Whole brain radiation therapy (WBRT) is a form of external beam radiation designed to treat the entire cranial vault. This treatment is administered over multiple sessions, aiming high-energy beams at the whole brain structure. WBRT is a common therapeutic option used to manage conditions where cancer has spread extensively within the brain, requiring a broad approach.
Why Whole Brain Radiation is Used
The primary reason for using WBRT is to treat multiple brain metastases—cancers that have spread to the brain from a primary tumor elsewhere. When numerous small tumors are present, or when cancer cells are too diffuse to be individually targeted, WBRT treats all known and microscopic disease simultaneously. This strategy controls tumor growth throughout the brain and reduces the chance of new lesions appearing.
WBRT is often employed with palliative intent, aiming to relieve symptoms, improve quality of life, and slow neurological deficits rather than cure the cancer. Symptoms like severe headaches, seizures, or motor weakness caused by the cancer can often be managed effectively. Furthermore, WBRT may be used prophylactically, such as in patients with small-cell lung cancer, to prevent the cancer from spreading. However, its use has become more selective as focused radiation techniques, like stereotactic radiosurgery, have advanced for patients with fewer lesions.
The Treatment Process
The WBRT process begins with a planning stage called simulation, often involving CT or MRI scans. During this step, a radiation oncology team maps the patient’s anatomy to precisely design the radiation beams. The patient is fitted with a custom-made immobilization device, typically a plastic mesh mask, which ensures the head is in the exact same position for every daily treatment session.
The fractionation schedule refers to the number of treatments and the dose given during each session. A common regimen involves delivering the total radiation dose over 10 to 15 fractions, typically given once per day, five days a week, spanning one to three weeks. During the daily treatment, the patient lies on a table while a machine called a linear accelerator rotates around them, delivering the radiation beams. The beam delivery is quick, generally lasting only a few minutes, though the total time in the room may be longer for setup.
Acute Side Effects and Recovery
Acute side effects are short-term physical reactions that occur during the course of radiation or in the weeks immediately following completion. The most common acute toxicity is profound fatigue, which can begin within two weeks of starting treatment and often peaks shortly after the final session. This fatigue can significantly impact a patient’s daily life.
Patients frequently experience temporary hair loss (alopecia) across the entire scalp because the radiation targets the hair follicles. Other common acute effects include mild headaches, scalp irritation, and transient nausea or vomiting, which are manageable with medication. To address potential brain swelling (edema), corticosteroids like dexamethasone are often prescribed to manage symptoms and prevent worsening neurological function. These acute side effects usually begin to resolve within a few weeks to months after the radiation course is finished.
Addressing Long-Term Cognitive Effects
The most concerning long-term side effect of WBRT is delayed neurocognitive decline, which can manifest months or even years after treatment. This delayed toxicity primarily affects higher-level brain functions, including memory loss, a decline in executive function, and reduced processing speed. The memory deficits are often linked to radiation damage to the hippocampus, the brain structure involved in learning and memory formation.
Modern radiation techniques focus on minimizing this damage to improve the patient’s long-term quality of life. One such technique is Hippocampal Sparing Whole Brain Radiation (HS-WBRT), which uses advanced targeting to reduce the radiation dose specifically to the hippocampal regions. The drug Memantine, an NMDA receptor antagonist, is also often prescribed to help prevent or delay cognitive deterioration. These strategies help maintain neurocognitive function for patients expected to have a longer survival time.