How can isotopes be used in medicine?
Unstable atoms can be used to produce radiation in order to treat cancer
As an unstable nucleus decays, it emits radiation. This radiation can then be used for many things in hospitals. Gamma radiation is concentrated and focused on a tumour in order to kill cancerous cells with as little damage to the surroundings as possible.
Gamma radiation can also be used to sterilise medical equipment, as it easily kills harmful microorganisms. Finally, small amounts of radioactive materials (unstable isotopes) can be put into a patients body and detected by medical tracers. Iodine 123 (not 131 as this emits beta radiation which is less preferable) is used in tracing to investigate issues with thyroid function.
So in conclusion, isotopes are useful in medicine for supplying radiation and helping to both diagnose, and treat, otherwise difficult illnesses.
For more examples, here is a useful link http://www.radiochemistry.org/nuclearmedicine/radioisotopes/ex_iso_medicine.htm
This information came from my GCSE and A level revision books (a fun hobby!) with cross referencing from BBC bitesize and the website I have provided a link to. Cgp books cover isotopes in medicine well for further reference. I hope I have helped, my apologies for any mistakes.