|Image courtesy of Elekta Synergy
Johns Hopkins University
What is radiation therapy?
Radiation therapy is a cancer treatment that uses high-energy radiation, in the form of waves (such as x-rays) or particles (such as protons), to kill cancer cells or prevent them from growing and dividing. Radiation therapy can prevent pancreatic tumors from growing and sometimes shrinks them. Since radiation therapy is directed to a specific (focused) area, it is considered a local treatment.
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.
Why is radiation therapy used?
Doctors may use radiation therapy to relieve pain caused by the tumor, to keep inoperable tumors from growing or to destroy cancer cells that may remain in the area after surgery. In contrast to chemotherapy, radiation therapy does not treat cancer cells that have spread to other parts of the body.
Radiation therapy can also be given as part of neoadjuvant therapy. Neoadjuvant therapy is treatment that is given before surgery. Neoadjuvant radiation therapy is given to reduce the size of the tumor so that it is more easily removed during surgery without leaving cancer behind.
In other cases, radiation therapy will be given as adjuvant therapy, or treatment given after the surgical removal of a pancreatic tumor. Adjuvant radiation therapy is given to kill microscopic cancer cells that may be left behind at the surgical site, in an attempt to keep the cancer from recurring locally.
Is chemotherapy given with radiation therapy?
Radiation therapy may be given alone or in combination with chemotherapy. When chemotherapy is given in combination with radiation, usually a low dose of chemotherapy is used. Chemotherapy acts as a “radiosensitizer” that can enhance the effect of the radiation on the tumor.
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.
Where and how often is radiation therapy given?
Radiation therapy is usually an outpatient treatment. Patients go to the hospital or clinic for radiation therapy, but rarely need to stay overnight in the hospital. Standard external beam radiation therapy is given 5 days a week for 3-6 weeks. Each treatment lasts only a few minutes.
Patients receiving IMRT will usually receive treatment 5 days a week for a number of weeks. Each treatment session usually takes between 10 and 30 minutes.
SBRT is given as high doses of radiation over just a few treatments, usually 1-5 sessions overall.
What type and dose of radiation will the patient receive?
The radiation oncologist will determine the right dose and type of radiation for the patient. The dose is based on the amount required to kill the cancer cells while minimizing the effect on surrounding healthy cells.
IMRT, SBRT (including CyberKnife®), proton therapy and internal radiation therapy have not proven to be more effective or to result in fewer side effects than standard radiation therapy in pancreatic cancer. The high dose radiation used in some of these treatments could be harmful if administered incorrectly. These radiation methods are most safely administered to pancreatic cancer patients inside the setting of a clinical trial.
What are the side effects of radiation therapy?
Radiation therapy treatments do not hurt. Individuals may experience some abdominal discomfort towards the end of the treatment series, but the actual treatment session is not painful.
The effects of radiation therapy can build up over time. The most common side effects of radiation therapy for pancreatic cancer are loss of appetite, nausea, diarrhea and fatigue. Patients may experience mild skin redness, but that is uncommon in pancreatic cancer treatment. Side effects usually peak 4-5 weeks after the first radiation treatment and resolve within 1-2 weeks after treatment is complete. Many of the side effects can be treated with medications and ointments prescribed by a healthcare professional.
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