Proton Beam Therapy Appears Safer than Prostatectomy, X-rays

CHICAGO—At California’s Loma Linda University, physicians have treated 1,800 patients with early-stage or locally advanced prostate cancer with proton beam radiation therapy using a synchrotron accelerator.

In 645 patients for whom 5-year disease-free (biochemical no evidence of disease) survival data are available, proton beam therapy proved as effective as surgery or conformal x-ray therapy, with fewer complications, Carl Rossi, MD, assistant professor of radiation medicine, said at a press conference held at the Radiological Society of North America (RSNA) annual meeting.

“Conventional photon beam (x-ray) radiation treatments for prostate cancer often cause damage to the nearby bladder or bowel. With proton beam therapy, we can treat prostate cancer aggressively while avoiding these adverse side effects,” Dr. Rossi said.

For the most favorable patients—those with pretreatment PSA levels less than 4.1 ng/mL, 5-year biochemical NED survival was 100%. Survival rates began to fall off in patients with higher pretreatment PSA levels: 88% for PSA between 4 and 10 ng/mL; 68%; for PSA between 10 and 15 ng/mL, and 48% for PSA between 20 and 50 ng/mL.

When the Loma Linda researchers compared their survival outcomes for early-stage prostate cancer patients with published survival data for surgical patients from Johns Hopkins University, they found “virtually identical” rates, when patients were matched by pretreatment PSA, Dr. Rossi said.

In an interview, he told Oncology News International that the 5-year survival data on all 645 patients, as well as the data on early-stage patients, have been submitted for publication.

The 645 proton beam therapy patients had about one-half the incidence of grade 1 or 2 complications as seen in patients treated with similar doses of conformal x-rays in published studies.

“We have not had any grade 3 or greater GI complications in the 645 patients for whom we have survival data; we’ve had two grade 3 GU complications (urinary outlet obstruction), for an incidence of three-tenths of 1%,” he said, adding that “with conformal x-ray therapy at similar doses, you would expect about a 5% to 6% incidence of grade 3 or greater complications.”

The incontinence rate for surgical patients, he noted, is about 40%, based on published literature.

The incidence of impotence (defined as any decline in potency from pretreatment status) with proton beam therapy is about 30% to 50%, which, Dr. Rossi said, is about as good as the best data from trials of nerve-sparing surgery.

Thoughts on Cost

Currently, Loma Linda University is the only hospital-based proton beam treatment center in the United States. “Another facility like ours is being completed at Massachusetts General Hospital and will be operational in the fall of 1998,” Dr. Rossi said. Physicians at Mass General have been treating prostate cancer patients with proton beam therapy using Harvard’s cyclotron, which was installed some 50 years ago.

The cost of proton beam treatment at Loma Linda is comparable to the cost of complex photon beam therapy, Dr. Rossi said. Although the initial investment is high (close to $50 million at present), the life of a synchrotron is long—30 to 40 years versus about 10 years for a linear accelerator—“so you have a long time to amortize the costs,” he said.

In addition, he pointed out that costs will come down as one-of-a-kind devices give way to larger-scale commercial manufacture.