Radiation therapy directs high-energy x-rays at targeted areas of the body to destroy tumor cells or interfere with their ability to grow. Because tumor cells may remain after surgery, radiation is used to help kill remaining tumor cells after a biopsy or after a total or partial surgical removal of a tumor. Radiation is also used to relieve symptoms, such as pain. When used for pain relief, the treatment is called palliative radiation. Radiation can be given internally (called brachytherapy) or externally (called external beam radiation).

External beam radiation

External beam radiation uses high-energy x-rays called photons, or high-energy positively charged atoms called protons, to kill tumor cells. For photon radiation therapy, a large machine called a linear accelerator directs x-rays to the precise portion of the body where the tumor is located. The treatment is usually given in doses measured in units called gray (Gy).

Radiation oncologists create an individualized treatment plan for each child using computers that combine images from magnetic resonance imaging (MRI), computerized tomography (CT), and positron emission tomography (PET) scans of the tumor and surrounding areas. This plan allows the radiation oncologist to aim the radiation directly at the tumor or surgical cavity and spare as much healthy tissue as possible.

Radiation is usually given every day for a specific number of days, excluding weekends. This process is called standard or conventional fractionation, and it is the most common way radiation is given to children and teens with solid tumors. Radiation given more than once a day is called accelerated fractionation, or hyperfractionation. It uses smaller amounts of radiation for each treatment. Hyperfractionation may reduce long-term side effects, but short-term side effects are sometimes worse.

Specific types of external beam radiation therapy are:

•  3D conformal radiation therapy. This type of therapy delivers high-dose photon radiation tailored to the precise area of the tumor, while delivering a lower dose to the normal tissue surrounding the tumor. It uses 3D images from CT, MRI, and PET scans to identify the margins of the tumor and their relationship to surrounding structures. Multiple radiation beams are delivered from several different directions so they overlap at the tumor. By using this technology, the tumor receives the high-dose radiation and the normal tissues surrounding it receive a lower dose.

•  Intensity modulated radiation therapy (IMRT). This type of 3D conformal photon radiation therapy can spare surrounding tissue by varying the intensity of the radiation beams. IMRT is the most advanced form of photon (x-ray) radiation available. A disadvantage of this type of radiation is that a lower dose of radiation is given to a larger amount of normal tissue.

•  Proton beam radiation. With this type of radiation, a machine called a synchrotron or a cyclotron accelerates (speeds up) the protons. Proton therapy delivers radiation to the tumor while limiting damage to surrounding healthy tissue, because the protons travel to a specific depth in the tissues based on their energy and deliver very little radiation to tissues beyond the specified depth. This advanced technique may result in fewer short- and long-term side effects than conventional x-ray radiation therapy. It is sometimes used in children with retinoblastoma to reduce the radiation dose to the orbit around the eye, or in children with soft tissue sarcomas in the head and neck. Children or teens with pelvic sarcomas sometimes get proton radiation to decrease the amount of radiation to the ovaries and pelvic bones. Proton beam therapy is only available at a few specialized centers, but it will soon be available at some major pediatric centers.

Children do not become radioactive from these types of radiation treatments, and no specific precautions or activity restrictions are necessary.

Internal radiation

Internal radiation—also called brachytherapy, implant therapy, or interstitial therapy—uses radioactive materials (called seeds or implants) placed directly into the tumor (interstitial implants) or applied to the surface of the tumor (plaques). It differs from external beam radiation because it typically provides a continuous low dose of radiation to the tumor over a predetermined time period rather than requiring weeks of daily treatments.

Your child is radioactive while receiving the internal radiation. He will need to stay in a special isolation room with a private bathroom during treatment. The room has plastic covers on all fixtures, and disposable serving plates and utensils are used. Parents are allowed to spend a limited amount of time with their child; the time allowed depends on the type of internal radiation the child receives. The rest of the time you can sit outside your child’s room to talk or read to him. Children and pregnant women cannot visit when your child is radioactive.

Other forms of radiation

Other ways radiation is used to treat children with solid tumors are described below.

•  Intraoperative radiation uses external beam radiation applied directly to a tumor site during a surgical procedure. The major advantage to intraoperative radiation is that it allows the doctor to give a very high dose of radiation to a single area while minimizing radiation exposure and damage to normal surrounding tissue.

•  Radioactive iodine meta-iodobenzylguanidine (I-131 mIBG) is administered intravenously to some children with neuroblastoma. Cancer cells absorb the radioactive material after it is injected into the body. The treatment is given in specially-built hospital rooms that have lead shielding. The child must stay in the room until the radioactive materials in the body have been excreted.

Experimental treatments used with radiation

In some clinical trials, radioimmunotherapy and chemical modifiers are used in conjunction with radiation to treat children with solid tumors.

Radioimmunotherapy uses radiolabeled antibodies as radiation carriers. The antibodies are attached (labeled) to a radioactive material and then injected into the body through a venous catheter or IV. Once injected, the antibodies begin a “seek and destroy” mission, searching for specific tumor cells. Radiolabeled antibodies lessen the chance of radiation damage to normal cells. Experience with this method of radiation in children is limited.

Chemical modifiers are compounds used at the same time as radiation therapy. Two classes of compounds are currently under study in children: radiation sensitizers and radioprotectors. Radiation sensitizers increase delivery of oxygen to tumor cells, making them more sensitive to the effects of radiation. Radioprotectors are drugs given with the radiation treatments; they are designed to shield normal cells from radiation damage by using substances absorbed by healthy normal cells but not by tumor cells. Studies using these compounds are ongoing or under development in the Children’s Oncology Group.