There are two broad categories of radiation therapy; both are designed to target the tumor while minimizing exposure to the healthy surrounding tissue. In the first category, the radiation is administered much like an x-ray — a procedure called external beam radiation therapy (EBRT). This type of radiation therapy is usually delivered by a machine called a linear accelerator, or linac. The second category is brachytherapy or internal radiation therapy. Brachytherapy treats cancer by placing radioactive sources inside the body, directly into or next to the treatment area.
External Beam Radiation Therapy
VMAT / RapidArc, is an advanced form of IMRT that was introduced in 2007. VMAT, or volumetric modulated arc therapy, uses special software and an advanced linear accelerator to deliver IMRT treatments up to eight times faster than what was previously possible. Unlike conventional IMRT treatments, during which the machine must rotate several times around the patient or make repeated stops and starts to treat the tumor from a number of different angles, VMAT can deliver the dose to the entire tumor in a single rotation — in less than two minutes.
IMRT, or intensity modulated radiation therapy with image-guidance, is a commonly performed radiation treatment technique for prostate cancer. This technique uses the 3-D scans of your body to guide the beams of radiation to the tumor from many different angles. At each of these angles, the intensity of the radiation is varied (modulated) and the shape of the beam is changed to match the shape of the tumor. These adjustments enable the prescribed amount of radiation to be delivered to each part of the tumor, minimizing exposure to the surrounding healthy tissue. Treatments are typically given up to five treatment times per week over a period of four to six weeks. Each session typically takes from 5 to 20 minutes. Talk to your oncologist about what you may expect with respect to your schedule.
IGRT, or image-guided radiation therapy, is an advanced type of external beam radiation therapy for prostate cancer. This technology utilizes images taken by several scans to create a detailed, three-dimensional picture of the target area and surrounding tissue, which enables your team to view the tumor and its position in your body before and during each treatment. The scans typically are produced by computed tomography (CT scan), magnetic resonance imaging (MRI), or positron emission tomography (PET scan).
SBRT, or stereotactic body radiation therapy, also uses image-guidance and IMRT, but differs from conventional treatments in one important way: rather than having treatment five days a week for several weeks, SBRT is delivered in a few very large radiation doses given in five or fewer sessions. The use of SBRT for prostate cancer is still being studied, and is not very common. Your radiation oncologist will determine if it's appropriate for your cancer.
Internal Radiation Therapy - Brachytherapy
In the second treatment category, the radiation is delivered by radioactive material placed inside the body near the cancer cells—a procedure called brachytherapy, implant radiation therapy, or internal radiation therapy. Brachytherapy (from the Greek word "brachy," which means "close") is a less common approach, but may be appropriate for some patients. Talk to your radiation oncologist about his or her treatment recommendation. There are two types of brachytherapy that are sometimes used to treat prostate tumors:
LDR (Low Dose Rate) Brachytherapy LDR uses tiny, sealed, low-strength radioactive seeds about the size of a grain of rice to deliver radiation to the target. These seeds are permanently implanted in the body. As the seeds emit radiation, they reduce in strength and in a few weeks no longer emit any appreciable amounts of radiation.
HDR (High Dose Rate) Brachytherapy HDR uses higher-strength radioactive sources (compared to LDR) to provide radiation to the target. As opposed to LDR, these sources are only implanted in the body temporarily, and taken out after each treatment session.