Radiation therapy (sometimes referred to as radiotherapy, x-ray therapy or irradiation) has been used to treat many types of cancer for more than 100 years. Radiation therapy refers to the careful use of various forms of radiation, which damages cells, to treat cancer.
The physicians who specialize in radiation therapy are called radiation oncologists. They work closely with other physicians and a large radiation oncology team including nurses, physicists and radiation therapists. Radiation therapy works by damaging the DNA (the control center) of cancer cells, destroying the ability of the cancer cells to divide, which can kill cancer cells and shrink tumors. When these damaged cancer cells die, the body naturally eliminates them. Normal cells may also be affected by radiation, but they can repair themselves in a way that cancer cells cannot.
Radiation can be used to shrink liver tumors to ease symptoms such as pain, pressure on other organs such as the stomach, or to prevent damage to bones that may contain metastatic tumors. The liver itself, and other abdominal organs such as the stomach and intestines, are very sensitive to the effects of radiation and can be damaged easily. Therefore, radiation to the liver and abdomen should be performed at a cancer center that specializes in giving radiation to the liver.
A specially trained radiation oncologist, who makes a detailed treatment plan for each individual patient, administers EBRT. The treatment plan is a map of the patient’s tumor that describes what total dose of radiation will be given over a certain number of days or weeks.
Newer radiation techniques such as proton beam radiotherapy, which uses a different form of energy that is absorbed specifically by tumors, enable the radiation oncologist to deliver somewhat higher doses of energy to the tumor, while sparing nearby normal tissue. In this way, the risk of the common side effects of radiation to the liver, such as nausea, ulcers in the stomach or intestines, are minimized. In general, smaller liver tumors are more easily and safely radiated than large tumors, however rapid advances in EBRT techniques are improving the effectiveness and safety of radiating large liver tumors.
Prior to radiation therapy, a simulation is conducted at which point a CT scan is usually done to help in the development of a radiation plan. Sometimes customized devices are used to help the patient remain in the same position during each radiation treatment. Patients are sometimes treated with repeat breath holds to reduce liver motion due to breathing. A computer is used to help design the best radiation treatment plan. After reviewing this information, the radiation oncologist decides the exact course of radiation therapy.
A machine referred to as a linear accelerator is used to direct high-energy rays at the cancer delivered through the skin. The linear accelerator is located outside body and does not touch your skin. Receiving external beam radiation is similar to having a CT scan. It is painless. It is usually given as a series of daily outpatient procedures, but can be delivered in one treatment (referred to as a “fraction”) or as many as 35 treatments over 7 weeks. Each radiation treatment usually takes 20 minutes or less, and can range from five to 60 minutes. Most of the time is taken for the patient to be positioned for treatment, for the equipment to be set up, and for imaging to locate the liver tumor immediately prior to therapy.
A common side effect of radiation therapy is fatigue. The exact cause of this side effect is unknown. Other less common side effects are nausea, vomiting, and diarrhea and temporary liver pain. The radiation will damage the liver surrounding the tumor.
This may lead to a change in how the liver functions, and the physician will be careful to reduce the risk of injury to the liver. If the stomach is included in the radiation field there may be an increased risk for developing an ulcer or bleed, so the physician may recommend medications to decrease the chance of ulcer development.
Several special types of radiation therapy delivery can be used to reduce the volume of normal tissues that need to be irradiated. These include:
- Three Dimensional Conformal Radiation Therapy (3D-CRT) uses computers to produce an accurate image of the tumor and surrounding organs. This allows multiple radiation beams to be shaped to the size and shape of the tumor.
- Intensity Modulated Radiation Therapy (IMRT) better shapes high doses around the tumor.
- Stereotactic Body Radiotherapy (SBRT) refers to the precise focused delivery of very potent radiation doses, delivered in fewer treatments (usually 5 or fewer treatments), requiring many more beams than conventional radiation therapy.
- Proton Beam Therapy compared to traditional photon beam radiation, a proton beam has some unique features that make it a particularly attractive option for treatment of liver tumors.
- First, it has a low “entrance dose” (the dose delivered along the path of the beam from the surface of the skin to the front of the tumor), thus minimizing dose to healthy tissues in front of the tumor and potentially reducing treatment-related side-effects.
- Second, it has virtually no “exit dose” beyond the tumor, again reducing dose to healthy tissues.
- Third, in the case of liver tumors, it travels through homogenous tissue (liver) to get to the tumor, making it less likely that changes in tissue density along its path may modify its characteristics (range of penetration).
- Lastly, it is able to deliver a very potent dose of radiation directly to the tumor.
Last Updated on 10/10/2011 10:18:11 AM