Which Patients Should Receive Atomic (Radioactive Iodine) Therapy After Thyroid Cancer Surgery?

Thyroid cancersare the most common endocrine (hormonal system) cancers, accounting for %95 of all endocrine cancers. They represent %1.5 of all cancers in adults and %3 in children. Although the disease generally has a favorable course, death occurs in %5-10 of patients.

The incidence of thyroid cancer has increased in recent years. More frequent use of radiological imaging methods and greater public awareness are thought to contribute. Small thyroid cancers are increasingly detected by computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET) and ultrasonography (USG); in %35 of newly diagnosed thyroid cancers, the tumor is smaller than 1 cm in diameter.

The treatment plan depends on the type of thyroid cancer. Differentiated thyroid cancer (DTC) accounts for more than %90 of thyroid cancers. Of differentiated thyroid cancers, approximately %85 are papillary, %10 are follicular and %3 are Hurthle cell carcinomas.

Papillary thyroid cancer tends to be indolent (slow-moving), grows slowly and spreads through the lymphatic system to cervical (neck) lymph nodes, causing regional metastasis . Follicular and Hurthle cell cancers tend to be more aggressive and spread to distant regions hematogenously (through the bloodstream). Although their biology and metastatic potential differ, papillary and follicular thyroid cancers have similar prognoses (disease course and outcomes) within their stages expressed from I to IV.

Overview of thyroid cancer treatment

Thyroid cancer treatment must be individualized for each patient and should consider risk factors for death and recurrence (cancer returning) .

When planning treatment:

• tumor size
• histology (cell type)
• spread outside the thyroid gland
• whether complete surgical removal has been achieved
• lymph node involvement
• distant metastatic disease
• and combined risk factors such as iodine avidity (affinity) are considered.

In general, thyroid cancer treatment should be directed by an endocrinologist with special expertise in thyroid cancer, together with a multidisciplinary team. The team should include a thyroid surgeon experienced in neck dissection and a nuclear medicine physician. In general, medical and radiation oncologists join the treatment plan when thyroid cancer is advanced.

Over the past 20 years, promising and extremely important advances have occurred in thyroid cancer treatment. These positive developments have changed treatment standards and improved survival times. One treatment closely associated with thyroid cancer is commonly known as atomic therapy , namely radioactive iodine therapy (RAI).

In early-stage thyroid cancer, surgery is the main treatment , but which patients should or should not receive postoperative adjuvant (protective) atomic therapy is often an important question for patients.

Radioactive iodine therapyis used to destroy thyroid cancer cells that may remain after surgery. This treatment has been seen to contribute significantly to survival, particularly in patients with papillary and follicular thyroid cancer.

After surgery, radioactive iodine is given as a liquid or pill orally . The radioactive iodine (I-131) accumulates in thyroid gland cells, and the radiation it emits stops thyroid cell growth and inhibits their activity without greatly harming other parts of the body. Cancerous thyroid tissues are thus destroyed.

Planning initial treatment and risk classification

Initial postoperative treatment is determined by TMN staging , which predicts mortality risk, and the American Thyroid Association (ATA) risk assessment, which predicts tumor recurrence risk.

Risk classification

ATA guidelines classify differentiated thyroid cancers according to the risk of recurrence or treatment resistance as low, intermediate and high risk . In reality, recurrence risk is a continuum determined by different variables. Various criteria are used to determine risk category and which patients are suitable for radioactive iodine treatment after thyroidectomy. the main ones are:

• neck ultrasound (USG) assessment (depending on the experience of the physician performing it)
• and blood levels, which may vary depending on the type of test used, of thyroglobulin (Tg) .

The risk of recurrence increases when:

• involved lymph nodes are > 3 cm
• the number of lymph nodes found during surgery is > 5 or
• there is tumor spread outside the thyroid

The risk of death increases when there is:

• involvement of lateral neck lymph nodes (stage 4A)
• gross invasion (invasion of a large amount of tissue) (stage 4B) or
• distant metastasis (stage 4C)

Should radioactive iodine therapy (RAI) be given to all patients who have undergone thyroid cancer surgery?

There is debate about whether routine radioactive iodine therapy should be given after total thyroidectomy to some low-risk and some intermediate-risk thyroid cancer patients. Unlike their American colleagues, European nuclear medicine specialists tend to use radioactive iodine routinely in these low- and intermediate-risk patients. The American Thyroid Association (ATA) guideline does not recommend RAI for patients with low-risk disease; intermediate-risk patients selected for radioactive iodine therapy are those with microscopic spread into tissues around the thyroid, vascular (blood vessel) involvement, lymph node metastasis or aggressive histology.

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However, an increasingly common view reports benefits from giving radioactive iodine even to microcarcinoma patients without metastasis .

An important factor behind much of the debate over radioactive iodine use in thyroid cancer treatment is that the indolent (slow-growing) nature of this cancer makes definitive evidence difficult to obtain .

Nuclear medicine has undergone major changes over the past 10 to 20 years, and it is time to reassess what it can offer for both diagnostic and therapeutic (treatment) purposes. Advances in nuclear medicine have led to more effective and widespread use of radioactive iodine.