Radioactive Iodine Therapy for Thyroid Malignancies

Anatomy and Physiology

The embryonic thyroid gland descends from the foramen cecum at the posterior tongue to its final position below the thyroid cartilage, between the C5 and T1 vertebral levels in the midline anterior neck by the seventh week of gestation.[7] The thyroid gland has 2 lobes connected by an isthmus at the level of the second and third tracheal rings. Approximately 10% to 30% of individuals have a normal anatomical variant called the pyramidal lobe, which extends from the isthmus.[8] The thyroid gland is attached to the trachea by the lateral suspensory ligament. The parathyroid glands and recurrent laryngeal nerves are closely approximated to the posterior thyroid surface.

Thyroid function relies on the availability of dietary iodine, which is absorbed from the gastrointestinal tract and distributed in extracellular fluid. Most absorbed iodine is concentrated in thyroid follicular cells through a sodium-iodide symporter. The fetal thyroid starts concentrating iodine at around 12 weeks of gestation.[9][10] Under the influence of thyroid-stimulating hormone (TSH), iodine is conjugated with tyrosine to form T₃ and T₄. Thyroid hormones are released from the thyroid gland, also under the influence of TSH, and travel to body tissues to regulate cellular metabolism. Iodine is predominantly excreted in the urine, with small amounts also found in feces, sweat, and saliva.

Each major type of thyroid carcinoma has a distinct pathogenesis. Malignancies derived from thyroid follicular epithelium generally harbor driver mutations that activate protein kinase pathways, promoting carcinogenesis. Most papillary thyroid carcinomas develop after activating the mitogen-activated protein kinase (MAPK) signaling pathway. Follicular thyroid carcinomas frequently exhibit mutations in RAS or components of the phosphatidylinositol-3 kinase (PI3K)/AKT signaling pathways.[11] Progression from well-differentiated to poorly differentiated thyroid cancer typically involves additional mutations that further alter cellular function.

Well-differentiated thyroid malignancies retain the ability to absorb iodine through the sodium-iodide symporter, making radioactive iodine an effective therapeutic intervention.[12] However, anaplastic and poorly differentiated malignancies have decreased symporter expression and do not respond well to radioactive iodine therapy. Sodium iodide I 131 induces cellular necroptosis through β-particle emission. Public radiation concerns are due to the γ-emission of 364-KeV high-energy photons.

Effective radioactive therapy requires delivering a total radiation dose at a sufficient rate—typically between 0.6 and 3.0 Gy/h—to prevent tumor cells from repairing sublethal radiation damage. Therefore, treatment efficacy depends on the adequacy of each administered dose rather than the cumulative effect of multiple smaller, insufficient doses.[13]

Indications

Radioactive iodine treatment is recommended for patients with differentiated thyroid cancer after thyroidectomy. Postoperative disease status should be assessed to optimize patient selection and determine the therapeutic dosing of ¹³¹I.[14] The assessment of postoperative disease status includes measuring serum thyroglobulin levels, conducting neck ultrasounds, and performing diagnostic whole-body radioactive iodine imaging. The 3 primary goals of radioactive iodine therapy in well-differentiated thyroid cancers are remnant ablation, adjuvant therapy, and treatment of known disease. Although these goals are listed separately, ¹³¹I used for remnant ablation may also have a tumoricidal effect, and ¹³¹I used for adjuvant treatment may destroy normal remnant thyroid tissue.[15]

Remnant ablation involves the destruction of presumably benign thyroid tissue after total or subtotal thyroidectomy. This process promotes the accurate interpretation of postoperative ¹³¹I whole-body imaging and serum thyroglobulin levels, reducing confusion between residual thyroid tissue, local disease recurrence, or metastatic disease. Adjuvant treatment is additional therapy administered after surgery to lower the risk of cancer recurrence in patients with an intermediate or high risk of recurrence. This therapy improves progression-free survival in patients without obvious evidence of disease but who may have subclinical micrometastases.

Treating a known disease involves destroying residual cancer or recurrent structural or biochemical disease with either curative or palliative intent. This therapy improves progression-free and overall survival. Radioactive iodine therapy is appropriate for patients with tumors larger than 2 cm and at least one risk factor, such as apparent extrathyroidal extension, age 45 or older, or lymph node or distant metastases. Radioactive iodine therapy is also recommended for tumors smaller than 2 cm if distant metastases are evident.[16] Based on the available data, selecting low- or intermediate-risk patients for remnant ablation or adjuvant treatment is challenging. Patients are classified into low-risk, intermediate-risk, and high-risk categories, as indicated below.[17]

• Low risk: Low-risk patients include individuals with papillary carcinoma who have undergone gross total thyroidectomy without distant metastases, lymph node involvement, invasion of adjacent structures or blood vessels, or aggressive histology. These patients also lack radioactive iodine uptake outside the thyroid bed, palpable lymph nodes, and pathological nodal micrometastases. Other low-risk conditions encompass the encapsulated intrathyroidal follicular variant of papillary thyroid cancer and well-differentiated intrathyroidal follicular carcinoma with capsular invasion, whether or not fewer than 4 foci of vascular invasion are present.

• Intermediate risk: Intermediate-risk patients typically have aggressive histology types such as oncocytic carcinoma, follicular thyroid cancer, columnar cell or tall cell variants, and insular carcinoma. This group also includes individuals with multifocal papillary microcarcinoma exhibiting extrathyroidal extension and those with clinically positive lymph nodes less than 3 cm in the largest dimension or more than 5 pathologically positive lymph nodes less than 3 cm in the largest dimension.

• High risk: High-risk patients include those with incomplete resection, gross extrathyroidal extension, pathologically positive lymph nodes where at least 1 is greater than 3 cm in the largest dimension, distant metastasis, and follicular carcinoma with more than 4 foci of vascular invasion.

The appropriate radioactive iodine dose should be determined using an interprofessional approach. Patients without imaging, biochemical, pathological, or clinical evidence of disease after initial definitive curative surgery should either be observed or undergo radioactive iodine treatment for remnant ablation or adjuvant therapy, depending on institutional protocols.

Radioactive iodine therapy is primarily used to treat differentiated thyroid cancers, such as papillary and follicular thyroid carcinoma, due to their ability to uptake iodine. Radioactive iodine therapy is typically recommended under several specific conditions, including the following:

• The cancer has spread significantly beyond the thyroid to other areas of the body (metastasis).
• The cancer has invaded blood vessels, which applies especially to follicular and oncocytic malignancies.
• The thyroglobulin level remains high 6 to 12 weeks after surgery, indicating the presence of residual thyroid cancer cells.
• The tumor was accompanied by large or more than 5 cancerous lymph nodes, suggesting a higher risk of recurrence.
• The tumor is a differentiated or hybrid carcinoma, which typically responds better to radioactive iodine therapy due to its iodine-absorbing properties.

Radioactive iodine therapy aims to destroy any remaining thyroid tissue or cancer cells after thyroid surgery, particularly in patients with a higher risk of recurrence or metastasis.[18]

Contraindications

Pregnancy and breastfeeding are absolute contraindications for radioactive iodine therapy, as the isotope can cross the placenta and damage the fetal thyroid. Therefore, a pregnancy test should be performed before treating women of childbearing age. Nursing mothers should stop breastfeeding because radioactive iodine is secreted through breast milk. Vomiting and diarrhea are also contraindications, as these gastrointestinal disturbances hinder radioactive iodine absorption and pose a risk of radiation exposure to others. Inefficiency and noncompliance with radiation protection, safety instructions, and recommendations are additional contraindications for therapy. A history of intake of interfering medications, recent imaging using iodinated contrast, and incontinence issues should be properly addressed.[19][20]

Patients should be advised regarding the necessity of radiation protection and procedures to safeguard household members and the general public. The healthcare team should obtain a comprehensive patient history relevant to the disease and any issues that could pose a risk of radiation exposure to others. A thorough pretreatment evaluation can lead to better outcomes and minimize radiation exposure to the public. 

A retrospective cohort study found no significant difference in cardiovascular disease risk between individuals with thyroid cancer who received radioactive iodine treatment and those who did not.[21] Clinicians should consider this finding when determining the suitability of the treatment for patients with preexisting cardiovascular disease.

Equipment

Proper equipment and materials are crucial for the safe and effective administration of radioactive iodine treatment in patients with thyroid cancer. The equipment and materials necessary for radioactive iodine treatment include the following:

• ¹³¹I: This radioactive isotope emits β- and γ-particles. The patient swallows radioactive iodine in either liquid or pill form. ¹³¹I accumulates within thyroid cancer cells, causing damage to those cells. ¹³¹I is highly effective due to its selective uptake in thyroid tissue, making it a critical component in treating differentiated thyroid cancer. 

• Radiation safety materials: Given the hazardous nature of radioactive iodine, radiation safety is essential. Facilities administering radioactive iodine must use lead-lined rooms and radiation shielding materials such as lead aprons and barriers to protect both healthcare workers and patients from exposure. Mobile shielding units may also be used to improve flexibility in radiation containment.[22]

• Dosimetry equipment: Dosimetry equipment, such as Geiger-Muller counters, ionization chambers, and scintillation detectors, is crucial in ensuring the correct radiation dose is delivered while minimizing exposure to healthcare personnel. Real-time dosimetry monitoring allows for increased precision and safety in radiation therapy.[23]

• Lead-lined containers: Radioactive iodine capsules or liquid solutions must be stored and transported in lead-lined containers to shield against radiation exposure. These containers are designed to minimize radiation exposure during handling, storage, and administration of radioactive materials.

• Radiation survey instruments: Handheld survey meters or detectors, such as Geiger-Muller counters, are used to monitor radiation levels in treatment rooms and adjacent areas. These devices ensure that radiation exposure remains within acceptable safety limits during and after treatment.

• Isolation facilities: Patients receiving high doses of radioactive iodine may require isolation to prevent radiation exposure to others. Isolation rooms must include appropriate shielding, ventilation systems, and specialized waste disposal. Remote monitoring technologies also help minimize contact with patients, improving overall safety.[24]

• Radiation safety accessories: Accessories such as lead aprons, gloves, goggles, and protective clothing are essential for healthcare staff to prevent contamination and reduce exposure during radioactive iodine treatments. Advances in lightweight and ergonomic protective materials have made these accessories more comfortable for extended use.

• Medical imaging equipment: This equipment includes instruments such as γ-cameras or scintillation cameras, which may be used to perform imaging studies before and after radioactive iodine treatment. These imaging modalities help assess the distribution of radioactive iodine within the body, evaluate treatment response, and detect any residual or metastatic disease. Hybrid imaging technologies such as positron emission tomography or computed tomography have greatly improved diagnostic accuracy.[25]

• Thyroid uptake systems: Devices such as thyroid uptake probes measure how much radioactive iodine the thyroid absorbs. This information helps determine the treatment dose and evaluates its effectiveness. Advanced thyroid uptake systems are susceptible and accurate.[26]

• Radiation detection badges: Healthcare personnel are required to wear radiation detection badges to monitor their exposure during radioactive iodine treatments. These badges are periodically read to ensure radiation exposure remains within occupational safety limits.

Overall, the equipment required for radioactive iodine treatment in thyroid cancer includes radioactive materials, radiation containment and shielding, dosimetry monitoring, patient isolation facilities, radiation safety accessories, and medical imaging equipment. These resources are essential for delivering radioactive iodine therapy safely and effectively while minimizing radiation risks to patients and healthcare personnel.

Personnel

The personnel involved in administering radioactive iodine for thyroid cancer typically include the following:

• Surgeon: This healthcare provider performs thyroidectomy before radioactive iodine therapy is administered.

• Endocrinologist: This specialist manages the patient's treatment plan, monitors thyroid function, and adjusts medication as needed before and after radioactive iodine administration.

• Medical oncologist: This specialist coordinates the overall cancer treatment plan, assesses the appropriateness of radioactive iodine therapy, and monitors the patient for any signs of recurrence or adverse reactions.

• Nuclear medicine clinicians: These professionals oversee the radioactive iodine treatment process, evaluating patients' suitability for radioactive iodine, determining the appropriate dosage, and supervising treatment planning and administration.

• Radiation oncologists: These specialists may be involved in treating patients with thyroid cancer who undergo radioactive iodine, especially in cases where the cancer has spread beyond the thyroid gland, requiring an interprofessional approach.

• Nuclear medicine technologists: These trained healthcare professionals prepare and administer radioactive materials, such as ¹³¹I, to patients undergoing radioactive iodine. Nuclear medicine technologists ensure proper radiation safety protocols during treatment and provide patient education and support.

• Radiation safety officers: These professionals oversee radiation safety practices and procedures within the healthcare facility. Radiation safety officers ensure compliance with regulatory requirements, conduct radiation safety training for staff, and monitor radiation exposure levels to minimize risks to patients and personnel.

• Medical physicists: These professionals specialize in radiation therapy and may provide expertise in treatment planning, dose calculation, and quality assurance for radioactive iodine therapy. Medical physicists ensure patients receive the prescribed radiation dose while minimizing exposure to surrounding tissues.

• Nursing staff: Nurses are crucial in caring for patients undergoing radioactive iodine treatment. These healthcare professionals provide pretreatment assessments, monitor patients during treatment, and offer supportive care to manage adverse effects and complications. Nurses also educate patients about radiation safety precautions and post-treatment care instructions.

• Radiology and imaging technicians: These professionals may assist in performing diagnostic imaging studies, such as whole-body scans or γ-camera imaging, before and after treatment. Such imaging modalities help assess treatment response and detect residual or metastatic disease.

• Administrative and support staff: These professionals assist with scheduling appointments, coordinating treatment logistics, and providing logistical support to patients undergoing radioactive iodine therapy within the nuclear medicine department or oncology clinics.

Other healthcare providers involved in the care of patients requiring radioactive iodine include physician assistants, nurses, psychologists, social workers, and rehabilitation specialists.[27] Each healthcare team member is critical to ensuring the safe and effective delivery of radioactive iodine for patients with thyroid cancer. Collaboration within the interprofessional team helps optimize treatment outcomes and enhance overall patient care.

Preparation

Proper preparation for radioactive iodine therapy is critical. The 2 key requisites for preparation are:

• Sufficient TSH elevation for maximal stimulation of remnant and tumor cell production of the sodium-iodide symporter, allowing radioactive iodine to accumulate within thyroid cells.
• Sufficient depletion of stable, nonradioactive iodine from the diet to avoid diluting the specific activity of the treatment dose.

The traditional method of elevating endogenous TSH is by withdrawing thyroid hormone therapy, causing hypothyroidism. A low-iodine diet for 1 to 2 weeks maximizes the absorption of ¹³¹I, as high blood pool iodide can compete with radioactive iodine.[28] Adequate TSH stimulation is necessary to optimize therapeutic benefit. Thyroid hormone withdrawal raises endogenous TSH, with the optimal TSH level being 30 mIU/mL or higher. Optimal TSH levels may also be achieved through the exogenous administration of recombinant human TSH (rhTSH), which may be given when thyroid hormone withdrawal can cause unwanted effects in patients.[29]

Renal function tests and a complete blood count should be checked before therapy. As ¹³¹I is primarily excreted through the urinary system, significant renal dysfunction can delay radioactivity clearance, increasing the risk of bone marrow suppression. The patient should fast for at least 2 to 4 hours before and 1 hour after radioactive iodine therapy. Informed consent should be obtained after explaining the treatment's purpose, possible adverse effects, the potential need for additional radioactive iodine therapy, and the requirement for hormone replacement therapy.

Radiation safety precautions to reduce exposure to others should be explained, and a written directive should be signed. Women of reproductive age should have a negative pregnancy test before starting therapy. Nursing mothers should discontinue breastfeeding entirely at least 6 weeks before treatment. Patients should be encouraged to drink plenty of water and frequently void to reduce the dose absorbed by urinary bladder cells.

The following criteria are essential when preparing a patient for radioactive iodine treatment.

• Thyroid hormone withdrawal or TSH stimulation: Patients may need to discontinue taking thyroid hormone medication for several weeks before radioactive iodine treatment. Withdrawing thyroid hormone medication or administering rhTSH injections is recommended to stimulate thyroid tissue and increase the uptake of radioactive iodine by cancerous cells. The approach depends on the patient's circumstances and the healthcare provider's preferences.

• Dietary restrictions: Patients may be instructed to follow a low-iodine diet for a specified period before radioactive iodine treatment. This diet restricts foods rich in iodine, such as iodized salt, seafood, dairy products, and certain vegetables, to minimize competition with thyroid cell uptake of ¹³¹I. The duration and extent of dietary restrictions vary, depending on the healthcare provider's recommendations.

• Assessment of pregnancy and breastfeeding status: Female patients of childbearing age are typically required to have a pregnancy test to ensure they are not pregnant before undergoing radioactive iodine treatment. In addition, breastfeeding mothers should discontinue breastfeeding for a specified period before and after radioactive iodine treatment to prevent radiation exposure to the infant.

• Baseline imaging and laboratory tests: Patients typically undergo imaging studies, such as a whole-body or diagnostic radioactive iodine scan, to evaluate the extent of thyroid cancer and detect any distant metastases before radioactive iodine treatment. Laboratory tests, including thyroid and renal function tests, are also performed to assess baseline thyroid and kidney function.

• Preparation for isolation: Radioactive iodine treatment often requires isolation precautions to minimize radiation exposure to others. Patients may be advised to stay in a designated isolation room in the hospital or at home for a specific period following radioactive iodine administration. Healthcare practitioners should provide clear instructions on radiation safety measures to follow during isolation, including guidelines for limiting close contact with others and handling bodily fluids.

• Hydration: Adequate hydration is essential both before and after radioactive iodine treatment to help flush radioactive iodine from the body more efficiently. Patients are typically encouraged to drink plenty of fluids, especially water, to promote urinary excretion of radioactive iodine and reduce radiation exposure to other organs, particularly the salivary glands.

• Patient education: Patients should receive detailed information about the radioactive iodine treatment procedure, potential adverse effects, radiation safety precautions, and post-treatment care instructions. Patient education should include guidance on managing symptoms such as nausea, dry mouth, and fatigue, and outline when to seek medical attention for any complications.

Careful patient preparation allows healthcare providers to maximize the therapeutic benefits of radioactive iodine therapy while minimizing risks and ensuring patient safety.

Technique or Treatment

Standard therapy, including surgical resection and radioactive iodine ablation, fails in about 10% of differentiated thyroid cancer cases and all anaplastic thyroid cancer cases. A multimodal approach, combining standard therapy with cytotoxic chemotherapy, has been used for advanced thyroid cancer but shows limited efficacy.

Radioactive iodine ablation is part of postoperative care for patients with persistent or recurrent disease, metastasis, or a high tumor recurrence risk. The benefit of radioactive iodine has been demonstrated in high-risk patients, reducing the risk of recurrence and disease-related mortality in this cohort.[30]

Radioactive iodine therapy is typically scheduled at least 3 weeks post-surgery or approximately 4 to 6 weeks after discontinuing levothyroxine to ensure an adequate TSH level. When exogenous TSH administration is necessary, a dosage of 0.9 mg of rhTSH is injected intramuscularly for 2 consecutive days, followed by radioactive iodine treatment 24 hours later. Radioactive iodine is commonly administered in pill form. The patient's identity should be confirmed before administration. For patients with a low risk of recurrence, a dose of approximately 30 mCi of radioactive iodine is generally sufficient for effective ablation.

The radioactive iodine dose may be increased to a maximum of approximately 250 mCi for moderate- and high-risk patients. A written informed consent should be obtained from the patient. The dose should be verified by an authorized user before administration. After therapy, the administration area should be surveyed to detect any contamination. Radioactivity released from the patient should be checked with a survey instrument before their discharge from the hospital. The calculation should ensure that the effective dose to caregivers and family members does not exceed 5 mSv before the patient is discharged.

The patient should drive directly home after therapy, preferably alone. If driving alone is not possible, the patient should choose a seat that maintains maximum distance from others in the vehicle. For 3 to 4 days following treatment, patients should be advised to restrict contact with others, sleep in a separate room, avoid kissing, use a separate bathroom, prevent cross-contamination with sweat and urine, flush the toilet twice after use, wash clothes and utensils separately, and avoid contact with children and pets. In addition, if the patient works in food service or childcare, they should request an extended leave to minimize radiation exposure to others.

The long half-life of radioactive iodine, which is 8.04 days, allows for imaging several days after therapy. This extended period enables the tracer to concentrate adequately on metastatic lesions, thereby enhancing the sensitivity of the whole-body scan. The patient can return to the nuclear medicine department 3 to 10 days after radioactive iodine therapy to obtain a whole-body image. The patient is advised to follow up with an endocrinologist for long-term hormone replacement therapy and other related issues.

Radiation may remain detectable using standard monitoring devices for several weeks after treatment. Hence, patients planning travel should be given adequate written records of treatment and contact information for the treatment facility.[31] Ablation is typically completed in 4 to 6 months, after which a follow-up ¹³¹I whole-body diagnostic scan may be obtained to determine the procedure's success. Retreatment is recommended if the disease persists.

Complications

Sodium iodide I-131 treatment-related toxicity may be classified as acute or chronic. Adverse effects of ¹³¹I are rarely lethal at typical therapeutic doses for thyroid cancer and Graves disease. The physiological concentration of ¹³¹I in the thyroid and salivary glands, and other organs such as the stomach, can lead to toxicity from emitted β–particle-related locoregional tissue injury. Sialadenitis, or salivary gland inflammation, secondary to ¹³¹I therapy is a frequent complication in the acute setting, observed in up to 20% of patients.[32] The risk of sialadenitis and xerostomia is dose-dependent.[33] Although not standardized, salivary gland stimulation and other measures, such as hydration and the use of sialagogues, may be used to minimize the risk of sialadenitis. 

Another acute adverse effect is dysgeusia, or taste dysfunction, secondary to taste bud injury, lasting several days to weeks after treatment.[34] Oral ¹³¹I may also cause acute radiation gastritis or enteritis after transiting through the stomach and small bowel, most frequently manifesting as nausea. Painful radiation thyroiditis may also occur in the presence of significant residual thyroid tissue in the neck, whether native tissue post-thyroidectomy or papillary or follicular cancer metastasis, often manifesting as neck pain or fever.[35] Nasolacrimal duct obstruction is another acute adverse effect of the treatment.

Although most patients do not have these complications, approximately one-third of patients who receive radioactive iodine develop variable reductions in their salivary output, with 10% experiencing severe xerostomia. Patients undergoing high-dose radioactive iodine therapy, especially those approaching 200 rad of red marrow exposure, may also develop a temporary platelet and leukocyte decrease, reaching a nadir occurring 4 weeks after treatment and recovering to baseline by 8 weeks.

Chronic toxicity resulting from ¹³¹I treatment includes the reduction of male fertility due to the radiosensitive nature of live sperm—a feature not shared by female oocytes. Other chronic ¹³¹I treatment-related toxicity manifestations include lung fibrosis, chronic xerostomia or sialadenitis, and epiphora secondary to chronic lacrimal gland damage and fibrosis. The risk of leukemia and salivary gland malignancy associated with ¹³¹I treatment is controversial and beyond the scope of this article.

Radioactive iodine treatment for differentiated thyroid carcinoma in children and young adults is linked to an increased risk of hematological malignancy, including leukemia, and several solid malignancies, such as uterine, salivary, and stomach cancers, with a particular predilection for female breast cancer, more than 20 years after exposure. These findings suggest that patients undergoing radioactive iodine therapy should be monitored for a long time.

Clinical Significance

Radioactive iodine serves both diagnostic and therapeutic purposes in thyroid cancer management, depending on the tumor's histopathology. Approximately 90% of thyroid cancers are well-differentiated and capable of taking up this isotope. Papillary thyroid carcinoma, the most common type, is twice as common in women as in men and shows lymphomatous spread to the cervical lymph nodes. In contrast, the common route of spread for follicular carcinoma is hematogenous, with frequent metastasis to the lungs and bones and less common spread to the liver and brain. Differentiated thyroid cancer typically has a good prognosis if appropriately treated. Among the differentiated thyroid cancers, Hurthle cell cancer often metastasizes and may not take up radioactive iodine.

Due to the risk of recurrence, patients may or may not be treated with radioactive iodine 6 to 8 weeks after total thyroidectomy, the definitive treatment for thyroid cancer, depending on the histopathology report. Patients may undergo a low-dose whole-body radioactive iodine scan approximately 2 months after thyroidectomy to check for any residual thyroid tissue, lymph node metastases, or distal metastases. The treating clinical team can determine the dose for the treatment, depending on the distribution of radioactive iodine on the scan.

Follow-up radioactive iodine scans and repeated ¹³¹I treatments may be performed depending on individual needs. A whole-body scan obtained 3 to 10 days after radioactive iodine treatment is more sensitive for detecting disease compared to a low-dose whole-body scan due to the higher radiation dose. Serum thyroglobulin level testing is recommended for the follow-up of patients who received thyroid cancer treatment. Multiple repeat treatments at 6-month to 1-year intervals are essential to ensure a complete response, considering the probable adverse effects and dose adjustments. The risk of radiation exposure to the treating staff and household members is high, as ¹³¹I emits high-energy γ-radiation and has a long physical half-life. Hence, radiation protection regulations should be strictly followed.[36]

A meta-analysis evaluating the role of radioactive iodine in pediatric differentiated thyroid cancer found that radioactive iodine therapy reduced the risk of recurrent disease in this population.[37] A cohort study indicated an association between urinary iodine excretion and progression-free survival, suggesting that urinary iodine excretion ≥200 µg/d may be linked to worse progression-free survival in radioactive iodine–treated patients with differentiated thyroid cancer. The presence of distant metastases was identified as a strong independent predictor of progression.[38]

Enhancing Healthcare Team Outcomes

The appropriate treatment for differentiated thyroid cancer involves surgery with or without postoperative radioactive iodine therapy. The need for and dosage of radioactive iodine are determined individually, depending on the patient's risk category and institutional protocols. Assessing patient risk along with the need for radioactive iodine therapy, selecting and administering the dosage, maintaining radiation safety protocol, and ensuring the patient complies with the protocol all require an interprofessional team approach. This healthcare team typically includes the primary care clinician, endocrinologist, pathologist, nuclear medicine physician, radiopharmacy and nursing staff, technologists, and radiation safety officer.

An evidence-based integrated management approach brings superior results. The interprofessional healthcare team should educate patients about the risks and benefits of radioactive iodine treatment and inform them of the importance of following a low-iodine diet before therapy. Efficient clinician-patient communication and proper radiation safety instructions are essential. Small children or pregnant partners should not accompany the patient while visiting for treatment. Female patients of reproductive age should have a negative serum pregnancy test result to proceed with radioactive iodine treatment. The patient should be aware of this therapy's possible short- and long-term adverse effects.

Using checklists can help explain all aspects of therapy to the patient, improve clinical outcomes, and reduce radiation exposure to the public. Patients should maintain a distance of at least 3 feet from others, especially pregnant women and children, for the first few days after radioactive iodine therapy. In addition, patients should be advised to use effective contraception for 6 to 12 months following the treatment. Routine follow-up, including thyroglobulin and TSH level testing, and radioactive iodine diagnostic whole-body scans, is recommended for patients after thyroid cancer treatment. Efficient communication and collaboration among interprofessional healthcare team members are essential for achieving optimal outcomes. 

Molecular Testing and Precision Medicine in Thyroid Cancer

The integration of molecular testing into managing differentiated thyroid cancer has gained prominence in recent years. Identifying genetic mutations, such as those involving BRAFV600E and RAS, has been valuable in making treatment decisions, including whether patients should receive radioactive iodine therapy. For example, patients with BRAFV600E mutations are more likely to benefit from radioactive iodine therapy due to the mutation's association with more aggressive disease and higher recurrence rates.[39]

Nursing, Allied Health, and Interprofessional Team Interventions

The core objective in managing ¹³¹I radiation risk is to keep exposure levels as low as reasonably achievable (ALARA). The United States Nuclear Regulatory Commission generally limits each worker's occupational radiation exposure to no more than 5000 mrem annually. This cumulative exposure is monitored through dosimetry tests using film badges worn by workers on their torsos. In addition, nuclear licensees, such as hospitals, must limit radiation exposure to members of the public, including hospital visitors, to no more than 100 mrem per year.

To achieve ALARA exposure rates, key principles such as time, distance, and shielding are crucial. The time spent exposed to a patient receiving radiation is generally limited to 30 minutes per person per shift. Nurses should bundle care tasks for maximum efficiency and transfer care to other team members once time limits are reached. Each nurse should be assigned to no more than one patient receiving radiation per shift. Patient safety risks, adverse effects, and needs may be frequently assessed through intercom between nursing visits to ensure effective monitoring and minimize radiation exposure.

Nurses should thoroughly educate patients receiving ¹³¹I before discharge to fulfill their obligation to minimize exposure to family members and the public. According to the American Thyroid Association guidelines, patients should maintain a personal distance of more than 6 feet from others, avoid sharing personal hygiene items or eating utensils, stay well-hydrated, shower daily for the first 2 days, and use flushable wipes to clean toilets after each use. A 2011 survey by Greenlee et al involving 311 clinicians and allied practitioners revealed a wide range of safety practices, from minimal to rigorous. Although guidelines help mitigate risk, a debate about the necessary degree of caution persists.[40]

As the incidence of iodine administration and thyroid cancer continues to rise, knowledge of radiation safety principles becomes essential for a growing number of nurses. The 3 key principles—time, distance, and shielding—should be used when caring for patients undergoing radiation treatment. Knowledge of these principles allows nurses to safely assist patients undergoing radioactive iodine, minimize occupational risk, and protect the public. Nurses are uniquely positioned to educate the healthcare team, patients, and families on these essential concepts of radiation safety, thereby safeguarding them from unnecessary risks.[41]

Radioactive iodine is typically administered orally, where it accumulates in the thyroid gland. In the first 48 hours after treatment, iodine is excreted in urine, sweat, and other bodily fluids. After this period, the thyroid becomes the primary site with remaining radioactivity. Before administering radioactive iodine, an authorized clinician must date and sign a written directive and treatment plan. The written directive should include the patient's name, treatment site, radiopharmaceutical, and prescribed dose.

Patients should receive the following instructions:

• Patients are restricted to their rooms.
• Patients should use disposable eating utensils, which should be placed in a special waste container after use.
• Patients should flush the toilet 2 or 3 times after each use to ensure that all radioactive urine is washed from the toilet bowl.
• Both male and female patients should sit on the toilet to prevent urine splatter.
• Adult family visitors are allowed but must avoid physical contact with the patient. Adult visitors should typically remain 3 feet or more away from the patient.

Nursing, Allied Health, and Interprofessional Team Monitoring

The floor and any objects the patient may come into contact with must be covered with plastic or other protective material to prevent contamination. After notification from the nuclear medicine physician, the environmental health and safety hazardous waste technician should prepare the room before administering radioactive iodine.

Before reassigning the room to another patient, the hazardous waste technician must survey the room for contamination and remove all radioactive waste. The room should also be decontaminated if necessary.