Which one of the following element's isotope is used in the treatment of cancer?

Radioisotopes are widely used in medical therapy for their ability to target and destroy malignant cells. Cobalt-60 is a prominent gamma-ray-emitting isotope used extensively in external-beam radiotherapy (teletherapy) for cancer treatment [2]. It is preferred for commercial and medical applications due to its high specific activity and energy efficiency [3]. While Iodine-131 is also used specifically for treating thyroid cancer [1][4], Cobalt-60 is the classic and most generalized answer in the context of standard science curricula for cancer treatment. Other isotopes mentioned in medical contexts include Sodium-24 for blood flow studies and Uranium-235 for nuclear power rather than direct therapy [1]. Cobalt-60's high-energy gamma radiation effectively penetrates tissues to reach tumors, making it a cornerstone of oncological treatment.

Sources

1. [2] https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/cobalt-60
2. [3] https://www.cdc.gov/radiation-emergencies/hcp/isotopes/iodine-131.html
3. [1] https://hhs.iowa.gov/media/7493/download?inline
4. [4] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 5: Environmental Pollution > Atomic explosion (Nuclear fatlout): > p. 83