A highly targeted form of radiation therapy may help younger men to avoid becoming impotent after treatment for prostate cancer, a preliminary study of nearly 100 men aged 55 and younger suggests.

Six months after undergoing proton therapy, 90% of participants who had been sexually active before treatment remained sexually active.

By 12 and 18 months after the treatment, 95%, and 94% of treated men were sexually active, reports Bradford Hoppe, MD, of the University of Florida Proton Therapy Institute in Jacksonville, and colleagues.

A year-and-a-half after treatment, proton therapy was also associated with an extremely low rate of recurrence and a low risk of side effects, the researchers say.

Still unknown, however, is whether these benefits justify the much higher price tag of proton therapy, compared with other treatments for prostate cancer, says Harvard Medical School's Anthony Zietman, MD, chairman of the American Society for Radiation Oncology (ASTRO). He was not involved with the study.

The findings were presented at ASTRO's annual meeting.

No Agreement on Optimal Management of Young Men with Prostate Cancer

Controversy exists over the optimal management of young men with prostate cancer due to concerns about late recurrences and side effects such as impotence, Hoppe says.

Several options have been proven effective for men whose tumor is still confined to the prostate. The most common are surgery to remove the prostate; seed implant therapy, or brachytherapy, in which surgeons implant tiny radioactive seeds into the prostate gland; and intensity modulated radiation therapy, or IMRT, in which multiple beams are focused at the prostate from many directions.

Proton beam therapy is a form of radiation treatment that uses protons rather than conventional photon X-rays to treat certain types of cancer and other diseases.

The beauty of the treatment, researchers say, is that radiation can be targeted to the site of the tumor.

Studies suggest that proton therapy is less likely to expose normal, healthy tissue and nearby organs to radiation than IMRT, Hoppe says.

Proton Therapy's Effectiveness About What Expected

The new study involved 98 men aged 55 and younger with prostate cancer. All received proton therapy; 14 also were given androgen deprivation therapy (ADT) to lower levels of male hormones that can fuel prostate tumors.

Eighteen months after treatment, PSA levels were rising in only one man. Rising prostate specific antigen, or PSA levels, after treatment for prostate cancer can signal a recurrence.

"That's about all you would expect with any treatment this early on," Zietman tells WebMD. "You don't start to see rising PSAs until two, three, four years out."

Much "more interesting," he says, "are the erectile dysfunction findings."

In addition to reporting high rates of sexual satisfaction after treatment, the men reported a relatively low rate of erectile problems, Zietman notes.

Low Rate of Erectile Problems

Erectile problems were assessed using the international index of erectile function (IIEF), which asks a series of questions about the effects erection problems have had on a man's sex life over the past four weeks. The maximum score in the study was 25 points, with higher scores indicating fewer problems, Hoppe says.

Participants' average IIEF score was 24 before treatment and then 22, 21, and 18 points at six ,12, and 18 months after proton therapy, respectively.

Other findings:

    * At 18 months after treatment, 35% of the men had genitourinary (GU) obstructive symptoms such as difficulty urinating that required prescription medication, compared with 14% before treatment.

    * Three percent of men had gastrointestinal symptoms such as painful rectal inflammation and bleeding that required prescription medication at 18 months, compared with none before treatment.

    * One man suffered serious side effects that required surgery. However, he was already on prescription medication for GU symptoms prior to proton therapy, Hoppe says.

8 U.S. Centers Offer Proton Therapy

Says Zietman, "No one is denying proton therapy is good. The side effect rate is low and its effectiveness appears to be in the same ballpark [as other treatments].

"The controversy centers on cost -- about twice the rate of regular radiation treatments," he says.

Other radiation treatments carry a price tag of $30,000 to $50,000 depending on where you live, according to Zietman.

While a study that directly compares proton therapy to other treatments are needed, "I applaud the authors for carefully collecting and honestly reporting the kind of data we need to start answering this question," he says.

Only about eight medical centers in the United States have the large, multimillion dollar machines needed to deliver proton therapy, but several other facilities are under construction, Zietman says. It is hoped that costs will come down as availability rises, he says.

This study was presented at a medical conference. The findings should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.