Brakytherapy Plus EBR (IMRT)

Choices
mrdezzy,

I have read many reports that indicate a combination of brachytherapy and IMRT has been quite effective in treating prostate cancer. I think, however, that your understanding of the very complex process of radiation is still a little fuzzy.

Directing the radiation beams is a complicated process and I have never heard of brachytherapy radioactive seeds being used to serve as reference points but I suppose it is possible.

Some forms of external beam radiation like CyberKnife (just one example) use implanted gold fiducials in the prostate to guide the radiation beams. These are about the size of a grain of rice and remain in the prostate permanently after placement. The tracking system takes continuous pictures of the prostate position using the fiducials as a reference and adjusts in real time the beam placement to compensate for the movement of the prostate. If the prostate moves outside of certain parameters then the radiation stop until the prostate settles down. Frequently special diets that minimize gas and stool passage through colon are encouraged because these normal bodily functions cause the prostate to move.

Other forms of radiation base their radiation plan on a one time look at the prostate before radiation or in older systems the use a CT scan of the prostate taken days before the actual radiation. These systems are inherently less accurate.

Some newer forms of IMRT use real time tracking techniques but not all of them so you would need to ask specific details about the equipment proposed for your procedure.

CyberKnife, for example, provides sub-millimeter accuracy in beam placement real time. During my treatment there were a few occasions where the machine actually shut down until the prostate moved back into a correct position.

Newer forms of radiation like CyberKnife and variants of IMRT send hundreds of different beams from different angles. No single beam by itself is enough to cause damage but the areas where they converge delivers the appropriate dose. Beam placement methods today thus enable a high concentrtion of radiation exactly in the 3-D space of the prostate and minimizes radiation to those nearby surruounding areas (bladder necks, testes, colon, etc.) where unwanted toxicity from side effects might develop. Using sophisticated computer modeling the radiation plan actually shapes the electron beams to fit exactly inside the prostate to the margins determined by the radiologist.

In actuality, you want a higher radiation dose for prostate cancer. There is something called the alpha-beta ratio of cancers which is a measure of how many cells might be undergoing mitosis at any given time. Since prostate cancer is generally a very slow growth disease, it has a relatively low alpha-beta ratio which makes it especially vulnerable to radiation treatment. The higher they dose that can be delivered, the better the outcome. The trick obviously, is to minimze damage to surrounding tissue and organs and the newer systems do this by using multiple beams and tracking systems.

You may know that brachytherapy delivers a relatively low dose of radiation (compared to external radiation sources) but over the active half life of the radioactive isotope (usually about three months) the right dosage levels is delivered. Brachytherapy also has a slightly higher incidene of unwanted side effects affecting bowel, erectile function, and urine toxicity. Seeds sometimes migrate and if they move up against the colon wall, for example, they can cause a radiation "burn" that can result in damage to the colon that could require corrective surgery.

The reason they use the gold fiducials I described above is that they can be more clearly seen by the continuous x-rays that are ongoing during treatment and since they are chemically inert, migration at some later date does not cause any harm.

Given you relatively low level of prostate cancer there are several methods of treatment that will likely have equally good outcomes. What I think your priorities should be is which of these treatments pose the least risk of side effects downstream in terms of urinary continence, bowel toxicity, and erectile dysfunction.

My research led me to conclude that CyberKnife was the best choice at the time I made my decision in March 2010. The pace of advancement continues and there may be other techniques you want to look at as well.

I suggest you research CyberKnife, RapidArc, Varian, and other systems available before you make a final decision.

Best of luck to you.

K