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.