General Cancer Information

Radiation Therapy for Prostate Cancer

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 that radiation therapy are delivered are through 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 interstital implantation, a physician places small pellets or seeds of radioactive material directly into the prostate gland Most patients receive one or the other kind of radiation and some patients receive both kinds of radiation therapy.

External Beam Radiation Therapy

External beam radiation therapy (EBRT) for prostate cancer is given on an outpatient basis, 5 days a week, for approximately 6 to 8 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.

Some radiation therapy centers will use a special CT scan and computer prior to the planning session to better locate the prostate gland and more precisely aim the radiation. This capability is known as three-dimensional conformal radiation therapy, or 3D-CRT. The use of 3D-CRT appears to reduce the chance of injury to nearby body structures, such as the bladder or rectum. Since 3D-CRT can better target the area of cancer, radiation oncologists are evaluating whether higher doses of radiation can be given safely while achieving greater cure rates. Preliminary data from several cancer programs suggests that the higher radiation dose delivered with 3D-CRT can reduce the rate of local cancer recurrence.

Another method of increasing the dose of radiation to the cancer is to combine EBRT 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 4-5 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, and 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?

The results of a review of 1,872 patients with early stage prostate cancer who were treated with either radical prostatectomy, EBRT, or interstitial implantation at the University of Pennsylvania Medical Center and Harvard Medical School were reported in 1998. High-risk patients (patients least likely to have cancer confined to the prostate) treated with implantable seeds were over twice as likely to experience cancer recurrence within 3-4 years of treatment compared to patients treated with radical prostatectomy or EBRT. Approximately 60% of patients treated with prostatectomy or EBRT survived without evidence of cancer recurrence, compared to approximately 35% of patients treated with implants. Patients at low risk (those with a high chance of having cancer confined to the prostate) did equally well 3-4 years from treatment whether they received EBRT, radical prostatectomy, or radiation using implantable seeds.

In summary, for patients with low-risk, early stage prostate cancer, treatment with radical prostatectomy, EBRT, or implants appears equivalent. In patients with high-risk disease, however, treatment with EBRT or radical prostatectomy may be superior to implants. It is important to realize that patients with low-risk disease have not been followed long enough to conclude there is no difference between these three therapeutic approaches. Lastly, this was not a direct comparison of three different treatment approaches in a controlled fashion, and a number of other factors could influence the outcome of the various treatment options. Hopefully, the results of this clinical analysis will help men and their families make more informed decisions as they sort through the maze of prostate cancer treatment options.

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. Most men have few side effects; however, 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%. Men appear to maintain potency more often with interstitial seed radiation than with external radiation.

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 depends 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 general, 75% of these patients treated with radiation after prostatectomy will still experience recurrence of cancer as evidenced by a rising PSA level within 5 years of radiation therapy. Patients with high Gleason scores, more advanced stages and higher PSA levels are more likely to have cancer recurrence following radiation than those with lower Gleason scores and lower PSA levels. The high rate of failure following radiation therapy occurs because the radiation could not kill all of the cancer cells, or many cancer cells had already spread beyond the limited reach of the radiation therapy. Patients must decide whether receiving additional radiation therapy (along with its inconvenience and side effects) is likely to be beneficial, or 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.

Simultaneous Radiation Therapy: Simultaneous radiation therapy employs permanent interstitial prostate brachytherapy followed by EBRT. The patient receives therapeutic doses of radiation from both the implant and the external beam. The timing of this combination of modalities is distinct from that of other combinations of EBRT and brachytherapy used for prostate cancer.

Newer Radiation Techniques: EBRT can be delivered more precisely to the prostate gland by using a special CT scan and targeting computer. This capability is known as three-dimensional conformal radiation therapy, or 3D-CRT. The use of 3D-CRT appears to reduce the chance of injury to nearby body structures, such as the bladder or rectum. Since 3D-CRT can better target the area of cancer, radiation oncologists are evaluating whether higher doses of radiation can be given safely while improving cancer cures.

Combination Radiation Therapy: Some radiation oncologists are combining EBRT and interstitial seed brachytherapy for patients with stage II or III cancers. The purpose of the EBRT is to treat the tissues surrounding the prostate gland and lymph nodes where cancer cells may have spread. The interstitial seeds serve to deliver extra radiation dose to the prostate where the cancer cells are greatest. The combination of internal and external radiation is being evaluated to allow higher doses of radiation to reach the cancer while minimizing side effects to surrounding organs.

Researchers recently evaluated the effectiveness of brachytherapy plus EBRT versus EBRT alone in the treatment of over 300 patients with advanced localized prostate cancer. Half of the patients received treatment consisting of both brachytherapy and EBRT and the other half received EBRT alone. Five years following treatment, high PSA levels existed in only 33% of patients that had received the combination of brachytherapy plus EBRT compared to 56% of patients that received EBRT alone. Since high PSA levels are an indication of the presence of cancer, these results suggest that brachytherapy plus EBRT may be more effective than EBRT alone in the treatment of advanced localized prostate cancer.

Whole Pelvic Radiation Therapy: Because certain patients are at higher risk of cancer involving the pelvic lymph nodes, some doctors have advocated expanding the radiation field to include the pelvic lymph nodes. This is referred to as whole pelvic radiation therapy (WPRT). Some, but not all, comparisons of WPRT to prostate only radiation therapy have demonstrated that WPRT may improve survival, and is not more toxic than radiation to the prostate only. Many doctors believe, however, that if cancer has spread to the pelvic lymph nodes, it has probably spread elsewhere in the body and expanding the radiation field will be of little benefit. Efforts to improve treatment might be better focused on systemic treatment approaches versus local treatment with radiation. Doctors in the United States are currently conducting a clinical study comparing WPRT to prostate only radiation.

Newer Radiation Machines: Most EBRT uses high energy x-rays to kill cancer cells. Some radiation oncology centers use different types of radiation which require special machines to generate. These different types of radiation, such as protons or neutrons, appear to 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.