Radiation therapy (RT) uses ionizing radiation (high-energy beams) to kill tumor cells. RT is frequently prescribed to kill residual (remaining) tumor cells two to four weeks following surgery. It can also be used when surgical resection is unsafe or to relieve symptoms later in the disease course.
RT kills tumor cells by damaging DNA. Normal brain cells are also damaged but are faster to recover. The amount of radiation delivered to normal cells is minimized by carefully selecting the radiation field (area to receive the radiation), the total radiation dose, the timing of treatment, and the delivery method.
- In external beam radiation therapy (EBRT), radiation directed at the tumor is delivered from outside the body using a special machine. Radiation oncologists use CT and MRI scans and sophisticated software to develop a treatment plan and target the glioma. Treatment is usually delivered in a series of treatments called fractions over several weeks.
- Stereotactic radiosurgery is another form of radiation therapy suitable for small tumors. This technique is not surgical (despite its name) but delivers radiation to the tumor from outside the body. It uses many small beams of radiation directed at a point within the tumor. Treatment usually takes place in a single session.
- Proton therapy is a radiation technique that uses protons instead of traditional x-rays. Proton therapy may be used in critical brain areas where damage to nearby tissues would not be tolerated.
Short-term side effects of RT usually occur within six weeks of treatment and include fatigue, hair loss, rash, and decreased appetite. Headaches, nausea, and a worsening of neurologic symptoms (seizures, weakness) may also occur.
Cognitive impairment (mild memory loss, confusion, decreased ability to perform complex tasks, poor concentration) sometimes develops months later. It may be caused by the RT, the chemotherapy, or the glioma itself.
Other long-term side effects are cataracts, and rarely, hearing loss, hormonal changes, new tumors, and radiation necrosis (dead tissue formed at the site of radiation).
RT is not curative but helps contain tumor growth and prolongs survival compared with surgery or chemotherapy alone.