Unable to walk after 3 months of brain radiotherapy

My father aged 60 had a brain tumor of GBM type in 2000 around the left frontal lobe. He was operated and then underwent radiotherapy treatment for 30 days. Thereafter he lived a normal life and was taking eptoin 100 mg. After 11 years he was diagonised as having a recurrence brain tumor. He was operated and and then underwent radiotherapy treatment for 28 days. This time he was prescribed tomazolamide of 120 mg. However this time he got side effects like memory problems, balance problem. The surgeon said that this is due to radiation side-effects. The treatment got over in the month of May 2011. However 2 weeks earlier that is in August 2011 he got a fit. He was told to take Frisium 10 mg in addition to eptoin 100 mg. Presently he is unable to walk and has some loss of strenght on the right leg. Please let me know why he is unable to walk? Is there any treatment by which he can atleast walk without any support?