So, what happens with external beam radiotherapy is that a machine called a linear accelerator (linac) creates very high energy x-rays (thousands of times more than the x rays used to take pictures - this is so they go through the body better). The radiation causes damage to the cancer cells DNA, which they can't repair, and die. Normal cells are affected too, but can repair themselves, and the treatment is given in many sessions or fractions to let as many repair themselves as possible
Before treatment, your friend will have a mask or 'shell' made which will hold him in exactly the right position for each of his 30 or so treatments. He will then have a CT scan wearing the shell.
The CT then is put into a planning computer and the doctor will outline where the tumour is on each slice of image, and decide how much radiation the tumour should get, and how much he is prepared to let organs like the spinal cord get.
A physicist will then work out the best way of delivering that radiation - they will use beams of xrays from several angles to get the dose to the tumour while giving as little radiation as possible. If your friend is lucky, he might get a form of radiotherapy called IMRT which does this very well.
Each treatment, he'll lie on a bed which moves in lots of directions, the radiographers will line him up using light beams, and then the linac (huge great machine) will rotate around him to give all the radiation as planned.
Treatment in that area usually gives patients a very sore throat, sore skin, and may make them feel a bit tired, but not usually too bad