Killing the Cancer

As we’ve said, ProstRcision® uses a combination of pinpoint irradiation and conforming beam irradiation to destroy the prostate from within.

The first step.

We begin by implanting tiny radioactive seeds into the prostate. The size of the seeds allows us to place them all around the cancerous cells and away from important muscles or nerves. The seeds emit most of their radiation over the course of a few months but will continue to release radiation for up to one year.

The seeds we use, I-125, are actually tiny titanium capsules that are one-fifth of an inch long and as thin as pencil lead. Radioactive iodine is attached to a small piece of silver inside each seed. The seeds kill the cancer by slowly producing low-energy gamma radiation. When we say we can attack the cancer with pinpoint accuracy, it’s because the area surrounding the seed is hit with a tremendous amount of radiation, but a few millimeters away, the radiation level drops off rapidly.

The seeds also make a good target.

Because the prostate does not show up on an X-ray, the seeds serve two purposes: they release radiation to kill the cancer and they map out the prostate on the X-ray. As we mentioned, the seeds have silver in them. We also inject gold seeds, which are larger and thicker, to outline the prostate on X-rays. Once we see the outline, we know exactly where to aim the second dose of irradiation.

Getting the rest of the cancer.

Using seeds is an excellent way to destroy the cancer within a prostate, but they do have limitations. They don’t effectively kill any cancer that may have leaked outside the prostate, and given the amount of close range radiation they give off, the seeds can’t be placed right next to the urethra without damaging it. It’s important to note that studies show 41 percent of men with prostate cancer have cancerous cells on or very near the urethra. This is one reason why we follow the seed treatment with another type of irradiation called linear accelerator irradiation. We also use the additional radiation to ensure that we kill all the cells within the prostate. Leaving even one cell, healthy or cancerous, could allow the cancer to come back over time.

To deliver this additional irradiation we use one of two methods, either a conformal beam or Intensity Modulated Radiotherapy Technique (IMRT). Using conformal beam irradiation, we can shape the beam of radiation into an exact outline of each patient’s prostate. We do this by using lead blocks. Each block is cut out by hand and placed in the accelerator machine before treatment. (See diagram at left.)

With IMRT, a computer actually shapes the blocks. IMRT allows for better control over the dose of radiation and can potentially keep the nearby organs from being over-exposed, while focusing the radiation on the prostate.

Using two methods for a better result.

To summarize, ProstRcision uses the two types of irradiation, with each method overcoming any disadvantage the other might have in killing the cancer. The seeds produce a high dose of radiation inside the prostate without harming the urethra or adjacent nerves and muscles, and the follow-up linear accelerator radiation goes after any cancer outside the prostate. The two treatments overlap, which produces the dose intensification required to kill the cancer.

For an in-depth look at ProstRcision, visit our Q & A section.

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