Linear Accelerator (LINAC)

A linear accelerator (LINAC) is the device most commonly used for external beam radiation treatments for cancer patients. The linear accelerator can also be used in stereotactic radiosurgery similar to that achieved using the gamma knife on targets within the brain. The linear accelerator can also be used to treat areas outside of the brain. It delivers a uniform dose of high-energy x-ray to the region of the patient's tumor. These x-rays can destroy the cancer cells while sparing the surrounding normal tissue. A linear accelerator is also used for Intensity-Modulated Radiation Therapy (IMRT).

The linear accelerator uses microwave technology (similar to that used for radar) to accelerate electrons in a part of the accelerator called the "wave guide" allowing these electrons to collide with a heavy metal target. As a result of the collisions, high-energy x-rays are scattered from the target. A portion of these x-rays is collected and then shaped to form a beam that matches the patient's tumor. The beam comes out of a part of the accelerator called a gantry, which rotates around the patient. The patient lies on a moveable treatment couch and lasers are used to make sure the patient is in the proper position. Radiation can be delivered to the tumor from any angle by rotating the gantry and moving the treatment couch.

Indications

• Primary brain tumors
• Metastatic brain tumors
• Head and neck tumors
• Spine, prostate and lung tumors
• Adjacent tissues which can be damaged by radiation

LINAC or Linear accelerator machines produce radiation that is referred to as high-energy x-ray. A linear accelerator machine is designed to be a general purpose radiation delivery machine and requires modifications to enable it to be used for radiosurgery or IMRT. Often the modification is the addition of another piece of machinery. LINAC technology is most often used in multi-session treatments in order to avoid damaging healthy surrounding tissue with too high a dose of radiation.

Benefits

1. most commonly used for external beam radiation treatments for patients with cancer
2. any lesion size
3. targeted radiation beam
4. reduces damage to adjacent tissue
5. less time, more radiation and computer-controlled
6. no hospitalization

The best usage of LINAC technology may be its ability to target larger brain and body cancers with less damage to healthy tissues. Known as the CyberKnife Stereotactic Radiosurgery/ Radiotherapy System, is a robotic-controlled linear accelerator that delivers pinpoint radiation to reduce or eliminate benign and metastatic tumors and arterio-venous malformations throughout the body. The CyberKnife is a dedicated technology with a small robotic industrial LINAC attached. It targets utilizing "image guided" technology similar to missile technology. Generally, three to five sessions are given.

Before radiation

1. physical examination and laboratory tests
2. appropriate clothing
3. nutritional support, 6-8 glasses of water, no alcohol, no tobacco
4. oral and dental hygiene
5. concomitant drug use
6. travel and accommodation

During and after radiation

1. care for markings
2. avoid topical cream or medications
3. bathing as usual, less scrub on affected skin
4. no hot bag, cold bag
5. appropriate clothing, not too tight
6. no powder on affected skin
7. avoid skin shaving

The patient's radiation oncologist prescribes the appropriate treatment volume and dosage. The medical radiation physicist and the dosimetrist determine how to deliver the prescribed dose and calculate the amount of time it will take the accelerator to deliver that dose. Radiation therapists operate the linear accelerator and give patients their daily radiation treatments.

Risks and side effects

1. skin changes
2. fatique
3. bone marrow suppression
4. mucositis, diarrhea
5. dry mouth
6. gastrointestinal irritation
7. brain irritation
8. reproductive organ , erectile dysfunction, vaginal stenosis