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External Beam Radiation

External beam radiation therapy (EBRT) has the advantage of being the only completely non-invasive treatment for prostate cancer. No anesthesia is involved, and the treatment is painless. Effectiveness is similar to the other major treatments in patients who have low-risk prostate cancer. EBRT has several subtypes with names like IMRT (intensity modulated radiation therapy), IGRT (image guided radiation therapy), Cyberknife, and proton beam radiation therapy. Your radiation oncologist can explain the differences between these. EBRT is a popular choice for patients who cannot tolerate or who wish to avoid anesthesia.

What is external beam radiation?

External beam radiation involves the use of focused beams of radiation that are produced electronically by a treatment machine (linear accelerator) to treat malignant and nonmalignant tumors. External beam radiation is a completely non-invasive technique; radiation is invisible, tasteless and odorless. No radiation remains with the patient after treatment. External beam radiation is typically delivered on a daily basis, five days a week over several weeks (seven to nine) for 15 to 20 minutes each day. Radiation can also be delivered internally with radioactive sources (brachytherapy).

How does radiation work?

Radiation works by damaging cancer cells and interfering with their ability to grow and divide. Normal cells can repair the effects of radiation but cancer cells cannot. By delivering radiation over several weeks, we take advantage of the damaging effect on tumor tissues and the ability of normal tissues to repair. The other way that we increase the radiation effect on tumor tissues is by accurately focusing radiation on the prostate and minimizing the dose to nearby normal tissues.

How is radiation directed at the prostate?

We combine precise imaging (CAT scans), using our dedicated simulator, sophisticated computerized treatment planning (IMRT) and accurate daily prostate localization (8-Mode Acquisition and Targeting, or BAT) to enable us to focus the radiation on the prostate and minimize the dose to the rectum and bladder, which are near the prostate.

With IMRT, we are able to assess, monitor and limit the dose of radiation to the bladder and rectum. With BAT ultrasound localization, we can adjust the location of the radiation beam to the exact location of the prostate at the time of treatment. By combining these two modalities, we can deliver high doses of radiation to the prostate while substantially decreasing the risk of rectal bleeding (from 15 percent to less than 2 percent, according to published studies). We are thus able to significantly reduce the use and side effects of hormone deprivation (Lupron and Zoladex) and achieve high cure rates for prostate cancer.

Who is involved in the radiation therapy process?

Due to the technically sophisticated nature of external beam radiation, many staff members are involved in developing the individualized plan for treatment and in the delivery of the treatment. These staff members include:

  • Radiation oncologist, the physician who oversees all aspects of your care while you undergo radiation therapy.
  • Physicists and dosimetrists who create the plan for treatment and perform the quality assurance on the treatment plan and its delivery.
  • Radiation therapists who deliver the daily radiation treatment.
  • Radiation oncology nurse who helps with scheduling and provides side-effect teaching and management.

What are the steps involved in receiving external beam radiation?

After consultation with your urologist and radiation oncologist, and once a decision to proceed with external beam radiation is made, the first step is to schedule a simulation. The simulation is a specialized radiation planning CT scan, which is performed with you lying on you back on the simulator table.

First, a mold is made to hold you in the same position throughout the treatment, and we then conduct a CT scan, which takes less than a minute. The CT images are downloaded into the simulator computer where the prostate is outlined by the radiation oncologist. Small localization tattoos are placed on the treatment site, and this concludes the first visit.

The computerized treatment planning process begins. All of the pelvic organs are delineated and the anatomy is recreated in the computer in 3-D. The physicist and dosimetrist, along with the radiation oncologist, develop a treatment plan that optimizes the dose to the prostate and minimizes the dose to the bladder and rectum. The dose limitations are known, and the plan is modified as needed to maintain the prescribed dose limitations. The planning and quality assurance process can take a week to complete.

After the plan meets the established, rigorous standards, you return to the hospital for verification films, and then the daily treatment begins. Each day, you arrive for treatment at the designated time, and the therapist positions you on the treatment couch. Before treatment, prostate localization is performed using a trans-abdominal ultrasound probe. The therapist can visualize the prostate, and the couch position is adjusted based on the prostate location. This takes less than two minutes. The therapist then leaves the room and the treatment is given. Typically, five treatment angles are used, and the treatment takes 15 to 20 minutes. After treatment, you can resume normal activity without limitations.

What are the side effects and risks?

Since external beam radiation is entirely non-invasive, you will not feel anything immediately after treatment. As treatments progress, some side effects may occur. The typical side effects include mild fatigue, which resolves in one to two months; possible bladder irritation or difficulty initiating a urinary stream, which can be commonly relieved with medications; rectal irritation or diarrhea, which can be controlled with diet or medications; and mild skin irritation, which is rare. The radiation oncologist and nurse will evaluate you weekly to help monitor and treat possible side effects.

Long-term (more than five years after treatment) side effects and complications from radiation therapy are uncommon. An example of this would be rectum or bladder damage that could result in bleeding or the need for surgery. Impotence commonly occurs several years after receiving radiation. There is also a low incidence of a secondary malignancy, such as bladder cancer, that can occur eight years or longer after receiving radiation therapy.

What are some of the drawbacks of radiation therapy?

One drawback is that if the cancer is not eliminated by the radiation treatment, that surgical removal of the prostate is usually not possible later. This is why prostate cancer doctors recommend radiation therapy for patients who have a high chance of cure. For patients with a lower chance of cure, additional treatment combinations may be recommended. An additional drawback is the need for seven to nine weeks of treatments at a center, five days a week.

What type of follow-up care is necessary?

Your urologist and radiation oncologist will typically follow you after radiation therapy, at intervals of three to six months. Follow-up usually entails a PSA blood test and physical examination. It can take two years or more for PSA to decline to its minimum value after radiation therapy.