External beam radiation therapy usually involves a series of outpatient treatments with a machine called a linear accelerator, or linac. Similar to a chest X-ray, treatment X-rays cannot be seen or felt and the machine does not touch you. Treatments are given daily, Monday to Friday, usually over three to seven weeks.
Before beginning treatment, you will be scheduled for a planning session to map out your treatment area. This procedure is called a simulation. Simulation involves a CT scan which is performed while lying on a table, usually with aid of a form-fitting mask to make sure treatment is delivered the same way each time. Your doctor will design an individualized treatment plan based on the results of the simulation scan together with other imaging studies you have completed including MRIs. Marks are made on the mask to help the radiation therapist precisely position you for daily treatment.
Different techniques can be used to give radiation for brain tumors. Three-dimensional conformal radiotherapy (3-D CRT) combines multiple X-ray beam treatment positions and beam shapes to deliver precise doses of radiation to the brain. Tailoring each of the radiation beams to the patient’s tumor allows coverage of the diseased cells while keeping radiation away from nearby organs, such as the eyes.
Intensity modulated radiation therapy (IMRT) is a form of 3-D CRT that further modifies the amount (intensity) and shape of the radiation within each of the radiation beams. At most centers, X-rays (photons) are used for treatment.
Image guided radiation therapy (IGRT) can be used with any of these techniques. IGRT uses imaging (X-rays, CT and MRI scans) to verify that you are positioned correctly each day before the radiation beam turns on.
These more precise treatment techniques can be used if the tumor is in a sensitive part of the brain or if you have had radiation treatments in the past. Ask your radiation oncologist about which radiation technique is best for treating your tumor.