I do not know why you have undergone radiotherapy for benign mixed tumour but if you have taken that, the problems you are having are because of radiation
. Please visit an ENT to get your ear cleaned properly and in an atraumatic way. After that. the granulations if any can be cauterised and antibiotic with steroid
cream can be applied. You can use steroid with antibiotic ear drops after wards. You may need few sittings of cleaning and with regular treatment, the ear should be fine. You may have itching afterwards occasionally but it can be very well tackled with steroid and antibiotic ear drops. Good luck.