Prosecution History: A Patentee’s Silence Can Be Motivating

In Elekta Ltd. v. ZAP Surgical Systems, Inc., the Federal Circuit affirmed a Patent Trial and Appeal Board decision in an inter partes review that invalidated patent claims relating to “a device for treating a patient with ionizing radiation for certain types of radiosurgery and radiation therapy.”[1]  81 F.4th 1368, 1370 (Fed. Cir. 2023) (affirming ZAP Surgical Sys., Inc. v. Elekta Ltd., IPR2019-01659, paper 48 (Mar. 30, 2021)).

One of the central issues in Elekta was whether the Board had substantial evidence for finding that a skilled artisan would have been motivated to combine two prior-art references, even though one pertained to “an imaging device” (the Grady patent) and the other to “a radiation device” (the Ruchala publication).  81 F.4th at 1373.  The Board based its decision, in part, on the ’648 patent’s prosecution history.

In the IPR, the patent owner argued “that Grady discloses a diagnostic imaging device and does not disclose anything about radiation treatment.”  IPR2019-01659, paper 48, at 30.  The patent owner argued that Ruchala, in contrast, “use[s] linacs for radiation treatment, operate[s] in the higher megavolt range, and require[s] more accurate aiming capability.”[2]  Id. at 31.  In response, the petitioner argued in part that during prosecution of the ’648 patent, references “directed to imaging devices were cited, and were not distinguished based on an argument that imaging devices were not relevant art.”  Id. at 32.

The Board found that a POSA “would have been motivated to combine the three-dimensional flexible targeting capabilities of Grady to treat tumors with radiation sources, such as linacs, as described in Ruchala, to arrive at a radiation therapeutic device” recited in the challenged claims.  Id. at 33.  The Board relied on KSR to remind us that the obviousness inquiry is “expansive and flexible” and that a POSA “is also a person of ordinary creativity, not an automaton.”  Id. at 33‑34.

The Federal Circuit affirmed, reasoning that the Board’s finding of a motivation to combine “the Grady device with Ruchala’s linac is supported by substantial evidence, including the prosecution history of the ’648 patent, the teachings of the asserted prior art references, and the expert testimony of record.”  81 F.4th at 1375.  While it was not the only evidence presented, the court emphasized that the patentee “did not argue that prior art references directed to imaging devices were not relevant art.”  Id.  The Federal Circuit called the absence of such an argument “notabl[e],” in fact.  Id.

In sum, Elekta stands for the proposition that a patentee can, through silence, concede that a seemingly disparate category of prior art asserted by an examiner is relevant to their invention.  A best practice, then, would be to expressly address whether and how a cited reference is from an inapt technology area.  Such an express disclaimer would hamper a patent challenger’s ability to leverage silence to bolster a motivation-to-combine argument in a later post-grant review or litigation.

[1] The challenged patent was U.S. Patent No. 7,295,648 (“the ’648 patent”), which is titled “Method and Apparatus for Treatment by Ionizing Radiation.”

[2] A “linac” is shorthand for a “linear acceleration,” which is a type of particle accelerator commonly used to provide external beam radiation treatments to cancer patients.  https://med.‌virginia.‌edu/‌radiation-oncology/‌about/‌advanced-technologies/‌linear-accelerator-treatments.