Medulloblastoma after effects. His head.

My husband was operated last November and it was confirmed to be medulloblastoma grade 4. even though all the symptoms he had was only 3 weeks earlier to surgery. he has issues with walking and slurred speech. he has completed radiation last month and they have asked to give chemotherapy as well, which we have not started yet. he was doing much better till now. he is again having issues with balance and saying that his head is spinning too much of he does anything like getting up tomorrow bed or lying back on bed as well as while sitting. Am so much worried if the chemo is really required since radiation is done just a month back and its side effect was really bad like he lost complete sense of taste and had radiation burns on his head.