What is Linear Accelerator (LINAC)?
What is this Equipment used for?Linear accelerators help medical experts to determine precisely where cancer cells are located and where healthy cells begin, which helps ensure that healthy cells are not accidentally targeted during radiation therapy. This feature or purpose of the equipment makes it extremely important especially in dealing with cancer because malignant tumors and lesions do not remain static but appear to shift minutely after each radiation session. In addition, the location of cancer cells may also shift in other conditions, for example, with any changes in the patient’s body weight when the organs concerned also shift slightly. This makes identification of the boundaries between cancer cells and healthy cells important before each stage of the treatment. The modern linear accelerator uses both x-ray and cone-beam CAT scan technology to look for cancer cells, making it capable of localizing the target in real time.
The most important use of the linear accelerator could be attributed to its role in external beam radiotherapy treatment. In this type of therapy, the tumor is treated with a single or several beams of high-energy x-rays. In this approach, the linear accelerator is the most commonly used device to generate the beams and target the site. No radioactive sources need to be placed within the patient’s body and with the machine, oncologists can seek and destroy cancerous cells without causing any harm to surrounding tissue. This approach is used in the treatment of a wide variety of conditions from breast and colorectal cancer to lung cancer and brain tumors. This approach to cancer treatment is often used to destroy the tumor altogether and prevent recurrence or to shrink the tumor before it is surgically removed.
How does the Equipment work?In medical grade LINACs, electrons are accelerated using a tuned-cavity waveguide within part of the accelerator called the ‘wave guide’. These accelerated electrons are directed in such a way as to collide with a high density metal target like tungsten. These collisions produce high energy x-rays (photons) that exit the machine, getting shaped to conform to the patient’s tumor. The high energy beams are shaped by either blocks or multileaf collimators that are incorporated in the head of the machine. The beam exits the machine from a part called the gantry. The customized shaped beam is then directed at the tumor, while the patient is made to recline on a moveable treatment couch. The gantry can in fact be rotated right around the patient, which means that the customized high energy radiation beam can be directed at the tumor from any angle through repositioning of the gantry or the treatment couch. Exposure of body cells to these high energy beams results in damage to the DNA in cells in the site exposed to the therapy.
The scope of modern advanced LINACs continues to grow as these new machines can also administer electrons instead of the high energy photons (x-rays), thereby making it useful even in the treatment of areas that are on or just beneath the skin surface. Image guided radiation therapy (IGRT) is the biggest advancement in linear accelerator usage, because these new machines have OBIs or ‘On Board Imagers’ that basically consist of a Kv x-ray unit and a detector. This new technology greatly improves imaging quality making image-guided radiotherapy a possibility. The precision with which this allows tracking and locating of the tumor and cancerous cells greatly improves the quality of treatment and minimizes various side effects associated with radiation therapy.
Who Operates this Equipment?Linear accelerators are most commonly used in radiotherapy for cancer treatment. While the treatment is planned and directed by a radiation oncologist along with a team of specialists, the equipment itself is handled by a medical radiation physicist and radiographers. The oncologist and medical radiation physicist first need to determine the appropriate dosage and method of delivery along with a dosimetrist. They also have to calculate how much time would be required to administer the dose using a linear accelerator. Radiation therapists are the specialists who actually operate linear accelerators for cancer treatment, administering daily radiation treatment to patients.
How is Safety Ensured?Safety is the biggest concern and several steps are taken to cross check diagnostics, results and treatment plans before any treatment is actually administered. Strict quality control procedures are also followed to ensure that the treatment is administered exactly as planned.
The linear accelerator has several inbuilt safety features to ensure the dosage of radiation does not exceed what is prescribed and the machine itself is checked daily to ensure that the machine is functioning optimally. It is tested on a weekly and monthly basis. Modern machines have safety features that will not even allow the machine to turn on if all safety requirements are not met.
Safety of the medical and technical staff is also addressed with the machine being confined to a room with lead and concrete walls shielding against high energy radiation. Technicians do not need to enter the room to turn the machine on or off and there is no radiation when turned off.