Radiation Therapy

Overview

Radiation therapy may be used alone or in combination with surgery and/or chemotherapy in the treatment of primary or metastatic brain cancers, which are also called brain tumors. The three primary ways that radiation therapy is administered in the treatment of brain tumors are with:

• External Beam Radiation Therapy (EBRT): a machine that directs radioactive beams from outside the body;
• Stereotactic Radiation Therapy (Gamma Knife): a computer and image guided technique that directs radiation only at the tumor; and
• Brachytherapy: a radioactive implant that is placed in or near the tumor.

EBRT is the conventional technique for administering radiation therapy to the brain, but stereotactic radiosurgery has also become a standard treatment. The most recent advance in the radiation treatment of brain tumors is the brachytherapy technique called GliaSite radiotherapy system, which involves placing a balloon in or near the tumor during surgery and then passing a radioactive material into the balloon for treatment.

The following is a general overview of radiation therapy for brain tumors. Radiation therapy may be delivered as EBRT, brachytherapy, stereotactic radiation therapy, or through another, innovative technique. Combining two or more of these treatment techniques has become an important approach for increasing a patient’s chance of cure and prolonging survival.

In some cases, participation in a clinical trial utilizing new, innovative therapies may provide the most promising treatment. Treatments that may be available through clinical trials are discussed in the section titled Strategies to Improve Treatment .

Circumstances unique to each patient’s situation may influence how these general treatment principles are applied. The potential benefits of combination treatment, participation in a clinical trial, or standard treatment must be carefully balanced with the potential risks. The information on this Web site is intended to help educate patients about their treatment options and to facilitate a mutual or shared decision-making process with their treating cancer physician.

• Procedures for Delivering Radiation Therapy to Brain Tumors
• Treatment Schedules
• Follow-up
• Retreatment with radiation
• Techniques for Delivering Radiation Therapy to Brain Tumors
• External beam radiation therapy (EBRT)
• Stereotactic radiosurgery
• Internal radiation therapy (brachytherapy)
• Side Effects and Complications of Radiation Therapy for Brain Tumors
• Strategies to Improve Radiation Therapy for Brain Tumors

Procedures for Delivering Radiation Therapy to Brain Tumors

Treatment schedules: Radiation therapy often begins a week or two after surgery, or as soon as the surgical wound heals. Conventional EBRT is usually given in 30–40 doses over a six-week period, five days a week. Brachytherapy may be administered for only a few days, followed by removal of the radioactive “seed”, and stereotactic radiation therapy is typically conducted in one single session

Follow-up examinations: Results of therapy might not be obvious for several months or longer. Tumor cells that have been damaged by radiation cannot reproduce normally and gradually die. The brain clears away the dead tumor cells, but this is a lengthy process. Scans taken immediately following therapy can be confusing because swelling and dead cells often appear larger than the original tumor, and can cause symptoms similar to the tumor. It takes a few months before scans show the full benefit of the radiation.

Re-treatment with radiation: Radiation kills normal cells as well as tumor cells. Since brain tissue cannot replace itself, the effects of radiation are cumulative, causing severe side effects beyond a certain degree of exposure to radiation. For this reason, re-treatment with conventional fractionated radiation is not often recommended. However, additional radiation is possible in selected circumstances, including:

Location of the tumor and its relation to critical brain tissue,

When the previous radiation was given,

The amount of radiation originally given, and

The type of tumor and the age of the patient.

Brachytherapy and stereotactic radiation therapy are frequently used for selected patients who may benefit from retreatment with radiation therapy. These patients typically have recurrent malignant gliomas or metastatic brain tumors and have previously undergone conventional EBRT.

For more information about radiation therapy procedures, go to What to Expect During Radiation Therapy.

Techniques for Delivering Radiation Therapy to Brain Tumors

The three primary techniques for delivering radiation therapy—external, internal, and stereotactic—have each been evaluated in the treatment of patients with brain tumors and may be utilized in different circumstances. While EBRT is the conventional treatment for brain tumors, SRS has also become a standard procedure. SRS has been used in the treatment of many types of brain tumors and been proven effective in the treatment of brain metastases. A recent advance in brachytherapy includes the FDA-approved GliaSite® radiation therapy system that involves passing a radioactive material into an implanted balloon.

External Beam Radiation Therapy (EBRT)

EBRT involves directing radiation beams from outside the body into the tumor. Machines called linear accelerators produce the high-energy radiation beams that penetrate the tissues and deliver the radiation dose deep in the body where the cancer resides. These modern machines and other state-of-the-art techniques have enabled radiation oncologists to significantly reduce side effects while improving the ability to deliver radiation directly to the tumor.

EBRT is typically delivered as an outpatient procedure for approximately six to eight weeks. EBRT begins with a planning session, or simulation, during which the radiation oncologist places marks on the body and takes measurements in order to line up the radiation beam in the correct position for each treatment. During treatment, the patient lies on a table and the radiation is delivered from multiple directions. The actual area receiving radiation treatment may be large or small, depending on the features of the cancer. Radiation can be delivered to one specific area or encompass the surrounding tissues, including the lymph nodes.

EBRT may be used to deliver radiation therapy to a part of the brain or the whole-brain. Whole-brain radiation therapy is usually recommended for a large or spreading brain tumor.

Proton radiation therapy: Proton radiation therapy is a form of EBRT that utilizes a beam of protons as the source of radiation rather than X-rays or gamma rays. Protons are released from atoms using technology similar to that employed in nuclear reactors. Computer-programmed blocks are precisely placed to direct the proton beam toward the tumor and match it to the shape of the tumor.

As a source of radiation, proton beams offer advantages over X-rays. In particular, a proton beam delivers a high dose of radiation to the tumor, but very little radiation affects normal tissue in front of and beside the tumor, and no radiation is deposited in the normal tissue behind the tumor. In this way, healthy brain tissue is spared from radiation damage. X-ray beams may deposit most of their dose in tissues in front of the tumor, causing damage to normal tissue and associated side effects.

Proton radiation therapy may have a role in the treatment of unusually shaped tumors and small tumors that are located deep in the skull, such as skull base tumors or pituitary tumors. Proton radiation therapy has been evaluated in the treatment of meningiomas and appears to be effective. In a clinical trial involving 16 patients with intracranial meningiomas, over 90% survived free of cancer progression for three years or longer. [1]

Stereotactic Radiation Therapy (Gamma Knife Therapy)

Stereotactic radiation therapy (SRT) is a noninvasive approach to the treatment of brain tumors that uses pencil-thin beams of radiation to treat only the tumor. SRT uses imaging techniques—including CT scans or MRI—and special computerized planning to precisely focus a high dose of radiation on the brain tumor, while sparing normal tissue. This focused technique allows radiation to be delivered in an area of the brain or spinal cord that might be considered inoperable, and can be delivered to tumors that are one and one-half inches in diameter or smaller. Another advantage to SRT is that radiation treatment is delivered in a single session.

SRT has become a standard treatment for primary and metastatic brain tumors and may be delivered as:

• An addition to conventional EBRT, called local “boost” radiation, when the patient has already received the maximum safe dose of conventional radiation therapy,
• The only technique used to deliver radiation therapy to some brain tumors, or
• A substitute for surgery for a metastatic brain tumor or a benign tumor (such as a pituitary, pineal region, or acoustic tumor).

Prior to SRT, the patient is fitted with a head frame. CT and/or MRI scans are performed with the head frame in place to locate the tumor and obtain information necessary for computerized treatment planning. Treatment is totally non-invasive and painless. Patients maintain their normal function and are completely awake and alert throughout the entire procedure.

Possible side effects of SRT include edema (swelling), occasional neurological problems, and radiation necrosis (an accumulation of dead cells). A second surgery to remove the build-up of dead tumor cells may be required.

Source : www.texasoncology.com