Radiation Therapy for Prostate Cancer
Radiation therapy, or radiotherapy, is a common way to treat early stage prostate cancer. Doctors who specialize in treating cancers with radiation are known as radiation oncologists. In radiation therapy, high-energy X-rays are used to kill cancer cells. In early-stage prostate cancer, radiation can be used instead of surgery, or it may be used after surgery to destroy any cancer cells that may remain in the area. In advanced stages of prostate cancer, it may be given to relieve pain or other problems.
Radiation therapy for early stage prostate cancer can be given in a variety of ways. The two most common ways are external beam radiation therapy and brachytherapy. External beam radiation therapy (EBRT) involves the delivery of radiation via a machine that aims X-rays at the body. During brachytherapy or interstitial implantation, a physician places small pellets or seeds of radioactive material directly into the prostate gland.
External Beam Radiation Therapy
External beam radiation therapy (EBRT) for prostate cancer is given on an outpatient basis, five days a week, for approximately six to eight weeks. EBRT begins with a planning session, or simulation, where marks are placed on the body and measurements are taken in order to line up the radiation beam in the correct position for each treatment. Patients lie on a table and are treated with radiation from multiple directions to the pelvis. The actual area of the pelvis receiving radiation treatment may be large or small, depending on the features of the cancer. Radiation can be delivered specifically to the prostate gland (prostate-only radiation) or encompass the surrounding pelvic lymph nodes in addition to the prostate gland (whole-pelvic radiation). Patients who are receiving treatment to a larger area of the pelvis may undergo another planning session to focus the radiation to the prostate gland, where cancer cells are greatest.
As the technology for delivering radiation therapy has evolved, important advances have been made in the ability of physicians to precisely target the area of the cancer with higher doses of radiation while sparing normal tissue to the extent possible. EBRT can be delivered more precisely in greater doses using a variety of newer techniques.1
Three-Dimensional Conformal Radiation Therapy (3D-CRT): 3D-CRT uses computers to precisely map the location of your prostate. Radiation beams are then shaped and aimed at the prostate from several directions, which makes it less likely to damage normal tissues.1
Intensity Modulated Radiation Therapy (IMRT): IMRT is an advanced form of 3D-CRT that allows doctors to customize the radiation dose by modulating, or varying, the amount of radiation given to different parts of the body being treated. The radiation intensity is adjusted with the use of computer-controlled, moveable “leaves” that either block or allow the passage of radiation from the many beams that are aimed at the treatment area. The leaves are carefully adjusted according to the shape, size, and location of the tumor. As a result, more radiation can be delivered to the tumor cells while less is directed at the normal cells that are nearby.2
Image-guided radiation therapy (IGRT): may be used in combination with other approaches such as IMRT. IGRT involves imaging during the course of radiation treatment, and is able to account for changes in the patient’s body or position that may shift the exact location of the cancer. The location of the prostate, for example, may vary somewhat depending on the contents of the bladder or rectum.
Proton Beam Therapy (PBT)
Proton beam therapy focuses beams of protons instead of x-rays on the cancer. Protons are positive parts of atoms. Unlike x-rays, which release energy both before and after they hit their target, protons cause little damage to tissues they pass through and release their energy only after traveling a certain distance. This means that proton beams can, in theory, deliver more radiation to the prostate while doing less damage to nearby normal tissues.
Proton beams can be aimed with similar techniques to 3D-CRT and IMRT. Although early results are promising, so far studies have not shown that proton beam therapy is significantly better in the long-run than other types of EBRT. Thus far some but not all studies suggest that PBT may have fewer short term side effects however PBT is substantially more costly than IMRT and does not appear to produce a difference in toxicity 12 months after treatment.2, 3
Internal radiation is known by a number of names: “interstitial brachytherapy,” “seeds,” or “implantation.” These terms refer to treatment where radioactive material is placed directly into the prostate gland. For prostate cancer, the most common method of interstitial brachytherapy is permanent implantation of radioactive seeds into the prostate gland through the perineum. The perineum is the area of skin between the scrotum and the anus. The implantation procedure is performed in the operating room while the patient is asleep or numb from the waist down. An imaging device known as an ultrasound is inserted into the rectum to visualize and guide placement of the seeds with needles into the prostate. After the procedure, the patient will temporarily contain a small amount of radiation from the seeds. Although this amount is not generally dangerous to most other people, some doctors may advise patients to avoid close contact with young children or pregnant women for several weeks.
Because implant radiation focuses the radiation closely around the prostate, this form of radiation works best in patients with early-stage prostate cancer. If the prostate-specific antigen (PSA) level or Gleason score is high, another form of treatment may provide improved results. Also, seed implantation does not work as well in patients who have had prior transurethral resection of the prostate (TURP), prior prostate infections, or in patients with large size prostate glands. There are 2 types of prostate brachytherapy. Both are done in an operating room and require some type of anesthesia.4
Permanent (low dose rate, or LDR) Brachytherapy: In this approach, pellets (seeds) of radioactive material (such as iodine-125 or palladium-103) are placed inside thin needles, which are inserted through the skin in the area between the scrotum and anus and into the prostate. The pellets are left in place as the needles are removed and give off low doses of radiation for weeks or months. Radiation from the seeds travels a very short distance, so the seeds can put out a very large amount of radiation to a very small area. This lowers the amount of damage done to the healthy tissues that are close to the prostate.
Usually, anywhere from 40 to 100 seeds are placed. Because they are so small, the seeds cause little discomfort, and they are simply left in place after their radioactive material is used up. This type of radiation therapy requires spinal anesthesia (where the lower half of your body is numbed) or general anesthesia (where you are asleep) and may require an overnight stay in the hospital.
Temporary (high dose rate, or HDR) Brachytherapy: This is a newer technique. Hollow needles are placed through the skin between the scrotum and anus and into the prostate. Soft nylon tubes (catheters) are placed in these needles. The needles are then removed but the catheters stay in place. Radioactive iridium-192 or cesium-137 is then placed in the catheters, usually for 5 to 15 minutes. Generally, about 3 brief treatments are given, and the radioactive substance is removed each time. The treatments are usually given over 2 days. After the last treatment the catheters are removed. For about a week after treatment, you may have some pain or swelling in the area between your scrotum and rectum, and your urine may be reddish-brown.
These treatments are usually combined with EBRT given at a lower dose than if used by itself. The total dose of radiation is computed so that it is high enough to kill all the cancer cells. The potential advantage of this approach is that most of the radiation is concentrated in the prostate gland itself.4
Possible Risks of Brachytherapy: If you receive permanent brachytherapy seeds, they will give off small amounts of radiation for several weeks. Even though the radiation doesn’t travel far, your doctor may advise you to stay away from pregnant women and small children during this time. You may be asked to take other precautions as well, such as wearing a condom during sex.
There is also a small risk that some of the seeds may move (migrate). You may be asked to strain your urine for the first week or so to catch any seeds that might come out. Be sure to carefully follow any instructions your doctor gives you. There have also been reports of the seeds moving through the bloodstream to other parts of the body, such as the lungs. As far as doctors can tell, this doesn’t seem to cause any ill effects and happens very rarely.
Side Effects From Radiation
Although patients do not feel anything while receiving a radiation treatment, the effects of radiation gradually build up over time. Many patients experience fatigue as treatment continues. Side effects increase with patient age and may be more or less common with EBRT or Brachytherapy. In general the occurrence of side effects continues to decrease as a result of more targeted radiation to the prostate. Its best to discuss the risk of various side effects with your treating physician as they can very significantly based on the institution and method of radiation delivery. Radiation may cause bowel and bladder dysfunction and impotence.5, 6 Learn more about side effects from radiation therapy.
Interstitial Brachytherapy or External Beam Radiation?
The decision to undergo radical prostatectomy, EBRT or radiation seed implantation is difficult. This is because these treatment strategies continue to evolve and improve making it difficult to directly compare them in well-designed clinical studies. The choice of radiation versus prostatectomy is often based on weighing the possible complications of treatment and the relative inconvenience of the treatments. It is important to be seen by more than one physician to determine the likely treatment outcome associated with the various options available in your community.4 Questions you may wish to ask your physicians include:
- What are the chances of this treatment curing the cancer?
- What is the risk of impotence and incontinence?
- What are the other possible complications from this treatment?
Treatment of Bone Metastases
Pain from bone metastases may also be relieved with radiation therapy directed to the affected bones. The side effects of radiation therapy for relief of bone pain depend on the area of the body being treated. Another method for treatment of bone pain is the use of radioisotopes which when given intravenously accumulates in the bones and kills prostate cancer cells by delivering small amounts of radiation. Clinical studies have shown that bone pain and the need for pain medications can be reduced in the majority of patients treated with a radioisotope. Since a radioisotope is given by vein, it can affect all bones in the body, whereas external radiation therapy is limited to only small areas of the body.
The following is a general overview of radiation therapy, covering:
1 Zietman AL, Bae K, Slater J, et al. Randomized trial comparing conventional-dose with high-dose conformal radiation therapy in early-stage adenocarcinoma of the prostate: Long-term results from Proton Radiation Oncology Group/American College of Radiology 95-09. Journal of Clinical Oncology. 2010; 28: 1106-1111.
2 Yu JB, Soulos PR, Herrin J, et al. Proton versus intensity-modulated radiotherapy for prostate cancer: Patterns of care and early toxicity. Journal of the National Cancer Institute. Published early online December 14, 2012. doi: 10.1093/jnci/djs463
3 Talcott JA, Rossi C, Shipley WU et al. Patient-reported long-term outcomes after conventional and high-dose combined proton and photon radiation for early prostate cancer. JAMA. 2010;303:1046-1053.
5 Nam RK, Cheung P, Herschorn S, et al: Incidence of complications other than urinary incontinence or erectile dysfunction after radical prostatectomy or radiotherapy for prostate cancer: a population-based cohort study.The Lancet Oncology. 2014; 15(2): 223-231.
6 Rudnick MJ, Koyama T, Fan KH, et al. Long-term functional outcomes after treatment for localized prostate cancer. New England Journal of Medicine. 2013; 368:436-445