Thyroid Cancer: Diagnosis, Radioiodine (I-131) Therapy & Advanced Nuclear Medicine Treatment

Thyroid cancer is one of the fastest-rising cancers globally and in India, with recent estimates suggesting over 38,000 new cases annually in the country alone. It is one of the most treatable cancers - if diagnosed and managed correctly.

At the same time, not every patient needs aggressive treatment. The key lies in accurate diagnosis, risk-based therapy, and personalised care.

This is where nuclear medicine plays a transformative role, helping doctors not only detect thyroid cancer early but also treat it precisely using targeted therapies like radioiodine (I-131).

Artemis Hospitals, Gurugram, offers a comprehensive and technology-driven approach to thyroid cancer care by integrating advanced nuclear medicine techniques, expert clinical evaluation, and multidisciplinary care. This enables accurate diagnosis, personalized treatment planning, and effective long-term monitoring for better patient outcomes.

What is Thyroid Cancer?

Thyroid cancer occurs when abnormal cells develop in the thyroid gland, a small, butterfly-shaped gland located at the base of the neck that plays a key role in regulating metabolism, heart rate, and body temperature. In most cases, thyroid cancer grows slowly and may not cause noticeable symptoms in its early stages, which is why it is often detected during routine examinations or imaging tests.

There are four main types of thyroid cancer. Papillary thyroid cancer is the most common and generally has an excellent prognosis. Follicular thyroid cancer is slightly less common but also highly treatable. Medullary thyroid cancer arises from different cells within the thyroid and may be associated with genetic conditions. Anaplastic thyroid cancer is rare but more aggressive and requires prompt, specialized care.

What are the Early Symptoms & Warning Signs of Thyroid Cancer?

Thyroid cancer often develops silently, and many patients may not notice any symptoms in the early stages. In fact, it is frequently detected incidentally during routine health check-ups or imaging done for other conditions. However, as the disease progresses, certain signs may begin to appear.

While early-stage thyroid cancer may not cause noticeable symptoms, regular check-ups and awareness are essential for early detection. Also, some of these symptoms can also be caused by non-cancerous thyroid conditions, which may require timely medical evaluation.

How is Thyroid Cancer Diagnosed?

Thyroid cancer diagnosis involves a combination of clinical evaluation, imaging, and specialized tests to confirm the presence of cancer and assess its extent. An accurate diagnosis is essential for planning the most effective treatment strategy.

Clinical Evaluation & Blood Tests

The initial assessment includes a physical examination of the neck to check for nodules or swelling. Blood tests may be advised to evaluate thyroid function and tumour markers, such as:

• Thyroid function tests (T3, T4, TSH)
• Thyroglobulin levels, which can be useful in certain types of thyroid cancer, especially during follow-up.

Imaging Techniques

Imaging plays a key role in identifying thyroid nodules and assessing their characteristics:

• Ultrasound (USG): First-line imaging to evaluate size, structure, and suspicious features
• CT/MRI: Used in selected cases to assess large tumors or spread to nearby structures

Fine Needle Aspiration Cytology (FNAC)

FNAC is the most important diagnostic test for thyroid nodules. A thin needle is used to extract cells from the thyroid, which are then examined under a microscope to determine whether they are benign or cancerous.

Role of Nuclear Medicine in Diagnosis

Nuclear Medicine can detect diseases at a molecular level, even before structural changes become visible. This helps the doctors identify hidden diseases, assess spread, and make more informed treatment decisions.

While conventional imaging focuses on the structure of the thyroid gland, nuclear medicine provides functional insights, showing how thyroid cells behave, which is crucial in thyroid cancer management. It plays a key role not only in diagnosis but also in staging, treatment planning, and follow-up.

Additionally, advanced technologies such as SPECT-CT, dual-head gamma cameras, and PET-CT combine functional and anatomical imaging to significantly improve diagnostic accuracy and enable a personalized approach to thyroid cancer care.

Role of Nuclear Medicine in thyroid cancer diagnosis involves the following:

• Thyroid Scan: It helps differentiate between functioning (“hot”) and non-functioning (“cold”) nodules, with cold nodules requiring further evaluation.
• Whole Body Iodine Scan: It is commonly performed after surgery to detect residual thyroid tissue or metastatic disease that may not be visible on routine imaging.
• PET-CT scan: Used in more complex cases, particularly when tumor markers such as thyroglobulin are elevated, but iodine scans are negative.

Thyroid Cancer Risk Management & Treatment Options: When Is Therapy Recommended?

After diagnosis, thyroid cancer is classified into low, intermediate, or high-risk levels based on how far the disease has spread and its clinical behavior. This classification plays a key role in deciding whether radioiodine (I-131) therapy is required or not.

Radioiodine (I-131) therapy is a targeted treatment that uses radioactive iodine to destroy remaining thyroid tissue and cancer cells after surgery. Since thyroid cells naturally absorb iodine, this therapy works precisely on cancerous cells while minimising impact on the rest of the body. Its use is guided by the patient’s risk level, ensuring effective and personalized treatment while avoiding treatment in low-risk patients:

Thyroid Cancer Treatment: What Happens After Risk Assessment?

Once the risk level of thyroid cancer is identified, the next step is to decide the most appropriate treatment plan. Since each patient’s disease behaves differently, treatment is carefully tailored based on risk category, ensuring the right balance between effective cancer control and avoiding unnecessary interventions.

Treatment Approach

Surgery (Thyroidectomy): Surgery is the primary and often the first step in treating thyroid cancer. Depending on the extent of disease, either a part of the thyroid (lobectomy) or the entire gland (total thyroidectomy) may be removed. In some cases, nearby lymph nodes are also removed if there is evidence of spread.

This step is crucial as it eliminates the main tumour and helps in accurate staging, which further guides the need for additional treatments such as radioiodine therapy.

What to expect After Surgery: After surgical removal of thyroid cancer, patients are risk-stratified based on histopathological findings. Depending on the risk category, additional evaluation may be performed, including a post-operative I-131 whole-body scan to assess residual thyroid tissue or metastatic disease.

Based on these findings, selected patients may be advised radioactive iodine (I-131) therapy.

Radioiodine (I-131) Therapy: Radioiodine (I-131) therapy is a key component of thyroid cancer treatment and one of the most effective applications of nuclear medicine. It is a targeted therapy that uses radioactive iodine to destroy remaining thyroid tissue and cancer cells after surgery.

Principle of treatment: I-131 therapy is based on the unique ability of thyroid cells, including most differentiated thyroid cancer cells to actively take up iodine. When radioactive iodine (I-131) is administered, it selectively targets and destroys thyroid cancer cells with minimal impact on surrounding healthy tissues. It is commonly used for:

• Remnant ablation (removing leftover thyroid tissue)
• Adjuvant therapy (reducing recurrence risk)
• Treatment of metastatic disease

What to expect After Surgery:After surgery, patients in intermediate and high-risk categories may require radioiodine therapy to destroy any remaining thyroid tissue or microscopic cancer cells. This treatment works on the principle that thyroid cells naturally absorb iodine.

Radioiodine Therapy (I-131)

Radioiodine (I-131) therapy is a key component of thyroid cancer treatment and one of the most effective applications of nuclear medicine. It is a targeted therapy that uses radioactive iodine to destroy remaining thyroid tissue and cancer cells after surgery.

What is I-131 Therapy?

I-131 is a radioactive form of iodine that is naturally absorbed by thyroid cells. When administered (usually as a capsule or liquid), it travels through the bloodstream and selectively concentrates in thyroid cells, including cancerous ones. The radiation then destroys these cells from within, while largely sparing surrounding healthy tissues.

Personalised Radioiodine Therapy: A Precision-Based Approach

While radioiodine (I-131) therapy is highly effective, not all patients require the same dose or treatment intensity. Modern thyroid cancer care is increasingly moving toward a personalized approach, where therapy is tailored to the individual patient rather than using a fixed, one-size-fits-all strategy.

What is Personalised (Dosimetry-Based) Therapy?

Dosimetry involves calculating how much radiation is absorbed by the tumour and normal tissues in each patient. This enables doctors to determine the optimal dose of I-131 needed to effectively treat cancer while minimising exposure to healthy organs. By individualising treatment, this approach helps avoid under-treatment in aggressive disease and reduces unnecessary radiation in low-risk cases, improving both safety and outcomes.

How It Improves Patient Care?

Preparing for Radioiodine Therapy: rhTSH vs Hormone Withdrawal

Before undergoing radioiodine (I-131) therapy, the body needs to have elevated levels of Thyroid Stimulating Hormone (TSH). Higher TSH levels help thyroid cells absorb more iodine, making the treatment more effective. This preparation can be achieved in two ways: recombinant TSH (rhTSH) or thyroid hormone withdrawal.

What is rhTSH?

Recombinant TSH (rhTSH) is an injectable form of TSH that stimulates iodine uptake without requiring patients to stop their thyroid hormone medication. This allows patients to continue their routine lifestyle without experiencing symptoms of hypothyroidism.

Two Approaches to Preparation

Post-Therapy Whole Body Scan

After radioiodine (I-131) therapy, a post-therapy whole body iodine scan is performed to evaluate how effectively the treatment has worked. This scan helps identify any remaining thyroid tissue or cancer cells, including areas of spread that may not have been visible on earlier imaging. By showing how radioactive iodine is taken up in the body, it provides valuable insight into both residual disease and treatment response.

Significance of Post-Therapy Whole Body Scan

Unlike conventional imaging, this scan provides functional information, showing how thyroid cells absorb iodine. In many cases, it can reveal areas of disease that were not detected on previous scans, helping doctors better understand the true extent of the condition.

PET-CT in Thyroid Cancer

While radioiodine scans are highly effective in most cases, there are situations where additional imaging is needed. PET-CT (Positron Emission Tomography–Computed Tomography) is particularly useful when thyroid cancer behaves differently or is not clearly visible on iodine-based scans.

PET-CT works by using a small amount of radioactive glucose (FDG), which is taken more actively by cancer cells due to their higher metabolic activity. This allows the scan to highlight metabolically active disease, even when structural changes are not clearly visible.

It helps detect disease that is:

• Not visible on iodine scans
• Recurrent or residual after treatment
• Spread to distant organs

When is PET-CT Needed?

• When thyroglobulin levels remain high after treatment, suggesting persistent disease, but iodine scans do not show any abnormality.
• When there is a strong suspicion of recurrence based on clinical findings or rising tumor markers.
• In aggressive or high-risk thyroid cancers, disease may not take up iodine effectively.
• When doctors need to assess the extent of spread before planning further treatment.

When Does Thyroid Cancer Becomes Radioiodine-Refractory?

In some patients, thyroid cancer may gradually lose its ability to absorb iodine, making radioiodine (I-131) therapy less effective or ineffective, a condition known as radioiodine-refractory thyroid cancer, often associated with more aggressive disease behaviour.

At the same time, these cancer cells may become more metabolically active, making them less visible on radioiodine scans but detectable on PET-CT. This pattern is known as the ‘flip-flop phenomenon,’ where thyroid cancer transitions from being iodine-avid to PET-avid. Clinically, this is significant as it often indicates a more aggressive or treatment-resistant form of disease. Recognising this transition allows doctors to adapt the treatment strategy, using advanced imaging and alternative therapies to ensure continued, personalised care.

Gamma Probe & Image-Guided Surgery

In certain cases of thyroid cancer, surgery can be further enhanced using gamma probe–guided techniques, which are part of advanced nuclear medicine applications. This approach helps surgeons locate and remove even small amounts of residual thyroid tissue or cancer that may not be easily visible during routine surgery.

How Does It Work?

A small amount of radioactive tracer is administered before or during surgery. A handheld gamma probe is then used by the surgeon to detect areas where the tracer has accumulated, helping precisely identify cancerous or residual thyroid tissue.

Why is It Useful?

Gamma probe–guided surgery adds an extra layer of precision by helping surgeons identify and target tissue that may otherwise be missed during conventional procedures. This improves overall surgical outcomes and supports more effective disease control.

• Improves accuracy of tumour removal: The probe helps pinpoint exact areas of concern, allowing surgeons to remove cancerous tissue more precisely.
• Detects residual or hidden disease: Even small or non-visible deposits of cancer can be identified during surgery, reducing the chances of leaving disease behind.
• Reduces the risk of incomplete surgery: By guiding real-time decision-making, it ensures a more thorough and confident surgical approach.
• May lower the risk of recurrence: More complete removal of cancerous tissue can contribute to better long-term outcomes and reduced chances of the disease returning.

Theranostics in Thyroid Cancer

Modern thyroid cancer care is increasingly moving toward theranostics, an advanced approach in nuclear medicine that combines diagnosis and therapy into a single, integrated process. This concept allows doctors to not only detect cancer more accurately but also treat it in a targeted and personalised way.

Side Effects & Safety of Radioiodine Therapy

Radioiodine (I-131) therapy is generally safe and well-tolerated, especially when performed under proper medical supervision. Since it specifically targets thyroid cells, the impact on the rest of the body is limited. However, like any treatment, some side effects may occur.

Common Short-Term Side Effects

• Dry mouth or reduced saliva: Due to temporary effects on salivary glands
• Altered taste or loss of taste: Usually temporary and improves over time
• Mild neck discomfort: Especially soon after therapy
• Nausea or fatigue: Short-lived in most cases

Less Common or Long-Term Effects

• Salivary gland swelling or irritation
• Temporary changes in menstrual cycle
• Rare effects on fertility (usually with higher doses

Safety Considerations

Radioiodine therapy is a targeted and controlled treatment, and with proper precautions, it remains a safe and effective option in the management of thyroid cancer. However, radioiodine therapy involves small amounts of radiation, which is why certain precautions are advised for a short period after treatment to protect others. These include:

• Maintaining safe distance from others, especially children and pregnant women
• Practicing good hygiene and hydration
• Following specific instructions provided by the treating team

Life After Radioiodine Therapy: What to Expect?

After receiving radioiodine (I-131) therapy, most patients can return to their normal routine within a few days. However, since the treatment involves a small amount of radiation, certain temporary precautions are necessary to ensure safety for both the patient and those around them.

Immediate Precautions After Therapy

• Maintain a safe distance from others, especially children and pregnant women.
• Avoid close or prolonged physical contact for a few days.
• Sleep separately if advised.

Daily Care & Recovery

• Stay well hydrated to help flush out excess radioiodine from the body.
• Maintain good personal hygiene, including frequent handwashing.
• Follow dietary or medication instructions given by your doctor.

When Can You Resume Normal Activities?

Most patients can gradually return to work and daily activities within a few days, depending on the dose received and individual recovery. Your doctor will provide specific guidance based on your treatment plan.

With simple precautions and proper guidance, recovery after radioiodine therapy is usually smooth, allowing patients to safely transition back to their normal lives while continuing follow-up care.

Special Situations in Thyroid Cancer Care

While thyroid cancer treatment is generally well standardised, certain situations require additional care and decision-making to ensure safety and effectiveness. Special situations highlight the importance of a personalised treatment approach, where decisions are adapted to the patient’s age, health status, and life circumstances.

Pregnancy & Fertility

Radioiodine (I-131) therapy is strictly avoided during pregnancy, as it can affect the developing baby. Women are usually advised to delay pregnancy for 6–12 months after treatment, depending on the dose and clinical situation. Breastfeeding must also be stopped before therapy.

In terms of fertility, most patients do not experience long-term issues. However, in selected cases, especially with higher doses, doctors may discuss fertility preservation or planning as part of treatment counseling.

Young Patients

Thyroid cancer in younger patients often has an excellent prognosis, with very high survival rates. The focus of treatment in this group is not only on cure but also on minimising long-term side effects.

Careful use of radioiodine therapy, personalised dosing, and regular follow-up are important to ensure effective treatment while preserving quality of life over the long term.

Elderly or Patients with Comorbidities

In older patients or those with existing medical conditions (such as heart disease or diabetes), treatment decisions are more carefully balanced.

Options like rhTSH preparation may be preferred to avoid the stress of hypothyroidism caused by hormone withdrawal. The goal is to ensure that treatment remains effective while being safe and well-tolerated.

Advanced Nuclear Medicine at Artemis Hospitals, Gurugram

Effective thyroid cancer care today goes beyond conventional treatment, as it relies on advanced imaging, targeted therapy, and precision-guided techniques. Artemis Hospitals, Gurugram, is equipped with state-of-the-art nuclear medicine technology to support accurate diagnosis, effective treatment, and long-term monitoring.

Why Choose Artemis Hospitals for Thyroid Cancer Care?

• Dedicated and experienced Nuclear Medicine Department with high-volume I-131 therapy
• Advanced imaging (SPECT-CT, PET-CT) for precise localisation
• Experience in managing complex and radioiodine-refractory cases
• Multidisciplinary team approach (Endocrinology + Oncology + Nuclear Medicine)
• Personalised dosimetry-based therapy (where indicated)

From initial diagnosis and surgery to radioiodine therapy and long-term follow-up, patients benefit from continuous expert guidance at every step.

Key Technologies & Capabilities

• SPECT-CT: Combines functional and anatomical imaging, allowing for more precise localisation of disease and improved diagnostic accuracy.
• Dual-Head Gamma Camera: Enables high-quality imaging for thyroid scans and whole body iodine scans, helping detect even small areas of disease.
• Advanced PET-CT Systems: Useful in detecting aggressive or iodine-resistant thyroid cancer, especially in complex or recurrent cases.
• Gamma Probe for Image-Guided Surgery: Assists surgeons in identifying and removing residual thyroid tissue or cancer during procedures.
• Hot Lab Facilities: Supports safe preparation and handling of radioactive tracers used in both diagnosis and therapy

Article by Dr. Noaline Sinha
Chairperson - Nuclear Medicine & Radio-Theranostics
Artemis Hospitals