The Science of Radiotherapy
"Doctor P. Can you explain radiation therapy in simple terms?"
"Not easily done Ms. F. - but I'll try.."
"It uses a type of energy -"ionizing"- to kill cancer cells and shrink tumors.
"We destroy cells in the "target tissue" by damaging their genetic material, making it impossible for them to grow and divide.
"About half of all cancer patients receive some type of radiation therapy. Although radiation damages cancer cells, it also affects normal cells. Most normal cells can recover -and function properly again. Of course one needs to limit any harm to healthy tissue.
"There are different types of radiation, different ways to deliver it. For example, some methods penetrate more deeply in the body than others. Some methods can be very finely controlled to treat perhaps one inch of tissue, without damage to nearby tissue or organs.
"Other methods are better for treating larger areas, the goal being to completely destroy an entire tumor. Another aim may be to shrink a tumor and relieve symptoms. In either case we plan treatment in very individual ways to spare as much healthy tissue as possible. Radiation is used by itself or often in combination with other treatments, such as chemotherapy or surgery".
Salome: "When is radiation therapy used?
Dr. Porter: "We use it treat almost every type of solid tumor -cancers of the brain, breast, cervix, larynx, lung, pancreas, prostate, skin, spine, stomach, uterus, or soft tissue sarcomas. And for cancer-related disease, leukemia and lymphoma for instance.
"The amount applied depends on a number of factors, the type of cancer, or whether there are tissues and organs nearby that may be damaged. For some, radiation may be given to areas with no immediate evidence of cancer, to prevent cancer cells becoming established. This is called "prophylactic radiation". We also use it to reduce pain that has spread to cancerous bone or other parts of the body. This is called "palliative radiation therapy".
Salome: "What is the difference between external. internal and systemic radiation?"
Dr. Porter: "You mean how do we choose which one to use?
"It depends on the type of cancer, where and how far into the body we need to go. Also on the patient's general health and medical history, and whether we decide that the patient needs other types of treatment.
"We use external radiation with a machine outside the body or internally by a placement (implant) inside the body.
"Systemic radiation uses unsealed radioactive material that passes through the body.
"Most people who receive radiation therapy for cancer have external radiation. Some receive a combination, one after the other, or at the same time. External radiation is the usual -on an outpatient basis without time in hospital. Often it's used to relieve pain or ease other problems when cancer spreads to body parts away from the primary site.
"Another use of radiation is called "Intra-operative" (IORT). That's external radiation given during surgery, of course in a hospital. IORT is used to treat localized cancers that can't be completely removed or have a high risk of coming back in nearby tissues.
"After most of the cancer is removed, one large, high dose of radiation is aimed directly at the tumor site during surgery (nearby healthy tissue is protected with special shields). The patient must recover in hospital. It is most often used for the thyroid, colorectal, gynecological, small intestine, and pancreas cancers and also being studied for brain tumors and pelvic sarcomas in adults.
"Prophylactic cranial irradiation (PCI) is also external radiation given to the brain when the primary cancer (for example, small cell lung cancer) has a high risk of spreading to the brain.
"Internal radiation therapy (also called brachytherapy) uses a radiation implant that is placed close to, or inside the tumor. The implant is put directly into the body and the patient may need a short stay in hospital.
"Usually it's delivered in one of two ways. Both methods use sealed implants to treat tumors of the head and neck, prostate, cervix, ovary, breast, perianal and pelvic regions. It is commonly used to treat uterine cancer. Researchers are studying internal radiation therapy for other cancers, including breast, bronchial, cervical, gallbladder, oral, rectal, tracheal, uterine and vaginal.
"Systemic radiation therapy uses radioactive materials such as iodine 131 and strontium 89. These may be taken by mouth or injected into the body. Systemic radiation therapy is sometimes used to treat cancer of the thyroid and adult non-Hodgkin's lymphoma. We are in close contact with researchers currently investigating these new treatments".
Salome: "What are these?"
Dr. Porter: "Well, Hyperthermia, the use of heat, is being studied in conjunction with radiation therapy. Researchers have found that the combination of heat and radiation can increase the response rate of some tumors. Researchers are also studying the use of radio-labeled antibodies to deliver doses of radiation directly to the cancer site.
"Antibodies are highly specific proteins that are made by the body in response to the presence of antigens (substances recognized as foreign by the immune system). Some tumor cells contain specific antigens that trigger the production of tumor-specific antibodies. Large quantities of these antibodies can be made in the laboratory and attached to radioactive substances (a process known as radio-labeling). Once injected into the body, the antibodies seek out cancer cells, which are destroyed by the radiation. This approach can minimize the risk of radiation damage to healthy cells. The success of this technique depends on identifying appropriate radioactive substances and determining the safe and effective dose of radiation that can be delivered in this way.
"Two of these treatments have been approved for advanced adult non-Hodgkin's lymphoma (NHL). Clinical trials of radio-immunotherapy are under way with a number of cancers, including leukemia, NHL, colorectal cancer, and cancers of the liver, lung, brain, prostate, thyroid, breast, ovary, and pancreas. Scientific advances now lead to new discovery. Investigation goes on to attract radioactive materials directly to cancer cells. Laboratory and clinical research is in progress using new molecular therapeutic agents. All this work will go on until.."
Salome: "You specialize in IMRT? Why? What is it?"
Dr. Porter: "This is a new form of radiation therapy Intensity Modulated Radiation Therapy using computer generated images to plan and then deliver more tightly focused radiation beams to cancerous tumors than is possible with conventional radiotherapy.
"We can deliver a precise radiation dose that conforms to the shape of the tumor while significantly reducing the amount of radiation to surrounding healthy tissue. Consequently the technique can increase the rate of tumor control while significantly reducing adverse side effects.
"Both breast cancer and prostate cancer patients are benefiting from this newly advanced therapy. IMRT also is used to treat cancer of the head and neck, cervix, colon, rectum and brain. The radiation consists of thousands of tiny beamlets, each focusing on a different area of the tumor. These beams can turn corners or make concave shapes. This degree of precision and control is not possible with other conventional radiation techniques. The powerful computer program optimizes our treatment plan designed by the physician to generate information about tumor size shape and location in the body.
"The equipment can be rotated around the patient to send radiation beams from the most favorable angles to give the tumor a higher dose while preserving normal healthy tissue. IMRT is so precise, we are able to deliver three times the normal radiation dose to the tumor. Basically this is a new type of 3D beam radiation of varying intensities that delivers different doses to small areas of tissue -all at the same time.
"A great advantage is that one can deliver higher doses within the tumor, and lower doses to nearby healthy tissue. Given daily this potentially shortens the overall treatment time and the ultimate success of the treatment.
"Because IMRT equipment is highly specialized, not every radiation oncology clinic has use of it. The cost of the equipment and the amount of specialized training needed to operate IMRT restricts its use worldwide to only a very few facilities at this time."
Salome: "Why is IMRT better?"
Dr. Porter: "It's the most precise form of radiation therapy available today, allowing an escalation of the radiation dose to cancer cells, and in some cases enabling extreme precision to specific regions within a tumor"
Salome: "Will radiation therapy make the patient radioactive?"
Dr. Porter: "Generally no. Precautions are always taken in all instances.
"External radiation therapy will not make the patient radioactive. One does not need to avoid being around other people because of your treatment. Even hugging, kissing or having sexual relations poses no risk of radiation exposure.
"Internal radiation therapy by sealed implants emits radioactivity and this is why hospital time may be needed. The sealed sources deliver most of their radiation mainly around the area of the implant, so while the area around the implant is radioactive, the patient's whole body is not.
"Systemic radiation therapy uses unsealed radioactive materials that travel throughout the body. Some of this radioactive material will leave the body in saliva, sweat and urine before the radioactivity decays, making these fluids radioactive. So, certain precautions are used for people who come in close contact with the patient. The patient's doctor or hospital nurse will provide information if these special precautions are needed".
Salome: "How do you know how much radiation to give?"
Dr. Porter: "Good question. This called the dose or dosage. Before 1985, dose was measured in a unit called a "rad" (radiation absorbed dose). Now it's called a "gray" (Gy). One Gy is equal to 100 rads; one centigray (cGy) is the same as 1 rad. Different tissues can tolerate various amounts of radiation (measured in centigrays). For example, the liver can receive a total dose of 3,000 cGy, while the kidneys can tolerate only 1,800 cGy.
"The total dose of radiation is usually divided into smaller doses given daily over a specific time period. This maximizes the destruction of cancer cells while minimizing the damage to healthy tissue. The doctor works with known ratios -"therapeutic ratio". This compares damage to cancer cells with damage to healthy ones. We can increase the damage to cancer cells without doing greater harm to healthy ones".
Salome: "Who plans and who gives the radiation treatment?"
Dr. Porter: "All our in-house medical staff are involved. The radiation therapy team includes the Senior Radiation Oncologist and other specialist doctors: there's a "Dosimetrist", who determines the proper radiation dose; the Radiation Physicist who makes sure that the machine delivers the right amount of radiation to the correct site in the body; and the Radiation Therapist, who actually delivers the treatment.
"Often, radiation treatment is only one part of the patient's total therapy. We use a combined modality therapy, using radiation along with the latest drug treatment. The radiation oncologist also teams with a patient's doctor, surgeon, radiologist, who may re-create x-rays and pathologist (who identifies disease by studying cells and tissue under a microscope).
"All these professionally qualified individuals plan together the patient's total course of therapy. A close working relationship between our team and, the patient's medical or pediatric doctor, surgeon or pathologist is also important to plan a total therapy".
Salome: "How do you plan a treatment?"
Dr. Porter: "Diagnosis, careful Individual assessment is just so vital. There are so many types of radiation now and so many ways to deliver it".
"Before radiation therapy is given, our therapy team must know the amount and type of radiation suitable. If the patient is to have external radiation, x-ray simulation defines the exact place on the body where the radiation will be aimed. Most patients have more than one.
"Simulation may also involve CT scans or other imaging studies to help the radiation therapist plan how to direct the radiation.
"Simulation may result in some changes to the treatment plan so that the greatest possible amount of healthy tissue is spared from radiation. The areas chosen are marked. These marks are recorded by computer to determine the exact site of the initial identification and for any treatment later."
"Body molds may be made from plaster or foam to keep the original position or prevent slight movement during treatment. Shields are used to protect organs and tissues near the treatment field. When the simulation is complete, the radiation therapy team meets to decide how much radiation is needed, how it should be delivered, and how many treatments the patient will need".
Salome: "What is the IMRT treatment program like?"
Dr. Porter: "The first visit is sometimes longer than subsequent ones so that all the x-ray films and quality assurance checks can be made.
"A typical treatment session lasts about 15 minutes. Radiation is usually given five days a week for six or seven weeks. For palliative care the course of treatment may last for two or three weeks. These types of schedules send small amounts of daily radiation rather than a few large doses help protect normal body tissues in the treatment area.
"Weekend rest breaks allow normal cells to recover. The total dose of radiation and the number of treatments depends on the size and location of the cancer, type of tumor, the patient's health etc. as I said.
"But it is typically dependent on the physician's approach. After a physical exam and review of x-rays and medical records, the radiation oncologist must determine the course of treatment for each patient as far as possible within the patient's schedule".
Salome: "How long is the treatment?"
Dr. Porter: "The procedure covers diagnostic x-rays, a pathology report, a physical exam, PET scan, CT and, or MRI treatment.
"We then specify the exact dose of radiation and its delivery method. Most cases require the simulation I have mentioned so the patient keeps to the same position every day. Small tattoos are used marking the skin to help align the equipment with the target area. Further X-rays may be taken.
"Following the simulation, a targeted CT scan is performed in the treatment position so that the doctor can define the tumor area. MRI and PET scan images also are again used to define the tumor absolutely when applicable. Simulation and CT scanning typically take an hour to an hour and a half. IMRT planning usually takes several days.
."When the plan is complete the patient is given an appointment to begin the radiation treatments.
Treatment sessions last typically 15- 20 minutes." |
