By: Mohammad Hassan Bagheri, MD Candidate and Fatemeh Jafari, MD
Photo Credit: The Defeating Epilepsy Foundation
Mohammad Hassan Bagheri, is an MD Candidate at Tehran University of Medical Sciences (TUMS), and Fatemeh Jafari, MD, is an Associate Professor of Radiation Oncology at Tehran University of Medical Sciences (TUMS). The Defeating Epilepsy Foundation thanks them for their research and for helping us provide important information to the epilepsy community.
For someone with a brain tumor, the possibility of having a seizure can be an added source of worry. Radiation therapy is an important part of treatment for many brain tumors, but the relationship between radiation and seizures is not always simple. The tumor itself, swelling or other changes in the brain, and a person’s history of seizures can all play a role.
Knowing what to expect and what symptoms to report can help you and your healthcare team respond to changes early.
Can radiation therapy cause seizures?
Not everyone who receives radiation therapy will have a seizure. When seizures occur during or after treatment, there may be more than one possible cause.
The brain tumor itself can trigger seizures. A tumor can irritate or disrupt nearby brain tissue and interfere with the brain’s normal electrical activity.
Radiation treatment can also cause swelling, or edema, around the treated area. This is often temporary, but depending on where the swelling occurs and how extensive it is, it may contribute to neurological symptoms, including seizures.
Another possible late effect is radiation necrosis. This occurs when tissue in or around the treated area becomes damaged after radiation. It can develop months or even years after treatment, and seizures can be one of its symptoms.
A seizure after radiation does not necessarily mean that radiation itself is the cause. Your healthcare team may use brain imaging, your medical history, and other tests to determine what is happening.
Can radiation be used to treat epilepsy?
Yes. In certain situations, a highly focused form of radiation called stereotactic radiosurgery (SRS) can be used to treat epilepsy.
SRS delivers radiation very precisely to a specific area of the brain. It has been studied for some forms of drug-resistant epilepsy, including epilepsy associated with hypothalamic hamartoma, an uncommon brain lesion that can cause difficult-to-control seizures.
This is not a treatment for most people with epilepsy. It is considered only for carefully selected patients when the location and characteristics of the abnormal brain tissue make radiosurgery an appropriate option.
What about seizures after SRS for brain metastases?
SRS is commonly used to treat brain metastases, which are cancerous tumors that have spread to the brain from another part of the body.
Seizures can occur after SRS, although most patients do not develop this complication. In a 2024 multicenter retrospective study of people with supratentorial brain metastases treated with SRS, 11.3% developed epilepsy after treatment. The median time to the first seizure was 21 days.
The risk was higher in patients whose tumors were located in the cortex or hippocampus, those with more extensive swelling around the tumor, and those with a history of epilepsy.
These findings come from one retrospective study and should not be interpreted as a risk that applies equally to everyone receiving SRS. Your individual risk depends on the characteristics of your tumor and your overall neurological history.
What if I already have seizures during radiation for a glioma?
People with gliomas can have seizures before treatment, and seizure activity may change during radiation therapy.
A prospective study of people receiving radiation and chemotherapy for high-grade gliomas found that 10 patients, or 45%, had an increase in seizure activity during treatment. In most of these patients, the change was an increase in seizure frequency. Because the study was small, its findings should not be taken as the expected risk for every person with a glioma.
If your seizures become more frequent, last longer, feel different, or otherwise change during treatment, let your healthcare team know. Your doctor may need to review your medications or look for another cause for the change.
Do I need seizure medication during radiation therapy?
Not everyone needs an anti-seizure medication simply because they have a brain tumor or are receiving radiation.
Current guidelines from the Society for Neuro-Oncology and the European Association of Neuro-Oncology recommend against routinely prescribing anti-seizure medications to people with newly diagnosed brain tumors who have never had a seizure, because available evidence does not show that preventive treatment reduces the risk of a first seizure.
Guidance for people with brain metastases similarly does not support routine preventive anti-seizure medication in patients who have never had a seizure.
The situation is different for someone who has already had a seizure. In that case, an anti-seizure medication may be part of the treatment plan. Your neurologist, epileptologist, oncologist, or other treating clinician can decide which medication is appropriate based on your individual circumstances.
Do not start, stop, or change an anti-seizure medication without talking with your healthcare team.
What symptoms should I report?
Seizures do not always involve full-body shaking or loss of consciousness. Some can be much more subtle.
Tell your healthcare team if you experience new or unusual symptoms such as:
- Repeated twitching or jerking in one part of the body
- Episodes of staring or loss of awareness
- Sudden unusual smells, tastes, sensations, or feelings
- Brief periods when you cannot respond normally
- Confusion after an episode
- A change in how often your seizures occur
- A seizure that feels different from your usual seizures
Keeping a seizure diary can also be useful. Recording when a seizure occurs, what you experienced, how long it lasted, and any possible triggers can give your healthcare team information that may help guide treatment.
What should I remember?
Radiation therapy does not mean that you will have a seizure. When seizures occur in people with brain tumors, the cause can be related to the tumor, swelling around it, treatment-related changes, or other factors.
If you already have epilepsy or seizures, your seizure pattern may change during treatment. Your healthcare team can monitor these changes and adjust your treatment when appropriate.
The most important thing is to report a change in your usual seizure pattern. New symptoms, more frequent seizures, or a seizure that is different from what you normally experience should be discussed with your healthcare team.
If you are receiving radiation for a brain tumor and are concerned about seizures, ask your radiation oncologist, neurologist, or epilepsy specialist about your individual risk and whether anything about your seizure treatment needs to change.
