Download Linear Accelerator (LINAC)

Linear Accelerator (LINAC)
Our group has taken Medical Technology as our title for our science computer subject’s
assignment. We have decided to research about a medical technology that is called the Linear
Accelerator or LINAC for short. The name “linear accelerator” comes from the fact that
electrons are produced in the machine and accelerated in a straight line.
A LINAC is a device that accelerates electrons through a linear tube to high speed and then
smashes these electrons into a metal target where the high speed electrons are stopped. When
these electrons are being stopped, they will emit a high energy x-rays in the initial direction of
their motion. The energy that came from the resultant x-rays is approximately the energy of the
electrons when they hit the metal target.
The electrons’ final speed will be determined by the electrical potential dropped across the
linear accelerator or LINAC for short. The electrical potential is on the order of 6 000 000 volts
or 6 Megavolts. Therefore, the energy that the x-rays emitted from the LINAC is approximately
6,000,000 volts. The higher the x-ray’s energy, the larger the electrical potentials which can lead
to a longer accelerating cavity. The normal length for a typical 6 Megavolts LINAC is
approximately 6 feet. These high energy x-rays are the one that have been used to irradiate the
patient’s tumor.
The LINAC is able to be pointed at a single point in space because the acceleration cavity is
mounted on a gantry but with the freedom to rotate through a full circle. The LINAC can be used
to treat lesions anywhere in or on the patient’s body.
LINAC is most commonly used for external beam radiation treatments for patients with
cancer. It can also be used in stereotactic radiosurgery similar to that achieved by using the
gamma knife on the targets that are within the brain. Other than that, it can also be used to treat
the areas outside of the brain. The LINAC delivers a uniform dose of high-energy x-ray to the
region of the patient’s tumor where these x-rays will destroy the cancer cells and sparing the
surrounding normal tissues.
The linear accelerator technology or LINAC for short is incredibly important because cancer
tumors and lesions will not stay in the exact same place after the patient undergoes each radiation
therapy session. The patient’s organs can shift even slightly when he or she gains or loses weight
or experiences other physical changes.
But with the LINAC therapy, it allows the doctors to deliver higher doses of radiation to the
tumor and limiting the damages taken to the surrounding healthy tissues and organs. So, it is very
important that before each radiation treatment, the physicians must be able to identify the exact
location of the cancerous cells end and healthy cells begin.
The device also has a number of other uses. The radiation that came from the device can quell
the rejection of an organ transplant. It can also suppress the immune system of a patient who is
undergoing blood and marrow transplantation. It can also correct a certain neurological and
cardiovascular disorders.
LINAC was invented to improve the accuracy of radiotherapy and develop cancer therapy
equipment. LINAC helps in visualizing the change in patients’ anatomy and physiology during
the treatment and this will directly improve the outcomes for cancer patients.
The invention of LINAC which can deliver bursts of highly-focused radiation to kill cancer
cells results in fewer side-effects and shorter treatment compared to another radiosurgery
treatment. This invention is clearly invented to help cancer patients to recover from cancer in a
more effective yet safe way.
In 1956, a young cancer patient is lucky enough that Henry Kaplan, MD, had already came to
Stanford with an unusual goal of his. That is to turn a device used by the physicists, the linear
accelerator into a tool for fighting cancer.
The patient, who is actually a 2 year-old boy who is suffering from a tumor in his eye, was the
first one to undergo x-ray treatment from a medical linear accelerator that Kaplan had developed
with the help of the physicists. The treatment was successful and it saved the child’s sight and he
lived the rest of his life with his vision intact.
It all came to Kaplan when he thought that he could find a way to focus an intense x-rays to
destroy a tumor without harming the surrounding healthy tissues and build a machine that could
be harnessed to deliver x-ray therapy that was superior to the unreliable, weak and unfocused
radiation therapy approaches of his day. He also thought that the physicists would be the ones to
help him to do so.
With the help of Ed Ginzton, PhD, professor of electrical engineering and of physics, Kaplan
developed the first medical linear accelerator in the Western Hemisphere and installed it at
Stanford-Lane Hospital in San Francisco. In January 1956, the machine was ready to be used and
their first patient was a boy with retinoblastoma in his one remaining eye after surgeons had
removed the tumor in the other eye. It would be impossible to destroy the tumor while sparing
the eye with earlier, less-focused radiation sources.
The patient’s radiation oncologist will prescribes the appropriate treatment volume and dosage
as over dosage can be harmful and bring many side effects to the patient. Then, the medical
radiation physicist and the dosimetrist will determine on how to deliver the prescribed dose to
the patient by his or her radiation oncologist and calculate the amount of time that it will take the
accelerator to deliver that dose to the patient. The one who operate the linear accelerator or
LINAC are the radiation therapists and they will give their patients daily radiation treatments.
History of the medical linear accelerator:
1952: Henry Kaplan and Edward Ginzton begin building a medical linear accelerator.
1956: The first medical linear accelerator in the Western Hemisphere is installed at Stanford
Hospital in San Francisco.
1959: Stanford medical school and hospital move to the Palo Alto campus, bringing the medical
linear accelerator.
1962: Kaplan and Saul Rosenberg begin trials using the linear accelerator with chemotherapy to
treat Hodgkin's disease, an approach that dramatically improves patient survival.
1994: First use of the CyberKnife, invented at Stanford, which uses sophisticated computerized
imaging to aim a narrow X-ray beam precisely.
1997: Stanford pioneers the use of intensity-modulated radiation therapy, which combines
precise imaging with linear accelerators that deliver hundreds of thin beams of radiation from
any angle.
2004: Implementation of four-dimensional radiotherapy, which accounts for the motion of
breathing during imaging and radiation delivery.
2006: 50th anniversary of the Stanford medical linear accelerator.
The tissues, organs and many tumors in the human body are not rigidly fixed in one position,
they move around inside the body due to natural physiological processes. For this exact reason,
they are not always in the exact same position during each time a patient is positioned for
treatment. Other than that, tumors move several centimeters due to a patient’s normal respiratory
cycle.
The medical linear accelerator or treatment machine, Dynamic Targeting IGRT, is outfitted
with a number of sophisticated imaging devices that that provide images that could help the
clinician to guide the treatment.
An x-ray system are mounted on a robotic arm is rotated around the body to gather the images
that can pinpoint a tumor’s exact location just prior to treatment. Then, the images will be
compared to reference images such as the MRI, CT or other kinds of scans in order to determine
if the tumor is where it is expected to be, or off by some margin. After that, sophisticated
software programs will be used to calculate on how to move the patient so that the tumor will be
directly in the center of the treatment beam.
Another accessory can be used to coordinate treatment with respiration. The accessory is called
“respiratory gating”. It is to compensate for the tumor motion due to the patient’s breathing. This
is very useful for treating lung cancer and other tumors in the chest or abdomen that moves as the
patient breathes.
The patient’s safety is very important and is assured in several ways. The treatment plan must
be developed and approved by the radiation oncologist in collaboration with the radiation
dosimetrist and physicist before the treatment is delivered to the patient. The plan must be
double-checked before the treatment is given and quality-control procedures ensure that the
treatment is delivered the same way as it was planned.
Other than that, the quality control of the linear accelerator is also a very important aspect. The
linear accelerator is built with several systems to ensure that it will not deliver a higher dose than
the radiation oncologist has prescribed. The radiation therapist will perform checks on the
machine each morning before any patients are treated by using an equipment called a tracker to
make sure that the radiation intensity is uniform across the beam and that it is working properly.
Besides that, the radiation physicist will conduct more detailed weekly and monthly checks on
the machine.
But, the modern linear accelerator nowadays has an internal checking systems to provide
further safety. It is to ensure that the machine will not turn on until all the treatment requirements
that are prescribed by your physician are perfectly fulfilled. The machine will turn on to provide
your treatment when all the checks are match and perfect.
The radiation therapist will continuously watches the patient through a closed-circuit television
monitor during the whole the treatment. The patient can also speak to the therapist if needed
because there is also a microphone in the treatment room. The x-rays taken with the treatment
beam which is called port films or other imaging tools are checked regularly to ensure that the
beam position does not vary from the original plan.
The safety of the staffs who is operating the linear accelerator is also very important. To shield
the high-energy x-rays, the linear accelerator sits in a room with lead and concrete walls because
the high-energy x-rays may also affect the staffs who is operating the machine. The linear
accelerator must be turn on from outside the treatment room by the radiation therapist. The risk
of accidental exposure is extremely low because the accelerator only gives off radiation when it
is actually turned on. The treatment room is shielded to such an extent that even a pregnant
woman could safely operate the linear accelerators.
Bibliography
https://www.wmhs.com. Linear Accelerator, 2015.
http://www.indiacarez.com. The Most Advanced Linear Accelerator Therapy in India, 2015.
http://www.abta.org. LINAC, 2014.
Mitzi Baker, (April 18, 2007). Medical Linear Accelerator Celebrates 50 Years of Treating
Cancer. Stanford News (Online). http://news.stanford.edu
http://sydney.edu.au. MRI-LINAC PROGRAM, 2015.
http://www.myradiotherapy.com. Radiotherapy Treatment Machine, March, 2015.
http://www.cancer.gov. Radiation Therapy for Cancer, June 30, 2010.