العلاج الإشعاعي الموضعي (البذور المشعة) لسرطان البروستاتا

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Brachy is Greek, meaning near or close. Brachytherapy is a form of radiation using radiation sources close to the cancer.  In this case; is implantation of radiation source directly inside the prostate gland.

How is it done?
It could be done by an open implantation after the urologist has exposed the prostate gland (by low abdominal incision).  However, the most recent and convenient approach is by transperineal implantation using transrectal ultrasound guided to localize the prostate gland.  The needles (hollow, with stylets) then are inserted into the prostate gland, avoiding the rectum and urethra and bladder.  The radiation sources (which are in the form of the seeds) will then be passed through the hollow needles and implanted into the prostate gland.  This sometime is called interstitial brachytherapy.  The strength of the radioactive source and the distribution were preplanned by the computer.
When patients with Prostate Cancer are treated by external standard conventional radiation, the radiation beam will pass the skin, the surrounding tissue such as rectum and bladder to the prostate. As prostate cancer is dose responsive (the higher the dose of radiation, the better the result in cancer cell killing) the adjacent rectum and bladder tissues will have to expose to higher dose of radiation as well. This will result in radiation damage of those organs, some of which may not be reversible.  The patients then may develop tenesmus, rectal bleeding, hemorrhagic cystitis, the incidences of which varies, from few percent to 10%. These complications are higher in patients who have underlying diabetes, hypertension, and are heavy chronic smoker.

The Interstitial Brachytherapy reduces the chance of surrounding tissue injury as radiation sources are within the prostate gland.  The character of the radiation source is that the radiation fall off rapidly according to the inverse square law. Thus the radiation emitted to the rectum and the bladder is low. As a result, the normal tissues are not damaged by radiation.

Another advantage of radioactive source is they slowly but constantly emit the radiation. For example, the I-125 seed which is commonly used in prostate cancer brachytherapy has a half-life of 60 days. This constant radiation will overcome the periods of radio resistant of the cell cycle. Slowly release radiation does not damage the normal surrounding tissue as does the rapid high dose.

Overall, the total radiation dose to the prostate gland is about twice that usually given by standard conventional radiation treatment.
There is still some chance of radiation reaction to the rectum, urethra (bladder tube) and bladder but much less than external standard radiation therapy. The procedure is performed under anesthesia (general or spinal) and the risk and complication from anesthesia is likely that of any other surgery. There is the chance of the seeds being migrated into vascular system into the lung but very very small and usually does not do any harm (like staple left in lung surgery). If one or two seeds get into the bladder, the urologist can remove them out by cystoscopy after finishing the procedure, or in case of subsequent event, the seeds would be coming out with the urine. However, the chance is almost nil in the experience hands.
The patients who are ideal for this Interstitial Brachytherapy could be treated by surgery (radical prostatectomy) and external irradiation with about the same results.

The disadvantage of radical prostatectomy is that the urologists have to open the pelvic cavity, the patient will be hospitalized for several days, need to wear Foley catheter. There are good chances for the patient developing urinary incontinence and sexual impotency. However, there is a technique of nerve sparing procedure which would not affect the sexual function. The problem is the cancer may be left behind if there is perineural lymphatic invasion by malignant cells.

The disadvantage of standard external radiation is the lengthy treatment course which is daily trips (5 days/week) for about 7 weeks. This may be inconvenient for the patients and disrupt the routine life of the supporting family members.

The Interstitial Brachytherapy is a one-time procedure. In some country where health insurances cover, the treatment is even done as an out patient.
Not every prostate cancer patients are suitable for this treatment. The ideal case is tumor confined within one lobe of the gland, low cancer grading, low PSA level and the size of the gland that is not too small (such as the case after transurethral resection of the gland due to bladder tube obstruction), or too large the gland size. However, in the patients who are not ideal, the treatment would be considered, depending on many factors and judgments of the physicians. Those whose prostate glands are large could be treated by hormone first so that the gland size is decreased.

In the patients who have more advanced disease, the treatment needed is to cover the large area such as draining pelvis lymph nodes as well as the primary tumor in the prostate gland. However, the primary cancer which is larger in size, with more cancer cell burden will require higher dose of radiation to eradicate the disease. The Interstitial Brachytherapy can be used as supplement or boost to the prostate gland while sparing surrounding normal tissue of rectum and bladder. The boost dose by this technique is likewise higher than by standard external radiation and thus higher chance of tumor eradication.

Another indication for Interstitial Brachytherapy is the salvage treatment in case the cancer has locally recurred after radical prostatectomy but has not yet has spread outside the primary prostate bed area. The other salvage treatment is for local recurrence after external radiation therapy when the rectum and bladder could not be exposed more to radiation.

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