Research in radiation therapy
Researchers are studying and using several new approaches to find out how effective radiation therapy is in treating different cancers. Researchers are also looking at improving how radiation is delivered so that it controls the tumour while preventing or lessening damage to normal cells.
Researchers are trying to make radiation therapy more accurate so that it targets a tumour and spares the healthy tissue around it. They are looking at how to improve external beam radiation therapy techniques such as conformal radiation therapy and intensity-modulated radiation therapy (IMRT).
Find out more about conformal radiation therapy, including IMRT.
Image-guided radiotherapy (IGRT) is another way researchers are trying to improve the accuracy of radiation treatment. It involves imaging a tumour and surrounding normal tissue prior to daily treatment. This helps ensure that the radiation therapy is given very accurately to the tumour and causes less damage to surrounding normal tissue.
Radiation treatments are usually given daily over a number of weeks. Fractionation means spreading the total dose of radiation over a number of days and weeks. New schedules for radiation treatments are now being used to treat cancer and hopefully 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 fractionation schedules.
Radiation treatment may be accelerated, or given over less time. This allows radiation treatments to be completed more quickly (for example, in 5 weeks instead of 7). The number of fractions, total dose and size of each dose per fraction can vary, depending on the overall length of treatment.
Hyperfractionation radiation divides the total dose of radiation into smaller doses that are given more frequently. Radiation treatments may be given 2 or more times a day (instead of once a day). This allows many smaller doses of radiation to be given for a higher overall dose, which may cause more damage to a cancer cell. The treatments are usually given about 4–6 hours apart to allow normal tissues to heal.
With hypofractionated radiation therapy, fewer radiation treatments are given. This is done by giving either a short course of daily treatments or it may be done by giving fewer large doses or sometimes just a single treatment.
Stereotactic radiation therapy delivers an accurate, high dose of radiation to a tumour area. It requires a person to be in a very precise position and stay very still. In tumours that move (such as lung tumours moving with each breathing cycle) stereotactic treatment is a way to accurately monitor the movement of the tumour. Stereotactic treatment first became popular in the treatment of brain metastases as well as benign brain tumours and conditions. This technique is now being used to treat other types of tumours including lung, liver, spine and prostate. A specialized linear accelerator or the Gamma Knife is used to deliver stereotactic radiation treatments.
Find out more about stereotactic radiation therapy.
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. IORT allows doctors to deliver higher doses of radiation to the cancer than conventional radiation therapy.
Researchers are studying IORT in breast, abdominal and pelvic cancers. They are also trying to find out if it will be effective for cancers that tend to come back, or recur, after treatment.
Proton beam radiation therapy is also called charged particle radiation therapy. It is a form of external beam radiation therapy that uses high-energy (charged) proton particles instead of x-ray beams. Protons deliver a higher dose of radiation but cause less damage to nearby tissues than conventional external beam radiation therapy because they can be aimed more precisely at the tumour.
Proton beam radiation therapy is not widely available in Canada. It is a complex procedure and the equipment needed is expensive. As a result, it is currently used to treat very specialized cases or in research studies.
Researchers are also studying other atomic particles in addition to protons to deliver radiation therapy. These include neutrons and ions such as the carbon ion.
Radiosensitizers are substances that make cancer cells more sensitive to radiation, so more cancer cells die with the same dose of radiation. Researchers are studying heat (hyperthermia) for its effectiveness as a radiosensitizer because it seems to make it harder for cancer cells to recover from radiation. Heat can be created by microwaves or ultrasound. Researchers are studying the effects of heat in combination with radiation for some cancers. Researchers are also studying chemotherapy and biological therapy drugs to see if they help radiation therapy work better. Find out more about biological therapy.
Radioprotectors are substances that may help protect normal tissues from the damaging effects of radiation. For example, amifostine (Ethyol) may help decrease dry mouth (xerostomia) when radiation therapy is given to treat head and neck cancers. Researchers are studying other drugs to see if they are effective radioprotectors.
Monoclonal antibodies can recognize abnormal proteins found on the outside of cancer cells. These antibodies can carry radioactive substances that deliver doses of radiation directly to cancerous tumours. This approach can deliver a high dose of radiation to the tumour and may help lessen radiation damage to surrounding healthy cells.
Some radiolabelled monoclonal antibodies have been approved for use. Others are currently only used to treat cancer in clinical trials in Canada.
Embolization is a procedure that blocks off a blood vessel to reduce blood flow. Radioembolization (also called selective internal radiation therapy) is a type of internal radiation therapy used to treat cancer in the liver. It delivers radioactive substances directly into the hepatic artery. This technique delivers radiation more effectively and blocks off the supply of blood to a liver tumour.
Researchers are studying radioembolization as a treatment option for primary liver cancer and cancer that spreads to the liver from another primary site. It is intended to be used as a type of palliative therapy that slows down the growth of a liver tumour and relieves symptoms.
Researchers are looking at ways of delivering radioactive substances with radioembolization, including the following.
Microspheres (such as TheraSpheres or SIR-Spheres) are tiny glass or resin beads that contain a radioactive isotope like yttrium-90.The microspheres are injected into the hepatic artery. They become stuck in the small blood vessels of the tumour and deliver a high dose of radiation to the tissue. Radiation is delivered over 2 weeks and gradually decreases until the microspheres are no longer radioactive. The tiny microspheres can stay in the liver and don’t need to be removed.
Lipiodol is a type of poppy seed oil that contains a radioactive isotope of iodine. Lipiodol builds up in the tumour and delivers radiation to the tissue.
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 2–3 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. Some research with oxygen includes the following.
Nicotinamide and carbogen
Nicotinamide is a type of vitamin B that can help increase blood flow to a tumour. Carbogen is a gas made up of a high concentration of oxygen. Doctors are trying to find out if giving a combination of nicotinamide and carbogen can increase oxygen levels in cancer cells and make them more sensitive to radiation.
Metformin is a drug used to treat diabetes but is also showing promise in radiosensitizing tumours to radiation. Metformin may increase oxygen levels in cancer cells by impairing a tumour’s metabolism. Clinical trials are underway to find out if it can help improve a tumour’s response to radiation.
Vascular targeting agents
Researchers are studying how biological therapy drugs that act on tumour blood vessel growth (angiogenesis), 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.
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.