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Research in radiation therapy

Radiation therapy uses high-energy rays or particles to destroy cancer cells. Radiation therapy may be directed as beams from the outside of the body (called external radiation therapy) or may be injected, swallowed or inserted into the body (called internal radiation therapy or brachytherapy).

Researchers are always looking for ways to improve radiation therapy treatment and reduce side effects. There are many clinical trials looking at different ways to use radiation therapy and new ways to give radiation therapy.

Ways to make radiation therapy more accurate

To make external radiation therapy more accurate means to better target a tumour so that less radiation hits healthy tissue. Some methods used to better target tumours are intensity-modulated radiation therapy (IMRT), image-guided radiation therapy (IGRT), volumetric-modulated arc therapy (VMAT), stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT). Many clinical trials are looking at the best ways to use these newer forms of radiation therapy and how to combine these with other treatments.

IMRT shapes the radiation beams to give different doses to different parts of the treatment area. Doctors can deliver a higher dose of radiation to the tumour and a lower dose to nearby normal tissues. IMRT can be used to treat tumours that are hard to reach, such as the spine, head, neck, prostate, lung and brain. It is also being studied in clinical trials for treating other cancer types, such as breast, pancreatic, esophageal, uterine and liver. For example, people had fewer side effects in clinical trials that gave partial radiation therapy using IMRT instead of whole breast radiation therapy.

IGRT uses imaging to make the radiation therapy more accurate. Repeated CT, MRI or PET scans are done before and during treatment, and computers process the images to show changes in the size of a tumour and the location compared to the last treatment. This allows the treatment team to adjust your position on the table or to change the radiation dose to be more accurate. IGRT can lessen the amount of tissue treated and the total dose of radiation received by normal tissue. IGRT may be used to treat tumours in parts of the body that are likely to move or tumours that are very close to vital structures or tissues. IGRT is being studied in clinical trials to treat lung, prostate and brain cancers and soft tissue sarcomas of the prostate and the lung.

VMAT is an advanced form of IMRT that gives a dose of radiation to the entire tumour in a 360-degree rotation. This shortens the treatment time. It is being studied in clinical trials to treat cancers such as prostate, lung, spine and breast.

SRS delivers high doses of radiation in a single session using Gamma Knife, CyberKnife and linear accelerators with specific modifications. It creates many small, thin beams of radiation from different angles that meet at the tumour to give the highest dose to the tumour and reduce the dose of radiation to healthy tissue around the tumour. It is used most commonly to treat brain and spinal cord tumours and brain metastases.

SBRT delivers high doses of radiation to tumours in fewer sessions. It is also called stereotactic ablative radiation therapy (SABR). The majority of SBRT treatments are delivered by linear accelerators but also can be done with a CyberKnife unit. SBRT is delivered with many beams of radiation from different angles that meet at the tumour. The tumour itself receives a high dose of radiation, while the individual beams that travel through surrounding tissue receive a low dose. This lowers the effects of radiation on healthy tissue surrounding the tumour. SBRT is given in fewer treatments than standard external radiation therapy. It can be used to treat tumours in the pancreas, lung and liver. Clinical trials are looking at using SBRT to treat other cancers, such as prostate, breast, kidney and cervical.

Schedule and dose of radiation therapy treatments

Clinical trials are looking at how changes in the schedule and dose of radiation therapy can make treatment work better and lessen side effects. Radiation treatments are usually given for about 5 to 8 weeks on Monday to Friday with no weekend treatments. New schedules for radiation treatments are being studied to treat cancer and lessen long-term side effects. With some new schedules, radiation is given twice a day. With others, it is given over fewer days. Some schedules include changes in the dose per treatment. Some of these newer schedules have already proven to be effective.

Researchers are studying the following schedules.

Accelerated fractionation means giving the total dose of radiation over a shorter period of time by giving radiation more than once a day. Radiation treatments can be completed more quickly (for example, in 5 weeks instead of 7). Accelerated fractionation does not change the total radiation dose. Accelerated radiation therapy is being studied in several cancers, such as breast, head and neck, and lung.

Hyperfractionation means giving the daily dose of radiation in 2 or more sessions each day. The total period of time to complete the treatment schedule does not change. By using more doses of radiation that are smaller, a higher overall dose can be given. This may cause more damage to a cancer cell. The treatments are usually given about 4 to 6 hours apart to allow normal tissues to heal. Hyperfractionated radiation therapy is being studied to treat several cancers, including head and neck, and lung.

Hypofractionation means giving fewer radiation treatments. This is done by either giving a small number of daily treatments or a few large doses or a single large dose. Hypofractionated radiation therapy is being studied to treat several cancers, including prostate and metastasis to the spine and is often used for older people with brain tumours.

Using different types of radiation

Clinical trials are looking at different types of radiation particles for radiation therapy. Proton therapy is one type of particle therapy that can be used to treat cancer.

Proton therapy uses protons (a positively charged particle) to treat cancer. It may also be called proton beam therapy. Proton therapy uses proton beams instead of x-ray beams. Protons release more energy after reaching a certain distance, while x-ray beams release energy before and after they hit their target. So protons cause less damage to tissues they pass through before reaching their target. Proton therapy causes the least amount of damage to nearby normal tissues. Proton therapy is not available in Canada. It is a complex procedure and the equipment is expensive. Proton therapy is being studied in clinical trials to treat cancers that are located in or near tissues that are very sensitive to radiation therapy, such as cancers in the lung, brain and left breast (over the heart). Proton therapy may have fewer side effects than standard external radiation therapy.

Combining radiation therapy with other treatments

Chemoradiation is when chemotherapy and radiation therapy are used together. Chemoradiation is used to treat many cancers. Giving chemotherapy at the same time as radiation therapy improves the effects of radiation on cancer cells. Chemoradiation is being studied in clinical trials to see if it may be better than the standard treatments for certain cancers, such as brain cancer and Hodgkin lymphoma.

Radioimmunotherapy(RIT) combines radiation therapy with monoclonal antibodies, a type of immunotherapy. Monoclonal antibodies specifically target cancer cells. When a RIT is injected into the body, the monoclonal antibody delivers the radioactive substance to the tumour. RIT can be used to treat certain cancers, in particular certain types of non-Hodgkin lymphoma. Some clinical trials are looking at radioimmunotherapy to treat other cancers. A few clinical studies are looking at using chemotherapy, radiation and immunotherapy (called chemoradioimmunotherapy) to treat pancreatic cancer.

Radioembolization combines radiation therapy with embolization. It is also called selective internal radiation therapy. It gives radiation directly to tumours using tiny radioactive beads (called microspheres). Using a catheter, these beads are placed inside the blood vessels that feed a tumour, delivering a high dose of radiation to the tumour and also blocking the supply of blood to the cancer cells. Radioembolization is a treatment used to treat metastasis to the liver. Researchers are studying radioembolization as a treatment option for primary liver cancer.

Intraoperative radiation therapy (IORT) gives radiation therapy during surgery. After the surgeon removes as much of the tumour as possible, radiation is given directly to the area where the tumour used to be (called the tumour bed). The surgeon moves normal tissues out of the way to protect them from radiation. Doctors can deliver higher doses of radiation to the cancer. Researchers are studying IORT in colon cancer, rectal cancer and in early stage breast cancer. The big advantage of IORT is that treatment takes much less time than standard external radiation therapy. Having standard radiation therapy and going to the hospital every day for 6 weeks can be tiring, especially if you live far from the treatment center. IORT may also result in better appearance of breast tissue after radiation than external radiation therapy.

Combining radiation therapy with hormone therapy is also being studied in clinical trials for treating cancers like prostate.

Increasing oxygen levels to help radiation work better

A low oxygen level (called hypoxia) in cancer cells is one of the factors that can make a tumour resistant to radiation treatment. Oxygen makes cells 2 to 3 times more sensitive to radiation therapy. Giving radiation therapy over several weeks (called fractionation) allows oxygen levels to rise in cancer cells in between treatments. This helps radiation therapy work better.

Researchers are studying other ways to increase oxygen levels in cells before radiation therapy is given. Research with oxygen includes the following:

Radiosensitizers are drugs that make cancer cells more sensitive to the effects of radiation. Radiation therapy is a common treatment for head and neck cancer. Many cancer cells have lower levels of oxygen in them than normal cells, and this makes it harder to treat them with radiation. Nimorazole is one radiosensitizer that is being studied in clinical trials for head and neck cancer.

Vascular targeting agents are targeted therapy drugs that act on tumour blood vessel growth (angiogenesis). These drugs may be used to improve radiation. Some drugs given before radiation might improve blood vessel function, so oxygen levels increase and make cancer cells more sensitive to radiation. Some drugs can also disrupt tumour blood vessel function, which deprives a tumour of oxygen. These drugs might work best when given after radiation is completed. Early studies are looking at sorafenib (Nexavar) with radiation therapy to make radiation therapy work better.

monoclonal antibody

A substance that can find and bind to a particular target molecule (antigen) on a cancer cell.

Monoclonal antibodies can interfere with a cell’s function or can be used to carry drugs, toxins or radioactive material directly to a tumour.

embolization

A procedure that blocks or slows down the blood supply to tissues or an organ.

Embolization can be used to block the flow of blood to a tumour so the cancer cells die.

catheter

A flexible tube used to carry fluids into or out of the body.

For example, an intravenous catheter delivers fluid into the body through a vein and a urinary catheter carries urine from the bladder out of the body.

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