Radioisotopes which is used in teletherapy: September 2011
**Core Concept**
Radioisotopes used in teletherapy are a type of ionizing radiation that is emitted by radioactive isotopes and is used to destroy cancer cells. This is achieved through external beam radiation therapy (EBRT), where the ionizing radiation is directed at the tumor from outside the body.
**Why the Correct Answer is Right**
The correct answer is Cobalt-60, which is a radioactive isotope that emits gamma rays (gamma radiation). Gamma rays have a high energy level and can penetrate deeply into the body, making them suitable for teletherapy. When Cobalt-60 is used in teletherapy, it is typically enclosed in a machine that directs the gamma rays at the tumor site, allowing for precise targeting of cancer cells while minimizing damage to surrounding healthy tissues.
**Why Each Wrong Option is Incorrect**
**Option A:** Iodine-131 is incorrect because it is primarily used for radioiodine therapy, where the radioactive iodine is ingested by the patient to target thyroid cancer cells or thyroid tissue.
**Option B:** Phosphorus-32 is incorrect because it is not commonly used in teletherapy; instead, it is used in brachytherapy for treating prostate cancer.
**Option C:** Cesium-137 is incorrect because, although it is a radioactive isotope used in radiation therapy, it is more commonly used in brachytherapy rather than teletherapy.
**Clinical Pearl / High-Yield Fact**
One key point to remember is that Cobalt-60 has a relatively long half-life of approximately 5.27 years, making it a reliable and long-lasting source of gamma radiation for teletherapy.
**Correct Answer: D. Cobalt-60**