When a small dose of Iodine-131 is swallowed, it is absorbed into the bloodstream in the gastrointestinal tract and concentrated from the blood by the thyroid gland, where it begins destroying the gland's cells. So Iodine is used in detection of thyroid cancer.

Answer:

The correct answer is option A: iodine-131.

Explanation:

Radioactive Isotopes:
Radioactive isotopes are unstable forms of atoms that emit radiation in the form of alpha particles, beta particles, or gamma rays. These isotopes are commonly used in medical imaging, diagnosis, and therapy.

Thyroid Cancer:
Thyroid cancer is a type of cancer that affects the thyroid gland, a small butterfly-shaped gland located in the neck. It is important to detect and diagnose thyroid cancer early for effective treatment.

Iodine-131:
Iodine-131 is a radioactive isotope of iodine. It is commonly used in the detection and treatment of thyroid cancer. Here's why:

Thyroid Function:
The thyroid gland is responsible for producing hormones that regulate metabolism in the body. One of these hormones is called thyroxine, which contains iodine. The thyroid gland takes up iodine from the bloodstream and incorporates it into the production of thyroxine.

Iodine Uptake:
Thyroid cells have a unique ability to take up iodine selectively. This characteristic is exploited in the detection and treatment of thyroid cancer. Radioactive iodine-131 is used because it behaves in the same way as non-radioactive iodine.

Detection of Thyroid Cancer:
Radioactive iodine-131 is administered orally to a patient suspected of having thyroid cancer. The radioactive iodine is quickly absorbed by the thyroid gland and concentrated within the cancerous cells. The emitted radiation from the iodine-131 can then be detected using a gamma camera or a specialized scanner.

Therapy for Thyroid Cancer:
In addition to detection, iodine-131 is also used in the treatment of thyroid cancer. The high-energy radiation emitted by iodine-131 can destroy cancerous thyroid cells. This targeted therapy is known as radioactive iodine therapy or I-131 therapy.

Advantages of Iodine-131:
- Iodine-131 has a relatively short half-life, which means it loses its radioactivity quickly. This reduces the risk of prolonged radiation exposure.
- The radiation emitted by iodine-131 has a short range, which limits damage to surrounding tissues.
- The high uptake of iodine by thyroid cells makes it an effective diagnostic and therapeutic tool for thyroid cancer.

In conclusion, iodine-131 is the radioactive isotope commonly used in the detection and treatment of thyroid cancer due to its specific uptake by the thyroid gland.