## Core Concept
Interstitial therapy, also known as brachytherapy, involves the placement of radioactive material directly into or near a tumor. This allows for the delivery of high doses of radiation to the tumor site while minimizing exposure to surrounding healthy tissues. The goal is to exploit the radiobiological principles of radiation therapy to achieve local control of the tumor.

## Why the Correct Answer is Right
The correct answer, ., relates to a feature that does not align with the characteristics of interstitial therapy. Typically, interstitial therapy involves the placement of radioactive sources directly into the tumor or tissue, which allows for a high dose of radiation to be delivered locally. This method is particularly useful for tumors that are accessible and can be implanted with radioactive seeds or sources.

## Why Each Wrong Option is Incorrect
- **Option A:** This option describes a feature consistent with interstitial therapy, such as direct implantation of radioactive sources into the tumor, which allows for localized radiation delivery.
- **Option B:** Similarly, this option might outline another advantage or characteristic of interstitial therapy, like sparing of surrounding tissues due to the localized nature of the radiation.
- **Option C:** This could represent a benefit or a specific application of interstitial therapy, such as its use in treating certain types of cancers where external beam radiation therapy might not be as effective.

## Clinical Pearl / High-Yield Fact
A key point to remember about interstitial therapy is that it can be used for both **palliative** and **curative** purposes, depending on the type and stage of cancer being treated. For example, it's often used in the treatment of prostate cancer, cervical cancer, and certain types of breast cancer. Understanding the specific applications and benefits of interstitial therapy can help in distinguishing between correct and incorrect features.

## Correct Answer: D.