Radiation Therapy in the Treatment of Glioma: An Overview

“The radiation we use for gliomas tends to be something that’s a little bit smaller dose spread out over a longer period of time, and that’s done so that the normal brain can be spared and not be injured by the treatment, but at the same time, killing the tumor cells,” Dr. Randy Jensen, a neurosurgeon at Huntsman Cancer Institute in Salt Lake City, Utah, tells SurvivorNet.

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.

One of the hallmarks of gliomas is their “infiltrative” behavior, meaning 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.

Why Surgery Alone May Not Be Enough

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

“If you were to do a biopsy of someone who had a glioma, if you were to take that biopsy and go out even four or five centimeters away from the tumor … you would find individual tumor cells scattered even that far away from the central area you call tumor,” he says.

Gliomas can 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.

“We hope that by doing surgery and then following with radiation and then [using] chemotherapy, we will be targeting those cells,” Dr. Jensen says.

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:

• 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.
• 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.
• 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.
• 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. Conventional 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, you come for 15 minutes to half an hour each day, get the treatment done. There’s a little bit of flexibility in how it’s done,” Dr. Jensen explains.

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

There are an array of side effects that may occur after radiation, with fatigue typically being the biggest complaint.

“Fatigue is really what we mostly hear,” Dr. Jensen explains. “There’s some hair loss that will go along with the brain therapy. A lot of that  dependent on where the radiation [is given]. Because the radiation that’s done is actually very targeted to the area where the tumor was. They don’t give radiation to the whole brain. It’s very specialized.”

“Most patients tolerate the radiation quite well, and in a lot of ways, I think maybe that’s an easier thing to undergo compared to the surgery,” he adds.

Side effects vary based on factors like the radiation dose, the treatment area, and personal medical history.

Some common effects include:

• Fatigue: Often accumulates over weeks of therapy but usually improves a few weeks after treatment ends
• Hair Loss: Occurs in the treated area (hair may regrow, but sometimes the texture or color changes)
• Skin Changes: Redness or dryness can develop on the scalp in the radiation field
• Headaches or Nausea: Generally mild and manageable with medication
• Cognitive Changes (Long-Term): Some people may experience issues with memory or concentration, particularly if large areas of the brain are treated or higher doses are used
• Radiation Necrosis (Rare): Can cause swelling and neurological symptoms, potentially requiring further interventions

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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