Radiation involves the killing of cancer cells with ionizing radiation or photons. Radiation damages the cancer cells DNA, the genetic material of the cancer cell, so it can’t survive or grow and spread, and subsequently the cancer cells die. Radiation therapy, like surgery, is very effective at killing localized or locally advanced prostate cancer and has the same cure rate as surgery.
External Beam Radiation Therapy
This is the most common type of radiation therapy. CT scans and MRIs are used to map out the location of the Tumor cells, and X-rays are targeted to those areas. There are many types of radiation therapy with a lot of acronyms. Here is a brief explanation of them all:
• 3D conformal radiotherapy: A simple form of radiation therapy that is less commonly used in the USA that targets the tumor effectively, but treats more healthy tissues (such as the rectum or bladder). For this reason 3D conformal radiation therapy is less favored today over more modern techniques that result in very low side effects.
• Intensity-modulated radiation therapy (IMRT): Using the power of modern computers and complex computer algorithms allow the radiation doctors to modulate, or shape, the intensity of the doses and radiation beams to better target the radiation delivered to the prostate, while simultaneously delivering lower doses to the bladder and rectal tissue.
• Image-guided radiation therapy (IGRT): This is a form of IMRT, but is even more accurate. IGRT utilizes multiple ways to ensure that the tumor is being treated every day and not any normal tissues with high doses of radiation. These methods include placing gold fiducials or electromagnetic beacons that track the prostate into the prostate (similar to how your biopsy was done), or performing a CT scan each treatment for centers that have built in CT scanners on their treatment machines. These techniques are always improving.
• Stereotactic body radiation therapy (SBRT): This is a form of IGRT (which is a form of IMRT). However, what is unique is that treatment is given in just 5 treatments instead of the usual 20 to 44 treatments with classical IMRT/IGRT. SBRT has been used for ~10 years for the treatment of prostate cancer, so it is one of the newest forms of radiation therapy. Studies have shown it to be safe and effective, but talk to you Doctor if it is something they feel you are eligible to receiving. Not all centers in the USA use SBRT, and usually for those centers that do it is limited to low and intermediate risk men.
• Proton beam: Protons are similar to x-rays or photons, in that they are both essentially radiation and kill the cancer similarly. Proton beam has never been shown in a clinical trial to improve the cure rate over other forms of radiation therapy, and there are mixed reports as to whether there are increased or decreased side effects with proton beam. Protons for prostate cancer should larger be viewed as an area of active research, and you should talk to your Doctor about them. Insurance companies often do not cover proton beam therapy (unless you are on a research study) given that it has not been shown to be any better than standard radiation therapy, and it is the most expensive form of treatment for prostate cancer.
In addition to the above types of EBRT, there are also different treatment durations or number of treatments that are used for different patients:
• Conventional: For decades radiation therapy has been delivered over 40-45 treatments every day (Monday through Friday).
• Moderate hypofractionation: Recently, there has been a lot of trials that have shown that as few as 20 treatments in 4 weeks has similar cure rates and side effects as conventional radiation over 8-9 weeks.
• Ultra-hypofractionation: This is essentially SBRT, or treatment delivered in just 5 treatments. This is rapidly becoming increasingly used given the favorable side effect profile, cure rates, and convenience. However, not all centers provide this, and not all patients are good candidates for this.
Regardless of the form of external radiation therapy, it is non-invasive and is done on an outpatient basis. Because it is non-invasive (no cutting) there is no down time or healing time as there is with surgery. You can be physically active every day of treatment and the months following. It is common though to have increased frequency of urination or bowel movements during the weeks of treatment, and 4-6 weeks after treatment is done these symptoms generally improve over the months following radiation therapy. Urinary incontinence is very rare (<1%), but increased frequency or urinary urgency is relatively common (~20% of men report this). Rectal bleeding is a “late” side effect that can occur months to years later, but is rare with modern treatment techniques (~2.5%). Many studies have shown that while surgery results in a more immediate loss of erectile function followed by a small period of partial recovery, radiation therapy results in a slower loss of erectile function over time in men who have good erectile function before treatment.
In order to receive any of the types of EBRT, you must first undergo what is called a “simulation” or “mapping” scan. This is usually a CT or MRI scan that is used by your radiation oncologist to determine where your prostate, rectum, and bladder are precisely so that radiation dosimetrists and physicists can work with the sophisticated computer treatment planning systems to design a personalized radiation plan for you.
Brachytherapy is internal radiation therapy, rather than external radiation therapy. It involved placing different types of radiation therapy inside the prostate the emit radiation a very short distance. Over the course of several months, the seeds give off radiation to the immediate surrounding area, thus killing the prostate cancer cells. By the end of the year, the radioactive material degrades, and the seeds that remain are harmless.
Radioactive seeds (LDR or low dose rate) or catheters (HDR or high dose rate) are placed directly into the prostate while you are asleep under anesthesia. It is usually done in 1 to 4 treatment sessions depending on the method used. The seeds are permanently placed into your prostate, while the catheters are only temporarily placed inside the prostate and then removed after treatment is done. Brachytherapy by itself is usually used only for low risk of very favorable intermediate risk patients. It is usually combined with some form of external beam radiation for higher risk patients. Brachytherapy, like surgery, is highly user dependent, and you want to find an experienced brachytherapist.
Compared with external radiation therapy, brachytherapy is less commonly used, but some patients prefer this option primarily because it doesn’t require daily visits to the treatment center. Side effects can include erectile dysfunction, urinary frequency and obstruction, and rarely rectal injury. Patients with large prostates or those patients with a lot of urinary problems are usually poor candidates for brachytherapy.
The Importance of Dose Planning
Just as surgical skill can play an important role in determining outcomes from Prostatectomy, the technical skill of your Radiation Oncologist can play an important role in radiation therapy outcomes.
The use of computer software, imaging, and 3-D technology to assist with dose planning and targeting of prostate tissue helps greatly, but the skill and experience of the radiation oncologist will make the biggest difference. When choosing a radiation oncologist, at a minimum, make sure he or she has broad experience with an assortment of approaches and can objectively help you decide on the best course of treatment.
Treatments that can be given with radiation therapy:
• Hormone therapy is the most common treatment given with radiation therapy. Hormone therapy usually consists of a shot that lowers your testosterone given every 1 to 6 months, and sometimes a daily pill that blocks testosterone from reaching the cancer cells. Hormone therapy has been shown to improve cure rates of prostate cancer for men receiving radiation therapy and is part of the standard of care:
o Hormone therapy should not be given to men with low risk prostate cancer.
o It is often given for intermediate risk cancer for 4-6 months (called short-term hormone therapy).
o Nearly all patients with high risk prostate cancer should receive hormone therapy for up to 3-years. Many men will be recommended ~18 months.
Treatment for Prostate Cancer: External-Beam...
Janet Farrar Worthington
If you have localized prostate cancer that needs curative treatment, you have two good options: Radiation and surgery. (You can read more about surgery here.)...