Proton therapy, which some studies show can kill cancerous tumors with fewer side effects than X-rays, is coming to San Diego County.

Scripps Health announced Tuesday that it will manage a $185 million proton center to be built in northern San Diego by Advanced Particle Therapy, a private health care company based in Minden, Nev.

Construction is expected to start in July on a 7-acre site in San Diego's Carroll Canyon business district near Mira Mesa.

The 102,000-square-foot facility is to include five treatment rooms, three with special gantries that allow a proton beam to be delivered to a patient at almost any angle.

Officials said the project is expected to be finished in 2013.

Proton therapy can be particularly useful in treating rare tumors in areas such as the head, but is more costly than still-effective treatments used for more common cancers, some experts have said.

When complete, the proton center will be the second of its kind in California; the closest available center is at Loma Linda University Medical Center in San Bernardino County.

The northern San Diego facility will require building a cyclotron ---- a 220-ton machine used to accelerate charged particles at close to the speed of light.

In proton therapy, protons ---- subatomic particles that compose the nucleus of atoms ---- are used to precisely target and eliminate tumors without the collateral damage often caused by X-ray-based radiation.

This is much different from the "radiosurgery" devices with names such as "Cyberknife" and "Gamaknife" that are in use throughout the region.

Those machines use tightly focused beams of radiation, rather than protons, to target tumors.

That approach focuses most of the radiation just where it is needed, but there is still some spillover into surrounding tissue.

Dr. Prabhakar Tripuraneni, head radiation oncologist at Scripps Green Hospital in La Jolla, said Monday that the ability to target a tumor and spare surrounding tissue, or vital organs, can be particularly important in some kinds of cancer treatment.

He said he recently had a patient with a tumor on the back of her eye who traveled to Boston for proton therapy because the Loma Linda center had a three-month wait.

Because of the tumor's location, Tripuraneni said, it would have been necessary to remove the eye had proton therapy not been used.

"It will be very good for patients in this area not to have to stay in a hotel for six weeks and travel across the country for proton therapy," he said.

Proton treatment is also known to be effective in treating tumors near the brain and spinal cord and certain types of juvenile cancer.

However, head tumors and juvenile cancer are rare, oncologists said.

At hospitals where proton treatment already exists, the technology has become increasingly popular for treating much more common prostate cancer in men.

Although protons do work on such cancers, the treatment is much more expensive ---- and not necessarily more effective ---- than using advanced X-ray technology, some specialists say.

In 2007, Dr. Andre Konski, a radiation oncologist now with the Karmanos Cancer Institute at Wayne State University in Detroit, published a paper in the Journal of Clinical Oncology that concluded that proton therapy was less cost effective than intensity-modulated radiation therapy at treating prostate cancer.

The paper found that the mean cost of proton beam therapy for a 70-year-old man was $63,511, compared with $36,808 for radiation therapy, which uses multiple low-dose X-rays to zap a tumor.

Konski said in a telephone interview Monday that prostate patients who get proton therapy do receive less radiation than those who undergo X-ray treatment.

However, he added that there is no perfect clinical data to prove that irradiated patients fare worse after treatment.

"What we don't know is if what we see on paper is really clinically meaningful," Konski said.

Jeff Bordok, CEO of Advanced Particle Therapy, said he believes that more recent studies are beginning to prove that there is less chance of secondary cancers cropping up after proton therapy.

But, he added, the public should not see the therapy as replacing radiation for cancer treatment.

"Protons are not here to get in the way of other treatments. But if we can enhance them or provide another option, then we think that's going to help everyone," Bordok said.

When operational, the new proton center is expected to see 2,400 patients per year.

It will be managed by Scripps, but all of the construction funding will come from private investors.

Chris Van Gorder, chief executive of Scripps Health, said the nonprofit health care network has been looking at building a proton therapy clinic for about six years, but said the finances did not line up until the partnership with Advanced Particle Therapy materialized.

"For us, and for our patients, this is a deal made in heaven," he said.

In addition to Loma Linda, there are six other proton centers are in the United States, although only two ---- one in Houston and another in Oklahoma City ---- are west of the Mississippi River.

Two more proton centers in New Jersey and Virginia are expected to open by 2012, meaning that the Scripps facility likely will be the 10th in the nation.

Call staff writer Paul Sisson at 760-901-4087.