Hi, welcome to HCM.
Main cause for convulsion
is gliotic area in brain. It means area which is damaged due to old pathology and it is now being shrunken in size. It leave multiple signals to brain cells, which are not cordinated . It causes seizures. It may be due to radiotheraphy.
Also if there is residual tumor
left then it may also cause convulsions. You need to consult operating surgeons and take proper advise for the same.