**Question:** Which of the following is used for permanent interstitial implant brachytherapy –

A. Platinum seeds
B. Copper seeds
C. Gold seeds
D. Iridium-192 seeds

**Core Concept:**
Brachytherapy is a form of radiation therapy in which radioactive sources are placed directly within or near the tumor tissue to deliver high doses of radiation to the target while minimizing damage to surrounding healthy tissues. Permanent interstitial implant brachytherapy involves placing radioactive sources permanently within the body, typically in the form of seeds or needles, to treat diseases like prostate cancer or cervical cancer.

**Why the Correct Answer is Right:**
D. Iridium-192 seeds

Iridium-192 seeds are widely used for permanent interstitial implant brachytherapy due to the following reasons:

1. High radioactivity: Iridium-192 has a relatively long half-life (half-life: 74.5 days) and emits beta particles (high energy beta rays) and gamma rays, providing a balance between reaching the tumor's depths and minimizing damage to surrounding tissues.
2. Stable isotope: Unlike some other radioactive sources, iridium-192 is a stable isotope, meaning it does not undergo radioactive decay over time, ensuring a consistent therapeutic dose over a prolonged period.
3. Compatibility with implantation techniques: Iridium-192 seeds are compatible with various implantation techniques, such as the Transpac system or the Seed Implanter, for precise and accurate placement within the tumor.

**Why Each Wrong Option is Incorrect:**

A. Platinum seeds: Although platinum is used in brachytherapy, platinum seeds (e.g., Platinum-103) are not typically used for permanent interstitial implant brachytherapy due to the following reasons:

- Relatively short half-life (half-life: 10 hours) and gamma rays, making them less effective in reaching deeper tumor depths.
- Less stable isotope, as Platinum-103 undergoes radioactive decay over time, potentially compromising the therapeutic dose.

B. Copper seeds: Copper-60 seeds are not used for permanent interstitial implant brachytherapy due to the following reasons:

- Short half-life (half-life: 56 days) and gamma rays, making them less effective in reaching deeper tumor depths.
- Less stable isotope, as Copper-60 undergoes radioactive decay over time, potentially compromising the therapeutic dose.

C. Gold seeds: Gold-198 seeds have a relatively long half-life (half-life: 64.4 days) and gamma rays, making them less effective in reaching deeper tumor depths.
- Less stable isotope, as Gold-198 undergoes radioactive decay over time, potentially compromising the therapeutic dose.

**Clinical Pearl:**

While gold, platinum, and copper are used in temporary brachytherapy, where radioactive sources are implanted for a short period