Radiation therapy

Definition

Radiation therapy, sometimes called radiotherapy, x-ray therapy radiation treatment, cobalt therapy, electron beam therapy, or irradiation uses high energy, penetrating waves or particles such as x rays, gamma rays, proton rays, or neutron rays to destroy cancer cells or keep them from reproducing.

Description

Radiation therapy is a local treatment. It is painless. The radiation acts only on the part of the body that is exposed to the radiation. This is very different from chemotherapy in which drugs circulate throughout the whole body. There are two main types of radiation therapy. In external radiation therapy a beam of radiation is directed from outside the body at the cancer. In internal radiation therapy, called brachytherapy or implant therapy, where a source of radioactivity is surgically placed inside the body near the cancer.

The protein that carries the code controlling most activities in the cell is called deoxyribonucleic acid or DNA. When a cell divides, its DNA must also double and divide. High-energy radiation kills cells by damaging their DNA, thus blocking their ability to grow and increase in number.

One of the characteristics of cancer cells is that they grow and divide faster than normal cells. This makes them particularly vulnerable to radiation. Radiation also damages normal cells, but because normal cells are growing more slowly, they are better able to repair radiation damage than are cancer cells. In order to give normal cells time to heal and reduce side effects, radiation treatments are often given in small doses over a six or seven week period.

External radiation therapy is the most common kind of radiation therapy. It is usually done during outpatient visits to a hospital clinic and is usually covered by insurance.

Once a doctor, called a radiation oncologist, determines the proper dose of radiation for a particular cancer, the dose is divided into smaller doses called fractions. One fraction is usually given each day, five days a week for six to seven weeks. However, each radiation plan is individualized depending on the type and location of the cancer and what other treatments are also being used. The actual administration of the therapy usually takes about half an hour daily, although radiation is administered for only from one to five minutes at each session. It is important to attend every scheduled treatment to get the most benefit from radiation therapy.

Recently, trials have begun to determine if there are ways to deliver radiation fractions so that they kill more cancer cells or have fewer side effects. Some trials use smaller doses given more often. Up-to-date information on voluntary participation in clinical trials and where they are being held is available by entering the search term "radiation therapy" at the following web sites:

• National Cancer Institute. <http://cancertrials.nci.nih.gov> or (800) 4-CANCER.
• National Institutes of Health Clinical Trials. <http://clinicaltrials.gov>.
• Center Watch: A Clinical Trials Listing. <http://www.centerwatch.com>.

The type of machines used to administer external radiation therapy and the material that provides the radiation vary depending on the type and location of the cancer. Generally, the patient puts on a hospital gown and lies down or sits in a special chair. Parts of the body not receiving radiation are covered with special shields that block the rays. A technician then directs a beam of radiation to a pre-determined spot on the body where the cancer is located. The patient must stay still during the administration of the radiation so that no other parts of the body are affected. As an extra precaution in some treatments, special molds are made to make sure the body is in the same position for each treatment. However, the treatment itself is painless, like having a bone x-rayed.

Internal radiation therapy is called brachytherapy, implant therapy, interstitial radiation, or intracavitary radiation. With internal radiation therapy, a bit of radioactive material is sealed in an implant (sometimes called a seed or capsule). The implant is then placed very close to the cancer. The advantage of internal radiation therapy is that it concentrates the radiation near the cancer and lessens the chance of damage to normal cells. Many different types of radioactive materials can be used in the implant, including cesium, iridium, iodine, phosphorus, and palladium.

How the implant is put near the cancer depends on the size and location of the cancer. Internal radiation therapy is used for some cancers of the head, neck, thyroid, breast, female reproductive system, and prostate. Most people will have the radioactive capsule implanted by a surgeon while under either general or local anesthesia at a hospital or surgical clinic.

Patients receiving internal radiation therapy do become temporarily radioactive. They must remain in the hospital during the time that the implant stays in place. The length of time is determined by the type of cancer and the dose of radioactivity to be delivered. During the time the implant is in place, the patient will have to stay in bed and remain reasonably still.

While the implant is in place, the patient's contact with other people will be limited. Healthcare workers will make their visits as brief as possible to avoid exposure to radiation, and visitors, especially children and pregnant women, will be limited.

The implant usually can be removed in a simple procedure without an anesthetic. As soon as the implant is out of the body, the patient is no longer radioactive, and restrictions on being with other people are lifted. Generally people can return to a level of activity that feels comfortable to them as soon as the implant is removed. Occasionally the site of the implant is sore for some time afterwards. This discomfort may limit specific activities.

In some cases, an implant is left permanently inside the body. People who have permanent implants need to stay in the hospital and away from other people for the first few days. Gradually the radioactivity of the implant decreases, and it is safe to be around other people.

Radioimmunotherapy is a promising way to treat cancer that has spread (metastasized) to multiple locations throughout the body. Antibodies are immune system proteins that specifically recognize and bind to only one type of cell. They can be designed to bind only with a certain type of cancer cell. To carry out radioimmunotherapy, antibodies with the ability to bind specifically to a patient's cancer cells are attached to radioactive material and injected into the patient's bloodstream. When these man-made antibodies find a cancer cell, they bind to it. Then the radiation kills the cancer cell. This process is still experimental, but because it can be used to selectively attack only cancer cells, it holds promise for eliminating cancers that have spread beyond the primary tumor.

PHOTON RADIATION. Early radiation therapy used x rays like those used to take pictures of bones, or gamma rays. X rays and gamma rays are high energy rays composed of massless particles of energy (like light) called photons. The distinction between the two is that gamma rays originate from the decay of radioacive substances (like radium and cobalt-60), while x rays are generated by devices that excite electrons (such as cathode ray tubes and linear accelerators). These high energy rays act on cells by disrupting the electrons of atoms within the molecules inside cells, disrupting cell functions, and most importantly stop their ability to divide and make new cells.

PARTICLE RADIATION. Particle radiation is radiation delivered by particles that have mass. Proton therapy has been used since the early 1990s. Proton rays consist of protons, a type of positively charged atomic particle, rather than photons, which have neither mass nor charge. Like x rays and gamma rays, proton rays disrupt cellular activity. The advantage of using proton rays is that they can be shaped to conform to the irregular shape of the tumor more precisely than x rays and gamma rays. They allow delivery of higher radiation doses to tumors without increasing damage to the surrounding tissue.

Neutron therapy is another type of particle radiation. Neutron rays are very high-energy rays. They are composed of neutrons, which are particles with mass but no charge. The type of damage they cause to cells is much less likely to be repaired than that caused by x rays, gamma rays, or proton rays.

Neutron therapy can treat larger tumors than conventional radiation therapy. Conventional radiation therapy depends on the presence of oxygen to work. The center of large tumors lack sufficient oxygen to be susceptible to damage from conventional radiation. Neutron radiation works in the absence of oxygen, making it especially effective for the treatment of inoperable salivary gland tumors, bone cancers, and some kinds of advanced cancers of the pancreas, bladder, lung, prostate, and uterus.

— Lorraine Lica

(medicine) The use of ionizing radiation or radioactive substances to treat disease. Also known as actinotherapy; radiotherapy.

For more information on radiation therapy, visit Britannica.com.

Key Terms: Anemia, Antibody, Chemotherapy, Computed tomography (CT or CAT) scan, Fractionation, Gamma rays, Hodgkin's disease, Magnetic resonance imaging.

Definition

Radiation therapy, sometimes called radiotherapy, x-ray therapy radiation treatment, cobalt therapy, electron beam therapy, or irradiation uses high energy, penetrating waves or particles such as x rays, gamma rays, proton rays, or neutron rays to destroy cancer cells or keep them from reproducing.

Purpose

The purpose of radiation therapy is to kill or damage cancer cells. Radiation therapy is a common form of cancer therapy. It is used in more than half of all cancer cases. Radiation therapy can be used:

• alone to kill cancer
• before surgery to shrink a tumor and make it easier to remove
• during surgery to kill cancer cells that may remain in surrounding tissue after the surgery (called intraoperative radiation)
• after surgery to kill cancer cells remaining in the body
• to shrink an inoperable tumor in order to reduce pain and improve quality of life
• in combination with chemotherapy

For some kinds of cancers such as early-stage Hodgkin's disease, non-Hodgkin's lymphomas, and certain types of prostate or brain cancer, radiation therapy alone may cure the disease. In other cases, radiation therapy used in conjunction with surgery, chemotherapy, or both, increases survival rates over any of these therapies used alone.

Precautions

Radiation therapy does not make the person having the treatments radioactive. In almost all cases, the benefits of this therapy outweigh the risks. However radiation therapy can have has serious consequences, so anyone contemplating it should be sure to understand why the treatment team believes it is the best possible treatment option for their cancer. Radiation therapy is often not appropriate for pregnant women, because the radiation can damage the cells of the developing baby. Women who think they might be pregnant should discuss this with their doctor.

Description

Radiation therapy is a local treatment. It is painless. The radiation only acts on the part of the body that is exposed to the radiation. This is very different from chemotherapy in which drugs circulate throughout the whole body. There are two main types of radiation therapy. In external radiation therapy a beam of radiation is directed from outside the body at the cancer. In internal radiation therapy, called brachytherapy or implant therapy, a source of radioactivity is surgically placed inside the body near the cancer.

How Radiation Therapy Works

The protein that carries the code controlling most activities in the cell is called deoxyribonucleic acid or DNA. When a cell divides, its DNA must also double and divide. High-energy radiation kills cells by damaging their DNA. This blocks their ability to grow and increase in number.

One of the characteristics of cancer cells is that they grow and divide faster than normal cells. This makes them particularly vulnerable to radiation. Radiation also damages normal cells, but because normal cells are growing more slowly, they are better able to repair radiation damage than are cancer cells. In order to give normal cells time to heal and reduce side effects, radiation treatments are often given in small doses over a six- or seven-week period.

External Radiation Therapy

External radiation therapy is the most common kind of radiation therapy. It is usually done during outpatient visits to a hospital clinic and is usually covered by insurance.

Once a doctor called a radiation oncologist determines the proper dose of radiation for a particular cancer, the dose is divided into smaller doses called fractions. One fraction is usually given each day, five days a week for six to seven weeks. However, each radiation plan is individualized depending on the type and location of the cancer and what other treatments are also being used. The actual administration of the therapy usually takes about half an hour daily, although radiation is only administered for one to five minutes at each session. It is important to attend every scheduled treatment to get the most benefit from radiation therapy.

Recently, trials have begun to determine if there are ways to deliver radiation fractions so that they kill more cancer cells or have fewer side effects. Some trials use smaller doses given more often. Up-to-date information on voluntary participation in clinical trials and where they are being held is available by entering the search term "radiation therapy" at the following web sites:

• National Cancer Institute. or (800) 4-CANCER.
• National Institutes of Health Clinical Trials.
• Center Watch: A Clinical Trials Listing. .

The type of machines used to administer external radiation therapy and the material that provides the radiation vary depending on the type and location of the cancer. Generally, the patient puts on a hospital gown and lies down or sits in a special chair. Parts of the body not receiving radiation are covered with special shields that block the rays. A technician then directs a beam of radiation to a pre-determined spot on the body where the cancer is located. The patient must stay still during the administration of the radiation so that no other parts of the body are affected. As an extra precaution in some treatments, special molds are made to make sure the body is in the same position for each treatment. However, the treatment itself is painless, like having a bone x-rayed.

Internal Radiation Therapy

Internal radiation therapy is called brachytherapy, implant therapy, interstitial radiation, or intracavitary radiation. With internal radiation therapy, a bit of radioactive material is sealed in an implant (sometimes called a seed or capsule). The implant is then placed very close to the cancer. The advantage of internal radiation therapy is that it concentrates the radiation near the cancer and lessens the chance of damage to normal cells. Many different types of radioactive materials can be used in the implant, including cesium, iridium, iodine, phosphorus, and palladium.

How the implant is put near the cancer depends on the size and location of the cancer. Internal radiation therapy is used for some cancers of the head, neck, thyroid, breast, female reproductive system, and prostate. Most people will have the radioactive capsule implanted by a surgeon while under either general or local anesthesia at a hospital or surgical clinic.

Patients receiving internal radiation therapy do become temporarily radioactive. They must remain in the hospital during the time that the implant stays in place. The length of time is determined by the type of cancer and the dose of radioactivity to be delivered. During the time the implant is in place, the patient will have to stay in bed and remain reasonably still.

While the implant is in place, the patient's contact with other people will be limited. Health care workers will make their visits as brief as possible to avoid exposure to radiation, and visitors, especially children and pregnant women, will be limited.

The implant usually can be removed in a simple procedure without an anesthetic. As soon as the implant is out of the body, the patient is no longer radioactive, and restrictions on being with other people are lifted. Generally people can return to a level of activity that feels comfortable to them as soon as the implant is removed. Occasionally the site of the implant is sore for some time afterwards. This discomfort may limit specific activities.

In some cases, an implant is left permanently inside the body. People who have permanent implants need to stay in the hospital and away from other people for the first few days. Gradually the radioactivity of the implant decreases, and it is safe to be around other people.

Radioimmunotherapy

Radioimmunotherapy is a promising way to treat cancer that has spread (metastasized) to multiple locations throughout the body. Antibodies are immune system proteins that specifically recognize and bind to only one type of cell. They can be designed to bind only with a certain type of cancer cell. To carry out radioimmunotherapy, antibodies with the ability to bind specifically to a patient's cancer cells are attached to radioactive material and injected into the patient's bloodstream. When these man-made antibodies find a cancer cell, they bind to it. Then the radiation kills the cancer cell. This process is still experimental, but because it can be used to selectively attack only cancer cells, it holds promise for eliminating cancers that have spread beyond the primary tumor.

Radiation Used to Treat Cancer

Photon Radiation

Early radiation therapy used x rays like those used to take pictures of bones, or gamma rays. X rays and gamma rays are high-energy rays composed of massless particles of energy (like light) called photons. The distinction between the two is that gamma rays originate from the decay of radioactive substances (like radium and cobalt-60), while x rays are generated by devices that excite electrons (such as cathode ray tubes and linear accelerators). These high-energy rays act on cells by disrupting the electrons of atoms within the molecules inside cells, disrupting cell functions, and, most importantly, by stopping their ability to divide and make new cells.

Particle Radiation

Particle radiation is radiation delivered by particles that have mass. Proton therapy has been used since the early 1990s. Proton rays consist of protons, a type of positively charged atomic particle, rather than photons, which have neither mass nor charge. Like x rays and gamma rays, proton rays disrupt cellular activity. The advantage of using proton rays is that they can be shaped to conform to the irregular shape of the tumor more precisely than x rays and gamma rays. They allow delivery of higher radiation doses to tumors without increasing damage to the surrounding tissue.

Neutron therapy is another type of particle radiation. Neutron rays are very high-energy rays. They are composed of neutrons, which are particles with mass but no charge. The type of damage they cause to cells is much less likely to be repaired than that caused by x rays, gamma rays, or proton rays.

Neutron therapy can treat larger tumors than conventional radiation therapy. Conventional radiation therapy depends on the presence of oxygen to work. The center of large tumors lack sufficient oxygen to be susceptible to damage from conventional radiation. Neutron radiation works in the absence of oxygen, making it especially effective for the treatment of inoperable salivary gland tumors, bone cancers, and some kinds of advanced cancers of the pancreas, bladder, lung, prostate, and uterus.

Recent Advances in Radiation Therapy

A newer mode of treating brain cancers with radiation therapy is known as stereotactic radiosurgery. As of the early 2000s, this approach is limited to treating cancers of the head and neck because only these parts of the body can be held completely still throughout the procedure. Stereotactic radiosurgery allows the doctor to deliver a single high-level dose of precisely directed radiation to the tumor without damaging nearby healthy brain tissue. The treatment is planned with the help of three-dimensional computer-aided analysis of CT and MRI scans. The patient's head and neck are held steady in a skeletal fixation device during the actual treatment. Stereotactic radiosurgery can be used in addition to standard surgery to treat a recurrent brain tumor, or in place of surgery if the tumor cannot be reached by standard surgical techniques.

Two major forms of stereotactic radiosurgery are in use as of 2003. The gamma knife is a stationary machine that is most useful for small tumors, blood vessels, or similar targets. Because it does not move, it can deliver a small, highly localized and precise beam of radiation. Gamma knife treatment is done all at once in a single hospital stay. The second type of radiosurgery uses a movable linear accelerator-based machine that is preferred for larger tumors. This treatment is delivered in several small doses given over several weeks. Radiosurgery that is performed with divided doses is known as fractionated radiosurgery. The total dose of radiation is higher with a linear accelerator-based machine than with gamma knife treatment.

Another advance in intraoperative radiotherapy (IORT) is the introduction of mobile devices that allow the surgeon to use radiotherapy in early-stage disease and to operate in locations where it would be difficult to transport the patient during surgery for radiation treatment. Mobile IORT units have been used successfully as of 2003 in treating early-stage breast cancer and rectal cancer.

Radiation sensitizers are another recent innovation in radiation therapy. Sensitizers are medications that are given to make cancer cells easier to kill by radiation than normal calls. Gemcitabine (Gemzar) is one of the drugs most commonly used for this purpose.

Preparation

Before radiation therapy, the size and location of the patient's tumor are determined very precisely using magnetic resonance imaging (MRI) and/or computed tomography scans (CT scans). The correct radiation dose, the number of sessions, the interval between sessions, and the method of application are calculated by a radiation oncologist based on the tumor type, its size, and the sensitivity of the nearby tissues.

The patient's skin is marked with a semi-permanent ink to help the radiation technologist achieve correct positioning for each treatment. Molds may be built to hold tissues in exactly the right place each time.

Aftercare

Many patients experience skin burn, fatigue, nausea, and vomiting after radiation therapy regardless of where the radiation is applied. After treatment, the skin around the site of the treatment may also become sore. Affected skin should be kept clean and can be treated like sunburn, with skin lotion or vitamin A and D ointment. Patients should avoid perfume and scented skin products and protect affected areas from the sun.

Nausea and vomiting are most likely to occur when the radiation dose is high or if the abdomen or another part of the digestive tract is irradiated. Sometimes nausea and vomiting occur after radiation to other regions, but in these cases the symptoms usually disappear within a few hours after treatment. Nausea and vomiting can be treated with antacids, Compazine, Tigan, or Zofran.

Fatigue frequently starts after the second week of therapy and may continue until about two weeks after the therapy is finished. Patients may need to limit their activities, take naps, and get extra sleep at night.

Patients should see their oncologist (cancer doctor) at least once within the first few weeks after their final radiation treatment. They should also see an oncologist every six to twelve months for the rest of their lives so they can be checked to see if the tumor has reappeared or spread.

Risks

Radiation therapy can cause anemia, nausea, vomiting, diarrhea, hair loss (alopecia), skin burn, sterility, and rarely death. However, the benefits of radiation therapy almost always exceed the risks. Patients should discuss the risks with their doctor and get a second opinion about their treatment plan.

Normal Results

The outcome of radiation treatment varies depending on the type, location, and stage of the cancer. For some cancers such as Hodgkin's disease, about 75% of the patients are cured. Prostate cancer also responds well to radiation therapy. Radiation to painful bony metastases is usually a dramatically effective form of pain control. Other cancers may be less sensitive to the benefits of radiation.

Resources

Books

Cukier, Daniel, and Virginia McCullough. Coping with Radiation Therapy. Los Angeles: Lowell House, 2001.

Periodicals

Goer, D. A., C. W. Musslewhite, and D. M. Jablons. "Potential of Mobile Intraoperative Radiotherapy Technology." Surgical Oncology Clinics of North America 12 (October 2003): 943–954.

Lawrence, T. S. "Radiation Sensitizers and Targeted Therapies." Oncology (Huntington) 17 (December 2003): 23–28.

Merrick, H. W. IIIrd, L. L. Gunderson, and F. A. Calvo. "Future Directions in Intraoperative Radiation Therapy." Surgical Oncology Clinics of North America 12 (October 2003): 1099–1105.

Nag, S., and K. S. Hu. "Intraoperative High-Dose-Rate Brachytherapy." Surgical Oncology Clinics of North America 12 (October 2003): 1079–1097.

Witt, M. E., M. Haas, M. A. Marrinan, and C. N. Brown. "Understanding Stereotactic Radiosurgery for Intracranial Tumors, Seed Implants for Prostate Cancer, and Intravascular Brachytherapy for Cardiac Restenosis." Cancer Nursing 26 (December 2003): 494–502.

Organizations

American Cancer Society. 1599 Clifton Rd. NE, Atlanta GA 30329-4251. (800) ACS-2345. .

International Radiosurgery Support Association (IRSA). 3005 Hoffman Street, Harrisburg, PA 17110. (717) 260-9808. .

National Association for Proton Therapy. 7910 Woodmont Ave., Suite 1303, Bethesda, MD 20814. (301) 913-9360.

Other

Radiation Therapy and You. A Guide to Self-Help During Treatment. National Cancer Institute CancerNet Information Service. .

—Lorraine Lica; Rebecca J. Frey, PhD

The use of ionizing radiation to treat disease; the method is also known as radiotherapy and therapeutic radiology. Radiotherapy was widely used in the past to treat diseases of the skin, lymph nodes, and other organs. However, because radiation can cause cancer and because alternative treatments for these diseases have been discovered, radiation therapy is now mainly limited to treating malignant tumors: the medical specialty is called radiation oncology. See also Oncology.

The exact mechanisms by which radiation kills cells remain uncertain. Most likely, electrons dislodged from water or biological molecules disrupt the bonds between atoms of the nuclear deoxyribonucleic acid (DNA), resulting in double-strand breaks. Although usually not immediately fatal, such damage may cause the death of cells when they attempt to divide. Complex enzymatic mechanisms can repair some of the damage if given sufficient time.

The fraction of cells surviving after irradiation depends on many factors. Radiation affects both normal and cancerous cells in a similar manner qualitatively, but different cell lines vary greatly in their quantitative sensitivity. Rapidly dividing tissues—such as the skin, bone marrow, and gastrointestinal mucosa—usually display the greatest sensitivity experimentally and the most immediate side effects clinically.

The goal of radiation therapy is either to cure the disease permanently (radical treatment) or to reduce or eliminate symptons (palliative treatment) by destroying tumors without causing unacceptable injuries to normal tissues. For many cancers—such as cancers of the reproductive organs, lymphomas, and small head and neck tumors—a cure usually is possible, and the chance of functionally significant complications is small. Some tumors, however, contain too many cells to be entirely destroyed by tolerable doses. Also, some neoplasms, such as sarcomas and glioblastomas, are relatively resistant to irradiation and are difficult to eradicate even when only small numbers of cells are present. Such situations are best handled by using surgery to remove all visible tumor. See also Cancer (medicine); Radiation biology.

The treatment of disease with any type of radiation.

This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (September 2009)

Radiation therapy of the pelvis. Lasers and a mould under the legs are used to determine exact position.

Varian Clinac 2100C Linear Accelerator.

Radiation therapy (also radiotherapy or radiation oncology, sometimes abbreviated to XRT) is the medical use of ionizing radiation as part of cancer treatment to control malignant cells (not to be confused with radiology, the use of radiation in medical imaging and diagnosis). Radiotherapy may be used for curative or adjuvant cancer treatment. It is used as palliative treatment (where cure is not possible and the aim is for local disease control or symptomatic relief) or as therapeutic treatment (where the therapy has survival benefit and it can be curative). Total body irradiation (TBI) is a radiotherapy technique used to prepare the body to receive a bone marrow transplant. Radiotherapy has several applications in non-malignant conditions, such as the treatment of trigeminal neuralgia, severe thyroid eye disease, pterygium, pigmented villonodular synovitis, prevention of keloid scar growth, and prevention of heterotopic ossification. The use of radiotherapy in non-malignant conditions is limited partly by worries about the risk of radiation-induced cancers.

Radiotherapy is used for the treatment of malignant tumors (cancer), and may be used as the primary therapy. It is also common to combine radiotherapy with surgery, chemotherapy, hormone therapy or some mixture of the three. Most common cancer types can be treated with radiotherapy in some way. The precise treatment intent (curative, adjuvant, neoadjuvant, therapeutic, or palliative) will depend on the tumour type, location, and stage, as well as the general health of the patient.

Radiation therapy is commonly applied to the cancerous tumour. The radiation fields may also include the draining lymph nodes if they are clinically or radiologically involved with tumour, or if there is thought to be a risk of subclinical malignant spread. It is necessary to include a margin of normal tissue around the tumour to allow for uncertainties in daily set-up and internal tumor motion. These uncertainties can be caused by internal movement (for example, respiration and bladder filling) and movement of external skin marks relative to the tumour position.

To spare normal tissues (such as skin or organs which radiation must pass through in order to treat the tumour), shaped radiation beams are aimed from several angles of exposure to intersect at the tumour, providing a much larger absorbed dose there than in the surrounding, healthy tissue.

Contents 1 Mechanism of action 2 Dose 2.1 Fractionation 3 Effect on different types of cancer 4 History of radiation therapy 5 Types of radiation therapy 5.1 External beam radiotherapy 5.1.1 Conventional external beam radiotherapy 5.1.2 Stereotactic Radiation 5.1.3 Virtual simulation, 3-dimensional conformal radiotherapy, and intensity-modulated radiotherapy 5.1.4 Particle Therapy 5.2 Radioisotope Therapy (RIT) 6 Side effects 6.1 Acute side effects 6.2 Medium and long-term side effects 6.3 Cumulative side effects 7 See also 8 References 9 Further reading 10 External links

Mechanism of action

Radiation therapy works by damaging the DNA of cells. The damage is caused by a photon, electron, proton, neutron, or ion beam directly or indirectly ionizing the atoms which make up the DNA chain. Indirect ionization happens as a result of the ionization of water, forming free radicals, notably hydroxyl radicals, which then damage the DNA. In the most common forms of radiation therapy, most of the radiation effect is through free radicals. Because cells have mechanisms for repairing DNA damage, breaking the DNA on both strands proves to be the most significant technique in modifying cell characteristics. Because cancer cells generally are undifferentiated and stem cell-like, they reproduce more, and have a diminished ability to repair sub-lethal damage compared to most healthy differentiated cells. The DNA damage is inherited through cell division, accumulating damage to the cancer cells, causing them to die or reproduce more slowly.

One of the major limitations of radiotherapy is that the cells of solid tumors become deficient in oxygen. Solid tumors can outgrow their blood supply, causing a low-oxygen state known as hypoxia. Oxygen is a potent radiosensitizer, increasing the effectiveness of a given dose of radiation by forming DNA-damaging free radicals. Tumor cells in a hypoxic environment may be as much as 2 to 3 times more resistant to radiation damage than those in a normal oxygen environment.^[1] Much research has been devoted to overcoming this problem including the use of high pressure oxygen tanks, blood substitutes that carry increased oxygen, hypoxic cell radiosensitizers such as misonidazole and metronidazole, and hypoxic cytotoxins, such as tirapazamine. There is also interest in the fact that high-LET (linear energy transfer) particles such as carbon or neon ions may have an antitumor effect which is less dependent of tumor oxygen because these particles act mostly via direct damage.

Dose

The amount of radiation used in radiation therapy is measured in gray (Gy), and varies depending on the type and stage of cancer being treated. For curative cases, the typical dose for a solid epithelial tumor ranges from 60 to 80 Gy, while lymphoma tumors are treated with 20 to 40 Gy.

Preventative (adjuvant) doses are typically around 45 - 60 Gy in 1.8 - 2 Gy fractions (for Breast, Head and Neck cancers respectively.) Many other factors are considered by radiation oncologists when selecting a dose, including whether the patient is receiving chemotherapy, whether radiation therapy is being administered before or after surgery, and the degree of success of surgery.

Radiation therapy plans are often evaluated using dose-volume histograms, which allow the clinician to assess the uniformity of the dose to the diseased tissue (tumor) and how well healthy structures are spared.

Fractionation

The total dose is fractionated (spread out over time) for several important reasons. Fractionation allows normal cells time to recover, while tumor cells are generally less efficient in repair between fractions. Fractionation also allows tumor cells that were in a relatively radio-resistant phase of the cell cycle during one treatment to cycle into a sensitive phase of the cycle before the next fraction is given. Similarly, tumor cells that were chronically or acutely hypoxic (and therefore more radioresistant) may reoxygenate between fractions, improving the tumor cell kill. Fractionation regimes are individualised between different radiotherapy centres and even between individual doctors. In North America, Australia, and Europe, the typical fractionation schedule for adults is 1.8 to 2 Gy per day, five days a week. In the northern United Kingdom, fractions are more commonly 2.67 to 2.75 Gy per day, which eases the burden on thinly spread resources in the National Health Service. In some cancer types, prolongation of the fraction schedule over too long can allow for the tumor to begin repopulating, and for these tumor types, including head-and-neck and cervical squamous cell cancers, radiation treatment is preferably completed within a certain amount of time. For children, a typical fraction size may be 1.5 to 1.8 Gy per day, as smaller fraction sizes are associated with reduced incidence and severity of late-onset side effects in normal tissues.

In some cases, two fractions per day are used near the end of a course of treatment. This schedule, known as a concomitant boost regimen or hyperfractionation, is used on tumors that regenerate more quickly when they are smaller. In particular, tumors in the head-and-neck demonstrate this behavior.

One of the best-known alternative fractionation schedules is Continuous Hyperfractionated Accelerated Radiotherapy (CHART). CHART, used to treat lung cancer, consists of three smaller fractions per day. Although reasonably successful, CHART can be a strain on radiation therapy departments.

Implants can be fractionated over minutes or hours, or they can be permanent seeds which slowly deliver radiation until they become inactive.

Effect on different types of cancer

Different cancers respond differently to radiation therapy.^[2][3][4]

The response of a cancer to radiation is described by its radiosensitivity. Highly radiosensitive cancer cells are rapidly killed by modest doses of radiation. These include leukaemias, most lymphomas and germ cell tumours. The majority of epithelial cancers are only moderately radiosensitive, and require a significantly higher dose of radiation (60-70Gy)to achieve a radical cure. Some types of cancer are notably radioresistant, that is, much higher doses are required to produce a radical cure than may be safe in clinical practice. Renal cell cancer and melanoma are generally considered to be radioresistant.

It is important to distinguish the radiosensitivity of a particular tumour, which to some extent is a laboratory measure, from the radiation "curability" of a cancer in actual clinical practice. For example, leukaemias are not generally curable with radiotherapy, because they are disseminated though the body. Lymphoma may be radically curable if it is localised to one area of the body. Similarly, many of the common, moderately radioresponsive tumours are routinely treated with curative doses of radiotherapy if they are at an early stage. For example: non-melanoma skin cancer, head and neck cancer, non-small cell lung cancer, cervical cancer, anal cancer, prostate cancer. Metastatic cancers are generally incurable with radiotherapy because it is not possible to treat the whole body.

Before treatment, a CT scan is often performed to identify the tumor and surrounding normal structures. The patient is then sent for a simulation so that molds can be created to be used during treatment. The patient receives small skin marks to guide the placement of treatment fields.^[5]

The response of a tumour to radiotherapy is also related to its size. For complex reasons, very large tumours respond less well to radiation than smaller tumours or microscopic disease. Various strategies are used to overcome this effect. The most common technique is surgical resection prior to radiotherapy. This is most commonly seen in the treatment of breast cancer with wide local excision or mastectomy followed by adjuvant radiotherapy. Another method is to shrink the tumour with neoadjuvant chemotherapy prior to radical radiotherapy. A third technique is to enhance the radiosensitivity of the cancer by giving certain drugs during a course of radiotherapy. Examples of radiosensiting drugs include: Cisplatin, Nimorazole, and Cetuximab.

History of radiation therapy

Radiation therapy has been in use as a cancer treatment for more than 100 years, with its earliest roots traced from the discovery of x-rays in 1895 by Wilhelm Röntgen.^[6]

The field of radiation therapy began to grow in the early 1900s largely due to the groundbreaking work of Nobel Prize-winning scientist Marie Curie, who discovered the radioactive elements polonium and radium. This began a new era in medical treatment and research.^[6] Radium was used in various forms until the mid-1900s when cobalt and caesium units came into use. Medical linear accelerators have been used to as sources of radiation since the late 1940s.

With Godfrey Hounsfield’s invention of computed tomography (CT) in 1971, three-dimensional planning became a possibility and created a shift from 2-D to 3-D radiation delivery; CT-based planning allows physicians to more accurately determine the dose distribution using axial tomographic images of the patient's anatomy. Orthovoltage and cobalt units have largely been replaced by megavoltage linear accelerators, useful for their penetrating energies and lack of physical radiation source.

The advent of new imaging technologies, including magnetic resonance imaging (MRI) in the 1970s and positron emission tomography (PET) in the 1980s, has moved radiation therapy from 3-D conformal to intensity-modulated radiation therapy (IMRT) and image-guided radiation therapy (IGRT). These advances have resulted in better treatment outcomes and fewer side effects.

Types of radiation therapy

Historically, the three main divisions of radiotherapy are external beam radiotherapy (EBRT or XBRT) or teletherapy, brachytherapy or sealed source radiotherapy, and systemic radioisotope therapy or unsealed source radiotherapy. The differences relate to the position of the radiation source; external is outside the body, brachytherapy uses sealed radioactive sources placed precisely in the area under treatment, and systemic radioisotopes are given by infusion or oral ingestion. Brachytherapy can use temporary or permanent placement of radioactive sources. The temporary sources are usually placed by a technique called afterloading. In afterloading a hollow tube or applicator is placed surgically in the organ to be treated, and the sources are loaded into the applicator after the applicator is implanted. This minimizes radiation exposure to health care personnel. Particle therapy is a special case of external beam radiotherapy where the particles are protons or heavier ions. Introperative radiotherapy^[7] is a special type of radiotherapy that is delivered immediately after surgical removal of the cancer. This method has been employed in breast cancer (TARGeted Introperative radioTherapy), brain tumours and rectal cancers.

External beam radiotherapy

Main article: External beam radiotherapy

The following three sections refer to treatment using x-rays.

Conventional external beam radiotherapy

Conventional external beam radiotherapy (2DXRT) is delivered via two-dimensional beams using linear accelerator machines. 2DXRT mainly consists of a single beam of radiation delivered to the patient from several directions: often front or back, and both sides. Conventional refers to the way the treatment is planned or simulated on a specially calibrated diagnostic x-ray machine known as a simulator because it recreates the linear accelerator actions (or sometimes by eye), and to the usually well-established arrangements of the radiation beams to achieve a desired plan. The aim of simulation is to accurately target or localize the volume which is to be treated. This technique is well established and is generally quick and reliable. The worry is that some high-dose treatments may be limited by the radiation toxicity capacity of healthy tissues which lay close to the target tumor volume. An example of this problem is seen in radiation of the prostate gland, where the sensitivity of the adjacent rectum limited theA detector system for imaging radiotherapeutic dose distributions in 4D dose which could be safely prescribed using 2DXRT planning to such an extent that tumor control may not be easily achievable. Prior to the invention of the CT, physicians and physicists had limited knowledge about the true radiation dosage delivered to both cancerous and healthy tissue. For this reason, 3-dimensional conformal radiotherapy is becoming the standard treatment for a number of tumor sites.

Stereotactic Radiation

Stereotactic radiation is a specialized type of external beam radiation therapy. It uses focused radiation beams targeting a well-defined tumor using extremely detailed imaging scans. Radiation oncologists perform stereotactic treatments, often with the help of a neurosurgeon for tumors in the brain or spine.

There are two types of stereotactic radiation. Stereotactic radiosurgery (SRS) is when doctors use a single or several stereotactic radiation treatments of the brain or spine. Stereotactic body radiation therapy (SBRT) refers to one or several stereotactic radiation treatments with the body, such as the lungs^[8].

Some doctors say an advantage to stereotactic treatments are they deliver the right amount of radiation to the cancer in a shorter amount of time than traditional treatments, which can often take six to 11 weeks. Plus treatments are given with extreme accuracy, which should limit the effect of the radiation on healthy tissues. One problem with stereotactic treatments is that they are only suitable for certain small tumors.

Stereotactic treatments can be confusing because many hospitals call the treatments by the name of the manufacturer rather than calling it SRS or SBRT. Brand names for these treatments include Axesse, CyberKnife, Gamma Knife, Novalis, Primatom, Synergy, X-Knife, TomoTherapy and Trilogy.^[9] This list changes as equipment manufacturers continue to develop new, specialized technologies to treat cancers.

Virtual simulation, 3-dimensional conformal radiotherapy, and intensity-modulated radiotherapy

The planning of radiotherapy treatment has been revolutionized by the ability to delineate tumors and adjacent normal structures in three dimensions using specialized CT and/or MRI scanners and planning software.^[10]

Virtual simulation, the most basic form of planning, allows more accurate placement of radiation beams than is possible using conventional X-rays, where soft-tissue structures are often difficult to assess and normal tissues difficult to protect.

An enhancement of virtual simulation is 3-Dimensional Conformal Radiotherapy (3DCRT), in which the profile of each radiation beam is shaped to fit the profile of the target from a beam's eye view (BEV) using a multileaf collimator (MLC) and a variable number of beams. When the treatment volume conforms to the shape of the tumour, the relative toxicity of radiation to the surrounding normal tissues is reduced, allowing a higher dose of radiation to be delivered to the tumor than conventional techniques would allow.^[5]

Intensity-Modulated Radiation Therapy (IMRT) is an advanced type of high-precision radiation that is the next generation of 3DCRT.^[11] IMRT also improves the ability to conform the treatment volume to concave tumor shapes,^[5] for example when the tumor is wrapped around a vulnerable structure such as the spinal cord or a major organ or blood vessel.^[12] Computer-controlled x-ray accelerators distribute precise radiation doses to malignant tumors or specific areas within the tumor. The pattern of radiation delivery is determined using highly-tailored computing applications to perform optimization and treatment simulation (Treatment Planning). The radiation dose is consistent with the 3-D shape of the tumor by controlling, or modulating, the radiation beam’s intensity. The radiation dose intensity is elevated near the gross tumor volume while radiation among the neighboring normal tissue is decreased or avoided completely. The customized radiation dose is intended to maximize tumor dose while simultaneously protecting the surrounding normal tissue. This may result in better tumor targeting, lessened side effects, and improved treatment outcomes than even 3DCRT.

3DCRT is still used extensively for many body sites but the use of IMRT is growing in more complicated body sites such as CNS, head and neck, prostate, breast and lung. Unfortunately, IMRT is limited by its need for additional time from experienced medical personnel. This is because physicians must manually delineate the tumors one CT image at a time through the entire disease site which can take much longer than 3DCRT preparation. Then, medical physicists and dosimetrists must be engaged to create a viable treatment plan. Also, the IMRT technology has only been used commercially since the late 1990s even at the most advanced cancer centers, so radiation oncologists who did not learn it as part of their residency program must find additional sources of education before implementing IMRT.

Proof of improved survival benefit from either of these two techniques over conventional radiotherapy (2DXRT) is growing for many tumor sites, but the ability to reduce toxicity is generally accepted. Both techniques enable dose escalation, potentially increasing usefulness. There has been some concern, particularly with 3DCRT, about increased exposure of normal tissue to radiation and the consequent potential for secondary malignancy. Overconfidence in the accuracy of imaging may increase the chance of missing lesions that are invisible on the planning scans (and therefore not included in the treatment plan) or that move between or during a treatment (for example, due to respiration or inadequate patient immobilization). New techniques are being developed to better control this uncertainty—for example, real-time imaging combined with real-time adjustment of the therapeutic beams. This new technology is called image-guided radiation therapy (IGRT) or four-dimensional radiotherapy.

Particle Therapy

Main article: Particle therapy

In particle therapy (Proton therapy), energetic ionizing particles (protons or carbon ions) are directed at the target tumor.^[13] The dose increases while the particle penetrates the tissue, up to a maximum (the Bragg peak) that occurs near the end of the particle's range, and it then drops to (almost) zero. The advantage of this energy deposition profile is that less energy is deposited into the healthy tissue surrounding the target tissue.

Radioisotope Therapy (RIT)

Systemic radioisotope therapy is a form of targeted therapy. Targeting can be due to the chemical properties of the isotope such as radioiodine which is specifically absorbed by the thyroid gland a thousand fold better than other bodily organs. Targeting can also be achieved by attaching the radioisotope to another molecule or antibody to guide it to the target tissue. The radioisotopes are delivered through infusion (into the bloodstream) or ingestion. Examples are the infusion of metaiodobenzylguanidine (MIBG) to treat neuroblastoma, of oral iodine-131 to treat thyroid cancer or thyrotoxicosis, and of hormone-bound lutetium-177 and yttrium-90 to treat neuroendocrine tumors (peptide receptor radionuclide therapy). Another example is the injection of radioactive glass or resin microspheres into the hepatic artery to radioembolize liver tumors or liver metastases.

A major use of systemic radioisotope therapy is in the treatment of bone metastasis from cancer. The radioisotopes travel selectively to areas of damaged bone, and spare normal undamaged bone. Isotopes commonly used in the treatment of bone metastasis are strontium-89 and Samarium-153-ethylene diamine tetramethylene phosphonate.^[14]

In 2002, the United States Food and Drug Administration (FDA) approved Ibritumomab tiuxetan (Zevalin), which is a monoclonal antibody anti-CD20 conjugated to a molecule of Yttrium-90. ^[15] In 2003, the FDA approved Tositumomab Iodine-131 (Bexxar), which conjugates a molecule of Iodine-131 to the monoclonal antibody anti-CD20. ^[16] These medications were the first agents of what is known as radioimmunotherapy, and they were approved for the treatment of refractory non-Hodgkins lymphoma.

Side effects

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Radiation therapy is in itself painless. Many low-dose palliative treatments (for example, radiotherapy to bony metastases) cause minimal or no side effects, although short-term pain flare up can be experienced in the days following treatment due to oedema compressing nerves in the treated area. Treatment to higher doses causes varying side effects during treatment (acute side effects), in the months or years following treatment (long-term side effects), or after re-treatment (cumulative side effects). The nature, severity, and longevity of side effects depends on the organs that receive the radiation, the treatment itself (type of radiation, dose, fractionation, concurrent chemotherapy), and the patient.

Most side effects are predictable and expected. Side effects from radiation are usually limited to the area of the patient's body that is under treatment. One of the aims of modern radiotherapy is to reduce side effects to a minimum, and to help the patient to understand and to deal with those side effects which are unavoidable.

The main side effects reported are fatigue and skin irritation, like a mild to moderate sun burn. The fatigue often sets in during the middle of a course of treatment and can last for weeks after treatment ends. The skin irritation will also go away, but it may not be as elastic as it was before. Patients should ask their radiation oncologist or radiation oncology nurse about possible products and medications that can help with side effects. ^[17]

Acute side effects

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Damage to the epithelial surfaces. Epithelial surfaces may sustain damage from radiation therapy. Depending on the area being treated, this may include the skin, oral mucosa, pharyngeal, bowel mucosa and ureter. The rates of onset of damage and recovery from it depend upon the turnover rate of epithelial cells. Typically the skin starts to become pink and sore several weeks into treatment. The reaction may become more severe during the treatment and for up to about one week following the end of radiotherapy, and the skin may break down. Although this moist desquamation is uncomfortable, recovery is usually quick. Skin reactions tend to be worse in areas where there are natural folds in the skin, such as underneath the female breast, behind the ear, and in the groin.

If the head and neck area is treated, temporary soreness and ulceration commonly occur in the mouth and throat.^[18] If severe, this can affect swallowing, and the patient may need painkillers and nutritional support/food supplements. The esophagus can also become sore if it is treated directly, or if, as commonly occurs, it receives a dose of collateral radiation during treatment of lung cancer.

The lower bowel may be treated directly with radiation (treatment of rectal or anal cancer) or be exposed by radiotherapy to other pelvic structures (prostate, bladder, female genital tract). Typical symptoms are soreness, diarrhoea, and nausea.

Swelling (edema or oedema). As part of the general inflammation that occurs, swelling of soft tissues may cause problems during radiotherapy. This is a concern during treatment of brain tumours and brain metastases, especially where there is pre-existing raised intracranial pressure or where the tumour is causing near-total obstruction of a lumen (e.g., trachea or main bronchus). Surgical intervention may be considered prior to treatment with radiation. If surgery is deemed unnecessary or inappropriate, the patient may receive steroids during radiotherapy to reduce swelling.

Infertility. The gonads (ovaries and testicles) are very sensitive to radiation. They may be unable to produce gametes following direct exposure to most normal treatment doses of radiation. Treatment planning for all body sites is designed to minimize, if not completely exclude dose to the gonads if they are not the primary area of treatment.

Medium and long-term side effects

These depend on the tissue that received the treatment; they may be minimal.

Fibrosis

Tissues which have been irradiated tend to become less elastic over time due to a diffuse scarring process.

Hair loss

This may be most pronounced in patients who have received radiotherapy to the brain. Unlike the hair loss seen with chemotherapy, radiation-induced hair loss is more likely to be permanent, but is also more likely to be limited to the area treated by the radiation.

Dryness

The salivary glands and tear glands have a radiation tolerance of about 30 Gy in 2 Gy fractions, a dose which is exceeded by most radical head and neck cancer treatments. Dry mouth (xerostomia) and dry eyes (xerophthalmia) can become irritating long-term problems and severely reduce the patient's quality of life. Similarly, sweat glands in treated skin (such as the armpit) tend to stop working, and the naturally moist vaginal mucosa is often dry following pelvic irradiation.

Fatigue

Fatigue is among the most common symptoms of radiation therapy, and can range from a few months, a few years, depending on the quantity of the treatment and cancer type. Lack of energy, reduced activity and overtired feelings are common symptoms.

Cancer

Radiation is a potential cause of cancer, and secondary malignancies are seen in a very small minority of patients, generally many years after they have received a course of radiation treatment. In the vast majority of cases, this risk is greatly outweighed by the reduction in risk conferred by treating the primary cancer.

Death

Radiation has potentially excess risk of death from heart disease seen after some past breast cancer RT regimens.^[19]

Cognitive decline

In cases of radiation applied to the head radiation therapy can cause cognitive decline

Cumulative side effects

Cumulative effects from this process should not be confused with long-term effects—when short-term effects have disappeared and long-term effects are subclinical, reirradiation can still be problematic.^[20]

See also

• Selective internal radiation therapy
• Fast neutron therapy

References

1. ^ Harrison LB, Chadha M, Hill RJ, Hu K, Shasha D (2002). "Impact of tumor hypoxia and anemia on radiation therapy outcomes". Oncologist 7 (6): 492–508. doi:10.1634/theoncologist.7-6-492. PMID 12490737. http://theoncologist.alphamedpress.org/cgi/pmidlookup?view=long&pmid=12490737. 
2. ^ CK Bomford, IH Kunkler, J Walter. Walter and Miller’s Textbook of Radiotherapy (6th Ed), p311
3. ^ “Radiosensitivity” on GP notebook http://www.gpnotebook.co.uk/simplepage.cfm?ID=2060451853
4. ^ “Radiotherapy- what GPs need to know” on patient.co.uk http://www.patient.co.uk/showdoc/40002299/
5. ^ ^{a b c} Camphausen KA, Lawrence RC. "Principles of Radiation Therapy" in Pazdur R, Wagman LD, Camphausen KA, Hoskins WJ (Eds) Cancer Management: A Multidisciplinary Approach. 11 ed. 2008.
6. ^ ^{a b} "University of Alabama at Birmingham Comprehensive Cancer Center, History of Radiation Oncology" (from the Wayback Machine). http://web.archive.org/web/20080105043216/http://www3.ccc.uab.edu/show.asp?durki=68504. 
7. ^ Vaidya J. "TARGIT (TARGeted Intraoperative radioTherapy)". http://www.targit.org.uk. Retrieved 2009-09-27. 
8. ^ http://www.astro.org/PressRoom/PressKit/AnnualMeeting/documents/Timmerman.pdf
9. ^ http://www.rtanswers.com/treatmentinformation/treatmenttypes/stereotacticradiation.aspx
10. ^ Bucci M, Bevan A, Roach M (2005). "Advances in radiation therapy: conventional to 3D, to IMRT, to 4D, and beyond.". CA Cancer J Clin 55 (2): 117–34. doi:10.3322/canjclin.55.2.117. PMID 15761080. http://caonline.amcancersoc.org/cgi/content/full/55/2/117. 
11. ^ Galvin JM, Ezzell G, Eisbrauch A, et al. (Apr 2004). "Implementing IMRT in clinical practice: a joint document of the American Society for Therapeutic Radiology and Oncology and the American Association of Physicists in Medicine". Int J Radiat Oncol Biol Phys. 58 (5): 1616–34. doi:10.1016/j.ijrobp.2003.12.008. PMID 15050343. 
12. ^ Intensity Modulated Radiation Therapy
13. ^ Brain tumour patient 'unaware' treatment was available on NHS
14. ^ Sartor O (2004). "Overview of samarium sm 153 lexidronam in the treatment of painful metastatic bone disease". Rev Urol 6 Suppl 10: S3–S12. PMID 16985930. 
15. ^ Fda Approves First Radiopharmaceutical Product To Treat Non-Hodgkin’S Lymphoma
16. ^ Tositumomab and Iodine I 131 Tositumomab - Product Approval Information - Licensing Action
17. ^ http://www.rtanswers.com/treatmentinformation/cancertypes/breast/possiblesideeffects.aspx
18. ^ Hall, Eric J. (2000). Radiobiology for the radiologist. Philadelphia: Lippincott Williams Wilkins. p. 351. ISBN 0781726492, 9780781726498. 
19. ^ Taylor CW, Nisbet A, McGale P, Darby SC (Dec 2007). "Cardiac exposures in breast cancer radiotherapy: 1950s-1990s". Int J Radiat Oncol Biol Phys. 69 (5): 1484–95. doi:10.1016/j.ijrobp.2007.05.034. PMID 18035211. 
20. ^ Nieder C, Milas L, Ang KK (2000). "Tissue tolerance to reirradiation.". Semin Radiat Oncol 10 (3): 200–9. doi:10.1053/srao.2000.6593. PMID 11034631. 

Further reading

• Ash D, Dobbs J, Barrett, A (1999). Practical radiotherapy planning. London: Arnold. ISBN 0-340-70631-7. 
• Williams JR, Thwaites DI (1993). Radiotherapy physics in practice. Oxford [Oxfordshire]: Oxford University Press. ISBN 0-19-963315-0. 
• Regine W, Chin L (2008). Principles of Stereotactic Surgery. Berlin: Springer. ISBN 0-387-71069-8. http://www.springer.com/medicine/surgery/book/978-0-387-71069-3.  Principles and Practice of Stereotactic Radiosurgery], Lawrence Chin, MD and William Regine, MD, Editors (2008)
• Radiotherapy in Treatment, McGarry, M (2002) AUSG Books

External links

Wikibooks has a book on the topic of Radiation Oncology

Information

• RT Answers – ASTRO: patient information site
• Proton Radiation Therapy
• The Radiation Therapy Oncology Group: an organisation for radiation oncology research
• RadiologyInfo -The radiology information resource for patients: Radiation Therapy
• Source of cancer stem cells' resistance to radiation explained on YouTube.
• Cancer Management Handbook: Priciples of Radiation Therapy

About the profession

• PROS (Paediatric Radiation Oncology Society)
• American Society for Radiation Oncology – ASTRO: the official site for radiation oncologists
• PACT: Programme of Action for Cancer Therapy Program to establish cancer care capacity and comprehensive cancer control in developing world with the help of radiation therapy
• European Society for Therapeutic Radiology and Oncology
• Academic Clinical Oncology and Radiobiology Research Network: A NCRI initiative to revitalise radiotherapy research (UK)
• Who does what in Radiation Oncology? - Responsibilities of the various personnel within Radiation Oncology in the United States
• Society of Radiographers (UK)

Accidents and QA

• Verification of dose calculations in radiotherapy

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