While radiotherapy has proven to be a very effective treatment for men with prostate cancer, the high doses of radiation required to kill cancer cells in this area have traditionally come with the risk of toxicity to organs that surround the prostate. The rectum, which sits directly behind the prostate, is of particular concern, with high energy X-rays potentially causing injury to the rectal wall, diarrhea, or bleeding.
To reduce the dose of radiation received by the rectum during treatment, radiation oncologists currently utilize intensity modulated radiotherapy (IMRT), a technique where the radiation beam is delivered from multiple directions with varying intensity, reducing the amount of rectum directly in the path of radiation. We also use image guided radiotherapy (IGRT) to precisely verify the location of the prostate and rectum to ensure the target is aligned correctly within the treatment machine. Still, neither of these approaches changes the fact that the rectal wall is in direct contact with the prostate, making it unavoidable that at least a small portion of the rectum will receive the full dose of radiation.
Looking for Solutions
To address the issue of the rectum’s close proximity to the prostate during treatment, several approaches can be considered to address the problem, although some are still in the experimental phase. The use of hyaluronic acid gel to physically separate the two organs is one approach being tested. Another product that may help reduce radiation from reaching the rectum are implanted calypso fiducial markers, which emit a radiofrequency signal that helps localize the prostate. In essence, it’s similar to a GPS that tracks the prostate’s motion during radiotherapy treatment to ensure accurate delivery of radiation.
One of the spacer products that has received FDA approval is a polyethylene glycol hydrogel that fills the plane between the prostate and rectum. The gel is injected as a liquid and solidifies where it’s placed, creating a barrier that prevents the rectum from receiving
the high dose radiation required to kill cancer cells in the prostate. Patients don’t experience any symptoms or discomfort related to the gel and it remains stable throughout radiation therapy before being absorbed by the body.
Reducing Toxicity
In a randomized, prospective clinical trial, it was demonstrated that the hydrogel is well tolerated by patients, easy to place, and, most importantly, significantly reduces the volume of rectum that receives high dose radiotherapy. This has directly translated to a reduction in rectal toxicity and its side effects among patients who received the product.
Another benefit to this approach is that it can be used with many different types of radiation, including:
• Fractionated radiotherapy – small to moderate doses of radiation given daily for four to eight weeks
• Stereotactic radiosurgery – high doses of radiotherapy delivered in four to five treatments over one to two weeks
• Brachytherapy – radioactive seed implants
Many doctors in the U.S. and overseas are now utilizing at least some of these approaches to benefit patients by minimizing rectal toxicity during the treatment of prostate cancer.
While radiotherapy has proven to be a very effective treatment for men with prostate cancer, the high doses of radiation required to kill cancer cells in this area have traditionally come with the risk of toxicity to organs that surround the prostate. The rectum, which sits directly behind the prostate, is of particular concern, with high energy X-rays potentially causing injury to the rectal wall, diarrhea, or bleeding.
