HI I have gone through your mail and as you said your wife is a patient of hypothyroid,and she had been given radiotheraphy for her breast cancer,and she had now developed dry irritable cough not responding to common treatment. After considering all your complaints few possibilities are there-(1) post radiation effect on throat leading to swelling and dryness and developing irritation and dry cough.(2) there might be local pathology in her throat as infection causing dry cough,this can be ruled out by culture and sensitivity of throat swab.(3)There may be associated sinus infection which causes post nasal drip thus cough may develop.(4)Since your wife is follow up case of cancer breast thus conditions like secondaries in throat and madiastinum should be also considered that can be rule out by C.T. scan of throat and chest.thus she is advice to consult E.N.T.specialist for physical examination and clinical co-relation with investigations to find out the cause for treatment.Thanks