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Radiation Therapy

What is Radiation Therapy?

Radiation therapy uses high doses of radiation (a stream of high-energy particles or waves, such as x-rays, gamma rays, or electrons) to kill cancer cells by preventing them from reproducing. Other names for radiation therapy include radiotherapy or x-ray therapy. The radiation is delivered in a way that allows high doses to reach the tumour whilst avoiding surrounding healthy tissue, which limits unnecessary damage. Several different techniques can be used to deliver the treatment, depending on the type, size and location of the targeted tumour. Radiation therapy may be used alone or in combination with other treatments (such as chemotherapy or surgery), and can be delivered before, during or after these. The radiation therapy team chooses which technique or combination of techniques to use and when they will be delivered in order to give the most effective treatment for each individual patient. Most radiation therapy treatments are given in small doses every day over several weeks, in order to minimize side effects.

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How does it work?

Normal tissue in the body is comprised of cells that grow and divide. This process is controlled by DNA strands within each cell, which contain the 'code' or instructions that determine that cell's activity. Cancer cells grow and divide more rapidly than normal cells, as a result of changes in their DNA. Radiation breaks the DNA strands in cells, which prevents them from growing and dividing. Cells that are dividing most rapidly (such as cancer cells) are the most sensitive to radiation.

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Goals of Radiation Therapy

Curative Radiation Therapy:

Radiation may be used alone for very early stage cancers, or cancers known to be particularly sensitive to radiation, to make the cancer shrink or disappear completely. For other cancers, it may be used before surgery to shrink the tumor (pre-operative therapy) or after surgery to prevent the cancer from coming back (adjuvant therapy). It may also be used along with chemotherapy in some situations.

Preventative Radiation Therapy:

If a type of cancer is known to spread commonly to a particular area, doctors often assume that a few cancer cells may have already spread there, even though imaging scans (CT or MRI scans) show no tumors. That area may be treated to keep these cells from growing into tumors. For example, people with some types of lung cancer may receive preventive radiation to the head because this type of cancer often spreads to the brain.

Palliative Radiation Therapy:

Some cancers may spread too far to be considered curable. But this does not mean they can't be treated. Radiation may help to relieve symptoms such as pain, trouble swallowing or breathing, or bowel problems that can be caused by advanced cancer. This is often referred to as palliative radiation.

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Radiation Therapy Techniques

The three main radiation therapy techniques are: external beam radiation therapy; stereotactic radiosurgery and brachytherapy. For more information on each of these, follow the links in the menu.

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External Beam Radiation Therapy

This is the most frequently used type of radiation therapy, and involves focusing a beam of radiation from outside the body through the skin to the targeted tumour, similar to the way an x-ray picture is taken. The machine that delivers the radiation is called a linear accelerator, nick-named "linac". These machines do not touch the skin or the tumour itself, and are very quiet. Linear accelerators can deliver radiation to any size area, from a tiny tumour up to a whole body if necessary. Each patient's treatment is individually planned using sophisticated planning software, CT and MRI scans, so that the size, shape and direction of the beam matches the needs of the patient. Using these plans, every treatment session starts with the treatment team positioning the patient and setting up the machine so that every treatment fraction is delivered identically.

External beam radiation therapy is a painless, bloodless procedure. Patients who undergo this treatment do not become radioactive and do not need to take special precautions to protect others from radiation.

There are several subtypes of external beam radiation therapy. Currently, Perth Radiation Oncology utilizes conventional two-dimensional radiation therapy as well as the newer three-dimensional conformal radiation therapy (3D-CRT). Within the next twelve months, we will also utilize Intensity Modulated Radiation Therapy (IMRT) as well as Image-Guided Radiation Therapy (IGRT).

Three-Dimensional Conformal Radiation Therapy (3D-CRT)

Tumours usually have an irregular shape. Three-dimensional conformal radiation therapy (3D-CRT) uses sophisticated computers and CT and/or MRI scans to create detailed, three-dimensional representations of the tumour and surrounding organs. Your radiation oncologist can then shape the radiation beams exactly to the size and shape of your tumor. The tools used to shape the radiation beams are multileaf collimators or blocks. Because the radiation beams are very precisely directed, nearby normal tissue receives less radiation exposure.

Intensity Modulated Radiation Therapy (IMRT)

Intensity modulated radiation therapy (IMRT) is a specialized form of 3D-CRT that allows radiation to be more exactly shaped to fit your tumor. With IMRT, the radiation beam can be broken up into many "beamlets," and the intensity of each beamlet can be adjusted individually. Using IMRT, it may be possible to further limit the exact amount of radiation that is received by normal tissues that are near the tumor. In some situations, this may also allow a higher dose of radiation to be delivered to the tumor, increasing the chance of a cure.

Image-Guided Radiation Therapy (IGRT)

Normal structures such as organs as well as tumours can move between treatments due to differences in organ filling (such as stomach or bladder fullness) or movements while breathing. IGRT is conformal radiation treatment guided by imaging equipment (CT and X-ray), taken in the treatment room just before the patient is given the radiation treatment. All patients first undergo a CT scan as part of the planning process. The digital information from the CT scan is then transmitted to console in the treatment room to allow doctors to compare the earlier image with the images taken just before treatment. During IGRT, doctors "fuse" these images to see if the treatment needs to be changed. This allows doctors to better target the cancer while avoiding nearby healthy tissue. In some cases, doctors will implant a tiny piece of material called a fiducial marker near or in the tumor to help them localize the tumor during IGRT.

Stereotactic Radiotherapy

Stereotactic radiotherapy is a technique that allows your radiation oncologist to precisely focus beams of radiation to destroy certain types of tumors. Since the beam is so precise, your radiation oncologist may be able to spare more normal tissue than with conventional external beam therapy. This additional precision is achieved through rigid immobilization, such as with a head frame as is used in the treatment of brain tumors. Although often performed in a single treatment, fractionated radiotherapy, where patients receive up to five treatments, is sometimes necessary. Stereotactic radiotherapy may be the only treatment if a very small area is affected. In addition to treating tumors, it can also be used to treat malformations in the brain's blood vessels and certain noncancerous (benign) brain tumors.

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Brachytherapy

Brachytherapy is also known as internal radiation therapy. This method of treatment involves placing small radioactive implants directly into a tumour or a nearby cavity. The advantage of this is that it is possible to deliver a high dose of radiation to a small area - useful in situations that require a dose of radiation that would be more than the surrounding normal tissues could tolerate if delivered externally.

The two forms of brachytherapy are:

• interstitial radiation: the radiation source is placed directly into or next to the tumor using small pellets, wires, tubes, or containers.
• intracavitary radiation: a container of radioactive material is placed in a cavity of the body such as the vagina.

Imaging tests such as X-rays, ultrasound, or CT scans are used to assist the doctor in putting radioactive source in the correct place. The placement can be permanent or temporary.

Permanent (low dose rate) brachytherapy

Involves using small containers, called pellets or seeds, which are about the size of a grain of rice. They are placed directly into tumors using thin, hollow needles. Once in place, the pellets give off radiation for several weeks or months. Because they are so small and cause little discomfort, they are simply left in place after their radioactive material is used up.

Temporary (high dose rate) brachytherapy

Involves temporarily placing hollow needles, tubes, or fluid-filled balloons into the area to be treated. Radioactive material can then be inserted for a short period of time and then removed. This process may be repeated over the course of a few days or weeks.

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