## **Core Concept**
Gamma Knife radiotherapy, also known as Gamma Knife radiosurgery (GKRS), is a form of **stereotactic radiosurgery (SRS)** that uses cobalt sources to deliver precise, high doses of radiation to specific areas of the brain. It is primarily used to treat **intracranial lesions**, such as brain tumors and vascular malformations, without damaging surrounding healthy tissue.

## **Why the Correct Answer is Right**
The correct answer, , highlights a key characteristic of Gamma Knife radiotherapy: its precision and non-invasive nature. Gamma Knife uses **cobalt-60 sources** to emit gamma radiation, which is focused on a small target volume in the brain. This precision allows for the delivery of a high dose of radiation to the lesion while minimizing exposure to surrounding brain tissue.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because Gamma Knife radiotherapy does not involve **external beam radiation** in the traditional sense; instead, it uses implanted cobalt sources.
- **Option B:** This option is incorrect as Gamma Knife is **not suitable for large brain tumors**; it's best for smaller lesions.
- **Option C:** This option might seem plausible but is incorrect because Gamma Knife **does not require surgical implantation** of radioactive material; it's a non-invasive procedure.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that Gamma Knife radiosurgery is **highly effective for treating certain types of brain lesions**, such as **acoustic neuromas**, **meningiomas**, and **arteriovenous malformations (AVMs)**, with minimal side effects. It's also noteworthy that patients can often return to their normal activities shortly after the procedure.

## **Correct Answer:** .