How Is Radiation Therapy Used for Prostate Cancer?
Radiation therapy for prostate cancer involves targeting high-energy particles or waves at cancer cells or tumors. This can be done with the intent to cure an individual’s prostate cancer, or can be used to relieve cancer-related symptoms. Typically, radiation therapy is used with the intention to cure in cases where an individual’s prostate cancer is in the prostate gland only, or has only advanced locally beyond the prostate gland. Radiation therapy utilized in advanced prostate cancer cases is generally intended to relieve quality of life-affecting symptoms such as bone pain when the cancer has metastasized to the bones or try to keep the cancer under control.1-4
How radiation therapy works
The high-energy rays emitted during treatment are designed to kill cancer cells by disrupting their DNA, preventing them from further multiplying. Although this can have a beneficial effect on slowing down cancer growth, these rays have the potential to impact healthy tissue as well. To prevent healthy tissues from being damaged, and to decrease side effects related to radiation therapy treatment, newer technologies, including better imaging techniques and radiation-delivering mechanisms have been developed, and are still in development.
The overall goal of radiation therapy is to target the cancer cells as precisely and efficiently as possible to avoid detrimental effects to the rest of the body. The exact dosage of radiation administered, the best way to administer it, and your dosage schedule will be determined by your radiation healthcare team, including radiation oncologists, and radiation therapists, among others.2-3
Radiation therapy can be used as a primary or first-line treatment option with the intent to cure, or as an add-on treatment to hormone therapy or surgery. It can also be used to treat recurrent or advanced cancer depending on your specific situation. When used as a first-line treatment, radiation therapy has a similar cure rate to radical prostatectomy (surgery to remove the prostate gland). Although these treatment options are similar in success rate, they are different in their potential side effects and risks, which is why the decision on how to treat your prostate cancer should be made on a case by case basis with your doctor. There are two main types of radiation therapy for prostate cancer, external beam radiation therapy (EBRT or EBT) and brachytherapy (internal radiation therapy).1-4
External beam radiation therapy
External beam radiation (also referred to as EBRT or EBT) involves focusing beams of radiation onto cancer cells or a tumor from outside of the body. Before starting treatment, it’s very important to determine the exact location of the cancer cells that are being targeted and how high of a dose needs to be given. This will all be assessed by your healthcare team and will happen during a simulation session that may involve imaging (including ultrasound, MRI, or CT scans). You also may be fitted with a plastic device similar to a body cast that will hold you in place during treatment. This is to ensure that your body is in the same location each time you’re receiving treatment.1
EBRT is typically given up to 5 days a week for anywhere from five to nine weeks, but your schedule will be tailored to what’s optimal for your case. The radiation itself only lasts a few minutes, with the majority of your time during treatment being spent on making sure your body is positioned correctly and calibrating the beams used. In total, most radiation sessions are shorter than 20 minutes. Common EBRT techniques include, but are not limited to:1-4
Three-dimensional conformal radiation therapy (3D-CRT)
This type of therapy uses computers and CT scans to determine your exact anatomy to shape and direct beams from all directions.
Intensity modulated radiation therapy (IMRT)
IMRT is a more advanced form of 3D-CRT and uses hundreds of CT scans to determine the 3D structure of both your anatomy and the tumor targeted. Further, this type of therapy involves different strengths, or intensities, of beams in order to target cancer cells as precisely as possible, and avoid damage to healthy tissues. This is the most common form of EBRT.
Image guided radiation therapy (IGRT)
IGRT is used during EBRT and involves taking images of your pelvis or any other area that may be getting irradiated each time you’re receiving treatment. Scanners can be built into the radiation delivery system to ensure that the location of your tumor or other bodily structures, such as your prostate, haven’t changed. Depending on how full your bladder or bowels are, your prostate may shift very slightly from day to day.
Stereotactic body radiation therapy (SBRT)
SBRT is a newer radiation technique that uses very advanced imaging techniques to deliver extremely high doses of radiation. The idea behind EBRT is that the radiation beams are aimed so precisely, higher doses are able to be administered during each treatment. SBRT can be completed in as few as several days instead of five weeks or more. Since SBRT is newer, more research needs to be completed to determine the long term side effects of the treatment and its long term effectiveness. SBRT may be called the same name as the machine used to deliver the beams, such as CyberKnife or Gamma Knife.5
Proton beam radiation therapy
Proton beam radiation involves directing beams of protons instead of X-rays. Protons release their energy only after they’ve traveled a specific distance, and therefore, may have the potential to avoid damaging the healthy tissues they need to pass through to get to the tumor they’re directed at. Proton therapy is not widely available as the machines needed to perform it are expensive and many insurance plans currently do not cover this treatment. Much more research and development needs to be done on this therapy.6
Brachytherapy, also known as internal radiation therapy, interstitial radiation therapy, or radioactive seed treatment, is a surgical procedure that irradiates cancer from the inside the prostate. There are two types of brachytherapy, permanent low dose rate (LDR), and temporary high dose rate (HDR). Both methods involve surgically implanting radioactive seeds (for LDR) or catheters that will administer radioactive elements (for HDR) directly into the prostate using ultrasound, MRI, or CT guidance. An individual receiving brachytherapy will be under anesthesia during the implantation process. Brachytherapy may be used in addition to other treatment options, including EBRT. Your doctor will determine what the best approach for your case is.1-2,4
LDR brachytherapy involves planting roughly up to 100 radioactive seeds containing elements, like iodine-125. The seeds will be placed using needles inserted between the scrotum and the anus into the prostate. The needles will be removed, but the seeds will not. The seeds are roughly the size of a grain of rice, and cause very little, if any discomfort. The seeds will continuously give off low doses of radiation that travel a short distance to nearby tissues. This process can continue for weeks or months. During this time, you may be instructed to strain your urine for seeds that become displaced, as well as to stay away from pregnant women or small children, during the time radiation is given off. Your doctor will determine if any of these precautions are necessary.1
HDR brachytherapy uses needles to go through the skin between the scrotum and anus into the prostate as well, however, these needles are used to guide in catheters. These catheters will remain in place for the next two days during treatment. Over these two days, radioactive elements including iridium-192 or cesium-137 are administered through these catheters multiple separate times, for approximately 5-15 minutes each time. After the last of the treatments, the catheters are removed.1
Side effects of EBRT and brachytherapy
Possible effects of EBRT and brachytherapy include:
- Urinary problems including radiation cystitis (inflammation of the bladder) leading to urinary incontinence, burning sensation while urinating, frequent urination, or blood in the urine
- Narrowing of the urethra (the tube that carries urine from the bladder out of the body)
- Bowel problems including radiation proctitis (irritation of the bowel) leading to diarrhea, bloody stool, and bowel incontinence
- Erectile dysfunction
- Lymphedema, or fluid retention and swelling due to the removal or damage of lymph nodes
This is not an exhaustive list of all side effects of EBRT or brachytherapy. You provider will help determine what side effects you are at risk for, how to reduce your risk, or how to treat these should they occur.1-2,4
Radiopharmaceuticals belong to a class of medications that are considered systemic radiation therapies. These medications contain radioactive substances that help alleviate pain when cancer metastasizes to the bones. The most common radiopharmaceuticals used in the treatment of prostate cancer-related bone pain include Strontium-89 (Metastron), Samarium-153 (Quadramet), and Radium-223 (Xofigo). These drugs are typically given as intravenous (IV) injections. Radiopharmaceuticals are typically indicated for individuals with prostate cancer that has metastasized to the bones and has accompanying pain. Radium-223 may be used for patients with castrate-resistant prostate cancer (prostate cancer that is not responding to treatment to lower the body’s level of testosterone) that has spread (metastasized) only to the bones and is causing symptoms, and has not spread to other areas of the body. Radium-223 may be a part of a patient's prostate cancer treatment to help them live longer, as opposed to only helping to relieve pain.
The radioactive elements in radiopharmaceuticals are attracted to areas in the body that are experiencing rapid bone turnover, such as where cancer has metastasized to the bones and is destroying them. Common side effects of certain radiopharmaceuticals include, but are not limited to, vomiting, diarrhea, nausea, swelling of the limbs, low blood cell counts, dehydration, and injection site reactions. When taking radiopharmaceuticals, you may be provided with strict safety guidelines that will help protect yourself and those around you from radiation-related risks. It is important to follow these guidelines exactly as you are instructed. Talk to your healthcare provider or pharmacist for further information.7-8