Prostate cancer develops in the prostate gland, a part of the male reproductive system. According to the National Cancer Institute, the disease develops primarily in older men and is the second most common cancer after skin cancer. Treatment for prostate cancer varies based on the stage of the disease (size of the tumor, and whether the tumor has spread to adjacent lymph nodes and organs or elsewhere in the body). Watchful waiting (observation without treatment), surgery, radiation therapy, hormone therapy and chemotherapy may all be used in prostate cancer treatment, according to the National Comprehensive Cancer Network. Radiation may be delivered in a variety of ways to kill cancer cells and prevent the spread (metastasis) of the disease.
External Beam Radiation Therapy
External Beam Radiation Therapy (EBRT) is delivered using a linear accelerator (a machine designed to generate high energy beams), a tomotherapy unit (a linear accelerator and CT scanner combined that delivers spirals of radiation around the body), a robotically controlled linear accelerator that tracks breathing or organ movement during treatment, or in rare instances, with a machine that contains a radioactive source, Cobalt-60. Determining where to deliver the radiation requires careful treatment planning. Conformal radiation therapy (3D-CRT) uses a three-dimensional model to shape the beams used for treatment. Intensity Modulated Radiation Therapy (IMRT) varies the strength of the beam to lessen damage to normal tissues during radiation administration. There are other targeting systems that are being developed to use with EBRT, according to The American Society for Radiation Oncology. Tomotherapy is considered a type of IMRT combined with image guided radiation therapy (IGRT).
Proton Beam Therapy
Proton therapy, one of the newest EBRT approaches, uses a machine that generates protons that attack the DNA of cells with high doses of energy at the tumor and low doses where the beam enters the body. Unlike radiation from a linear accelerator, proton accelerators deliver proton beams that travel a calculated distance through normal tissue before releasing their energy in the prostate. Some insurance companies consider proton beam therapy experimental, and there are limited numbers of centers providing this service, according to the American Society of Radiation Oncology.
Stereotactic Radiotherapy
Stereotactic radiotherapy uses a machine that is designed to precisely deliver radiation to an organ such as the prostate. While similar to a linear accelerator, it moves in many more directions around the body, allowing more precise targeting. It is a form of IMRT, and often is described using the names of the machine such as CyberKnife or Novalis Tx. It is still considered external beam radiation therapy.
Permanent Brachytherapy
There are several ways to administer internal radiation therapy, or brachytherapy. Permanent, low dose rate brachytherapy using small radioactive seeds (or pellets) of iodine-125 or palladium-103, each about the size of a grain of rice, are placed in the prostate in a procedure requiring general anesthesia. The seeds are left in place, and there is some radioactivity given off through the body, but it decreases over time. Seed implants are usually used in early stage prostate cancer.
Temporary Brachytherapy
Temporary, high-dose brachytherapy uses a machine called a high-dose remote afterloader and catheters placed in the prostate. Radioactive iridium-192, or cesium-137, are moved through the catheters into the prostate, and then removed. The patient is not radioactive with temporary brachytherapy. These treatments may be combined with EBRT. Brachytherapy has the advantage of concentrating the radiation in the prostate gland rather than surrounding areas such as the bladder and rectum.
Intraoperative Radiation Therapy
In rare instances, radiation may be used immediately after an operative procedure to remove the prostate gland, and before the incision is closed. This procedure is considered experimental and usually is performed as part of a research effort (clinical trial, research protocol).
Investigational Radiation Therapy
The advances in radiation therapy strategies for prostate cancer are increasing rapidly. Systemic radiation therapy (a radioactive substance is swallowed and travels to the tumor), or radioimmunotherapy (radiolabeled antibodies that travel to the tumor and interfere with the cancer cells growth) are just two new therapies under discussion.
