Thank you for your question. I am so sorry that your son is going through this condition, as well as all of the surgeries and other treatments.
We are in the process of locating an expert to help answer your questions, and will reply with more information as soon as we receive it.
In the meantime, have you been able to review these resources (located at the bottom of the Astrocytoma conditions page): https://www.empowher.com/media/reference/astrocytoma.
Your son's doctor is also a great resource, if you are able to ask him/her these important questions. Do you feel your son's doctor (or nurse) is able to provide you with the time to thoroughly address your questions and concerns?
How is your son doing now? How old is he?