Diagnostic Radiology. MR Imaging (MRI) Body. Cancer Care Information January 5, 2004

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1 All information included in this document was collected from Diagnostic Radiology MR Imaging (MRI) Body What is Magnetic Resonance Imaging (MRI) of the Body? What are some common uses of the procedure? How should I prepare for the procedure? What does the equipment look like? How does the procedure work? How is the procedure performed? What will I experience during the procedure? Who interprets the results and how do I get them? What are the benefits vs. risks? What are the limitations of MRI of the Body? What is Magnetic Resonance Imaging (MRI) of the Body? Magnetic resonance imaging (MRI) uses radiofrequency waves and a strong magnetic field rather than x-rays to provide remarkably clear and detailed pictures of internal organs and tissues. The technique has proven very valuable for the diagnosis of a broad range of pathologic conditions in all parts of the body, including cancer, heart and vascular disease, stroke, and joint and musculoskeletal disorders. MRI requires specialized equipment and expertise and allows evaluation of some body structures that may not be as visible with other imaging methods. What are some common uses of the procedure? Because MRI can give such clear pictures of soft-tissue structures near and around bones, it is the most sensitive exam for spinal and joint problems. MRI is widely used to diagnose sports-related injuries, especially those affecting the knee, shoulder, hip, elbow, and wrist. The images allow the physician to see even very small tears and injuries to ligaments and muscles. In addition, MRI of the heart, aorta, coronary arteries, and blood vessels is a fast, noninvasive tool for diagnosing coronary artery disease and heart problems. Physicians can examine the size and thickness of the chambers of the heart, and determine the extent of damage caused by a heart attack or progressive heart disease. Organs of the chest and abdomen including the lungs, liver, kidney, spleen, pancreas, and abdominal vessels can also be examined in high detail with MRI, enabling the diagnosis and evaluation of tumors and functional disorders. MRI is growing in popularity as an alternative to traditional x-ray mammography in the early diagnosis of breast cancer. Because no radiation exposure is involved, MRI is often the preferred diagnostic tool for examination of the male and female reproductive systems, pelvis and hips, and the bladder. How should I prepare for the procedure? Because the strong magnetic field used for MRI will pull on any ferromagnetic metal object implanted in the body, MRI staff will ask whether you have a prosthetic hip, heart pacemaker (or artificial heart valve), implanted port (brand names Port-o-cath, Infusaport, Lifeport), intrauterine D:\Cancer Modalities.doc 1

2 device (IUD), or any metal plates, pins, screws, or surgical staples in your body. In most cases, surgical staples, plates, pins and screws pose no risk during MRI if they have been in place for more than four to six weeks. Tattoos and permanent eyeliner may also create a problem. You will be asked if you have ever had a bullet or shrapnel in your body, or ever worked with metal. If there is any question of metal fragments, you may be asked to have an x-ray that will detect any such metal objects. Tooth fillings usually are not affected by the magnetic field, but they may distort images of the facial area or brain, so the radiologist should be aware of them. The same is true of braces, which may make it hard to "tune" the MRI unit to your body. You will be asked to remove anything that might degrade MRI images of the head, including hairpins, jewelry, eyeglasses, hearing aids, and any removable dental work. The radiologist or technologist may ask about drug allergies and whether head surgery has been done in the past. If you might be pregnant, this should be mentioned. Some patients who undergo MRI in an enclosed unit may feel confined or claustrophobic. If you are not easily reassured, a sedative may be administered. Roughly one in 20 patients will require medication to reduce the anxiety associated with claustrophobia. What does the equipment look like? The conventional MRI unit is a closed cylindrical magnet in which the patient must lie totally still for several seconds at a time, and consequently may feel "closed-in" or truly claustrophobic. However, new "patient-friendly" designs are rapidly coming into routine use. The "short-bore" systems are wider and shorter and do not fully enclose the patient. Some newer units are open on all sides, however the image quality may vary. How does the procedure work? MRI is a unique imaging method because, unlike the usual radiographs (x-rays), radioisotope studies, and even Computed Tomography (CT) scanning, it does not rely on ionizing radiation. Instead, radiofrequency waves are directed at protons, the nuclei of hydrogen atoms, in a strong magnetic field. The protons are first "excited" and then "relaxed," emitting radio signals, which can be computer-processed to form an image. In the body, protons are most abundant in the hydrogen atoms of water the "H" of H2O so that an MRI image shows differences in the water content and distribution in various body tissues. Even different types of tissue within the same organ, such as the gray and white matter of the brain, can easily be distinguished. Typically an MRI examination consists of two to six imaging sequences, each lasting two to 15 minutes. Each sequence has its own degree of contrast and shows a cross-section of the body in one of several planes (right to left, front to back, upper to lower). How is the procedure performed? The patient is placed on a sliding table and positioned comfortably for the MRI examination. Then the radiologist and technologist leave the room and the individual MRI sequences are performed. The patient is able to communicate with the radiologist or technologist at any time using an intercom. Also, many MRI centers allow a friend or, if a child is being examined, a parent, to stay in the room. Depending on how many images are needed, the exam will generally take from 15 to 45 minutes, although a very detailed study may take longer. You will be asked not to move during the actual imaging process, but between sequences some movement is allowed. Patients are generally required to remain still for only a few seconds to a few minutes at a time. D:\Cancer Modalities.doc 2

3 Depending on the part of the body being examined, a contrast material may be used to enhance the visibility of certain tissues or blood vessels. A small needle connected to an intravenous line is placed in an arm or hand vein. A saline solution will drip through the intravenous line to prevent clotting until the contrast material is injected about two-thirds of the way through the exam. When the exam is over the patient is asked to wait until the images are examined to determine if more images are needed. A radiologist experienced in MRI will analyze the images and send a report with his or her interpretation to the patient's personal physician. This should take only a few days or less. What will I experience during the procedure? MRI causes no pain, but some patients can find it uncomfortable to remain still during the examination. Others experience a sense of being "closed in," though the more open construction of newer MRI systems has done much to reduce that reaction. You may notice a warm feeling in the area under examination; this is normal, but if it bothers you the radiologist or technologist should be notified. If a contrast injection is needed, there may be discomfort at the injection site, and you may have a cool sensation at the site during the injection. Most bothersome to many patients are the loud tapping or knocking noises heard at certain phases of imaging. Ear plugs may help. Who interprets the results and how do I get them? A radiologist, who is a physician experienced in MRI and other radiology examinations, will analyze the images and send a signed report with his or her interpretation to the patient's personal physician. The patient receives MRI results from the referring physician who ordered the test. New technology also allows for distribution of diagnostic reports and referral images over the Internet at many facilities. What are the benefits vs. risks? Benefits Images of the soft-tissue structures of the body such as the heart, lungs, liver, and other organs are clearer and more detailed than with other imaging methods. MRI can help physicians evaluate the function as well as the structure of many organs. The detail makes MRI an invaluable tool in early diagnosis and evaluation of tumors MRI contrast material is less likely to produce an allergic reaction than the iodine-based materials used for conventional x-rays and CT scanning. MRI enables the detection of abnormalities that might be obscured by bone with other imaging methods. MRI provides a fast, noninvasive alternative to x-ray angiography for diagnosing problems of the heart and cardiovascular system. Exposure to radiation is avoided. Risks An undetected metal implant may be affected by the strong magnetic field. D:\Cancer Modalities.doc 3

4 MRI is generally avoided in the first 12 weeks of pregnancy. Doctors usually use other methods of imaging such as ultrasound on pregnant women, unless there is a strong medical reason to use MRI. What are the limitations of MRI of the Body? Bone is better imaged by conventional x-rays in some cases, and CT is preferred for patients with severe bleeding. MRI may not always distinguish between tumor tissue and edema fluid, and does not detect calcium when this is present within a tumor. In most cases the examination is safe for patients with metal implants, with the exception of a few types of implants, so patients should inform the technician of an implant prior to the test. The examination must be used cautiously in early pregnancy. MRI typically costs more than CT scanning. Computed Tomography (CT) Body What is CT Scanning of the Body? What are some common uses of the procedure? How should I prepare for the procedure? What does the equipment look like? How does the procedure work? How is the procedure performed? What will I experience during the procedure? Who interprets the results and how do I get them? What are the benefits vs. risks? What are the limitations of CT Scanning of the Body? What is CT Scanning of the Body? CT (computed tomography), sometimes called CAT scan, uses special x-ray equipment to obtain image data from different angles around the body, and then uses computer processing of the information to show a cross-section of body tissues and organs. CT imaging is particularly useful because it can show several types of tissue lung, bone, soft tissue, and blood vessels with great clarity. Using specialized equipment and expertise to create and interpret CT scans of the body, radiologists can more easily diagnose problems such as cancers, cardiovascular disease, infectious disease, trauma, and musculoskeletal disorders. CT of the body is a patient-friendly exam that involves little radiation exposure. What are some common uses of the procedure? Because it provides detailed, cross-sectional views of all types of tissue, CT is one of the best tools for studying the chest and abdomen. It is often the preferred method for diagnosing many different cancers, including lung, liver, and pancreatic cancer, since the image allows a physician to confirm the presence of a tumor and to measure its size, precise location, and the extent of the tumor's involvement with other nearby tissue. CT examinations are often used to plan and properly administer radiation treatments for tumors, to guide biopsies and other minimally invasive procedures, and to plan surgery and determine surgical resectability. CT can clearly show even very small bones, as well as surrounding tissues such as muscle and blood vessels. This makes it invaluable in diagnosing and treating spinal problems and injuries to the hands, feet, and other skeletal structures. CT images can also be used to measure bone mineral density for the detection of osteoporosis. In cases of trauma, CT can quickly identify injuries to the liver, spleen, kidneys, or D:\Cancer Modalities.doc 4

5 other internal organs. Many dedicated shock-trauma centers have a CT scanner in the emergency room. CT can also play a significant role in the detection, diagnosis, and treatment of vascular diseases that can lead to stroke, kidney failure, or even death. How should I prepare for the procedure? You should wear comfortable, loose-fitting clothing for your CT exam. Metal objects can affect the image, so avoid clothing with zippers and snaps. You may also be asked to remove hairpins, jewelry, eyeglasses, hearing aids, and any removable dental work, depending on the part of the body that is being scanned. You may be asked not to eat or drink anything for one or more hours before the exam. Women should always inform their doctor or x-ray technologist if there is any possibility that they are pregnant. What does the equipment look like? The CT scanner is a large, square machine with a hole in the center, something like a doughnut. The patient lies still on a table that can move up or down, and slide into and out from the center of the hole. Within the machine, an x-ray tube on a rotating gantry moves around the patient's body to produce the images, making clicking and whirring noises as the table moves. Though the technologist will be able to see and speak to you, you will be alone in the room during the exam. How does the procedure work? In many ways, CT scanning works very much like other x-ray examinations. Very small, controlled amounts of x-ray radiation are passed through the body, and different tissues absorb radiation at different rates. With plain radiology, when special film is exposed to the absorbed x-rays, an image of the inside of the body is captured. With CT, the film is replaced by an array of detectors, which measure the x-ray profile. Inside the CT scanner is a rotating gantry that has an x-ray tube mounted on one side and an arcshaped detector mounted on the opposite side. An x-ray beam is emitted in a fan shape as the rotating frame spins the x-ray tube and detector around the patient. Each time the x-ray tube and detector make a 360 degree rotation and the x-ray passes through the patient's body, the image of a thin section is acquired. During each rotation, the detector records about 1,000 images (profiles) of the expanded x-ray beam. Each profile is then reconstructed by a dedicated computer into a twodimensional image of the section that was scanned. Multiple computers are typically used to control the entire CT system. You might think of it like looking into a loaf of bread by cutting it into thin slices. When the image slices are reassembled by computer, the result is a very detailed, multidimensional view of the body's interior. A relatively new technique, spiral (helical) CT has improved the accuracy of CT for many diseases. A new vascular imaging technique spiral CT angiography is noninvasive and less expensive than conventional angiography, and allows doctors to see blood vessels without the need for more invasive procedures. The term "spiral CT" comes from the shape of the path taken by the x-ray beam during scanning. The examination table advances at a constant rate through the scanner gantry while the x-ray tube rotates continuously around the patient, tracing a spiral path through the patient. This spiral path gathers continuous data with no gaps between images. D:\Cancer Modalities.doc 5

6 With spiral CT, refinements in detector technology support faster, higher-quality image acquisition with less radiation exposure. The current spiral CT scans are called multidetector CT and are most commonly four- or 16-slice systems. Using 16-slice scanner systems the radiologist can acquire 32 image slices per second. A spiral scan can usually be obtained during a single breath hold. This allows allows scanning of the chest or abdomen in 10 seconds or less. Such speed is beneficial in all patients but especially in elderly, pediatric, or critically ill patients, populations in which the length of scanning was often problematic. The multidetector CT also allows applications like CT angiography to be more successful. With conventional CT, small lesions may go undetected when a patient breathes differently on consecutive scans, as a lesion may be missed by unequal spacing between scans. The speed of spiral scanning and single breath hold increases the rate of lesion detection. How is the procedure performed? The technologist begins by positioning the patient on the CT table. The patient's body may be supported by pillows to help hold it still and in the proper position during the scan. As the study proceeds, the table will move slowly into the CT scanner "doughnut." Depending on the area of the body being examined, the increments of movement may be so small that they are almost undetectable, or large enough that the patient feels the sensation of motion. A CT examination often requires the use of different contrast materials to enhance the visibility of certain tissues or blood vessels. The contrast material may be injected through an IV directly into the blood stream, swallowed, or administered by enema, depending on the type of examination. Before administering the contrast material, the radiologist or technologist will ask whether the patient has any allergies, especially to medications or iodine, and whether the patient has a history of diabetes, asthma, a heart condition, kidney problems, or thyroid conditions. These conditions may indicate a higher risk of reaction to the contrast material or potential problems eliminating the material from the patient's system after the exam. A CT examination usually takes from five minutes to half an hour. When the exam is over, the patient may be asked to wait until the images are examined to determine if more images are needed. What will I experience during the procedure? CT scanning causes no pain, and with spiral CT, the need to lie still for any length of time is reduced. For different parts of the body, the patient preparation will be different. You may be asked to swallow either water or a positive contrast material, a liquid that allows the radiologist to better see the stomach, small bowel, and colon. Some patients find the taste of the contrast material mildly unpleasant, but most can easily tolerate it. Your exam may require the administration of the material by enema if the colon is the focus of the study. You will experience a sense of abdominal fullness and may feel an increasing need to expel the liquid. Be patient; the mild discomfort will not last long. Commonly, a contrast material is injected into a vein to better define the blood vessels and kidneys, and to accentuate the appearance between normal and abnormal tissue in organs like the liver and spleen. Some people report feeling a flush of heat and sometimes a metallic taste in the back of the mouth. These sensations usually disappear within a minute or two. Some people experience a mild itching sensation. If it persists or is accompanied by hives (small bumps on the skin), the itch can be treated easily with medication. In very rare cases, a patient may become short of breath or experience swelling in the throat or other parts of the body. These can be indications of a more D:\Cancer Modalities.doc 6

7 serious reaction to the contrast material that should be treated promptly, so tell the technologist immediately if you experience these symptoms. Fortunately, with the safety of the newest contrast materials, these adverse effects are very rare. You will be alone in the room during the scan; however, the technologist can see, hear, and speak with you at all times. In pediatric patients, a parent may be allowed in the room with the patient to alleviate fear, but will be required to wear a lead apron to prevent radiation exposure. Who interprets the results and how do I get them? A radiologist, who is a physician experienced in CT and other radiology examinations, will analyze the images and send a signed report with his or her interpretation to the patient's personal physician. The personal physician's office will inform the patient on how to obtain their results. New technology also allows for distribution of diagnostic reports and referral images over the Internet at some facilities. What are the benefits vs. risks? Benefits Unlike other imaging methods, CT scanning offers detailed views of many types of tissue, including the lungs, bones, soft tissues, and blood vessels. CT scanning is painless, noninvasive, and accurate. CT examinations are fast and simple. For example, in trauma cases, they can reveal internal injuries and bleeding quickly enough to help save lives. Diagnosis made with the assistance of CT can eliminate the need for invasive exploratory surgery and surgical biopsy. CT scanning can identify both normal and abnormal structures, making it a useful tool to guide radiotherapy, needle biopsies, and other minimally invasive procedures. CT has been shown to be a cost-effective imaging tool for a wide range of clinical problems. Risks CT does involve exposure to radiation in the form of x-rays, but the benefit of an accurate diagnosis far outweighs the risk. The effective radiation dose from this procedure is about 10 msv, which is about the same as the average person receives from background radiation in 3 years. See the Safety page for more information about radiation dose. Special care is taken during x-ray examinations to ensure maximum safety for the patient by shielding the abdomen and pelvis with a lead apron, with the exception of those examinations in which the abdomen and pelvis are being imaged. Women should always inform their doctor or x-ray technologist if there is any possibility that they are pregnant. Nursing mothers should wait for 24 hours after contrast injection before resuming breast feeding. The risk of serious allergic reaction to iodine-containing contrast material is rare, and radiology departments are well equipped to deal with them. What are the limitations of CT Scanning of the Body? D:\Cancer Modalities.doc 7

8 Very fine soft-tissue details in areas such as the knee or shoulder can be more readily and clearly seen with magnetic resonance imaging (MRI). In some situations, soft tissues may be obscured by nearby bone structures in a CT. The exam is not generally indicated for pregnant women. Positron Emission Tomography (PET Imaging) What is Positron Emission Tomography (PET)? What are some common uses of the procedure? How should I prepare for the procedure? What does the equipment look like? How does the procedure work? How is the procedure performed? What will I experience during the procedure? Who interprets the results and how do I get them? What are the benefits vs. risks? What are the limitations of Positron Emission Tomography? What is Positron Emission Tomography? Positron emission tomography, also called PET imaging or a PET scan, is a diagnostic examination that involves the acquisition of physiologic images based on the detection of subatomic particles. These particles are emitted from a radioactive substance given to the patient. The subsequent views of the human body are used to evaluate function. What are some common uses of the procedure? PET scans are used most often to detect cancer and to examine the effects of cancer therapy by characterizing biochemical changes in the cancer. These scans are performed on the whole body. PET scans of the heart can be used to determine blood flow to the heart muscle and help evaluate signs of coronary artery disease. Combined with a myocardial metabolism study, PET scans differentiate non-functioning heart muscle from heart muscle that would benefit from a procedure, such as angioplasty or coronary artery bypass surgery, which would re-establish adequate blood flow. PET scans of the brain are used to evaluate patients who have memory disorders of an undetermined cause; who have suspected or proven brain tumors; or who have seizure disorders that are not responsive to medical therapy, and therefore, are candidates for surgery. How should I prepare for the procedure? PET is usually done on an outpatient basis. Your doctor will give you detailed instructions on how to prepare for your examination. You should wear comfortable, loose-fitting clothes. You should not eat for four hours before the scan. You will be encouraged to drink water. Your doctor will instruct you regarding the use of medications before the test. Note: Diabetic patients should discuss specific diet guidelines to control glucose levels during the day of the test. What does the equipment look like? D:\Cancer Modalities.doc 8

9 You will be taken to an examination room that houses the PET scanner, which has a hole in the middle and looks like a large, doughnut. Within this machine are multiple rings of detectors that record the emission of energy from the radioactive substance in your body. While lying on a cushioned examination table, you will be moved into the hole of the machine. The images are displayed on the monitor of a nearby computer, which is similar in appearance to the personal computer you may have in your home. How does the procedure work? Before the examination begins, a radioactive substance is produced in a machine called a cyclotron and attached, or tagged, to a natural body compound, most commonly glucose, but sometimes water or ammonia. This process is called radiolabeling. Once this attached substance is administered to the patient, the radioactivity localizes in the appropriate areas of the body and is detected by the PET scanner. Different colors or degrees of brightness on a PET image represent different levels of tissue or organ function. For example, because healthy tissue uses glucose for energy, it accumulates some of the radiolabled glucose, which will show up on the PET images. However, cancerous tissue, which uses more glucose than normal tissue, will absorb more of the substance and appear brighter than normal tissue on the PET images. Scientifically speaking, the radioactive substance decay leads to the ejection of positive particles called positrons. A positron travels about one to two millimeters before colliding with an electron. The collision results in a conversion from mass to energy, resulting in the emission of two gamma rays heading off in exact opposite directions. Special crystals, called photomultiplier-scintillator detectors, within the PET scanner detect the gamma rays. The scanner's special camera records the millions of gamma rays being emitted, and a connected computer uses the information and complicated mathematical formulas, called algorithms, to map an image of the area where the radioactive substance has accumulated. How is the procedure performed? A nurse or technologist will take you into a special PET examination room. You will lie down on an examination table and be given the radioactive substance as an intravenous injection (although, in some cases, it will be given through an existing intravenous line or inhaled as a gas). It will then take approximately 30 to 60 minutes for the substance to travel through your body and be absorbed by the tissue under study. During this time, you will be asked to rest quietly in a partially darkened room and to avoid significant movement or talking, which may alter the localization of the administered substance. After that time, scanning begins. This takes an additional 30 to 45 minutes. Some patients, specifically those with heart disease, may undergo a stress test in which PET scans are obtained while they are at rest, then after undergoing the administration of a pharmaceutical to alter the blood flow to the heart. Usually, there are no restrictions on daily routine after the test, although you should drink plenty of fluids to flush the radioactive substance from your body. What will I experience during the procedure? D:\Cancer Modalities.doc 9

10 The administration of the radioactive substance will feel like a slight pinprick if given by intravenous injection. You will then be made as comfortable as possible on the examination table before you are positioned in the PET scanner for the test. You will be asked to remain still for the duration of the examination. Patients who are claustrophobic may feel some anxiety while positioned in the scanner. Also, some patients find it uncomfortable to hold one position for more than a few minutes. You will not feel anything related to the radioactivity of the substance in your body. Who interprets the results and how do I get them? Patients undergo PET because their referring physician has recommended it. A radiologist who has specialized training in PET will interpret the images and forward a report to your referring physician. It usually takes one to three days to interpret, report, and deliver the results. What are the benefits vs. risks? Because PET allows study of body function, it can help physicians detect alterations in biochemical processes that suggest disease before changes in anatomy are apparent on other imaging tests such as CT or MRI scans. Because the radioactivity is very short-lived, your radiation exposure is extremely low. The substance amount is so small that it does not affect the normal processes of the body. The radioactive substance may expose the fetus of patients who are pregnant or the infants of women who are breast-feeding to the radiation. The risk to the fetus or infant should be considered related to the potential information gain from the result of the PET examination. What are the limitations of Positron Emission Tomography? PET can give false results if a patient's chemical balances are not normal. Specifically, test results of diabetic patients can be adversely affected because of blood sugar or blood insulin levels. Also, because the radioactive substance decays quickly and is effective for a short period of time, it must be produced in a laboratory near the PET scanner. It is important to be on time for the appointment and to receive the radioactive substance at the scheduled time. PET must be done by a radiologist who has specialized in nuclear medicine and has substantial experience with PET. Most large medical centers now have PET services available to their patients. Medicare and insurance companies cover many of the applications of PET, and coverage continues to increase. Finally, the value of a PET scan is enhanced when it is part of a larger diagnostic work-up. This often entails comparison of the PET scan with other imaging studies such as CT or MRI. Interventional - Cancer Patients Select a procedure from the following list: Catheter Embolization Chemoembolization Cryotherapy Radiofrequency Ablation of Liver Tumors Ultrasound-Guided Breast Biopsy D:\Cancer Modalities.doc 10

11 Vascular Access Procedures X-ray Guided Breast Biopsy Radiation Therapy Procedures - External Beam Therapy (EBT) What is external beam therapy and how is it used? Who will be involved in this procedure? What equipment is used? Who operates the equipment? Is there any special preparation needed for the procedure? How is the procedure performed? What is external beam therapy and how is it used? External beam therapy (EBT) is a method for delivering a beam of high-energy x-rays to the location of the patient's tumor. The beam is generated outside the patient (usually by a linear accelerator, see below) and is targeted at the tumor site. These x-rays can destroy the cancer cells and careful treatment planning allows the surrounding normal tissues to be spared. No radioactive sources are placed inside the patient's body. External beam therapy can be used to treat the following diseases as well as many others. Breast Cancer - see breast cancer page Colorectal Cancer (Bowel Cancer) - see colorectal cancer page Head and Neck Cancer - see head and neck cancer page Lung Cancer - see lung cancer page Prostate Cancer - see prostate cancer page Who will be involved in this procedure? Delivery of external beam therapy requires a treatment team, including a radiation oncologist, radiation physicist, dosimetrist, and radiation therapist. The radiation oncologist is a physician who evaluates the patient and determines the appropriate therapy. He or she determines what area to treat and how much radiation to deliver. Together with the radiation physicist and the dosimetrist, the radiation oncologist determines what techniques to use to deliver the prescribed dose. The physicist and the dosimetrist then make detailed treatment calculations. The radiation therapists are specially trained technologists who deliver the daily treatments. What equipment is used? Radiation oncologists use linear accelerators or cobalt machines to deliver external beam therapy. Your radiation oncologist will determine the equipment most suited to your treatment. The linear accelerator is the most commonly used device for external beam therapy. Linear Accelerator - see linear accelerator page Who operates the equipment? D:\Cancer Modalities.doc 11

12 The equipment is operated by a trained radiation therapist, a highly trained technologist. The overall treatment plan is created by the radiation oncologist, a highly trained physician specializing in treating cancer with radiotherapy Is there any special preparation needed for the procedure? The process of external beam therapy can be divided into three parts: Simulation Treatment Planning Treatment Delivery During simulation, the radiation therapist places the patient in the treatment position on a special x- ray machine or CT scanner and takes simulation x-rays. Masks, pads, or other devices may be used to help the patient to hold still during the simulation and treatment processes. The radiation oncologist then locates the tumor volume and the region to be treated on these images. The dosimetrist and the radiation oncologist determine the best arrangement of radiation beams needed to treat the patient, and the radiation therapist places small marks on the patients to help guide the daily treatments. For treatment planning the dosimetrist, radiation physicist, and radiation oncologist use a special computer to calculate the radiation dose that will be delivered to the patient's tumor and the surrounding normal tissue. They calculate how long the treatment beam must be left on to deliver the prescribed dose. In certain cases, this process may employ such techniques as threedimensional conformal therapy or intensity-modulated radiation therapy. After the simulation and treatment planning have been completed, the treatment itself can begin. How is the procedure performed? The radiation therapist brings the patient into the treatment room and places him/her on the treatment couch of the linear accelerator in exactly the same position that was used for simulation using the same immobilization devices. The therapist carefully positions the patient using the alignment lasers and the marks that had been placed on the patient during simulation. The therapist goes outside the room and turns on the linear accelerator from outside. Beams from one or more directions may be used and the beam may be on for as long as several minutes for each field. The treatment process can take from 10 to 30 minutes each day and most of the time is often spent positioning the patient. Patients usually receive radiation treatments once a day, five days a week, for a total time ranging from two to nine weeks. The patient's diagnosis determines the total duration of treatment. Occasionally, treatments are given twice a day. What will I feel during this procedure? External beam therapy is painless, but you will hear a buzzing noise during treatment. Equipment - Linear Accelerator D:\Cancer Modalities.doc 12

13 What is this equipment used for? How does it work? Who operates this equipment? How is safety ensured? What is this equipment used for? A linear accelerator (LINAC) is the device most commonly used for external beam radiation treatments for patients with cancer. The linear accelerator can also be used in stereotactic radiosurgery similar to that achieved using the gamma knife to targets within the brain. The linear accelerator can also be used to treat areas outside of the brain. It delivers a uniform dose of highenergy x-ray to the region of the patient's tumor. These x-rays can destroy the cancer cells, while sparing the surrounding normal tissue. How does it work? The linear accelerator uses microwave technology (similar to that used for radar) to accelerate electrons in a part of the accelerator called the wave guide and then allows these electrons to collide with a heavy metal target. As a result of these collisions, high energy x-rays are scattered from the target. A portion of these x-rays is collected and then shaped to form a beam that matches the patient's tumor. The beam comes out of a part of the accelerator called a gantry, which rotates around the patient. The patient lies on a moveable treatment couch and lasers are used to make sure the patient is in the proper position. Radiation can be delivered to the tumor from any angle by rotating the gantry and moving the treatment couch. Who operates this equipment? The patient's radiation oncologist prescribes the appropriate treatment volume and dosage. The medical radiation physicist and the dosimetrist determine how to deliver the prescribed dose and calculate the amount of time it will take the accelerator to deliver that dose. Radiation therapists operate the linear accelerator and give patients their daily radiation treatments. How is safety ensured? Patient safety is very important. During treatment the radiation therapist continuously watches the patient through a closed-circuit television monitor. There is also a microphone in the treatment room so that the patient can speak to the therapist if needed. Port films (x-rays taken with the treatment beam) are checked regularly to make sure that the beam position doesn't vary from the original plan. The linear accelerator sits in a room with lead and concrete walls so that the high-energy x-rays do not escape. The radiation therapist must turn on the accelerator from outside the treatment room. Because the accelerator only gives off radiation when it is actually turned on, the risk of accidental exposure is extremely low. Indeed, pregnant women are allowed to operate linear accelerators. Quality control of the linear accelerator is also very important. There are several systems built into the accelerator so that it won't deliver a higher dose than the radiation oncologist prescribed. Each morning, before any patients are treated, the radiation therapist uses a piece of equipment called a tracker to make sure that the radiation intensity is uniform across the beam. In addition, the radiation physicist makes more detailed weekly and monthly checks of the accelerator beam. D:\Cancer Modalities.doc 13

14 Equipment - Gamma Knife What is this equipment used for? How does it work? Who operates this equipment? How is safety ensured? What is this equipment used for? The gamma knife, and its associated computerized treatment planning software, enables physicians to locate and irradiate relatively small targets in the head (mostly inside the brain) with extremely high precision. Intense doses of radiation can be given to the targeted area(s), while largely sparing the surrounding tissues. The gamma knife can be used for a wide variety of problems. For example, it can be used to treat selected malignant tumors that arise in or spread to the brain (primary brain tumors or metastatic tumors), benign brain tumors (meningiomas, pituitary adenomas, acoustic neuromas), blood vessel defects (arterio-venous malformations) and functional problems (trigeminal neuralgia). Possible future uses for epilepsy and Parkinson's disease currently are being evaluated. The gamma knife loses its ability to spare surrounding normal tissues as the number of targets increases; is not suitable for large targets (larger than three to four centimeters in size); and is not used for targets outside of the head. How does it work? The gamma knife works by a process called sterotactic radiosurgery, which uses multiple beams of radiation converging in three dimensions to focus precisely on a small volume, such as a tumor, permitting intense doses of radiation to be delivered to that volume safely. A special headframe that has three-dimensional coordinates built into it is attached to the patient's skull by four screws placed under local anesthesia. Then magnetic resonance imaging (MRI) and/or a computed tomography (CT) scan and/or a catheter angiogram are obtained and the results are sent to the gamma knife's planning computer system. Physicians (neurosurgeons, radiation oncologists and/or neuroradiologists) and medical radiation physicists then use the planning computer to determine the exact relationship between the target lesions and the frame and calculate how to set the controls of the gamma knife to treat the targets optimally. Targets often are best treated by combinations of several aimings, commonly known as "shots." The physicians and physicists routinely consider numerous fine-tuning adjustments until an optimal plan is created. Simultaneously, an optimal dose is selected. Using the three-dimensional coordinates determined in the planning process, the frame is then precisely attached to the gamma knife unit to guarantee that when the unit is activated, the target is placed exactly in the center of approximately 200 precisely-aimed, converging beams of (Cobalt- 60 generated) gamma radiation. Treatment takes anywhere from several minutes to a few hours to complete, depending on the shape of the target and the dose required. Patients do not feel the radiation. Following treatment, the headframe is removed; each target generally requires only one treatment session. Who operates this equipment? D:\Cancer Modalities.doc 14

15 A multidisciplinary team approach provides patients with the greatest safety. The team is most commonly comprised of a radiation oncologist, a medical radiation physicist and a neurosurgeon all specially trained in the use of the gamma knife with support from nursing staff, anesthesiologists (for patients who are unable to cooperate, such as children) and radiation therapists who work together to provide patients with the high quality care they deserve. How is safety ensured? Because placement accuracy of the shots is critical to localization of the radiation (to the fraction of a millimeter) anything that would degrade this precision is unacceptable. Rigid attachment of the headframe, geographic targeting accuracy of the MRI, shaping of the volume of tissue to be treated (selection of the number, size and relative intensity of the shots), and accuracy of attachment of the frame to the gamma knife unit are all critical. As is true of all radiation therapy, correct selection and calculation of the amount of radiation to deliver are essential. A qualified medical physicist assures that the imaging and treatment planning computers and software are correct and acceptable. The mechanical functions of the machine are tested on a regular basis to ensure the safety of patients and medical staff. D:\Cancer Modalities.doc 15