For a low-grade tumour, like Glioma, the doctor usually keeps the patient under observation. For a high-grade tumour, the treatment could be radiation or chemotherapy. For metastatic tumour, the patient has already known or suffered cancer somewhere else in his body, the treatment involves surgery followed by focus radiation. For Meningioma, the treatment after surgery involves observation. There are certain meningiomas that need more treatment than just surgery. They may regrow or they may have biological potential and are little more aggressive. Those might need radiations.