**Core Concept**
Permanent implant brachytherapy involves the placement of radioactive sources directly into or near tumors to deliver high doses of radiation while minimizing damage to surrounding healthy tissues. This technique is commonly used to treat various cancers, including prostate, breast, and cervical cancer.

**Why the Correct Answer is Right**
The correct answer is based on the type of radioactive sources used for permanent implant brachytherapy. Iodine-125 seeds and Palladium-103 seeds are commonly used for prostate cancer treatment due to their low energy emission and short half-life, which allows for a gradual release of radiation over time. The seeds are implanted directly into the prostate gland, providing a high dose of radiation to the tumor while minimizing damage to surrounding tissues.

**Why Each Wrong Option is Incorrect**
* **Option A:** Iodine-125 seeds are indeed used for permanent implant brachytherapy, making this option incorrect.
* **Option B:** Palladium-103 seeds are also commonly used for permanent implant brachytherapy, making this option incorrect.
* **Option D:** Gold grains were historically used for permanent implant brachytherapy, but they have largely been replaced by more modern radioactive sources like Iodine-125 and Palladium-103 seeds.

**Clinical Pearl / High-Yield Fact**
When considering permanent implant brachytherapy, it's essential to remember that the type and number of radioactive sources used can affect the duration and intensity of radiation delivery. This can impact treatment outcomes and the risk of side effects.

**Correct Answer: D. Gold grains were historically used for permanent implant brachytherapy, but they have largely been replaced by more modern radioactive sources like Iodine-125 and Palladium-103 seeds.**