**Intra Cavitary Radiotherapy (ICRT) Core Concept**
Intra cavitary radiotherapy is a type of brachytherapy involving the placement of radioactive sources inside body cavities to deliver localized radiation therapy. This technique is particularly useful for treating tumors located within or near body cavities, such as the cervix, prostate, or brain.

**Why the Correct Answer is Right**
ICRT works by placing radioactive sources, such as cesium-137 or iridium-192, directly into the body cavity adjacent to the tumor. The high dose rate of radiation delivered to the tumor site allows for effective killing of tumor cells while minimizing exposure to surrounding healthy tissues. The radiation dose can be carefully controlled and adjusted to achieve optimal therapeutic effects.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because ICRT is not typically used for treating systemic diseases or conditions that require widespread radiation coverage.
**Option B:** While brachytherapy is a form of internal radiation therapy, ICRT specifically refers to the placement of radioactive sources within body cavities, not solid organs.
**Option C:** This option is incorrect because ICRT is not commonly used for treating superficial skin cancers or lesions.

**Clinical Pearl / High-Yield Fact**
Intra cavitary radiotherapy requires precise placement of radioactive sources to avoid complications and ensure optimal therapeutic effects. The use of ICRT should be carefully considered and planned by a multidisciplinary team of radiation oncologists, medical physicists, and other healthcare professionals.

**Correct Answer:** C. Brain tumors.