Overview

Radiation therapy, or radiotherapy, is a common way to treat 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 can be given in a variety of ways. The two most common ways to deliver radiation therapy 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 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. For example, EBRT can be delivered more precisely by using a special computed tomography (CT) scan and a targeting computer. This capability is known as three-dimensional conformal radiation therapy, or 3D-CRT. A newer approach that may be used is 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 area 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.

A technique known as 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.

Finally, EBRT may be combined with implant radiation placed directly into the prostate gland. Radiation implants are further described in the section below. When these two methods are combined, the EBRT is given for four to five weeks, and the final “boost” of radiation to the prostate gland is given with the internal radiation.

Interstitial Brachytherapy

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.

Some doctors have patients leave several hours later on the same day of the procedure or after an overnight hospital stay. Following the procedure, some patients may experience some pain or aching in the perineum. Some patients may experience burning or discomfort during urination. Occasionally, a patient will be unable to urinate, and may require a bladder catheter for several days or weeks to allow passage of urine. Also infrequently, a patient may lose control of urine; this seems to occur more often in men who have had a previous transurethral resection of the prostate (TURP). Approximately 30% of men lose their ability to get an erection following placement of brachytherapy seeds. Men receiving external radiation therapy for prostate cancer can permanently lose their ability to get an erection. Men appear to maintain potency more often with interstitial seed radiation than with external radiation.

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) or prior prostate infections or in patients with large size prostate glands.

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 have never been directly compared 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. 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?

Side Effects From Radiation Therapy

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. Loose stools or diarrhea are also common. Urination may become more frequent or uncomfortable. Some patients may experience loss of pubic hair or irritation of the skin, particularly between the buttocks. Men receiving radiation therapy for prostate cancer can permanently lose their ability to get an erection. The risk of impotence is approximately 20-40%.

In some patients, prostate cancer cells can escape the prostate gland and spread to other areas of the body. Cancer cells have a tendency to spread to bones of the body and can cause pain and other problems. This pain can often be relieved with EBRT 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.

Is Radiation Necessary After Prostatectomy?

Radiation therapy may be recommended to patients following surgical prostatectomy if they are found to have cancer involving the margins of the surgical specimen, the PSA remains persistently elevated, or the PSA returns to normal and then begins rising again.

Patients with cancer involving the surgical margins and a persistently elevated or a rising PSA all have evidence that some cancer was not removed by surgery. For some patients, the remaining cancer will be confined to an area near the prostate gland. For many patients, the cancer will have spread to more distant locations in the body. The difficult question faced by the patients is: What is the chance persistent cancer can be eliminated with additional radiation therapy?

In a study of men treated with radical prostatectomy and found to have pT3 prostate cancer (cancer that extends beyond the prostate capsule), adjuvant treatment with radiation therapy reduced the risk of post-treatment PSA increase.[1]

Patients must decide whether receiving additional radiation therapy (along with its inconvenience and side effects) is likely to be beneficial. They may also consider whether participation in clinical studies directed at treating cancer that has already spread away from the radiation field are more appealing in offering potential benefit from additional treatment.

Strategies to Improve Treatment

The progress that has been made in the treatment of prostate cancer has resulted from improved development of radiation treatments and surgical techniques and participation in clinical trials. Future progress in the treatment of prostate cancer will result from continued participation in appropriate clinical trials. Currently, there are several areas of active exploration aimed at improving radiation treatment of prostate cancer.

Higher Doses of Radiation: In men with early-stage prostate cancer, some studies have suggested that higher doses of radiation therapy may improve cancer control without substantially increasing the risk of side effects.[2] [3]

Newer Radiation Machines: Most EBRT uses high energy X-rays to kill cancer cells. Some radiation oncology centers use different types of radiation that require special machines to generate. These different types of radiation, such as protons or neutrons, may kill more cancer cells with the same dose. Combining protons or neutrons with conventional X-rays is one method of radiation therapy being evaluated in clinical trials.

References


[1] Wiegel T, Bottke K, Steiner U et al. Phase III postoperative adjuvant radiotherapy after radical prostatectomy compared with radical prostatectomy alone in pT3 prostate cancer with undetectable prostate-specific antigen: ARO 96-02/AUO AP 09/95. Journal of Clinical Oncology. 2009;27:2924-30.

[2] 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.

[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.

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