The same GPS technology in your car is now helping Seattle doctors navigate tumors to make radiation treatment much more effective.

It's called GPS for the body and was developed by a local company.

When Robert Heinkle was about to face radiation for prostate cancer, he had one goal: to minimize the side-effects.

"That was my whole defensive decision process - find the least offensive to the body that wouldn't give you long-term side-effects like incontinence," he said.

It's a very real concern.

"With standard radiation we have to treat a larger volume of tissue because the prostate is moving during the treatment and so we end up treating some tissue we would rather not," said Dr. John Sylvester, Swedish Cancer Institute.

The Calypso System solves that problem by implanting three small transponders in the tumor, each about the size of a grain of rice. Then, just like standard GPS, doctors are able to track the location of the tumor in real time during treatment, which appealed to an engineer like Robert Heinkle.

"That seemed like the solution. It certainly was a significant enough step that I was willing to drive down here every day – about a 130 mile roundtrip to get treatment here," he said.

For radiation oncologist John Sylvester, the technology represents much more.

""This is a breakthrough. Never before in a hundred years of radiation therapy for cancer have we been able to actually see what we were treating while were treating it," he said.

For now the Calypso GPS System is only FDA-approved for prostate cancer, but it has the potential to treat other tumors, as well.

"That's the beauty of the Calypso technology is that it will work anywhere in the body," said Nelson Wright, Calypso Medical.

The Swedish Cancer Institute now has the distinction of being the first hospital in the world to offer this approach.