BRAIN STEM GLIOMA

my father (age 50) is suffering from Brain Stem Glioma,which was discovered 7 months ago through gate abnormality...after that he recievd Radition Therapy,after which there was a considerable improvement and tumor waz destroyed to some extant ...after this doctors suggested to go for the 12 dose of " Biomab Injections"..we went fot that also...now in the last MRI there is reduction in the size of tumor from one side but from the other side it has increased a bit...doctors have now suggested us to go for the 6 dose of AUASTIN Q Injection (which is really costly) ..i want to ask what should we do now??why is there an increase in the tumor size from one side??