This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
[{'content': 'Isotope (s) used in high dose rate brachytherapy – a) lr192b) Co–60c) Cs–l33d) Ra 226 e) Pd103 \nSelect and explain. \nA. ac, B. a, C. ab, D. bc', 'role': 'user'}, {'content': 'Answer: C \nExplanation: "Although cobalt - 60 and cesium - 137 have been used in the past, iridium - 192 is the most commonly used\xa0radioisotope in HDR brachytherapy".\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0 — The physics of radiation therapy\nNote - Cs-137 is used in HDR brachytherapy, while option c i.e. Cs - 133 (not Cs - 137).', 'role': 'assistant'}]