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