Which one of the following radioisotope is not used as permanent implant:
**Question:** Which one of the following radioisotopes is not used as permanent implant?
A. Technetium-99m
B. Iodine-125
C. Cobalt-60
D. Gold-198
**Core Concept:** Radioisotopes are radioactive elements or compounds used in medical imaging and therapy, particularly in permanent implants to treat cancerous or benign tumors.
**Why the Correct Answer is Right:** Gold-198 (Au-198) is not used as a permanent implant due to its short half-life (60 hours) and high energy gamma emission (100 keV). These properties make it unsuitable for long-term implantation, unlike other options like Iodine-125 (10 years half-life, low energy beta and gamma emission) and Cobalt-60 (5.27 years half-life, high energy gamma emission).
**Why Each Wrong Option is Incorrect:**
**Option A:** Technetium-99m (Tc-99m) is used as a temporary radioisotope in single photon emission computed tomography (SPECT) imaging due to its short half-life (6 hours).
**Option B:** Iodine-125 (I-125) has a longer half-life (10 years) and lower energy gamma emission (35 KeV), making it suitable for permanent implantation in brachytherapy for cancer treatment.
**Option C:** Cobalt-60 (Co-60) has a longer half-life (5.27 years) and high energy gamma emission, making it suitable for permanent implantation in brachytherapy.
**Option D:** Gold-198 (Au-198) has a short half-life (60 hours) and high energy gamma emission, rendering it unsuitable for permanent implantation in brachytherapy.
**Core Concept:** Radioisotopes are used in medical procedures to treat cancer or diagnose diseases based on their half-life, energy emission, and suitability for specific applications like temporary or permanent implantation.
**Clinical Pearl:** The choice of radioisotopes depends on their properties to ensure optimal therapeutic and diagnostic outcomes while minimizing side effects.