antithyroid therapy were included in the study.

INTERVENTION

The patients were assigned to an ablative target-absorbed dose of 200 Gy (n = 78) or randomly to 100 or 120 Gy of nonablative dose (n = 99).

MAIN OUTCOME MEASURES

The measures were incidences of hyperthyroidism, euthyroidism, and hypothyroidism at 12-month follow-up.

RESULTS

At follow-up there were 25 hyperthyroid, 44 euthyroid, and 108 hypothyroid patients. Compared with 96 patients with a hypoechogenic gland, in 81 patients with a normoechogenic gland, there were more hyperthyroid (22 vs. 7%) and euthyroid (41 vs. 11%), but less hypothyroid outcomes (37 vs. 81%; P < 0.0001). The other independent predictor of increased radioresistance was the large gland volume.

CONCLUSION

In patients with Graves' disease, normoechogenic and large glands are associated with increased radioresistance.

Two-day thionamide withdrawal prior to radioiodine uptake sufficiently increases uptake and does not exacerbate hyperthyroidism compared to 7-day withdrawal in Graves' disease

The appropriate period of antithyroid drug (ATD) discontinuation before radioiodine therapy is the most critical problem in Graves' disease patients under going treatment with ATD. To determine the optimal period that does not alter the outcome of radioiodine therapy or exacerbate hyperthyroidism, we compared serum FT4 levels at radioiodine uptake (RAIU) and therapy outcomes between a 2-day withdrawal group and 7-day withdrawal group. We prospectively recruited 43 patients for the 2-day withdrawal protocol and retrospectively reviewed 49 patients treated with radioiodine following the protocol of 7-day withdrawal. There was no significant difference in RAIU between the 2 groups. The mean serum FT4 level measured on the first day of 24-h RAIU of the 7-day group was significantly higher than that in the 2-day group. There were no significant differences in the outcomes at each point (6 months, 1 year, and 2 years after therapy) between the 2 groups. Our results indicated that withdrawal of ATD for 2 days is superior to 7 days in that 2 days discontinuation did not exacerbate hyperthyroidism. In order to prevent serum thyroid hormone increase after ATD withdrawal and radioiodine therapy, a 2-day ATD withdrawal period before radioiodine therapy may be useful for high-risk patients such as the elderly and patients with cardiac complications. We believe that the 2-day ATD withdrawal method may be useful for patients undergoing treatment with ATD who are to undergo radioiodine therapy.

Change in the intrathyroidal kinetics of radioiodine under continued and discontinued antithyroid medication in Graves’ disease

PURPOSE

This study evaluated the thyroidal kinetics of radioiodine in Graves' disease under continued thiamazole medication and after discontinuation of thiamazole for 1-2 days, with a view to keeping the period of discontinuation as short as possible and to exploring the underlying mechanism of a postulated radioprotective effect of antithyroid drugs.

METHODS

In 316 patients, diagnostic and therapeutic radioiodine kinetics were followed up for 2 days by ten uptake measurements each and were defined mathematically by a two-compartment model.

RESULTS

Without thiamazole or when thiamazole was discontinued for at least 2 days, all uptake curves could be fitted perfectly by a simple in- and output function; the mean square error (mse) was 0.38 (test) and 0.28 (therapy). Under continued thiamazole medication (11.0+/-7.0 mg/day), the energy dose delivered to the thyroid was lowered by factor of 2.5. Uptake curves were deformed (mse: 1.06, test and 0.86, therapy) and appeared two peaked, suggesting coexistence of follicles with blocked and follicles with intact hormone synthesis and hence heterogeneous radioiodine uptake in the thyroid. In patients with maximally altered uptake curves, the success rate was as low as 31%. One day after discontinuation of thiamazole, mse was still increased (0.78, test), while 2 days afterwards it had normalised (0.36, test) and 3 days afterwards (mse: 0.24, therapy) the success rate was 87%.

CONCLUSION

Efficacy of radioiodine therapy under continued thiamazole medication is reduced not only by a lower uptake and shorter half-life of radioiodine, but also by a heterogeneous energy dose distribution in the thyroid. Discontinuation of thiamazole (but probably not of propylthiouracil) for at least 2 days is required to restore the efficacy of radioiodine.

Outcome of radioiodine therapy without, on or 3 days off carbimazole: a prospective interventional three-group comparison

PURPOSE

Carbimazole ameliorates hyperthyroidism but reduces radioiodine uptake and adversely affects the outcome of simultaneous radioiodine therapy. We explored whether withdrawal of carbimazole for 3 days can restore the outcome of radioiodine treatment without concurrent exacerbation of hyperthyroidism. By generating three groups with comparable radioiodine uptake, we also investigated whether the effect of carbimazole depends on the radioiodine uptake.

METHODS

Stratified by a radioiodine uptake >30%, 227 consecutive adult patients were prospectively assigned to radioiodine therapy (target dose 200 Gy) without, on or 3 days off carbimazole. Patients were clinically (Crooks-Wayne score) and biochemically (T(3), fT(4), TSH) followed up after 3, 6 and 12 months. Primary endpoint was outcome 12 months after radioiodine therapy.

RESULTS

A total of 207 patients completed follow-up (toxic nodular goitre, n=117; Graves' disease, n=90). The overall success rate was 71.5%. Patients without and 3 days off carbimazole had similar biochemical (81.4% and 83.3%, respectively; p=0.82) and clinical outcomes [median (range) Crooks-Wayne score 0 (0-16) and 1 (0-10), respectively; p=0.73], which were both higher than in patients on carbimazole [42.6%, p<0.001; Crooks-Wayne score 3 (0-30), p<0.03]. Time to achieve cure was delayed on carbimazole. No changes in thyroid hormone levels occurred after 3 days' discontinuation of carbimazole. Logistic regression revealed that all observed cure rates were independent of entity, sex, age, thyroid volume, radioiodine uptake, radioiodine half-life, fT(4), T(3) and TSH.

CONCLUSION

Patients under carbimazole treatment can be referred for radioiodine therapy after withdrawal of carbimazole for only 3 days. Three days of carbimazole withdrawal is long enough to restore the success of radioiodine therapy and short enough to avoid the risk of exacerbation of hyperthyroidism.

Low failure rate of fixed administered activity of 400 MBq 131I with pre-treatment with carbimazole for thyrotoxicosis: the Gateshead Protocol

BACKGROUND

Thyrotoxicosis is associated with significant morbidity, therefore adequate control of the disease is paramount. The outcome of treatment of thyrotoxicosis using radioiodine shows variable failure rates depending, amongst other things, on the administered activity of radioiodine and the use of anti-thyroid drugs. Thus, management should follow an evidence based protocol, which has a low failure rate.

METHOD

We prospectively analysed the outcome of treatment using our Gateshead protocol of a fixed administered activity of radioiodine therapy (400 MBq) given to 201 patients (including 140 with Graves' disease, 48 with toxic multinodular goitre (TMNG) and 13 with toxic nodule) followed up for a median period of 12 months (range, 6-77 months). Carbimazole was discontinued in patients rendered euthyroid 16 days prior to radioiodine. No routine anti-thyroid drugs or thyroxine were given following radioiodine unless hypothyroidism or thyrotoxicosis occurred.

RESULTS

Following the Gateshead protocol led to a failure rate of 6.5% (eight females with Graves' disease, four females with TMNG and one female with toxic nodule), 29% euthyroidism and 64% hypothyroidism. The rates of hypothyroidism for women and for men were: in Graves' disease 77% and 79%, in TMNG 29% and 75%, in toxic nodule 42% and 0%, respectively.

CONCLUSIONS

Our observations show that withholding an antithyroid drug in excess of just over 2 weeks prior to administering a fixed administered activity of radioiodine in patients with thyrotoxicosis leads to the lowest reported failure rate, irrespective of the underlying cause. One possible mechanism for this could be the avoidance of drug induced radio-resistance.

Propylthiouracil reduces the effectiveness of radioiodine treatment in hyperthyroid patients with Graves' disease

In order to assess the effect of propylthiouracil (PTU) or methimazole (MMI) pretreatment on patient outcome after radioiodine therapy, we examined 100 patients with Graves' disease 3, 6, 9, and 12 months after administration of a 10-mCi standard single dose of 131I. They were assigned to one of three groups: no drug (ND) treatment (30 cases); MMI (45 cases); and PTU (25 cases). Antithyroid drugs (ATD) were withdrawn 15 days before radioiodine administration. The groups were similar concerning age, gender, ATD pretreatment duration, goiter size, and initial serum triiodothyronine (T3), thyroxine (T4), free thyroxine (FT4), antithyroid autoantibody levels, 24-hour radioiodine uptake and 131I dose administered per gram of thyroid tissue. ND and MMI groups presented a similar rate of cure of 73.3% and 77.8% respectively (p = NS). In contrast, the PTU group showed a rate of cure of only 32% (p < 0.05). Logistic regression analysis indicated that PTU administration (p = 0.003) and thyroid size (p = 0.02) were the variables related to radioiodine therapy failure. Our data demonstrate that the chance of 131I treatment failure is higher in individuals using PTU than in patients using MMI or not using any ATD before radioiodine (odds ratio [OR] 5.84; 95% confidence interval [CI] 1.82-18.76) suggesting that PTU should be avoided in the treatment of patients with Graves' disease.

Radioiodine therapy in patients with hyperthyroid disorder: standard versus dosimetric activity application

Due to its high success rate and non-invasive character, an increasing demand for radioiodine therapy can be seen. This study was conducted to determine whether standardized 131I activities can be used to facilitate management of patients with hyperthyroid disorder or whether a pre-therapeutic radioiodine test is advisable to determine an adequate therapeutic activity. The therapeutic uptake of 218 patients with benign thyroid disorders were determined and compared with 24 h and 48 h test uptake measurements as well as with calculated standard uptake values. Since there is a linear relationship between iodine uptake and delivered radiation dose, the effect of the different therapeutic approaches on the latter parameter was analysed. Special care was taken to assess possible differences between the various thyroid disorders. A mean deviation between pre-therapeutic test uptake and actual therapeutic uptake of 14.7% was observed in contrast to one of 29.1% when using disease specific standard values per millilitre of thyroid tissue. Furthermore, the proportion of patients with large deviations of more than 40% increased drastically when using standard uptake values (with radioiodine test, 4.1%; with standard values, 18.8%). In conclusion, the dosimetric approach with a pre-therapeutic radioiodine test proved to be the most accurate therapeutic procedure. Both the 24 h and 48 h test uptake measurements gave analogous results and yielded a correlation coefficient of 0.91 when compared with the therapeutic uptake. While it may be tempting to use standard activities to facilitate patient management, the findings of this study confirm that, for precise therapy planning, a pre-therapeutic radioiodine test is advised. Since no significant difference could be found between the 24 h and 48 h test uptake values, an early measurement 24 h after administration of the test activity is recommended.