Hi, Windy ~
I'm terribly sorry to learn about this sudden hearing loss you've experienced. Unfortunately, I have heard of this occurring post-radiation, although it is more often a gradual loss of hearing. However, I'm not a physician and cannot credibly offer any medical advise as to what, exactly, caused this to happen. The steroids should help but you shouldn't need a heavy 'dose'. An MRI is likely prudent, if only for your peace of mind that the AN hasn't suddenly re-grown, which in my (non-physicians) opinion, is highly unlikely. Still, anything is possible so the MRI is definitely a good idea at this point. I leave others more knowledgeable than I to offer you further commentary and possibly some advice. Meanwhile, I hope and will pray that this issue can be quickly resolved with no further loss of hearing.
Jim