What is External Beam Radiation for Prostate Cancer?


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For men who have localized or locally advanced prostate cancer, one of the main treatment options is external beam radiation therapy (EBRT). (Removal of the prostate, or radical prostatectomy, is the other main treatment choice.) External beam radiation therapy (EBRT) is the use of high-energy particles or rays to kill cancer cells. EBRT is typically recommended for men with prostate cancer who meet any of the following criteria:

  • Localized or locally advanced prostate cancer (disease that has spread to tissue just beyond the prostate but not to other organs)
  • Locally advanced prostate cancer also being treated with hormone therapy
  • Prostate cancer that has returned (recurred) after prostatectomy
  • For advanced cancer as a means to reduce tumor size and thus provide some symptom relief

External beam radiation for prostate cancer is available in a variety of forms, and it has evolved over the years with advances that now allow healthcare providers to deliver more sophisticated radiation treatment than in the past. If you are considering external radiation as treatment for prostate cancer, you should discuss the different forms of radiation therapy with your healthcare provider.

Are you a candidate for external beam radiation?

Although you may have a form of prostate cancer that can respond to external beam radiation, not all men are candidates for this treatment approach. Generally, men who have a history of bowel conditions such as Crohn’s disease or ulcerative colitis, as well as men who have poorly controlled diabetes should not receive external beam radiation for prostate cancer.

External beam radiation is most effective when used in men who have small to moderate prostate tumors. When men have large prostate tumors, physicians typically recommend a three- to six-month course of hormone treatment before starting radiation to help shrink the tumor.

Types of external beam radiation therapies

Improvements in x-ray technology have resulted in new radiation therapy techniques, including 3-dimensional conformal radiotherapy (3D-CRT), intensity-modulated radiotherapy (IMRT), proton beam radiation, and stereotactic radiotherapy.  These radiation techniques are superior to conventional radiation treatment because they allow practitioners to deliver a greater dose to the tumor while minimizing damage to nearly normal tissues. For the first three techniques mentioned, a typical treatment sessions lasts about 15 minutes, and the entire course of treatment usually runs five days a week over a period of six to eight weeks. Stereotactic radiotherapy is a much shorter but intense program.

3-Dimensional conformal radiotherapy

The 3D-CRT approach utilizes sophisticated imaging techniques (computed tomography or magnetic resonance imaging [MRI]) that precisely identify the location of the tumor. Once the treatment area has been determined, men receive radiation to their prostate tumor from multiple directions. Because the 3D-CRT approach is so precise, it allows clinicians to accurately treat the prostate cancer with escalating doses of radiation without significant complications to the surrounding healthy tissue. In many facilities, 3D-CRT has been replacing conventional external beam radiation.

Results of 3D-CRT have been superior to conventional EBRT because of the ability to more safely treat the cancer with higher doses of radiation. In follow-up studies, the rates of no evidence of disease in men treated with 3D-CRT who had PSA levels of 10 to 20 ng/mL prior to treatment were about 30% better than those in men who were treated with conventional EBRT at 5 years.

Intensity-modulated radiation therapy (IMRT)

This form of radiation therapy also can focus radiation to a prostate tumor without affecting the surrounding healthy tissue. What makes this form of external beam radiation special is that it delivers a number of beams that vary in intensity. That means where the tumor is thick, the radiation beam is at maximum while where it is thinnest, the beam is minimum.

A computer determines how each individual man’s prostate cancer will be treated with IMRT. The intensity of the delivered radiation also changes throughout the course of treatment.

In a recent (July 2012) study published in European Urology, researchers at the University of Michigan compared the effectiveness of two forms of external beam radiation in men with localized prostate cancer. The investigators reviewed data from 11,039 men who underwent IMRT and 6,976 men who had 3D-CRT between 2001 and 2007.

Compared with men treated with 3D-CRT, low-risk patients treated with IMRT had a similar risk of needing hormone therapy because of cancer recurrence and similar risks of experiencing a complication that required treatment. However, a subgroup of men at higher risk who were treated with IMRT who did not receive hormone therapy were less likely to need salvage therapy than were men treated with 3D-CRT.

Proton beam radiation

Proton beam radiation is similar to 3D-CRT, except treatment is delivered in the form of protons instead of x-rays. Protons are a component of atoms that can penetrate healthy tissues and attack cancer cells while causing minimal damage. The reason protons are capable of this action is that they release their energy after they pass through tissues and travel a certain distance. X-rays, on the other hand, cause more damage to tissues because they release energy both before and after they arrive at their target.

This special feature of protons allows clinicians to deliver more energy to the tumor while doing less damage to surrounding tissues. Currently, the number of machines to deliver proton therapy is limited because of their high cost, so proton beam radiation is not widely available.

Stereotactic body radiation therapy

Stereotactic body radiation therapy (SBRT) uses focused radiation to target tumors that have been located using computerized imaging techniques and three-dimensional planning. During the set-up process before radiation is delivered, tiny gold tracking seeds are embedded near the tumor to help technicians track the radiation. SBRT is unique in that it involves high-level radiation treatment that can be completed in one to five sessions instead of dozens of sessions over many weeks.

A recent study of SBRT reported in the International Journal of Radiation Oncology, Biology, Physics revealed the findings concerning 67 men who were treated with SBRT and followed for a mean of 2.7 years. The investigators from the University of California, Los Angeles, noted that the 4-year relapse-free survival rate was 94 percent, which “compares favorably with other definitive treatments,” and that long-term side effects were similar to those of other external beam radiation treatments. They concluded that “current evidence supports consideration of stereotactic body radiotherapy among the therapeutic options for localized prostate cancer.”

Side effects of external beam radiation

The side effects associated with any type of external beam radiation come in two phases: those that may appear during treatment (acute) and those that may occur sometime after treatment ends (late). First, here are the most common acute side effects:

  • Diarrhea develops in 30 to 50 percent of men after about two to three weeks of treatment. The good news is that diarrhea goes away about two weeks after treatment has ended.
  • Fatigue typically appears toward the end of treatment and lasts for several weeks once radiation has ended
  • Irritated bladder symptoms develop in about 30 percent of men and can include urinary frequency, urinary urgency, and burning sensation when urinating
  • Irritated rectum can occur in 30 to 50 percent of men and is associated with rectal burning, discharge, leakage, and/or pain
  • Skin changes typically appear in most men starting about one to two weeks after treatment begins and lasting up to one to two weeks after radiation ends. Symptoms affect the treated area and can include dryness, itchiness, redness, and scaling

Late side effects may include the following:

  • Bladder inflammation (cystitis), which may be accompanied by blood in the urine. Approximately 1.5 to 2 percent of men experience this side effect.
  • Erectile dysfunction can develop slowly over time in as many as 30 to 40 percent of men younger than 65 and about half of men who are older. The risk of erectile dysfunction following radiation therapy appears to be lower (about 15%) for 3D-CRT. Erectile dysfunction typically appears about two to five years after radiation treatment ends.
  • Radiation proctitis, which is damage to the rectal wall associated with treatment, occurs in about 1.5 to 3 percent of men who undergo 3D-CRT and may be higher (15% or greater) with conventional EBRT. Symptoms include rectal bleeding, painful rectal spasms, and leakage.
  • Urinary incontinence is rare among men who have no symptoms of incontinence prior to undergoing radiation treatment

For men with localized or locally advanced prostate cancer, external beam radiation therapy is one of the main treatment options they can consider. In the category of EBRT, there are several variations, and the field continues to evolve, so men are encouraged to explore the alternatives and discuss the risks and benefits of each with their healthcare providers while they are making their decision.

Read more in our Prostate Cancer Health Center.

References

Jacobs BL et al. Comparative effectiveness of external-beam radiation approaches for prostate cancer. European Urology 2014 Jan; 65(1): 162-68

King CR et al. Long-term outcomes from a prospective trial of stereotactic body radiotherapy for low-risk prostate cancer. International Journal of Radiation Oncology, Biology, Physics 2012 Feb 1; 82(2): 877-82