Hi, Thanks for writing in. Astrocytoma is a type of brain tumor and if it has been operated up on then it is likely that he had a low grade astrocytoma. Please refer to biopsy details to conform a low grade astrocytoma. Chemotherapy and radoation thearapy are recommended for most cancers after doing surgery. This is because some cancer cells persist after surgery and it can regrow in to the tumor once again. Also tumors in the brain are difficult to operate and usually a little bit is intentionally left behind due to its adherence to adjacent structures. His weakness is due to the chemotherapy and radiation which he is presently taking. Chemotherapy causes the cancer cells to die and get shed in the circulation. There is also a release of toxic substances and then leads to weakness. Please give him lots of fluids and diet rich in proteins. You can also add vitamin supplements to give him more energy and daily supply of nutrients. It is possible to give you information on cancer treatment if you can give details about your location. Please do not worry.