There are many types of CNS tumors, both benign and malignant, that can be treated with radiotherapy either as the sole treatment or as a component of a multimodality approach. Depending on tumor type, site, and size, various different radiation techniques (external beam radiotherapy with 3D conformal or IMRT techniques, fractionated stereotactic radiotherapy, radiosurgery, or brachytherapy) could be employed. This is a very broad topic, though, so I agree that your best starting point is a radiation oncology text (perhaps Perez).
