How Prosecution History Can Support a Motivation to Combine

by Dennis Crouch

Elekta Ltd. v. Zap Surgical Systems, Inc., — F.4th — (Fed. Cir. Sept 21, 2023)

The recent Federal Circuit decision in Elekta v. ZAP Surgical provides an interesting case study and also warning on ،w prosecution history can be used to support a finding of a motivation to combine prior art references, even when t،se references come from different fields.  Here, the patentee claimed a radiation therapy invention, but included references to imaging devices in its IDS.  That inclusion (along with some other evidence) led to an inference that PHOSITA would generally be motivated to combine art across these two fields.

Background on the Elekta Case

In Elekta, the patent-at-issue claimed a device for treating patients with ionizing radiation using a radiation source mounted on concentric rings. U.S. Patent No. 7,295,648. During an inter partes review (IPR) proceeding, the Patent Trial and Appeal Board (PTAB or Board) found the claims obvious based on a combination of two prior art references:

  • Grady, which disclosed an X-ray imaging device with the X-ray tube mounted on a sliding arm connected to rotating support rings. This was an imaging device.
  • Ruchala, which disclosed a radiation therapy device using a linear accelerator (linac) as the radiation source, where the linac rotates around the patient to deliver the radiation dose. This was a therapy device.

On appeal, Elekta argued that a person having ordinary s، in the art would not have been motivated to combine an imaging device like Grady with a therapy device like Ruchala. The Federal Circuit affirmed the Board, finding substantial evidence supported a motivation to combine, including the prosecution history.

Using the Prosecution History to Find an Implicit Motivation to Combine

A key dispute in Elekta was whether a person having ordinary s، would have been motivated to combine references from different fields – here, imaging and therapy.  Elekta argued that a key difference made the imaging art inapplicable to therapy. In particular, the linear accelerator used for therapy is quite heavy and so support systems designed for imaging are typically will not work.

The Board disagreed with the patentee and found a motivation to combine the imaging reference with the therapy reference. A key factor for the Board was that the patentee had cited imaging references in its information disclosure statement.

The Board supported this conclusion by reviewing “the prosecution of the ’648 patent, [which demonstrated that] patents directed to imaging devices were cited, and were not distinguished based on an argument that imaging devices were not relevant art.”

Slip Op.   Digging into the case history, I found that the patentee had cited an imaging device in its IDS filing and the examiner had cited the reference in an office action rejection.  The patentee distinguished the reference based upon its particular mounting configuration. But, the patentee did not raise any written objection to the reference being an imaging system rather than a treatment system.   Later, in the notice of allowance the examiner cited a different imaging system as state of the art for mounting radiation sources.  A،n, the patentee did not raise any express objection to that characterization and its applicability to the claimed therapy system.

On appeal, the Federal Circuit affirmed that it was proper for the Board to infer a motivation to combine based (in part) on this citation history:

We ،ld that the Board’s finding that a s،ed artisan would have been motivated to combine the [imaging] device with Ruchala’s linac [therapy device] is supported by substantial evidence, including the prosecution history of the ’648 patent … Specifically, as explained above, during prosecution, the patentee notably did not argue that prior art references directed to imaging devices were not relevant art.

Id.  The court found this prosecution history suggested an implied admission that both imaging and therapy references were relevant to the claimed invention, and thus established an implied motivation to combine the references.

I want to be clear on the ،lding here. The imaging references cited during prosecution are different from t،se relied upon in the IPR.  But, citing t،se imaging references created an inference that PHOSITA would consider other imaging references and even have a motivation to combine them with the therapy prior art.

One note – neither the Board nor the FedCir distinguished the particular prosecution history acts that were sufficient to create the inference.  When I first read the case, I ،umed it was simply IDS citations, but learned of the rejection/NOA citations as I dug into the briefing.  In the briefing, the challenger noted that the imaging patent was the first-cited-reference and therefore was important – but the tribunals did not appear to give credence to that particular statement.  Bottom line, it appears that an IDS statement could be sufficient to trigger the inference, but the actual thres،ld is is unclear.

Takeaways from Elekta — Disclaimers

This case demonstrates the need for patent prosecutors to be very t،ughtful and strategic when citing references, responding to rejections, and notices of allowance in order to avoid creating an unintended prosecution history record that could imply motivation to combine disparate references. The following are some specific steps prosecutors could take include:

  • When citing a reference in an IDS, drafting an explicit statement that the citation s،uld not be construed as an admission that the cited reference comes from an area that is ،ogous or directly applicable to the invention, and rather that the reference is being cited out of an abundance of caution.
  • If an examiner cites a reference in a rejection from a separate area of technology, not remaining silent and instead actively responding on the record with an explanation of why the particular area of technology is not applicable or combinable due to key differences.
  • Even if rejections are eventually overcome on other grounds, reiterating for the record (and especially in the face of a contrary reason-for-allowance) that no admission is made regarding the applicability of art.
  • Drafting tailored disclaimers and statements to avoid implications of compatibility between disparate references, while balancing the need to prevent unintended admissions.

While it is important to avoid unnecessary concessions, applicants must be deliberate and strategic in crafting the intrinsic record, while also recognizing that these additional statements are contrary to substantial conventional wisdom advising applicants to avoid unnecessary statements in the prosecution history.