Glioblastoma is an aggressive type of brain cancer that originates from star-shaped brain cells called astrocytes, which provide support to nerve cells. This tumor grows rapidly and infiltrates surrounding brain tissues, often leading to symptoms such as headaches, seizures, and changes in cognition or personality, depending on its location. Radiation therapy is a common and established part of the comprehensive treatment plan for glioblastoma, aiming to target and eliminate cancer cells.
Purpose and Process of Radiation Therapy
Radiation therapy serves multiple purposes in glioblastoma management, primarily to destroy any remaining cancer cells after surgery, slow tumor growth, and alleviate symptoms. It is frequently administered after surgical removal of as much of the tumor as possible. For individuals unable to undergo surgery, radiation therapy, sometimes combined with chemotherapy, may be the primary treatment approach.
The process begins with meticulous treatment planning, involving advanced imaging like MRI and CT scans to precisely map the tumor’s location, size, and shape, as well as nearby healthy brain structures. This imaging guides treatment planning and monitors the tumor’s response. Patients typically undergo a simulation session, which is a practice run, to ensure accurate positioning for each treatment session.
Radiation is usually delivered in daily sessions over several weeks, often five times a week for about six weeks, with a total dose of around 60 Gy delivered in 2-Gy fractions. This precise targeting minimizes exposure to healthy brain tissue, although some radiation exposure to healthy cells is unavoidable.
Common Radiation Techniques
External beam radiation therapy (EBRT) is the most common method for treating glioblastoma, involving high-energy beams directed at the tumor from outside the body. Intensity-Modulated Radiation Therapy (IMRT) is an advanced form of EBRT that uses computer-controlled machines to deliver highly precise radiation doses. IMRT allows the radiation beams to be shaped and their intensity modulated to conform to the tumor’s three-dimensional shape.
Stereotactic Radiosurgery (SRS) and Stereotactic Radiation Therapy (SRT) are highly focused radiation techniques that deliver a high dose of radiation in fewer sessions, often one to five treatments. SRS, a non-invasive treatment, uses advanced imaging and computer technology to precisely target tumor cells. It is typically used for smaller, well-defined tumors or to treat residual tumor cells after conventional surgery.
Proton therapy is another specialized radiation technique that uses charged particles called protons instead of X-rays. Protons have a unique property known as the Bragg peak, which allows them to deliver a concentrated dose of radiation precisely at the tumor depth and then stop. While proton therapy shows promise in minimizing side effects by sparing healthy brain tissue, it is not as widely available as traditional X-ray radiation therapy and may be considered for tumors in sensitive brain areas or as part of clinical trials.
Expected Side Effects
Radiation therapy for glioblastoma can cause various side effects, which can be categorized as acute or late. Acute side effects often appear during or shortly after treatment and may include fatigue, nausea, vomiting, and skin irritation or redness at the treatment site, known as radiation dermatitis. Hair loss in the treated area is also common, though often temporary. Headaches and seizures can also occur due to swelling in the brain, which may be managed with medication.
Late side effects can develop months or even years after treatment completion. These may include cognitive changes such as impaired concentration, memory problems, or speech difficulties. Radiation can also affect hearing, especially if the brainstem or ear received radiation, and vision, if the optic nerve was in the treatment field, potentially leading to cataracts. Hormonal imbalances can also occur if the pituitary gland or hypothalamus is affected.
The healthcare team closely monitors patients for these effects, and supportive care, including physical therapy, occupational therapy, or cognitive rehabilitation, can help manage symptoms and improve quality of life.
Treatment Outcomes and Challenges
Radiation therapy, typically combined with surgery and chemotherapy, is a standard treatment for glioblastoma and can extend survival and improve quality of life. Studies indicate that patients who receive both surgery and radiation therapy generally live longer than those treated with surgery alone. Radiation can effectively shrink or kill tumor cells, reducing tumor size and slowing progression.
Despite these advancements, glioblastoma remains a challenging disease due to its aggressive and infiltrative nature. Tumor cells often spread into surrounding healthy brain tissue, making complete surgical removal difficult and leading to high recurrence rates, with approximately 90% recurring locally within two years. Inherent factors such as tumor hypoxia (low oxygen levels), the presence of radioresistant glioblastoma stem cells, and upregulated DNA damage response mechanisms contribute to treatment resistance.
The median survival for glioblastoma patients remains relatively low, typically ranging from 12 to 15 months, with only a small percentage of patients surviving beyond five years. The blood-brain barrier also presents a challenge, limiting the effective delivery of chemotherapy drugs to the tumor. These factors contribute to the difficulty in achieving a lasting cure.