**Core Concept**
Intracavitary brachytherapy is a type of radiation therapy used to treat cervical cancer by delivering high doses of radiation directly to the tumor within the cervix. This approach involves inserting radioactive sources into the uterine cavity to target the cancer cells.

**Why the Correct Answer is Right**
The correct answer is **Cobalt-60**, a radioactive isotope used for brachytherapy in cervical cancer treatment. Cobalt-60 emits gamma rays that can effectively kill cancer cells within the cervix. The radiation is delivered directly to the tumor site, minimizing damage to surrounding healthy tissues. The use of Cobalt-60 in intracavitary brachytherapy allows for precise dose delivery, making it an effective treatment option for cervical cancer.

**Why Each Wrong Option is Incorrect**
**Option A:** **Iridium-192** is another radioactive isotope used in brachytherapy, but it's more commonly used for interstitial brachytherapy, where radioactive seeds are implanted directly into the tumor tissue.

**Option B:** **Radium-226** was historically used in brachytherapy, but it's no longer the preferred choice due to its relatively short half-life and potential toxicity.

**Option D:** **Cesium-137** is another radioactive isotope used in brachytherapy, but it's not typically used for intracavitary brachytherapy in cervical cancer treatment.

**Clinical Pearl / High-Yield Fact**
When using brachytherapy for cervical cancer, it's essential to carefully plan the radiation dose and delivery to ensure that the tumor receives the optimal dose while minimizing damage to surrounding healthy tissues. This requires close collaboration between radiation oncologists, medical physicists, and other healthcare professionals.

**Correct Answer:** C. Cobalt-60.