An exciting breakthrough in the mechanics of delivering radiation treatment to the prostate may help prevent one of the most common side effects: bleeding from the rectum. Radiation treatment planning and delivery keeps getting better, and advances in recent years – including intensity-modulated radiation therapy (IMRT ) and the use of imaging to target the radiation more precisely to the prostate – have reduced many complications, says radiation oncologist Danny Song, M.D. “But the rectum has remained at risk because of its location.” The rectum and prostate are immediate next-door neighbors; think of townhouses sharing a wall. The anterior wall of the rectum is little more than a hair’s breadth from the prostate, and this part of the rectum receives a high dose of radiation during treatment for prostate cancer. “About 5 to 15 percent of patients develop bleeding from the rectum several months after treatment is completed,” says Song.
"The rectum and prostate
are immediate next-door
neighbors; think of townhouses
sharing a wall."
If there were just a bit more distance between the rectum and the prostate, much of this damage could be avoided. In an effort to create that space, Song and Theodore DeWeese, M.D., Ph.D., Chairman of Radiation Oncology and Molecular Radiation Science, have been working with a temporary filler – a biodegradable gel. “Polyethylene glycol is a substance that has been around for years and is used in several medications,” says Song. “When it is turned into a gel, it doesn’t last forever; it is eventually broken down and absorbed by the body.”
But what this gel does is provide a much-needed cushion. In previous experiments using cadavers, Song and DeWeese successfully showed that they could inject polyethylene glycol between the rectum and prostate and push the rectum away from the danger zone, the high-dose radiation target area. With clinical collaborators in Europe, Song and DeWeese recently demonstrated that men who were injected with the gel before they started radiation treatment had “significant reductions in the amount of radiation received by the rectum,” says Song, “and these patients went on to have very low rates of rectal toxicity.” Based on this work, FDA approval for the gel is pending. “Soon, our patients who are starting radiation treatment for prostate cancer will be offered the ability to receive this side effect-sparing treatment.” This work is currently in press with the International Journal of Radiation Oncology, Biology, and Physics.
What this gel does is provide a
much-needed cushion. It pushes
the rectum away from the danger
zone, so that the radiation only
goes to the tissue that needs it: