Thanks for your question on HCM. Radiation therapy for brain can cause damage to surrounding vital structures and can produce brain edema (inflammatory). This edema also compress surrounding brain structures and can produce defects. So in my opinion your wife is having edema, that is why shgiven dexan. Dexan is steroid and reduces inflammatory edema. So if she is not improving in 1-2 week better to get done repeat CT or MRI to see for edema. If worsening edema than craniotomy is required to release the pressure.