What are radiation therapies?

Quick Answer
The use of high doses of radiation to kill cancer cells and prevent metastasis (the spread of disease).
Expert Answers
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Cancers treated: Most, such as breast, prostate, thyroid, and gynecological cancers

Why performed: Radiation therapies are performed to kill, stop, or slow the growth of cancer cells in the body. Cancer is usually treated with surgery, chemotherapy, and radiation, which is called multimodal therapy. Radiation, as a component of this combined approach to care, may be used before, during, or after surgery; in combination with chemotherapy; or alone. Some patients who are not able to tolerate aggressive surgeries or chemotherapies may benefit, to some degree, from radiation therapy. Many patients develop side effects from their cancers that may be treated with radiation. Spinal cord compression or bony metastases may be treated to reduce paralysis or pain.

There are three ways to administer radiation to a patient. When a machine outside the body delivers radiation to a tumor inside the body, the process is called external beam radiation therapy (EBRT). Internal beam radiation therapy (IBRT) uses sources, applicators, or a high-dose remote afterloader to place radioactive material in the body near the cancer site. Systemic radiation therapy uses a radioactive substance that is injected or swallowed and then travels to cancer cells in tissues of the body.

EBRT uses x-ray beams that may be given by a linear accelerator, a machine that generates high-energy radiation beams; by a machine with a radioactive source, cobalt 60; by a tomotherapy unit, which is a linear accelerator coupled with a computed tomography (CT) scanner that delivers radiation in spirals around the body; or by a robotically controlled accelerator that delivers radiation while tracking and controlling for patient movement or organ movement during the treatment. Proton beam therapy uses a machine that generates protons to damage the deoxyribonucleic acid (DNA) of cancer cells. With proton therapy, the radiation beam of protons enters the body with a low dose of radiation, deposits its highest dose at the site being treated, and then stops without traveling through the body.

Advances in external beam therapy, based on the ability to better plan therapies, continue to develop rapidly. Conformal radiation therapy (3D-CRT) develops a three-dimensional model of the tumor and then uses shaped beams to treat the cancer from several directions. Intensity-modulated radiation therapy (IMRT) uses sophisticated treatment planning to vary the strength of the radiation beam in an attempt to lessen damage to the normal tissues surrounding the tumor. Tomotherapy is considered a type of IMRT and image-guided radiation therapy (IGRT), as the beams spiral around the body, allowing for precise and focused radiation beams based on data from a CT scan. IGRT is used to visualize the tumor location prior to treatment, as tumor movement occurs daily, and to control for tumor movement with respiration (respiratory gating). In addition to a CT scan, ultrasound may be used.

Stereotactic radiosurgery is a type of radiation therapy that delivers a large, precise dose to a defined tumor site. It is most commonly used for brain tumors, but applications in the abdomen and other sites are being explored. A cobalt 60 source machine is used with a head frame for brain tumors, and a robotically control linear accelerator may be used for both brain tumors and tumors outside the head (extracranial tumors). It is called radiosurgery because of its accuracy. The radiation beam is considered as accurate as a knife (or scalpel) and may treat tumors that surgeons cannot reach using traditional surgical techniques.

Intraoperative radiation therapy is used at the time of surgery to deliver external beam radiation directly to the tumor during the surgical procedure. The surgeon locates the cancer and moves normal tissues and organs out of the way, and then an accelerator delivers radiation directly to the tumor. The patient is asleep (under anesthesia) during the procedure, which is done in a special lead-lined operating room.

IBRT is delivered by several methods and is often referred to as brachytherapy. IBRT using a remote-controlled machine called a high-dose remote afterloader (HDR) unit sends high-dose radioactive material through catheters or needles placed in the patient for a period of minutes, and then the sources are withdrawn, so that the patient is not radioactive. When patients are exposed to radiation sources for a period of hours or days, the process is called low-dose-rate brachytherapy. Applicators or cases that house radioactive sources are placed in the patient and left for a prescribed period of time. The area around the patient is considered radioactive until the source is removed. Therefore, staff must limit their exposure to the patient, and visitors are not allowed. Permanent brachytherapy is a type of low-dose therapy in which radioactive seeds are placed in the patient and remain while giving off low doses of radiation for weeks or months. The patient gives off some radioactivity in very small doses. The primary safety consideration is to keep children away from the area of the implant. For example, a man undergoing permanent brachytherapy for prostate cancer must not allow children to sit on his lap.

Systemic radiation therapy is given as a capsule or liquid swallowed by the patient, or it may be given in a vein (injected intravenously). The radioactive liquid then moves throughout the body. The patient may stay in a special room in the hospital, and body fluids are handled carefully, as the radiation materials are eliminated from the body through urine, saliva, and sweat. When the radioactivity has dipped to safe levels, the patient may be discharged from the hospital. In some cases, the patient may be able to go home after treatment with special instructions about handling wastes.

Breast cancer is one of the most commonly treated cancers using external beam radiation therapy. Use of an HDR unit decreases the treatment time of several weeks to just five days. This procedure is often referred to as Mammosite therapy, named for the company that initially developed the procedure for commercial use. Prostate cancer may also use external beam radiation, an HDR unit, or implantable seeds (low-dose brachytherapy) to kill cancer cells. Thyroid cancer is often treated with radioactive iodine, a systemic radiation therapy in a liquid form that is swallowed by the patient. Gynecological cancers may be treated with an HDR unit or low-dose brachytherapy with an applicator that is left in for a period of time.

Patient preparation: The radiation oncologist, a physician with specialized training in radiation therapy care, will see the patient in a consult visit to determine if radiation therapy is appropriate for his or her cancer. Patients are generally referred to the radiation oncologist by the patient’s surgeon or medical oncologist. The physicians treating the patient will discuss whether external, internal, or systemic radiation is most appropriate. Prior to receiving treatment, patients have a simulation using a CT scanner or fluoroscopic simulator to allow the physician to visualize the area to be treated. A simulation may take up to two hours. To assist in positioning the patient for treatment, small marks may be placed on the skin. Later in the treatment room, the marks will be used with wall-mounted positioning lasers to place the patient in the correct position to receive the treatment. The simulation data are used to plan the radiation dose amounts to be given by the linear accelerator, the HDR unit, or any other source of radiation, such as implantable seeds. The simulation information is given to the physicist and dosimetrist, who load the data into a sophisticated treatment-planning computer. The physician then verifies the treatment site, the treatment plan, and the radiation dose to be given.

Steps of the procedure: The steps of the radiation treatment will depend on the type of radiation therapy that the patient receives. Regardless of whether external, internal, or systemic therapy is used, treatment planning is still the key to accurate radiation placement and dosing. For external beam therapy, the treatment plan will outline the patient position on the treatment table, determine the shape of the beam, define the number of treatments to be given, and prescribe the daily and cumulative doses the patient is to receive. The patient has four to six weeks of treatment depending on the treatment plan, five days a week, with two days a week off for normal cells to rest and recover. If an HDR unit is to be used, then catheters may be implanted at the time of surgery, or hollow needles may be placed just before the treatment. HDR treatments usually take place once or twice a day for approximately five days.

For patients receiving internal radiation, a simulation and treatment plan are still necessary. For low-dose brachytherapy, such as prostate seed implants, additional imaging studies may be needed. Seeds are implanted during a surgical procedure with the patient under general anesthesia. Low-dose brachytherapy, such as used in gynecological cancers, may use applicators that are placed in a treatment room and then loaded with the radioactive source. Patients receiving systemic radiation also need treatment planning to determine the amount of radioactive liquid needed to treat the cancer.

After the procedure: Most external beam treatments are done on an outpatient basis, and the patient may leave immediately after the daily treatment. Patients are not radioactive during treatments. A few external beam treatments, such as intraoperative radiation therapy and select stereotactic radiosurgery, may require hospitalization. Internal beam radiation treatments may be done on either an inpatient or an outpatient basis, depending on the method used to deliver the radiation therapy. If an HDR unit is used to deliver high-dose radiation, then the patient may be able to go home between treatments. If the internal beam radiation therapy requires that the radioactive source stay in the patient for a period of hours or days, then the patient is usually hospitalized, as the bodily fluids are emitting radioactive waste. Systemic radiotherapy may be either inpatient or outpatient in nature.

Risks: The risks from radiation depend on the site being treated and the type of radiation therapy being used. EBRT is a local treatment, so risks involve the area around the site being treated. For example, if abdominal radiation is used, then bowel and bladder problems may develop. Skin reactions, similar to sunburn, may occur. Hair loss, called alopecia, may occur if radiation is given to the head or other body areas with hair follicles. Xerostomia, or dry mouth, may occur with radiation of the head and neck areas, and dental problems may also occur with this radiation site. Fatigue is often associated with any radiation procedure. Side effects usually go away within two to three months after therapy is completed. Late side effects, those developing six or more months after therapy is completed, may include infertility, lymphedema, joint pain, or other problems, as well as a risk of a second cancer due to the radiation. There is always a risk that not all cancer cells will be killed by the radiation.

Results: Cancer cell kill is expected after any method of radiation treatment.

Bibliography

Bourland, J Daniel. Image-Guided Radiation Therapy. Boca Raton: Taylor, 2012. Digital file.

Dupuy, Damian E., Yuman Fong, and William N. McMullen. Image-Guided Cancer Therapy: A Multidisciplinary Approach. New York: Springer, 2013. Digital file.

Hoskin, Peter J. Radiotherapy in Practice: External Beam Therapy. 2nd ed. Oxford: Oxford UP, 2012. Print.

Penson, D. F., M. S. Litwin, J. L. Gore, et al. “Quality of Life after Surgery, External Beam Irradiation, or Brachytherapy for Early Stage Prostate Cancer.” Urologic Oncology 25.5 (2007): 442–43. Print.

Tao, Y., D. Lefkopoulos, D. Ibrahima, et al. “Comparison of Dose Contribution to Normal Pelvic Tissues among Conventional, Conformal, and Intensity-Modulated Radiotherapy Techniques in Prostate Cancer.” Acta Oncologica 28 Sept. 2007: 1–9.

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