I am a brain tumor survivor, had 5400 rad s in 1985. just within last 2 month have experienced significant hearing loss. is this to be expected?

Possibly: It depends on whether the inner ear was radiated to a dose higher than its tolerance (typically, starting above 45 gy or 4500 cgy.) you can ask your radiation oncologist to evaluate their radiation treatment plan to check. Audiologists can determine if the hearing loss is conductive (middle ear problem) or sensorineural (inner ear problem.).

While 54Gy: Is not supposed tocause such effects, you are a very long term survivor (good for you), and few have achieved this benefit or period of observation. You need to be worked up by ENT and meur surg/rad onc, and an mri.