Radiation therapy uses high-energy beams, such as X-rays or protons, to kill cancer cells. These beams damage DNA inside cells, which can result in the death of cancer cells and/or the slowing of cancer growth. While radiation is also toxic to healthy cells, cancer cells are especially vulnerable to DNA damage because of their quick division. Radiation Therapy is often used as the first treatment for cancer found in the prostate gland. Some forms of radiation are also beneficial for men with advanced disease or recurring prostate cancer.
External Beam Radiation:
EBRT is the most common method of radiation used to treat prostate cancer. Radiation is delivered from outside the body using a large machine that aims radiation at tumor cells. The radiation passes through skin and other tissues to reach the tumor. There are several different types of ERBT, the most common types are discussed below.
3D Conformal Radiation Therapy (3D CRT):
This form of radiation targets tumor cells with X-ray radiation. To minimize the exposure of healthy cells to radiation, MRI, CT, and/or PET images are used to generate a three-dimensional (3D) image of the tumor. A computer program then shapes the radiation beams to match the shape of the tumor so the highest dose of radiation can destroy the cancer cells within the prostate with minimal exposure to the healthy cells nearby.
Intensity Modulated Radiation Therapy (IMRT):
IMRT is a more advanced form of 3D CRT which uses multiple X-ray beams that can be adjusted in their intensity or strength to limit the dose of radiation reaching healthy tissues. IMRT can more precisely and accurately target tumor cells which may result in fewer side effects and higher cure rates.
Volumetric modulated arc therapy (VMAT):
VMAT is a variation of IMRT that delivers radiation quickly as a machine rotates around the body. VMAT reduces treatment duration, however, its effectiveness compared to IMRT has not yet been studied.
Image Guided Radiation Treatment (IGRT):
As the prostate can move slightly within the body, and tumors may change shape between radiation treatments, IGRT, or imaging of the tumor just before or during radiation treatments, can improve the accuracy of 3D CRT and IMRT.
Proton Beam Therapy:
Proton beam therapy focuses beams of protons instead of x-rays onto cancer. In comparison to x-rays, protons cause less damage to tissues they pass through and release their energy only after traveling a certain distance. This means that proton beam radiation can deliver more radiation to tumors while doing less damage to nearby healthy tissues. Proton beam radiation can be aimed with techniques similar to 3D CRT and IMRT. Proton treatment is especially useful for treating localized tumors before they spread beyond the prostate. Unfortunately, very few medical institutions are equipped to use proton beam therapy in the United States, and the treatment can be expensive. There are no studies yet showing if proton beam therapy is more effective than x-ray based treatments.
Stereotactic Body Radiotherapy (SBRT):
Before treatment with SBRT, markers are placed around the tumor to faciliate the delivery of large doses of radiation precisely to the tumor. During treatment, the intensity and direction of the beams are constantly adjusted to target the tumor and spare healthy tissue. The beams can also be adjusted to accommodate breathing and digestive movements. SBRT is often used to deliver a course of treatment in a few visits. There is some research to suggest that side effects may be worse with SBRT compared to IMRT, however further studies are needed.
Brachytherapy or Internal Radiation Therapy:
This treatment uses small radioactive implants, often called "seeds" which are placed in the prostate through a surgical procedure. Like with EBRT, 3D CRT is used to map the tumor and to calculate the dose and placement of the seeds. There are two approaches to brachytherapy, low-dose rate (LDR) and high-dose rate (HDR). LDR brachytherapy uses placement of seeds, which give off low doses of radiation for weeks or months. Radiation from the seeds travels a very short distance, so the seeds can give off a large amount of radiation in a very small area, which limits the amount of damage to nearby healthy tissues. Because the seeds are so small, they rarely cause discomfort, and are left in place after their radioactive material is used up. Conversely, HDL brachytherapy uses seeds, which give off higher doses of radiation and are only left in place for several minutes. HDL brachytherapy is typically given as several exposures over the course of a few days, after the last treatment, the seeds are removed.
Side Effects
Along with any medical procedure radiation can have side effects. The following are some common side effects of radiation treatment:
- Impotence
- Incontinence
- Upset Stomach
- Diarrhea
- Frequent & Painful Urination
- Fatigue
- Skin Irritation in Treatment Areas
- Rectal Irritation or Rectal Bleeding
- Lymphedema