Which of the following radioactive isotopes is not used for brachytherapy –
**Core Concept**
Brachytherapy involves the placement of radioactive sources within or near a tumor to deliver a high dose of radiation to the tumor site while minimizing damage to surrounding healthy tissues. Various radioactive isotopes are used for brachytherapy, each with distinct physical and radiological properties.
**Why the Correct Answer is Right**
The choice of radioactive isotope for brachytherapy depends on its half-life, emission type, and energy. For instance, I-125 and Ir-192 are commonly used for permanent and temporary implants, respectively. Another isotope, Cs-137, is used in some brachytherapy applications due to its beta emission. However, not all isotopes are suitable for brachytherapy.
**Why Each Wrong Option is Incorrect**
**Option A:** I-125 is a commonly used isotope for brachytherapy due to its low energy X-rays and long half-life, making it suitable for permanent implants.
**Option B:** Cs-137 is used in some brachytherapy applications due to its beta emission, which can be used to treat tumors.
**Option C:** The correct answer is **Option C:** Ra-226, which is no longer used for brachytherapy due to its high energy gamma emissions and short half-life.
**Clinical Pearl / High-Yield Fact**
Not all radioactive isotopes are suitable for brachytherapy, and the choice of isotope depends on its physical and radiological properties. Ra-226 is an example of an isotope that is no longer used due to its high energy gamma emissions and short half-life.
**Correct Answer:** C. Ra-226