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Initial Radioiodine Ablation
Abstract
Radioiodine has been used to treat thyroid cancer for more than 70 years and is an important aspect in the management of well-differentiated thyroid cancer. It has been historically used in two ways: to ablate residual thyroid tissue (adjuvant therapy) and to treat known metastatic disease. However, the indications and dosages of radioactive iodine use for patients with well-differentiated thyroid cancer are changing, with physicians advising treatment less often and lower doses for adjuvant therapy in recent years. As the practice of radioactive iodine continues to evolve with the availability of large, rigorous clinical studies, it is likely that adjuvant radioactive iodine will be reserved for larger tumors with more aggressive histology and/or for recurrent disease.
The treatment for differentiated thyroid cancer (DTC) consists of a thyroidectomy followed by radioactive iodine therapy (RIT), in which the patient remains in isolation until the exposure rate of the radioactive iodine reaches a certain limit. The present research intends to estimate the length of stay of patients subjected to RIT with radiometry analysis performed throughout the patient's admission. Methods: Information such as age, gender, weight, height, prescribed activity, liquid intake, and the use of recombinant human thyrotropin (rhTSH) was gathered from a total of 204 patients with DTC, subjected to RIT. During the admission, the exposure rates were periodically measured. The data served as variables for a multiple regression, in which the coefficients and significance of each were verified as a function of the exposure rate. Results: The results showed that the length of stay, the administered activity, the intake volume of liquids, the use of rhTSH, and the patient's weight impacted significantly on the dose rate. The average effective half-life of the 131I, considering all patients, was 12.61 ± 3.28 h, and the average time for their radiological release was 15.23 ± 5.50 h. Based on the results it was possible to develop a tool to estimate a patient's length of stay and effective half-life times. Conclusion: The results can contribute to an optimization of the radiological protection of patients submitted to RIT, as well as allow better logistics of their admission, which can lead to more appropriate accommodation for the patient with a better use of resources.
Thyroid cancer incidence is increasing all over the world - mostly due to an increase in the detection of small tumors that were previously undetected. A small percentage of these tumors lose the ability to uptake and/or to respond to radioiodine (RAI) therapy, especially in metastatic patients. There are several new therapeutic options that have emerged in the last 5 years to treat RAI refractory thyroid cancer patients, however it is very important to properly identify RAI refractory patients and to clarify those appropriate for these treatments. In this review, we discuss the RAI refractory definitions and the criterias that have been suggested based RAI uptake in the post therapy scan as well as the response after RAI therapy and the possible molecular mechanisms involved in this process. We offer a review of the therapeutic options available at the moment. and the therapeutic considerations based upon a patient's individualized personal characteristics, primary tumor histology, tumor burden and location and velocity of lesion growth.
Previous studies on the extent to which radioactive iodine (RAI) therapy for thyroid cancer increases the risk of subsequently developing breast cancer have given conflicting results.
To evaluated the effect of RAI treatment on breast cancer development and recurrence among female patients with primary thyroid cancer.
This was a retrospective cohort study. The risk of subsequent breast cancer associated with RAI and its dose in hazard ratios (HRs) with 95% confidential intervals (CIs) were calculated using time-dependent Cox proportional hazard models.
A total of 6,150 thyroid cancer patients enrolled between 1973 and 2009 were followed until December 2012. Of these, 3,631 (59.0%) received RAI therapy. During the follow-up period, 99 primary breast cancers were diagnosed.
Risk of breast cancer development according to RAI therapy and RAI dose during treatment for primary thyroid cancer.
RAI therapy did not significantly increase the incidence of subsequent breast cancer among female patients (HR, 0.49; 95% CI, 0.22-1.06) when a 2-year latency period was accounted for. High dose RAI (≥120 mCi) was associated with a reduced incidence of subsequent breast cancer (HR, 0.17; 95% CI, 0.05-0.62) in the cohort with a 2-year latency period.
The long-term follow-up results of this study suggest that RAI treatment for thyroid cancer patients may not increase the risk or recurrence of breast cancer.
Differentiated thyroid carcinomas are typically treated with total thyroidectomy as initial therapy. Subsequent radioactive iodine (RAI) ablation destroys post-surgical thyroid remnants, can additionally provide adjuvant therapy of residual and metastatic thyroid cancers, and enhances the sensitivity and specificity of further diagnostic studies. There is current controversy regarding whether a large number of patients, broadly considered to have "low-risk" disease, should be provided RAI ablation. This is consequent to over-reliance on short-term studies, under-appreciation of the value of RAI remnant ablation, and inflation of the side effects of RAI therapy. A balanced assessment of all of these issues provides justification to utilize post-surgical radioiodine ablation, even in cases that are considered low risk on the basis of surgical findings.
A retrospective comparison was performed of whole body scans obtained before and after 143 131I treatments in 93 patients with thyroid carcinoma. Pretreatment scans were performed with 74-185 megabecquerel 131I, and posttreatment scans were performed 5-12 days after dosing with 1.1-7.4 GBq. In 38 (27%) treatment cycles, the results of posttreatment and pretreatment scans differed. Only 14 (10%) posttreatment scans detected new locations of metastatic disease. Seventeen posttreatment scans demonstrated metastatic locations that were already known from previous studies but not seen on the pretreatment scan. Among parameters evaluated (including demographic and histological characteristics), only the combination of age at diagnosis less than 45 yr and history of previous 131I therapy contributed to the likelihood of a new finding on posttreatment scan (relative risk, 3.8). Five of the 14 new posttreatment scan findings were subsequently corroborated by other radiographic studies or thyroglobulin elevations, all in patients with extrathyroidal extension of the primary tumor. Seven (5%) posttreatment scans were unable to detect a focus of uptake seen on the corresponding pretreatment scan. In conclusion, posttreatment scans were most likely to reveal clinically important new information in young patients who had previously received 131I therapy. In older patients and those without previous 131I therapy, posttreatment scans rarely yielded new information that would potentially alter the patient's prognosis.
Background: Thyroid nodules are a common clinical problem, and differentiated thyroid cancer is becoming increasingly prevalent. Since the American Thyroid Association's (ATA's) guidelines for the management of these disorders were revised in 2009, significant scientific advances have occurred in the field. The aim of these guidelines is to inform clinicians, patients, researchers, and health policy makers on published evidence relating to the diagnosis and management of thyroid nodules and differentiated thyroid cancer. Methods: The specific clinical questions addressed in these guidelines were based on prior versions of the guidelines, stakeholder input, and input of task force members. Task force panel members were educated on knowledge synthesis methods, including electronic database searching, review and selection of relevant citations, and critical appraisal of selected studies. Published English language articles on adults were eligible for inclusion. The American College of Physicians Guideline Grading System was used for critical appraisal of evidence and grading strength of recommendations for therapeutic interventions. We developed a similarly formatted system to appraise the quality of such studies and resultant recommendations. The guideline panel had complete editorial independence from the ATA. Competing interests of guideline task force members were regularly updated, managed, and communicated to the ATA and task force members. Results: The revised guidelines for the management of thyroid nodules include recommendations regarding initial evaluation, clinical and ultrasound criteria for fine-needle aspiration biopsy, interpretation of fine-needle aspiration biopsy results, use of molecular markers, and management of benign thyroid nodules. Recommendations regarding the initial management of thyroid cancer include those relating to screening for thyroid cancer, staging and risk assessment, surgical management, radioiodine remnant ablation and therapy, and thyrotropin suppression therapy using levothyroxine. Recommendations related to long-term management of differentiated thyroid cancer include those related to surveillance for recurrent disease using imaging and serum thyroglobulin, thyroid hormone therapy, management of recurrent and metastatic disease, consideration for clinical trials and targeted therapy, as well as directions for future research. Conclusions: We have developed evidence-based recommendations to inform clinical decision-making in the management of thyroid nodules and differentiated thyroid cancer. They represent, in our opinion, contemporary optimal care for patients with these disorders.
Initial treatments for patients with differentiated thyroid cancer (DTC) are supported primarily by single-institution, retrospective studies, with limited follow-up and low event rates. We report updated analyses of long-term outcomes following treatment in patients with DTC.
Examine effects of initial therapies on outcomes.
Prospective multi-institutional registry.
4,941 patients; median follow-up 6 years.
Total/near-total thyroidectomy (T/NTT), postoperative radioiodine (RAI), thyroid hormone suppression therapy (THST).
Overall (OS), disease-free survival (DFS) using product limit and proportional hazards analyses.
Improved OS was noted in NTCTCS stage III patients who received RAI (risk ratio [RR] 0.66, p=0.04) and stage IV patientswhoreceived both T/NTT and RAI (RR 0.66, 0.70, combined p=0.049). In all stages, moderate THST (TSH maintained subnormal-normal) was associated with significantly improved OS (RR stages I-IV: 0.13, 0.09, 0.13, 0.33) and DFS (RR stages I-III: 0.52, 0.40, 0.18); no additional survival benefit was achieved with more aggressive THST (TSH maintained undetectable- subnormal). This remained true, even when distant metastatic disease was diagnosed during follow-up. Lower initial stage and moderate THST were independent predictors of improved OS during follow-up years 1-3.
We confirm previous findings that T/NTT followed by RAI is associated with benefit in high-risk but not low-risk patients. In contrast with earlier reports, moderate THST is associated with better outcomes across all stages, and aggressive THST may not be warranted even in patients.
Over the past decades, the incidence of differentiated thyroid carcinoma (DTC) has steadily increased, with especially a growing number of low-risk patients. Whereas DTC used to be treated rather aggressively, it is now acknowledged that aggressive treatment does not affect outcome for low-risk patients and that it can induce adverse effects. In this review an overview of the most clinically relevant adverse effects of radioiodine treatment and thyroid hormone suppression therapy (THST) is presented, and the trend toward less aggressive treatment for low-risk patients is outlined. Salivary gland dysfunction occurs in roughly 30% of patients, and is probably due to the concentration of radioiodine in the salivary glands by the sodium/iodide symporter. Beta radiation from radioiodine can result in sialoadenitis and eventually fibrosis and loss of salivary function. Furthermore, patients can experience bone marrow dysfunction following radioiodine treatment. Although this is in general subclinical and transient, patients that receive very high cumulative radioiodine doses may be at risk for more severe bone marrow dysfunction. THST can induce adverse cardiovascular effects in patients with DTC, such as diastolic and systolic dysfunction, and also adverse vascular and prothrombotic effects have been described. Finally, the effects of THST on bone formation and resorption are outlined; especially postmenopausal women with DTC on THST seem to be at risk of bone loss. In the past years, advances have been made in preventing low-risk patients from being overtreated. Improved biomarkers are still needed to further optimize risk stratification and personalize medicine.
The majority of halogenated drugs contain fluorine, followed by chlorine, while those with bromine are rare. Only a few iodine-containing drugs are known such as the thyroid hormone thyroxine, an anti-herpesvirus, antiviral drug, idoxuridine (IDU), and a class III antiarrhythmic agent, amiodarone. Amiodarone prolongs phase III of the cardiac action potential, the repolarization phase in which there is normally decreased calcium permeability and increased potassium permeability. But amiodarone should only be used in life-threatening arrhythmia due to its fatal side effects and severe allergic reactions. IDU is a clinically used anti-herpes drug even though its use is somewhat restricted due to its high general cell toxicity. IDU is mainly used topically to treat herpes simplex keratitis.