External beam radiation therapy is a common cancer treatment that uses high-energy beams to target specific areas within the body. As a non-invasive procedure, it does not involve surgical incisions. The treatment directs radiation from a machine toward a tumor with the goal of destroying cancerous cells while minimizing harm to surrounding healthy tissue.
The Mechanism of Beam Treatment
External beam radiation therapy works by damaging the DNA within cancer cells. High-energy beams cause breaks in the DNA, which disrupts the cells’ ability to grow and divide. While radiation affects both cancerous and normal cells, healthy cells have a greater capacity to repair this type of damage.
Cancer cells divide rapidly and are less proficient at repairing DNA damage. This vulnerability leads to apoptosis, or programmed cell death, in the damaged cancer cells. To enhance this effect, treatment is delivered in a series of smaller doses, a technique known as fractionation. This approach allows healthy tissue time to recover between sessions while cumulatively damaging the cancer cells.
Conditions Treated with Beam Therapy
External beam radiation is a versatile treatment used for many types of cancer, including those affecting the breast, prostate, lung, colon, head, and neck. The specific application depends on the cancer’s type, stage, and location, as well as the patient’s overall health. The treatment intent can vary:
- Curative therapy aims to completely eliminate the cancer.
- Adjuvant therapy is administered after a primary treatment like surgery to destroy remaining cancer cells and reduce the risk of recurrence.
- Neoadjuvant therapy uses radiation to shrink a tumor before the main treatment to make the procedure more effective.
- Palliative radiation is used when a cure is not possible to relieve symptoms like pain or obstruction, improving the patient’s quality of life.
Types of External Beam Radiation Therapy
The technology for external beam radiation therapy has advanced, allowing for more precise and effective treatments. An early form of modern radiotherapy is 3D Conformal Radiation Therapy (3D-CRT), which uses imaging scans like CTs to create a three-dimensional map of the tumor. This allows radiation beams to be shaped to match the tumor’s contours, reducing exposure to nearby healthy tissue.
Building on this, Intensity-Modulated Radiation Therapy (IMRT) is a more advanced technique that varies the strength of the radiation beams across the treatment area. This allows for higher, more targeted doses to be delivered to the tumor while further sparing adjacent tissues. Volumetric Modulated Arc Therapy (VMAT) enhances IMRT by delivering a continuous, rotating beam of radiation, which can shorten treatment times.
For smaller, well-defined tumors, Stereotactic Body Radiation Therapy (SBRT), or Stereotactic Radiosurgery (SRS) for brain tumors, deliver very high doses of radiation with high precision in just a few sessions. These methods are non-surgical and are effective for tumors in the lung, liver, spine, and brain. Another approach is proton therapy, which uses proton beams instead of X-rays. Protons deposit most of their energy at the tumor site, minimizing the radiation dose to tissues beyond the target.
The Treatment Process and Patient Experience
The process begins with a consultation with a radiation oncologist. During this meeting, the doctor reviews the patient’s medical history and test results, explains the treatment process, and discusses potential benefits and side effects. This allows patients to ask questions and make an informed decision about their care plan.
After the consultation, the patient has a planning session called a simulation. During this step, a CT scan creates a detailed map of the treatment area. To ensure precise positioning for each session, the team may create immobilization devices like custom molds or masks and make small, permanent ink marks on the skin.
Using the simulation data, a team including a medical physicist and a dosimetrist uses computer software to design the treatment plan. This plan details the angles, shapes, and intensities of the radiation beams needed to target the tumor while avoiding healthy organs. This planning phase can take several days to complete.
The treatment sessions are quick and painless, lasting 15 to 30 minutes, with the radiation active for only a few minutes. Patients lie on a table while a linear accelerator moves around them to deliver radiation from different angles. The machine may make sounds, but the patient will not feel the radiation, nor are they radioactive after treatment.
Managing Treatment Side Effects
Side effects from external beam radiation are localized to the area being treated. These effects are either acute, occurring during or shortly after treatment, or chronic, developing months or years later. Most side effects are acute and temporary.
The most common side effect is fatigue, a feeling of tiredness that rest may not alleviate, as the body is expending energy to heal. Patients are advised to get plenty of rest, maintain a balanced diet, and engage in light exercise, such as short walks, to help manage fatigue.
Skin reactions in the treatment area are also frequent, ranging from redness and dryness to itching and peeling, similar to a sunburn. The care team provides specific instructions for skin care, which include being gentle with the skin, avoiding harsh soaps, and protecting the area from sun exposure. Following the care team’s advice is important for managing these effects.