Radiotherapy: What is a Linear Accelerator?
Radiotherapy is a localized cancer treatment that uses ionizing radiation to destroy cancer cells while sparing the surrounding healthy tissue. It can be used at different stages of the treatment process and for various purposes:
- As a stand-alone therapy for treating primary and secondary tumors.
- To shrink a tumor prior to surgery.
- In combination with other treatments, such as chemotherapy.
- For palliative purposes, to relieve pain.
What Is a Linear Accelerator (LINAC)?
A linear accelerator, or LINAC, typically uses high-energy X-rays, known as photons, to treat tumors. Photons are painless but can penetrate deep into the body to target and destroy cancer cells. In some cases, electrons are used instead — they don’t penetrate as deeply, making them more suitable for treating skin cancers or tumors located close to the surface.
Linear accelerators allow for highly precise targeting of tumors, revolutionizing cancer treatment with a personalized approach tailored to each patient and each type of cancer.
Radiation doses are shaped to match the three-dimensional form and size of the tumor. During treatment, the radiation acts directly on the tumor, destroying cancer cells while sparing surrounding healthy tissue.
What Types of Radiotherapy Can a LINAC Deliver?
There are three main types of radiation therapy for cancer:
- External Beam Radiation Therapy (EBRT): Uses a machine outside the body — the linear accelerator — to deliver radiation directly to the tumor. Most patients receive EBRT, which is effective for many types of cancer.
This treatment helps destroy cancer cells, improves long-term survival chances, and reduces the risk of recurrence. - Internal Radiation Therapy (Brachytherapy): Radiation oncologists place a radiation source inside the body, directly on the tumor, for a limited amount of time.
- Systemic Radiation Therapy: Involves the use of radioactive drugs administered orally or intravenously. This treatment works throughout the body and is used, for example, for cancers that have spread to the bones or thyroid.
External Beam Radiation Therapy (EBRT): The Different Techniques
LINACs used for EBRT can deliver several types of radiation treatments, each with specific characteristics and clinical indications:
3D Conformal Radiation Therapy (3D CRT)
In 3D CRT, doctors shape the radiation beams to conform to the tumor’s shape. Beams are delivered from multiple angles, minimizing exposure and damage to surrounding healthy tissues.
Image-Guided Radiation Therapy (IGRT)
IGRT uses advanced medical imaging techniques to precisely plan and monitor each radiation session. Since the tumor’s size and position — as well as the patient’s anatomy — can change over time, IGRT allows real-time treatment adjustments.
It is especially suited for tumors located in areas subject to movement, such as the lungs, liver, pancreas, and prostate.
LINACs equipped with IGRT may integrate several imaging modalities, including:
- Computed Tomography (CT-LINAC)
- Magnetic Resonance Imaging (MRI-LINAC)
- Ultrasound, using integrated probes and transducers
Intensity-Modulated Radiation Therapy (IMRT)
Similar to 3D CRT, IMRT not only shapes the radiation beams but also modulates their intensity in specific areas of the tumor. This technique enables higher doses to be delivered with greater precision, reducing the risk of side effects.
It is a complex technique that requires advanced planning and generally involves longer treatment sessions.
Volumetric Modulated Arc Therapy (VMAT)
VMAT is an advanced form of IMRT. During delivery, the LINAC rotates around the patient, continuously and precisely delivering modulated radiation.
This technique allows treatment to be completed in one or two sessions, maximizing effectiveness and patient comfort.
Stereotactic Radiosurgery (SRS)
SRS is a highly precise, non-invasive radiation technique used to treat brain tumors and spinal lesions.
SBRT (Stereotactic Body Radiation Therapy) is a variant used for tumors in hard-to-reach areas of the body.
Both techniques can be delivered in a single session or in a maximum of 2–5 fractions (fractionated SRS/SBRT).
In all cases, the radiation oncologist works with the patient to evaluate treatment options and recommend the most appropriate type of radiation therapy based on the tumor type, location, and overall clinical condition.
Learn more about the radiation therapy treatments available at our centers: