Radiology Which of the following radioisotopes is commonly used as a source for external beam radiotherapy in the treatment of cancer patients – A Strontium–89 B Radium–226 C Cobalt–59 D Cobalt–60 💡 Explanation Which of the following radioisotopes is commonly used as a source for external beam radiotherapy in the treatment of cancer patients – ✓ Correct Answer: D. Cobalt–60