What is Radiation?
Radiation describes the way energy moves from one place to another. Sometimes this is in the form of particles such as protons, while other times it is in the form of waves like x-rays or visible light. The various types of radiation are grouped according to how much energy they contain. Low energy radiation, like radio waves and heat, is known as non-ionizing radiation. High energy radiation, such as ultraviolet (UV) light from the sun and x-rays, is known as ionizing radiation because it has enough energy to break chemical bonds and knock electrons (negatively charged particles) out of atoms. When these changes take place in cells, it can sometimes cause enough damage to kill the cells. As a result, such high-energy x-rays or other particles can be used to destroy cancer cells in a treatment called radiation therapy.
What is Radiation Therapy?
Radiation therapy is the use of high-energy x-rays or other particles to destroy cancer cells. A doctor who specializes in giving radiation therapy to treat cancer is called a radiation oncologist. The most common type of radiation treatment is called external-beam radiation therapy, which is radiation given from a machine outside the body. A radiation therapy regimen (schedule) usually consists of a specific number of treatments given over a set period of time.
When it is Prescribed?
Radiation therapy may be given for pancreatic cancer in the following situations:
* After surgery for patients who have a high risk of their cancer coming back in the area of surgery. This includes patients with a tumor that is large or was removed with close or positive surgical margins, meaning that cancer cells are seen up to or very close to the edge of the tissue removed during surgery.
* Before surgery to try to shrink a borderline resectable tumor.
* For patients with locally advanced, unresectable disease.
* To relieve severe pain for people with metastatic cancer.
What are the different types of radiation therapy?
There are two main types of radiation therapy, external beam radiation therapy and internal radiation therapy.
External beam radiation therapy delivers radiation by using a machine outside the body which directs a beam or multiple beams of radiation through the skin to the tumor or tumor bed. External beam radiation therapy is commonly used in treating pancreatic cancer patients.
Internal radiation therapy (brachytherapy) delivers radiation through radioactive material implanted in or near the cancer. This type of radiation therapy is rarely used in pancreatic cancer patients.
In addition to standard external beam radiation therapy, the following two methods of planning and delivering external beam radiation are currently used in pancreatic cancer treatment. These specialized methods are able to minimize the amount of radiation delivered to normal tissues and are used when a higher dose of radiation is recommended:
Intensity-modulated radiation therapy (IMRT) is a type of external beam radiation therapy that delivers focused radiation to the tumor by modulating (varying) the intensity of the radiation beam under precise computer control. By using three-dimensional computer imaging to determine the size, shape and location of the tumor, and by varying the intensity of the radiation dose, IMRT allows a higher dose of radiation to be administered to the tumor while minimizing the amount of radiation delivered to healthy tissue near the pancreas, such as the duodenum (the first portion of the small intestine). This may lead to fewer side effects and allow higher doses of radiation to be delivered safely, compared to standard radiation therapy.
Stereotactic body radiation therapy (SBRT) is a type of external beam radiation therapy designed to deliver high doses of radiation precisely to small tumors, usually in five or fewer treatments. SBRT uses multiple narrow radiation beams to target small, well-defined areas. In order for SBRT to be delivered safely in pancreatic cancer patients, the tumor must remain motionless or the machine delivering the radiation must be able to adjust for any movement of the tumor, such as during breathing. Patients may be fitted with a customized device to keep the body perfectly still or the treatment machine may have the ability to limit, monitor and adjust for any movement during the treatment. Also, small metallic seeds may be implanted near the tumor before treatment begins to better track the location of the tumor during treatment. CyberKnife is one type of SBRT. Some studies have suggested that the delivery of high doses of radiation in a few treatments is difficult to accomplish without damaging the intestinal tract.
There is currently no evidence that this type of radiation therapy is better than standard radiation therapy for pancreatic cancer. In fact, one study has shown that stereotactic radiation for pancreatic cancer caused ulcers to develop in the duodenum. There are ongoing studies to determine the appropriate radiation dose and frequency of radiation doses given using SBRT to avoid damaging the duodenum. Therefore, SBRT is still being studied in clinical trials for pancreatic cancer and its usage is only recommended as part of a clinical trial.
Proton beam radiation therapy is a type of external beam radiation therapy that uses proton beams rather than x-rays. Protons are charged particles that deposit most of their energy at a very narrow area within the body. Because of this characteristic, proton beam therapy allows a higher, more conformed dose of radiation to be delivered to the tumor, while sparing surrounding healthy tissue. Therefore, it generally causes fewer side effects. Proton therapy is only available at very few centers throughout the country and is being studied in clinical trials for pancreatic cancer.
Chemotherapy Given with Radiation Therapy
Often, chemotherapy will be given at the same time as radiation therapy because it can enhance the effects of the radiation therapy, which is called radio-sensitization. Combining chemotherapy and radiation therapy may occasionally help shrink the tumor enough so it can be removed by surgery. However, chemotherapy given at the same time as radiation therapy often has to be given at lower doses than when given alone.
It is important to note that radiation may be helpful for decreasing the likelihood of a pancreatic cancer returning or re-growing at the original location, but that there remains much uncertainty as to how much, if at all, it lengthens a person’s life.
The chemotherapy drugs most commonly used with radiation therapy are fluorouracil (5-FU), capecitabine (Xeloda®) and gemcitabine (Gemzar®). 5-FU is used most often since there is more experience using this drug in combination with radiation and there are generally fewer side effects.
Some of the common side effects of radiation therapy include:
* Skin changes (like a sunburn) in areas getting radiation
* Nausea and vomiting
* Poor appetite
* Weight loss
Radiation can also lower blood counts and can increase the risk of serious infection.
Usually these effects go away a few weeks after the treatment is complete. When radiation is given with chemotherapy the side effects are often worse. Ask your doctor what side effects to expect and how to prevent or relieve them.
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