|Image courtesy of Elekta Synergy
Johns Hopkins University
What is radiation therapy?
Radiation therapy uses high-energy x-rays or other types of high energy waves to kill cancer cells or prevent them from dividing. Radiation treatment often prevents pancreatic tumors from growing and sometimes shrinks them. Since radiation therapy only affects the cancer cells in the area at which it is directed, 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 uses a machine outside the body called a linear accelerator to focus x-rays directly on the tumor or tumor bed.
- Internal radiation, or brachytherapy, involves the implantation of a small amount of radioactive material in or near the cancer. This type of radiation is rarely used in pancreatic cancer patients.
There are three investigational types of radiation treatment.
- Intensity-Modulated Radiation Therapy (IMRT) is an advanced treatment that uses computer-controlled x-ray machines to deliver precise doses of radiation to a malignant tumor or specific areas within the tumor. The radiation dose is designed to match the three-dimensional (3-D) shape of the tumor. Compared with conventional radiation therapy, a higher dose can be used while minimizing exposure to surrounding normal tissues which leads to fewer side effects. In contrast to stereotactic radiation (described below), the treatment is usually delivered over the course of five to six weeks, and does not require implantation of metallic seeds.
- CyberKnife® is a stereotactic radiation treatment meaning that it uses very accurately aimed doses of radiation to treat tumors. CyberKnife® is an outpatient procedure that uses a robotic arm to deliver x-rays with a high degree of precision from many different angles to the tumor without damaging surrounding tissue. In order for this treatment to be delivered safely and effectively in pancreatic cancer patients, the tumor must remain motionless and the duodenum, or top portion of the small intestine, must be protected. To address these difficulties, metallic seeds are implanted in the tumor before treatment and the patient is asked to hold their breath while the machine is on. CyberKnife® treatment is usually given as large doses of radiation in 1-3 treatments. Very few centers do this complex treatment well and there is currently no evidence that it is better than conventional radiation therapy for pancreatic cancer. In fact, one study has shown that stereotactic radiation for pancreatic cancer caused ulcers to develop in the duodenum. CyberKnife® treatment is still being studied in clinical trials for pancreatic cancer.
- Proton Beam Radiation Therapy uses a machine called a cyclotron to produce high-energy proton beams. Protons are subatomic charged particles (particles that are less complex than an atom) that kill cancer cells in a similar way to x-rays. The main difference is that proton beams can be focused on the target area with less radiation hitting surrounding tissues. Therefore, there are generally fewer side effects compared with conventional radiation therapy.
Why is radiation therapy used?
Doctors may use radiation therapy to relieve pain caused by the tumor, to try to shrink the tumor before surgery or to destroy cancer cells that may remain in the area after surgery. Radiation therapy is also used to keep inoperable pancreatic tumors from progressing. In contrast to chemotherapy, radiation does not treat cancer cells that have spread to other parts of the body.
Is chemotherapy given with radiation therapy?
Radiation therapy may be given alone or in combination with chemotherapy. Chemotherapy that is given in conjunction with radiation is usually a lower dose than what is generally administered when chemotherapy is given alone. Chemotherapy acts as a “radiosensitizer” which can enhance the effect of the radiation on the tumor.
The chemotherapy drugs most commonly used together with radiation therapy are fluorouracil (5-FU) and gemcitabine (Gemzar®). 5-FU is used most often since there is more experience using this drug combination with radiation and there are fewer side effects.
How often and where is radiation therapy given?
Radiation therapy is usually given five days a week, for two to five weeks. Each treatment lasts only a few minutes. Patients go to the hospital or a clinic for radiation therapy, but it is generally an outpatient treatment so patients do not have to stay overnight in the hospital.
What type and dose of radiation will the patient receive?
A healthcare team, including the radiation oncologist and technicians will determine the right dose of radiation. This dose will be based on the amount required to kill the cancer cells while minimizing the effect on surrounding healthy cells. Conventional external radiation is the standard of care radiation treatment for pancreatic cancer patients.
Proton therapy, brachytherapy, IMRT and CyberKnife® treatment are not proven to be more effective or to result in fewer side effects than conventional radiation treatment in pancreatic cancer. Higher doses of radiation with 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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