Frequently Asked Questions

External Beam

Q. What is External Beam Radiation ?
A. EBRT is radiation that is generated by an external source, typically a linear accelerator, and directed much the way diagnostic x-rays are directed at a patient. Multiple beams are used generally that converge on the target region. This allows sparing of the normal tissues (skin, normal bowels and bladder, hip joints, rectum). There are several manufacturers of linear accelerators used commercially. The Swedish Cancer Institute has modern equipment from primarily Elekta and Varian primarily. The energy of the primary beam can be adjusted to create different dose-depth characteristics and the shape of the beams are custom designed for each patient based on their anatomy and cancer location and stage.

Q. How much radiation will a patient normally receive from EBRT? Do you recommend either EBRT or conformal 3D radiation?
A. A Typical dose for pre-implant EBRT is 4500 cGy. For definitive treatment alone, doses range from 75.6 Gy all the way up to 81 Gy plus. All radiation therapy performed today for prostate cancer is 3-D planned with multiple fields, with or without IMRT (described below). The initial fields for this treatment are purposely designed to treat the prostate, seminal vesicles and occasionally the lymph nodes. Standard EBRT is given daily, treating anywhere from four to 9 fields. With the 3D technique, multiple fields and sophisticated blocking are done to shape the beam and avoid high doses to the rectum and bladder.

Q. I have heard that IMRT radiation is used often for prostate cancer treatment. What is IMRT?
A. IMRT is intensity modulated radiation therapy. IMRT represents a significant advance in radiation therapy and we use IMRT both for treatment of the prostate alone and in coordination with a brachytherapy boost. There are two aspects of IMRT that improve radiation delivery. First, we can alter the ‘fluence’ of any individual beam. Think of 3D conformal radiation as delivering say 4 to 9 beams all shaped uniquely to treat the tumor. Each beam however, like a flashlight, has the same strength across the beam. With IMRT we are not restricted to having one strength for each beam. Leaves can move into and out of the field while the beam is on to alter the fluence. In its most elegant form, IMRT can even allow treatment of a ‘doughnut’ where a rim of radiation can be delivered while sparing the center. The second advance is inverse planning. Altering fluence requires computing speed and mathematical calculations far beyond what a human could envision. With inverse planning, we can tell the computer what structures to treat to a particular dose, which structures to spare, and various weighting criteria for each ‘rule’. The computer then iteratively tests hundreds of thousands of plans and angles and alterations to optimize and select the best plan. This often takes the computer hours due to the complexity involved. These two features allow us more flexibility in designing fields. Presently we use IMRT both for treatment of the pelvis and for the prostate and essentially use for virtually all cases of localized prostate cancer.

Q. What side effects might be expected from either EBRT or conformal radiation?
A. The side effects are similar from either technique. Radiation to the prostate region can affect the bladder, urethra and rectum. Typical symptoms during treatment include increased urinary frequency, slower stream, irritation during urination, rectal tenderness, slight diarrhea and tiredness. These symptoms usually resolve shortly after the treatment is completed.

Q. Am I radioactive after I leave the radiation room?
A. With EBRT, one is not radioactive after treatment. This is unlike brachytherapy, where a very low dose of radiation can be measured outside the body constantly and with a constant decay. With EBRT, treatment is like a beam of light, when the beam is off the radiation is gone.

Q. How many days long is EBRT radiation?
A. Treatment times vary. For treatment of the pelvis and the surrounding prostate tissues before an implantation, 5 weeks is most commonly used (45 Gray). If no brachytherapy is planned and a full dose delivered with EBRT, treatment times are increased to approximately 7.5 to 8 weeks.

Q. Is the Cyberknife a type of External Beam Radiation?
A. Yes, the Cyberknife is an advanced radiation machine in which the linear accelerator has been miniaturized and placed on a sophisticated robotic arm. This can allow very precise and focal treatments. Cyberknife is being used for localized prostate cancer and we are lead investigators on a nationwide protocol for this treatment.

Q. I have read that extraneous x-rays are bad. Is radiation damaging to other normal tissue?
A. This is generally a question of relative risk/benefit. Generally speaking, radiation is to be avoided especially in the workplace or at home (such as Radon). Medical x-rays such as CT scans should be used only when medically necessary. The same is true of radiation therapy for prostate cancer. There is a very small risk of initiating a second cancer. In an adult and expecially an older adult this risk is tiny. Generally it takes 15 years for a cancer to develop if it were to develop at all. However we remain careful to minimize the tissue exposed to radiation. During the course of treatment, normal tissue can repair DNA damage caused by radiation and this is the basis for ‘fractionating’ or spreading the treatment over several days. Normal cells take at least 6 hours to repair from DNA damage. In terms of second tumors, the risk of this has to be weighed against the risk of the prostate cancer spreading or the risks of alternative procedures such as surgery. Generally when all is compared side-by-side, the second malignancy issue is so small as to not be clinically relevant in the decision making process.

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