Radiotherapy consists of high-energy light beams that can be focused on tumor tissue with relative sparing of adjacent normal tissue. These radiation beams split strands of DNA (the substance of a cell's genes) and render the cell incapable of dividing. Modern technology, with the use of three-dimensional and conformal radiotherapy (the tight controlling of what receives radiation) planning, increases the margin of safety for this treatment.
The total dose of radiation delivered is dependent on the age of the patient as well as the location and type of brain tumor. The radiation treatment is focused on the tumor and a small margin around the tumor to control for invasive tumor cells. Radiotherapy is typically delivered in fractions once a day. Other, newer radiotherapy techniques include radiosurgery, intensity-modulated radiation therapy (IMRT) and stereotactic fractionated radiotherapy. Radiosurgery is the total destruction of tissue with radiation. A single large dose of radiation is given in a precise way to kill all tissue in a small volume. Stereotactic fractionated radiosurgery takes advantage of modern computer technology to deliver smaller factions of radiotherapy in a highly precise fashion.
Radiotherapy is typically reserved for children older than 3 years at the time of diagnosis. The serious side effects of radiotherapy (such as injury to normal brain and vascular tissues and secondary malignancies) usually take a long time to evolve.