Health care leaders broke ground Aug. 5 on a $185 million proton therapy center that Scripps Health will use to treat cancer patients. It will be the first facility in San Diego County and only the second such center in the Western United States to offer the advanced therapy.

Grading is under way and construction is expected to start in October. A Scripps Health statement said the center is expected to be open for patient care by spring 2013.

Located on a 7-acre site on Summers Ridge Road in San Diegos Mira Mesa area, the 102,000-square-foot center will have the capacity to treat approximately 2,400 patients annually.

The facility is being developed through collaboration among Scripps Health, Scripps Clinic Medical Group and Advanced Particle Therapy LLC of Minden, Nev. The architect and general contractor is Haskell Design Build of Jacksonville, Fla.

The facility will have five treatment rooms, three of which will include rotational machines designed to deliver therapeutic beams at precise angles prescribed by a physician. The other two treatment rooms will have fixed-beam machines.

The centerpiece will be a 90-ton cyclotron, about the same weight as a fully loaded 737 jetliner, but just 5 feet high and 10 feet wide, according to Scripps Health. The cyclotron accelerates protons to extremely fast speeds - roughly 100,000 miles per second - creating a beam that can reach tumors that are up to 14 inches deep.

The beams can also be shaped in three dimensions to avoid hitting surrounding healthy tissues, targeting tumors with unprecedented accuracy, according to Scripps Health.

The center will also offer magnetic resonance imaging and CT scan diagnostic services in support of proton therapy; 16 patient exam rooms; and offices for 14 physicians.

- Lou Hirsh