Hello, Even though antibiotic associated symptoms such as delirium, anxiety, confusion and more such symptoms related to nervous system disorders, they are very rare in Incidence. You havent mentioned the full history of the patient as to why he was started on the radiation therapy. Your concerned symptoms could be a cause of the Antibiotic but like I have mentioned already they are very rare, and it is possible the symptoms might be more related to the pre existing condition that required the radiation therapy or as an after effect of the radiation therapy itself. I suggest you visit your concerned Physician in person at the earliest possible and explain the symptoms your husband is having.