Question: Our physician provided monitored anesthesia care (MAC) during radiotherapy for a medulloblastoma. How should I code this? Illinois Subscriber Answer: Report 01922 (Anesthesia for non-invasive imaging or radiation therapy), and append modifier QS (Monitored anesthesia care service) to designate MAC. Also know that MAC modifier G9 (Monitored anesthesia care for patient who has history of severe cardio-pulmonary condition) may apply (if the patient has a heart condition) and your state accepts it. In that case, G9 will replace the QS modifier.