## **Core Concept**
The treatment of deep-seated tumors often requires radiation that can penetrate tissues effectively. Different types of radiation have varying abilities to penetrate tissues, which is crucial in treating tumors located at different depths.

## **Why the Correct Answer is Right**
The correct answer, , refers to **Cobalt-60** or more broadly, **Gamma Rays**. Gamma rays are highly penetrating electromagnetic radiation, making them suitable for treating deep-seated tumors. They can be focused on the tumor from multiple angles to minimize damage to surrounding healthy tissue. Gamma rays are used in radiation therapy, particularly in **Gamma Knife** radiosurgery for brain tumors and in **Brachytherapy** for various cancers.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option likely refers to **Alpha particles**. Alpha particles have low penetration power and are stopped by a sheet of paper or the outer layers of human skin, making them unsuitable for treating deep-seated tumors but useful for superficial tumors or in certain types of brachytherapy.
- **Option B:** This could refer to **Beta particles**. Beta particles have moderate penetration power, sufficient to treat superficial tumors or tumors just beneath the skin but not deep-seated tumors.
- **Option D:** This might refer to **X-rays**. While X-rays can be used to treat tumors and have varying energies (and thus penetration depths), they are not as penetrating as gamma rays for very deep-seated tumors.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the choice of radiation type for cancer treatment depends on the tumor's location, size, and depth. **Gamma rays** are particularly useful for deep-seated tumors due to their high penetration.

## **Correct Answer:** . Gamma Rays