The acronym XRT stands for X-ray Therapy, which is an interchangeable term for External Beam Radiation Therapy (EBRT) or Radiotherapy. This treatment uses high-energy beams directed from a machine outside the body to precisely target and eliminate diseased cells, primarily cancer cells. XRT is a localized treatment, meaning it affects only the area of the body being treated. It represents a significant modality in modern oncology care.
Defining XRT and Its Cellular Mechanism
XRT employs high-energy ionizing radiation, typically generated by a linear accelerator (LINAC), to deliver a controlled dose of energy to a target volume inside the body. The goal is to damage the genetic material, or DNA, within cancer cells, which prevents them from successfully dividing and ultimately leads to their death. This is achieved through two main pathways: direct DNA damage and indirect damage via free radicals.
The radiation beam can directly sever the strands of the DNA double helix, which is difficult for cells to repair. More commonly, the radiation interacts with water molecules within the cell, creating highly reactive oxygen species, or free radicals, that chemically attack and damage the DNA.
Cancer cells are particularly susceptible to this damage because they are rapidly dividing and often have poor DNA repair mechanisms compared to healthy cells. Healthy cells, which are also exposed to the radiation as it passes through the body, generally possess more robust repair systems and a slower division rate, allowing them to recover more effectively. By delivering the total treatment dose in small, daily increments called fractions, the medical team maximizes the damage to the tumor while giving the surrounding healthy tissues time to repair themselves.
The Patient Journey: Planning and Delivery
The process of undergoing XRT begins with a meticulous planning stage to ensure maximum precision. The initial step is the simulation, where the patient is positioned on a table in the exact posture that will be used for every treatment session. Imaging scans, such as a computed tomography (CT) scan or magnetic resonance imaging (MRI), are performed to map the tumor’s precise location and its relationship to nearby healthy organs.
To maintain this exact position for daily treatments, customized immobilization devices, such as body molds or headrests, may be created. Small, permanent reference marks may be placed on the skin to help the therapists align the patient correctly each day. This level of detail is necessary because even minute differences in positioning can affect the accuracy of the radiation delivery.
Following simulation, a team including a radiation oncologist and a physicist collaborates on the treatment plan. They use sophisticated software to calculate the optimal radiation dosage, beam angles, and beam shapes to conform the dose precisely to the tumor volume while sparing adjacent critical structures. This calculation process, known as dosimetry, can take several days before the first session is scheduled.
Treatment delivery involves the patient lying on the LINAC table for a short period, typically just a few minutes, while the machine rotates around them, delivering the radiation from various angles. The actual beam-on time is very brief, and the patient does not feel the radiation during delivery. Treatment is usually administered daily, five days a week, over a course that can range from a single session to several weeks, depending on the specific cancer and treatment goal.
Primary Medical Applications
XRT is a highly versatile tool in oncology, employed with three distinct goals: to cure the disease, to work alongside other therapies, or to relieve patient symptoms. When used with curative intent, the radiation is delivered at a high dose over many weeks to eliminate all cancer cells within the treatment area. This is often the primary treatment for localized tumors, such as early-stage prostate, head and neck, or certain lung cancers.
XRT also plays a significant role in combination with surgery and chemotherapy, known as adjuvant or neoadjuvant therapy. Neoadjuvant therapy is given before surgery to shrink a large tumor, making it easier to remove completely. Adjuvant therapy is administered after surgery to destroy any microscopic cancer cells that might remain, reducing the chance of recurrence. This strategy is commonly used for cancers of the breast, rectum, and soft tissues.
The third primary application is for palliative intent, which focuses on improving a patient’s quality of life when the cancer is advanced or widespread. In these cases, XRT is used to alleviate pain caused by tumors pressing on nerves or bones, to stop bleeding, or to manage symptoms like difficulty swallowing. Palliative treatments typically involve a much shorter course of radiation, sometimes just one or a few fractions, to provide rapid relief.
Common Treatment Side Effects and Management
The side effects experienced during XRT are directly related to the area of the body being treated. Unlike systemic therapies, such as chemotherapy, XRT rarely causes generalized effects like hair loss. Side effects are typically categorized as acute, occurring during or immediately after treatment, or late, developing months or years later.
A common acute effect is fatigue. Skin in the treatment area may also become irritated, resembling a sunburn, with redness, dryness, or itching, which usually resolves within a few weeks of treatment completion.
Site-specific acute effects can include nausea and diarrhea if the abdomen or pelvis is treated, or a sore throat and difficulty swallowing if the head and neck area is targeted. Managing these acute effects is a constant focus of the medical team, which provides supportive care to keep patients comfortable and ensure they complete the prescribed course.
Supportive care includes prescribing anti-nausea or anti-diarrhea medications, recommending skin creams, and arranging dietary consultations to maintain nutrition and hydration. While most acute effects are temporary, late effects, such as mild tissue scarring or changes to organ function, can occur, which requires long-term follow-up.