RADIATION THERAPY FOR BRAIN CANCER

What are brain tumors?

A brain tumor is a group of abnormal cells that grow in or around the brain and destroys healthy brain cells. These cancer cells can damage healthy cells by damaging other brain parts and causing inflammation, swelling, and pressure within the skull.

Brain tumors are either malignant or benign. A malignant tumor grows rapidly and often damages healthy areas of the brain. Benign brain tumors are usually non-cancerous and slow-growing.

Brain tumors can be primary or metastatic. Primary brain tumors begin within the brain. A metastatic tumor develops when cancer from other body parts travels to the brain. While primary brain tumors may be benign or malignant, metastatic brain tumors are mostly malignant. Factors that determine the tumor grade are the rate at which the cells multiply, the blood supply to the cells, and how similar the cancerous cells are to normal cells.

What is radiation therapy?

Radiation therapy is a therapy that uses high-energy rays to destroy cancer cells. Radiation therapy also affects normal cells. The healthy cells can repair themselves in a way, but cancer cells won't be able to. Radiation can treat both primary and metastasized tumors. Radiation therapy takes time to work. It may take days or weeks of treatment before cancer cells start to die, and they keep dying for weeks or months after radiation therapy.

A doctor who uses radiation as the mode of treatment is known as a radiation oncologist. Radiation therapy is the treatment of choice for different indications:

• Post-surgery to kill remaining tumor cells
• As a primary form of treatment 
• To prevent or relieve tumor symptoms 

Radiation Therapy For Brain Tumors

Your doctor may prescribe radiation therapy alone or in combination with surgery with or without chemotherapy for primary or metastatic brain cancer treatment. Radiation therapy uses beams of x-rays, gamma rays, or protons to destroy cancer cells and shrink brain tumors. 

Types of radiation therapy

There are three primary techniques for radiation therapy.

• External beam radiation therapy (EBRT):  - When the radiation targets the tumor from a source outside the body, it is known as EBRT. Before initiating the treatment, it is essential to determine the correct angles for aiming the radiation beams and the proper radiation dose. This process is called simulation, and the radiation oncologist does it with the help of imaging tests, such as CT or MRI scans. In most cases, the total dose of radiation spreads over several weeks. During the treatment, the patient lies on a specialized table while a machine delivers the radiation from precise angles. 

• Three-dimensional conformal radiation therapy (3D-CRT):  - In this therapy, imaging test results from MRI and special computers map the tumor location precisely. This technology creates a specific arrangement of x-ray beams adhering to the tumor shape to maximize tumor dose and minimize damage to surrounding tissue. This treatment form is adaptable to the patient's specific anatomy and tumor location. 

• Intensity-modulated radiation therapy (IMRT):  - IMRT is an advanced form of high-precision 3D therapy that utilizes computer-controlled x-ray accelerators to deliver precise radiation doses to the tumor. The radiation dose targets the 3-D tumor shape and regulates the radiation beam intensity to focus a higher radiation dose on the tumor while minimizing exposure to healthy cells. 

• Volumetric modulated arc therapy (VMAT):  - This technique is similar to IMRT. In VMAT beam modulation in each and every step. A computer controls the beam intensity and keeps the radiation focused on the tumor. 

• Stereotactic radiosurgery (SRS) - SRS is a specialized type of highly precise radiation therapy form that directs narrow beams of radiation to the tumor from different angles. CT scan or MRI scan results help the doctor identify the tumor's exact location. A specialized radiation machine regulates targeted radiation to the tumor precisely. The tumor gets a high radiation dose while the surrounding healthy brain tissue gets little. Your doctor may not recommend SRS for all brain tumors. It may be an alternative to neurosurgery.

• Stereotactic radiotherapy (SRT) - Stereotactic radiotherapy is similar to radiosurgery but involves fractionation (multiple treatments). Your doctor may recommend it for large tumors or tumors within or close to critical structures in the brain that cannot tolerate a large single dose of radiation. 

• Image-guided radiation therapy (IGRT): - IGRT uses frequent imaging during radiation therapy courses to improve the precision and accuracy of the radiation treatment. In IGRT, machines that deliver radiation have unique imaging technology which allows the physician to image the tumor immediately before or even during the radiotherapy. The radiation oncologist uses specialized computer software to compare these images to the reference images taken during the simulation and adjusts according to the patient's position and radiation beams. It precisely targets the radiation at the tumor and minimizes damage to the surrounding tissues.

• Brachytherapy (internal radiation therapy):  - Brachytherapy involves inserting radioactive material directly into or near the tumor. The high dose of radiation it produces can travel for a short distance only, thus, affecting only the tumor. The radiation oncologist uses this technique with external radiation to treat the surrounding areas of the tumor with a lower dose.

Steps for Delivering Radiation Therapy to Brain Tumors

• Treatment schedule:  EBRT is generally given in 5 days a week, once 5-6 weeks, and stereotactic radiation therapy in 1-5 session.
• Follow-up examinations: Results may not be visible for several months. Tumor cells damaged by radiation die as they cannot reproduce normally. The brain clears the dead tumor cells, but it is a lengthy process. It may take months to see a visible difference in scans.
• Re-treatment with radiation: 

Radiation kills both normal cells and tumor cells. The effects of radiation cause severe side effects beyond a certain degree of radiation exposure. Your oncologist may avoid re-treatment with conventionally fractionated radiation. In some cases, patients may receive additional radiation depending on:

• Location and the type of the tumor 
• Time of the previous radiation
• Amount of radiation previously given
• Age of the patient

Side Effects of Radiation Therapy for Brain Tumors

Radiation therapy side effects generally occur in the treatment area and are usually temporary, but in some cases, may last for a few months or years. The radiation effect is more on tumor cells than on normal cells. 

Patients may experience side effects at different rates and different degrees. 

General side effects may include:

• Hair loss
• Darkening of skin
• Nausea and vomiting
• Fatigue
• Loss of appetite
• Headaches

• Problems with thinking and memory: 

The patient may lose brain function if large areas of the brain are exposed to radiation therapy. Problems such as memory loss, personality changes, and loss of concentration may occur. 

• Edema: 

Brain swelling may be present among individuals undergoing radiation therapy to the brain. If the patient experiences a headache or a feeling of pressure, report it to the oncologist. 

• Radiation necrosis: 

After radiation therapy, a mass of dead (necrotic) tissue forms at the tumor site in the months or years after radiation treatment. It is a rare case. Your doctor may prescribe steroid drugs or sometimes surgery to remove the necrotic tissue in some cases.

Conclusion

Your doctor may recommend radiation therapy for many purposes, such as post-surgery to kill remaining tumor cells and as a primary treatment form to prevent or relieve tumor symptoms. Radiation therapy can be alone or in combination with surgery with or without chemotherapy for primary or metastatic brain cancers. There are three primary techniques for radiation therapy external, internal, and stereotactic. In some cases, additional radiation is recommended depending on various factors. Radiation therapy can have multiple side effects, including nausea, memory problems, and fatigue.