The "neurovascular bundles of Walsh," discovered by Patrick C. Walsh, M.D., are tiny, delicate, and important: they contain the nerves that control erection. "An unfortunate risk of any treatment for prostate cancer is that many men who undergo curative surgery or radiation will subsequently develop erectile problems," explains radiation oncologist Danny Song, M.D. For men who undergo surgery, the nerve-sparing techniques discovered by Walsh have been shown to help preserve sexual function.

But until now, "there has been no clear understanding of what exactly leads to this side effect in patients undergoing radiation," says Song, who recently set out to change this. "Prior studies have attempted to answer this question by evaluating the dose of radiation received by the neurovascular bundles, which are tiny cables of blood vessels and nerves that run along the sides of the prostate. However, these studies have not shown a difference in erectile function when comparing patients who received high vs. low doses to these structures." So Song took a different approach. In a recent study of 366 men who underwent brachytherapy (the implantation of radioactive seeds at precise points to kill prostate cancer), Song and colleagues measured radiation doses to various anatomic structures around the prostate.

"We also looked at the area where the nerves converge at the apex of the prostate, the place where the urethra joins the prostate," Song says. "These nerves are essentially the combined neurovascular bundles from both sides of the prostate, which join on their way down to the penis. One could consider this to be the main 'hub' where the nerves meet on their way down to the penis." Song and colleagues discovered that the risk of erectile dysfunction was high in men who received higher doses to the cavernosal nerves, "but patients who received lower doses to the cavernosal nerves had less risk of erectile problems. We are excited by these results and hope that, armed with a better understanding of the area that needs to be avoided when placing seeds, radiation oncologists will be able to use this knowledge to improve sexual function and quality of life for their patients."