Yes cannabis can help with brain cancer, headaches and nerve pains. The cannabinoids (CBD, THC, CBN, CBG and many others) work best when they are utilized in a whole plant preparation. Isolated cannabinoids are far less effective, as the cannabinoids work together in a synergystic fashion. I would try a sublingual tincture of whole plant cannabis extract with CBD, THC and the other components found in cannabis. You can vary the ratio and see what works best for you and your lifestyle. With more THC you may find more pain relief, but you may experience more psychoactive effects, changes in perception and short term memory. When utilizing the tincture, allow it to absorb in your mouth, so that it goes directly into your bloodstream. Try a small dose (5-10 milligrams of cannabinoids), and wait for half an hour to see if you experience relief. Increase the dose as needed. Vaporizing cannabis will provide more immediate relief and is often a bit easier to titrate the appropriate dose. You may also try topical cannabis rubs or a transdermal patch applied to the most painful area.