**Question:** Which one of the following radioisotope is not used as a permanent implant:

A. Technetium-99m
B. Iodine-131
C. Cobalt-60
D. Strontium-90

**Core Concept:** Radioisotopes are radioactive elements used in medical imaging, therapy, and research. Permanent radioisotope implants are used for cancer treatment by emitting radiation to kill or damage cancer cells.

**Why the Correct Answer is Right:** Strontium-90 is a beta-emitting radioisotope with a half-life of 28.8 years. It is used in bone pain palliation and localized hyperplasia treatment, but not as a permanent implant due to its relatively short half-life.

**Why Each Wrong Option is Incorrect:**

A. Technetium-99m (half-life: 6 hours) is a gamma-emitting radioisotope mainly used for diagnostic purposes, not suitable for a permanent implant.
B. Iodine-131 (half-life: 8 days) is utilized for thyroid cancer treatment, not suitable for a permanent implant.
C. Cobalt-60 (half-life: 5.27 years) is a gamma-emitting isotope, used for cancer treatment but not considered a permanent implant due to its relatively short half-life.

**Clinical Pearl:** Permanent radioisotope implants are typically beta-emitting with a half-life ranging from several months to a few decades. They are used for localized therapy, ensuring continuous radiation exposure over an extended period to target tissues. A correct choice for a permanent implant should have a long half-life, enabling sustained radiation delivery.

**Correct Answer:** D. Strontium-90 (half-life: 28.8 years) is not suitable for a permanent implant due to its relatively short half-life. Permanent radioisotope implants, on the other hand, must have a longer half-life for continuous radiation delivery.