Weak, memory problems and headache? If he is 6 months into the treatment, then he is probably suffering from the effects of the chemo and the late effects of the radiation. Is he on any steroid to reduce swelling of the brain? The 3 symptoms you describe are typical of the brain swelling. Even if he is on the steroid, he is still likely to have some degree of weakness, and short term memory loss is classic, so consider how the treatments are affecting him, try not to worry too much, and just keep yourself informed about how things change over time. Tell him to keep a close watch out for clots that show up in the calf of the leg, or sudden increased weakness in any particular body part that was not before, or vision changes, or seizure activity. So sorry you are so far away from him.
Donna L