Radiation's Role in Glioma Treatment
- While surgery is often the primary treatment option for patients, radiation can play an important role.
- When and how radiation is given will depend on glioma type and grade, patient age, overall health status, and ability to remove the tumor (with surgery).
- Radiation therapy can be used after surgery, in combination with chemotherapy, or as a primary therapy when surgery is not feasible.
- While radiation can be an important part of the treatment plan, patients should be aware of potential side effects, such as fatigue, skin reactions, and headaches — as well as potential late (or delayed) side effects.
- Regarding grade II tumors it should be noted that tumors that are IDH mutant may be eligible for vorasidenib, which is now being recommended in lieu of radiation and chemo. As a result knowing the IDH mutation status is critical.
After a diagnosis of glioma is made, they can be split generally into two groups with low-grade gliomas (Grade 1-2) being slow-growing, while high-grade gliomas (Grade 3-4), including glioblastoma multiforme (GBM), are typically more aggressive. For gliomas, surgery is the primary treatment with maximal safe surgical resection being the goal. This means that when surgery is performed, the neurosurgeon will operate with the goal of taking out as much of the glioma as possible while avoiding important normal tissue. Sometimes a surgery to remove the tumor is not possible and a biopsy alone will be taken to confirm the diagnosis.
Read MoreAmong the available treatment options for gliomas, radiation therapy often plays an important role helping to improve survival and reduce the rates of disease recurrence. Radiation therapy can be used after surgery, in combination with chemotherapy, or as a primary therapy when surgery is not feasible. Again, the specific timing and use of radiation depends on several factors. It should be noted that for patients with grade 2 tumors that are IDH mutant, vorasidenib may now be recommended in place of radiation and chemotherapy. As a result, knowing the IDH mutation status is critical.
What is Radiation & How Does it Work?
Radiation is energy that travels through space often as waves or particles. Radiation can be split into two categories: ionizing radiation and non-ionizing radiation. Non-ionizing radiation is a lower energy wave or particle and is common in day to day life. It includes things such as radio waves, microwaves, and visible light. Ionizing radiation refers to very high energy waves or particles that are able to interact with atoms and cause chemical reactions or ionizations.
These chemical interactions can then lead to several downstream effects, one of them being DNA damage. Radiation therapy used in the medical setting, utilizes high levels of ionizing radiation in very focused target areas with the goal of creating high levels of DNA damage. DNA is the blueprint for our cells and plays a vital part in cell function and division. If DNA is damaged extensively, this can make it impossible for the cell to function and divide leading to cell death. When this process is focused on a tumor or tumor cells this causes the cancerous tumor cells to die.
How is Normal Tissue Protected?
Normal cells have mechanisms in place to fix DNA damage caused by radiation, while cancer cells are more sensitive to the effects of radiation because they are unable to properly fix the DNA damage which continues to accumulate.
Additionally, extensive planning takes place prior to the start of radiation in order to create an optimal radiation plan that adequately covers the tumor with an effective dose of radiation while keeping dose to normal tissue as low as possible. Additionally, radiation plans are designed so radiation doses to normal tissue stay below critical thresholds to reduce the risk of significant long term side effects.
Adjuvant Radiation Therapy
Radiation therapy for gliomas is primarily administered after surgery. This is also called adjuvant therapy. Gliomas are typically infiltrative, meaning they spread into surrounding brain tissue, making complete surgical resection difficult. So even when an MRI shows a clear tumor and the neurosurgeon is able to remove all visible cancer, there is often microscopic tumor cells within the normal brain tissue remaining which can be responsible for recurrence.
If there is a high risk of residual tumor cells being present which can cause an earlier recurrence, radiation is often recommended in order to kill the residual cancer cells and reduce the risk of recurrence which leads to an improved survival. Radiation therefore, is delivered by targeting the areas where residual tumor cells are most likely to reside.
When is Adjuvant Radiation Administered with Gliomas?
- In grade I gliomas, a complete surgical resection or removal of the tumor is often sufficient and can be observed with no additional treatment after surgery.
- In grade II gliomas the need for radiation following surgery can depend on several factors including age, symptoms, and how much of the tumor was resected. If radiation is given, it is typically delivered by itself and chemotherapy is delivered after radiation has been completed.
- In grade III gliomas radiation is almost always recommended after surgery. Chemotherapy is given after the completion of radiation.
- With grade IV gliomas, radiation and chemotherapy are typically given together (also called chemoradiation), and followed then by additional chemotherapy and tumor treating fields (optune). Per Dr. Shankar: “For glioblastoma (Grade IV glioma) it is standard of care to follow surgery with a combination of chemotherapy as well as radiation.”
In cases where surgery is not feasible—either because of the tumor’s location or the patient’s health status—radiation therapy can serve as the primary treatment. This is particularly common for older patients with glioblastoma. While radiation therapy alone is generally not curative in these cases, it can control tumor growth and improve quality of life by alleviating symptoms such as headaches, seizures, and neurological deficits.
Radiation for Glioma: What to Expect
Now that we have covered what radiation is, why it works, and when it is recommended in the treatment of gliomas, we can go over what the day to day looks like for someone undergoing radiation treatment for glioma and common terminology.
CT Simulation and Planning Your Treatment
There is a lot of work and preparation that goes into creating a safe and effective radiation treatment plan that is approved by the physician prior to your starting radiation treatment. This first step starts with a CT simulation.
This is essentially a special CT scan done in the radiation department that provides the physician with important information about location of the tumor and normal tissue that needs to be protected. During this time, immobilization is often used in the form of a face mask. This same immobilization (as a face mask) is used every day of treatment to ensure there is as little movement as possible during and between radiation treatments. Following the CT simulation scan there is typically a 1-2 week wait before the actual radiation treatment is started.
Radiation Treatment Planning
Following the CT Simulation, the physician gets to work on planning the radiation which includes highlighting the target area which is to be treated with the higher doses of radiation as well as the normal organs that need to be avoided. There are guidelines which help the physician determine which area to treat, as well as the appropriate amount of radiation to deliver to the target and the maximum radiation that can be delivered to normal tissue.
The plan is sent to a dosimetrist, who uses the targets and guidelines provided to create a plan that can be delivered by the radiation machine. These plans are called intensity-modulated radiation therapy, or IMRT, which are a highly precise form of radiation therapy that uses computer-controlled radiation machines (linear accelerators) to deliver radiation doses tailored to the shape of the tumor.
The highly precise beams are delivered from multiple angles and the amount of radiation delivered by each beam can be adjusted. IMRT allows oncologists to target the tumor more accurately while sparing healthy tissue. Once the plan is approved and determined to be safe and deliverable, you return to start treatment.
Starting Radiation Treatment
To minimize damage to healthy tissue, radiation is delivered in fractions—small doses over a period of time—allowing healthy cells time to repair while cancer cells, which divide more rapidly, are less able to recover. In glioma treatment, the standard fractionated radiation therapy is given five days a week, once daily over approximately six weeks, for a total dose of around 54-60 Gray (Gy). Each daily dose is approximately 1.8 – 2 Gy. This approach reduces side effects while maximizing the effectiveness of the treatment. The treatment itself only takes a few minutes each day.
The radiation treatment itself is painless. You cannot touch, hear, or feel the radiation that is actively being delivered. For the first several treatments you will likely have no or minimal side effects. As treatment progresses and the total dose delivered increases you are more likely to experience side effects.
Side Effects and Management
While radiation therapy is critical in controlling tumor growth, it does come with side effects, which can vary based on the dose, location of the tumor, and the patient’s overall health.
Side effects may include:
- Fatigue: The most common side effect, fatigue typically worsens as treatment progresses but usually resolves within a few months after therapy ends.
- Skin Reactions: Patients may experience redness, irritation, or dry skin at the site where radiation is administered.
- Headaches: You may experience increased pressure or headaches as radiation progresses due to the associated inflammation and swelling
- Hair Loss: Radiation can cause hair loss in the treated area, which may be permanent depending on the dose and location.
Late side effects can occur months to years following treatment. Some possible side effects include but are not limited to:
- Cognitive Decline: Radiation to the brain can affect memory, attention, and other cognitive functions. This is especially true for higher doses and when large areas of the brain are treated.
- Radiation Necrosis: A rare but serious side effect where irradiated brain tissue becomes necrotic (dead), leading to swelling and neurological symptoms. This can occur months to years after treatment and may require surgical intervention or corticosteroids to manage.
- Small increased risk of secondary cancer
Combination Therapy: Radiation & Chemotherapy
While radiation therapy is typically delivered by itself in grade II and III gliomas and then followed with chemotherapy, the combination of radiation therapy with chemotherapy together are the current standard of care for grade IV gliomas or glioblastomas. Temozolomide is the chemotherapy typically administered with radiation. Temozolomide, an oral alkylating agent, makes tumor cells more sensitive to radiation by preventing them from repairing the DNA damage caused by radiation. This synergy leads to more effective tumor cell death.
Radiation therapy continues to evolve with advances in technology and biology. Research is ongoing to optimize dosing schedules, improve precision, and combine radiation with novel therapies such as immunotherapy and targeted molecular therapies.
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