Possibility of limiting the un-justified irradiation in 131I therapy of Graves' disease: A thyroid mass-reduction based method for the optimum activity calculation

Efficacy of radioactive iodine treatment of graves' hyperthyroidism using a single calculated 131I dose

Objective

To evaluate the success rate of therapeutic administration of a single calculated ¹³¹I activity for eliminating hyperthyroidism due to Graves’ disease.

Methods and materials

Patients with Graves’ hyperthyroidism underwent pinhole thyroid imaging, 24-h radioactive iodine uptake (RAIU) measurements and clinical examination and received a calculated ¹³¹I activity of 0.2 mCi per estimated gram of thyroid tissue, adjusted for the 24-h RAIU. The goal of RAI treatment was to achieve hypothyroidism within 3–6 months of ¹³¹I administration. Response to RAI therapy was assessed at 7 weeks and 3 months by clinical and biochemical follow-up.

Results

The study included 316 hyperthyroid patients with Graves’ disease (F238:M78, mean age 42.1 ± 16 y, 4–94). 179 patients (56.6%) had no prior therapeutic intervention (treatment-naive patients), whereas 6 patients had prior thyroid surgery, and 131 (41.5%) had been treated with anti-thyroid medications.

The mean estimated thyroid gland size was 50.2 g ± 18, range 15–100. Mean RAIU was 0.57 ± 0.17 (normal 0.07–0.30). RAI doses ranged from 5 to 70 mCi (mean dose = 18.1 mCi). Successful treatment of hyperthyroidism at our institution was obtained after a single therapeutic 131-I activity administration in 295 of 316 (93.3%) patients. Multivariate logistic regression analysis demonstrated that failure of ¹³¹I therapy was associated with previous PTU therapy (p <  0.001).

The mean response time after successful RAI therapy was 110.2 days, with cumulative response of 25% at 61 days, 50% by 84 days and 75% by 118 days after radioiodine administration. The mean time to respond for those on prior PTU medications was 297 days compared to 116 days for those on MMI and 109 days for those not previously treated with antithyroid medications. In patients with persistent hyperthyroidism, failure of RAI therapy was documented in 16 patients (76.2%) within (less than) one year after ¹³¹I administration and in 5 patients (23.8%) more than one year after initial therapy, considered late failure.

Conclusion

Successful ¹³¹I therapy for Graves’ hyperthyroidism with a single calculated dose can be achieved in the majority (> 90%) of patients, adjusting for the thyroid size and 24 h uptake measurement.

Clinical and Dosimetric Variables Related to Outcome After Treatment of Graves' Disease With 550 and 1110 MBq of 131I: Results of a Prospective Randomized Trial

: Therapy of Graves' hyperthyroidism (HTG) with I is still mostly performed on an empirical basis. The present study was carried out to evaluate clinical and dosimetric variables associated with outcome in HTG therapy, which could contribute to planning and defining the most appropriate activity to be administered.

METHODS

Patients with HTG were randomly assigned to therapy with 555 MBq (15mci) or 1110 MBq (30 mCi) of I. Estimation of thyroid radiation absorbed dose was made according to MIRD methodology. Success was defined as clinical/laboratory euthyroidism or hypothyroidism one year after therapy. The association between clinical, laboratory, and dosimetric variables with 1-year outcome was measured using bivariate analysis, followed by logistic regression.

RESULTS

Ninety-one patients included completed the follow-up. Therapeutic success was observed in 77 (84.6%) of them, in a greater proportion when 1110 MBq of I was administered as compared with 550 MBq (94.8% vs 77.4%, P = 0.02). Besides administered activity, multivariate analysis indicated that outcome was related to patient age and gland mass. A higher therapeutic success rate was achieved with doses greater than 300 Gy as compared with doses less than 300 Gy (89% vs 60%, P = 0.01).

CONCLUSION

Administered activity, age, and gland mass were related to the outcome. Radiation absorbed dose, although not significant according to multivariate analysis, may be used as a quantitative parameter in therapy planning, with a target dose of 300 Gy. In cases where a rapid and efficient response to radioiodine treatment is required, adoption of a simplified protocol employing high activities is justified.

Effect of radioactive iodine therapy on carotid intima media thickness in patients with hyperthyroidism

OBJECTIVE

The aim of this study was to evaluate the carotid intima media thickness (IMT) in patients with thyrotoxicosis who received radioactive iodine (RAI) treatment.

METHODS

This study was planned to be conducted with two different groups of people. There were 87 patients in the patient group and 98 controls. Participants were evaluated for atherosclerosis risk factors. Mean carotid IMT was measured from three consecutive traces at the common carotid artery bifurcation.

RESULTS

The mean carotid IMT was 0.81 ± 0.20 in patient group and this was higher than the controls (0.68 ± 0.19) (p < 0.01). IM thickening was positively correlated with the applied RAI dose levels in the treatment group (p = 0.029). In patients with only HT, the data of the two groups showed a significant difference, with the average IMT being higher in the patient group than that of the control group (p: 0.011).

CONCLUSION

RAI used in the treatment of thyrotoxicosis increases the IMT of carotid artery independent of age and sex. This treatment yields better results with higher doses, and this effect is more marked in patients with HT. Hence, we believe that it is necessary to calculate the dose properly for hyperthyroid cases in which treatment with RAI is planned. In particular, the patients with HT need to be treated with the minimum possible dose. Further, carotid arteries should be evaluated with US following RAI treatment.

A new method to evaluate the residual activity in patients undergoing (131)I thyroid therapy

The radioiodine administration is a standard therapeutic approach to both benign thyroid diseases, such as hyperthyroidism, and carcinomas. The high administered (131)I activities are of radiation protection concern, due to relevant patient residual contamination. The aim of this work was to develop a new procedure based on external radiometric surveys and on a mathematical model in order to estimate the (131)I activity in patients undergoing hyperthyroidism radioiodine therapy. In the first stage of this study, a suitable detector was chosen and its response vs. activity was characterized. The experimental verification was performed measuring the ambient dose equivalent rate from patients receiving radioiodine administration. The results confirm the reliability of the proposed method, as shown by the slight differences between the administered activities and the ones calculated from external measurements. Furthermore, the same procedure was applied to detect the percentage residual activity in patients at two preset time intervals: 4 hours and 4 days after the radioiodine administration. The obtained results clearly highlight that the method can ensure a level of reliability compatible with the radiation protection purposes.

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.

Efficacy of different protocols of radioiodine therapy for treatment of toxic nodular goiter: systematic review and meta-analysis of the literature

CONTEXT

To evaluate treatment success and hypothyroidism following main methods of radioiodine therapy of toxic nodular goiter (TNG); calculated versus fixed dose and high versus low dose of radioiodine.

EVIDENCE ACQUISITIONS

We searched MEDLINE and SCOPUS databases from inception till July 2013, for clinical trials that compared two different methods of radioiodine administration in TNG. The trials were classified into two groups, those that compared fixed versus calculated dosimetry method and those that assessed high fixed dose versus low fixed dose method. Treatment response was defined as euthyroidism or hypothyroidism, one year after radioiodine administration. We calculated the risk ratio and risk difference of treatment response as well as permanent hypothyroidism as outcome variables. Random effects model was used for data pooling.

RESULTS

The literature search yielded 2538 articles. Two randomized and five non-randomized clinical trials with 669 patients met the eligibility criteria for the meta-analysis. Patients with TNG who were treated according to the calculated method had 9.6% higher cure rate (risk ratio=1.17) and only 0.3% more permanent hypothyroidism compared to patients treated with the fixed dose method. There was no significant difference in the amount of administered radio-iodine in the two groups. Patients treated with fixed high dose had 18.1% more cure rate (risk ratio = 1.2) and 23.9% more permanent hypothyroidism (risk ratio = 2.40) compared to patients treated by fixed low dose protocols.

CONCLUSIONS

Calculated radioiodine therapy may be preferred to fixed dose method in patients with TNG. High dose methods are associated with more response and more hypothyroidism.

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.