You might want to note that oleander extract crosses the blood brain barrier and has had notable success against brain cancers. It also helps potentiate radiation as well as alleviate its side effects.
No matter how much radiation you receive, you must address and eliminate the root cause of the cancer to prevent it from returning. The natural immune system is the primary natural defense against cancer, and too much radiation can cause irreperable harm to the immune system (it destroys the bone marrow, an essential part of the immune system) as well as damage healthy cells near the cancer tumors being irradiated, so proceed with caution.