Radiation Therapy: An Important Tool In Glioma Treatment

Of course, each patient’s treatment is customized based on the tumor’s location, grade, and other health factors that can impact the body’s ability to handle treatment. Many patients undergo surgery first to remove glioma. Radiation is often added afterwards to ensure as much of the cancer as possible has been removed.

Rethinking the Timing of Radiation for Some Glioma Patients

At the same time, the arrival of IDH inhibitors—targeted drugs designed to block a cancer-driving mutation in the IDH gene and slow tumor growth—has begun to change how neuro-oncologists think about the timing of radiation for certain patients. For people with IDH-mutant, lower-grade gliomas, these targeted therapies can slow tumor growth and control disease for extended periods, giving some patients the option to delay radiation rather than start it immediately. This can be especially meaningful for younger patients, since radiation—while highly effective—can carry long-term risks to cognition and quality of life. As a result, neuro-oncologists are increasingly able to offer select patients a choice: proceed with radiation right away, or begin with an IDH inhibitor and reserve radiation for later, if and when it’s needed.

Why Surgery Alone May Not Be Enough

Glioma is a diffuse, or wide-spread disease, Dr. Alnahhas explains.

“We always say that there is more than what meets the eyes with gliomas, because gliomas tend to be microscopic … what we call infiltrative,” he explains. “So, the cancer cells try to intermingle with the normal brain cells, therefore there is no really complete resection [removal] … that’s why surgery is not a cure alone for gliomas because there’s always something happening at the molecular level that we cannot see.”

This is one of the hallmarks of gliomas: their “infiltrative” behavior, which means they can spread into normal tissue. Even if a large portion of the tumor is removed surgically, small clusters of tumor cells can remain in surrounding healthy tissue, potentially leading to recurrence if not addressed with additional therapies.

Gliomas can also extend into areas of the brain where complete removal is not possible without risking serious neurological side effects. Although surgery aims to remove as much tumor as possible, microscopic cells often persist. These remaining cells can later grow and cause the tumor to return.

To help reduce this risk, radiation therapy (and sometimes chemotherapy) is recommended to target any cancer cells left behind.

When Is Radiation Recommended?

Deciding whether or not radiation therapy is needed depends on several factors, including the tumor’s grade, genetic makeup, the extent of surgical removal, and overall health.

Here’s a breakdown of what treatments may be recommended based on grade.

• Grade I gliomas: Lower-grade gliomas are often managed successfully with surgery alone if the tumor is completely removed.
• Grade II gliomas: These may or may not require radiation after surgery. This decision depends on factors like patient age, symptoms, tumor genetics, and how much of the tumor was resected. Some grade II tumors with certain genetic markers (e.g., IDH mutations) may be treated with newly approved targeted therapies instead.
• Grade III gliomas: These typically require radiation therapy after surgery, followed by chemotherapy.
• Grade IV gliomas (glioblastoma): Advanced tumors are commonly treated with radiation plus chemotherapy immediately after surgery, followed by additional chemotherapy and possibly tumor-treating fields. This combination approach aims to control tumor growth and delay recurrence.

For those who are not candidates for surgery — whether due to tumor location or other medical considerations — radiation therapy can be the primary method of treatment to help slow the growth of the tumor and alleviate symptoms.

How Radiation Therapy Works

Radiation therapy uses high-energy beams (often X-rays) to damage the DNA of cancer cells, making it difficult for them to grow and multiply. Because gliomas can be widespread within the brain, radiation is targeted to areas where residual cells are most likely to remain.

To protect healthy tissue, radiation is delivered in small doses (fractions) over several weeks. This approach allows normal cells more time to repair between treatments, while cancer cells, which divide rapidly, have a harder time recovering from DNA damage.

The planning process for radiation typically involves the following steps:

1. CT simulation: A specialized CT scan is performed to map the treatment area. An immobilization device (often a custom-fitted face mask) is used to keep the head still and ensure precise targeting.
2. Contouring: Using information from the CT scan and often an MRI, the radiation oncologist outlines the exact tumor area and critical brain structures that must be protected, such as the brainstem or optic nerves.
3. Dosimetry & treatment planning: A dosimetrist (radiation planner) designs a plan that delivers the right radiation dose to the tumor while limiting exposure to healthy brain tissue. Techniques like Intensity-Modulated Radiation Therapy (IMRT) or Volumetric Modulated Arc Therapy (VMAT) precisely focus the beams.
4. Quality assurance & verification: The plan is reviewed by a medical physicist to ensure accuracy. Before the first session, additional imaging confirms everything is aligned correctly.

Proton Therapy vs. Photon Therapy

Different types of radiation may be used to treat glioma. Conventional photon therapy uses X-rays that pass through the tumor and out of the body, delivering some radiation to healthy tissues along the way.

Proton therapy uses charged particles (protons) that deposit most of their energy at a specific depth (the “Bragg Peak”), which can reduce radiation exposure to surrounding healthy tissue.

This can be particularly helpful if a glioma is located near sensitive structures like the brainstem or optic nerves.

Proton therapy is not available in all treatment centers and may not be recommended for every case. Insurance coverage also varies, so discussing this option with the care team is important.

Undergoing Radiation: The Day-to-Day

Radiation is typically done five days per week for several weeks. As an outpatient, patients come for 15 minutes to half an hour each day to get the treatment done.

Radiation treatment itself is painless. Patients lie on a treatment table wearing a fitted mask for head stabilization. There may be some side effects throughout the radiation process and afterwards.

Most individuals can continue their daily routines, including work, with possible adjustments for fatigue or other side effects.

Possible Side Effects

“Even though it’s very, very effective for the treatment of these tumors, radiation is not without side effects at the end of the day,” Dr. Alnahhas explains. Even though radiation is very focused on the area of the tumor, these side effects are still possible.

“One of my mentors actually used to say that radiation is a gift that keeps on giving. So even if radiation ends after say five to six weeks, the effects of radiation are long-lasting,” he adds.

Some common effects include:

• Fatigue
• Hair loss (in the treated area)
• Skin changes (redness/dryness)
• Headaches
• Nausea

Some patients may also have long-term cognitive changes. Some may experience issues with memory or concentration, particularly if large areas of the brain are treated or higher doses are used.

Another potential, though rare, side effect is radiation necrosis. This can cause swelling and neurological symptoms, potentially requiring further interventions.

“We’ve seen cases of what we call radiation necrosis, which is a happily, not very common. [This is a] complication of radiation therapy where areas of the normal brain that have been radiated get damaged because of radiation,” Dr. Alnahhas explains. “And we’ve seen cases of radiation necrosis even years after radiation, eight or 10 years even after radiation. Again, even though the radiation therapy has been completed, its effects can be long lasting.”

It’s important to report side effects to the medical team to receive supportive care and guidance.

After Radiation: Follow-Up & Long-Term Care

Patients are required to get regular imaging after glioma treatment. MRI scans help monitor for any remaining tumor cells and detect recurrence early.

Depending on the grade, patients may continue after radiation with chemotherapy (such as temozolomide) or use other therapies like tumor-treating fields.

Physical therapy, occupational therapy, and speech therapy can help address any neurological impacts.

Questions To Ask Your Doctor

• Do I need radiation therapy based on my tumor’s grade and characteristics?
• Is proton therapy an option for my situation, or is conventional photon therapy more appropriate?
• What side effects can I expect, and how can I manage them?
• How often will I need follow-up imaging and appointments?
• Are there clinical trials or newer treatments that could be beneficial for my diagnosis?

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