An interesting – and decidedly non-intuitive – feature of FDA 510(k) regulatory clearance is highlighted by the effort ofXoft(Fremont, California) to gain U.S. commercialization for its Axxent Electronic Brachytherapy system without having first demonstrated clinical efficacy.

The company has carried out animal and “bench” testing but won’t move forward with human trials until after approval, Marga Ortigas-Wedekind, vice president of marketing and development for the company, told Medical Device Daily.

No matter. The important fact is that Xoft has built a case for the equivalence of its Electronic Brachytherapy technology to brachytherapy delivered by the current standard of using radioisotopes, primarily iridium 192, which she calls “the most commonly used” radioisotope.

“What we’ve done is try to define our [radiation] source mathematically. And then what we’ve done internally is to create our source so it looks like Iridium 192,” Ortigas-Wedekind said. This equivalent radiation is then delivered to a breast cavity following tumor resection.

“Our goal,” she adds, “is to create enough physics evidence, if you will, so that it looks like iridium 192.” Put another way, she says that the intent is “to bridge electronic data to isotope data.”

A similar goal was pursued by Mark Rivard, PhD, associate professor and chief medical physicist in the department of radiation oncology at Tufts-New England Medical Center (Boston).

Not looking at efficacy, his recent study, “Calculated And Measured Brachytherapy Dosimetry Parameters In Water For The Xoft Axxent X-Ray Source: An Electronic Brachy-therapy Source,” established the clear dosing parameters for the Xoft technology.

Rivard told MDD that the establishment of dosing for brachytherapy – much more complicated than drug dosing, since requiring a kind of 3-D analysis and presentation – has been historically slow to develop. And he notes too that the use of standard isotopes has meant dependence on a “limited inventory,” without wide ranges of dosages.

“3-D planning – that’s key,” Rivard says. “We basically overlaid the dose distribution [with] a computer to see what the actual patient would get.”

He says that the effort really started with the World War II era attempt to analyze the effects of radiation on matter.

“Now, we’re able to take peacetime uses and use the same types of computer codes to predict how radiation interacts with matter. We measured the Axxent source [of non-isotope radiation] in water and could characterize it in a computer.” This was done using water “phantoms” that simulated the water-dominant human body to calculate the distribution of Axxent radiation.

That data is then put into “standardized formats,” thus setting a higher standard to “undergo and pass the peer review process,” he said.

Rivard reported that his work on Axxent dosing would be published in a future issue of the journal Medical Physics.

Don Long, Managing Editor