Reasonable Expectation of Success : CAFC Alert

Ramification of Silence in Prosecution History and Reminder on Formulating Effective Obviousness Arguments

| November 17, 2023


Decided: September 21, 2023

Before Reyna, Stoll, and Stark.  Opinion by Reyna.


The CAFC held that motivation to combine references is supported by substantial evidence including the patent prosecution history where relevancy of certain prior art, similar to an asserted reference in the IPR, was not contested by the applicant. The CAFC also rejected the patent owner’s arguments on lack of requisite findings on reasonable expectation of success, where such findings can be implied from express findings on motivation to combine as the two issues are interrelated to each other.


Elekta’s U.S. Patent No. 7,295,648 (the “’648 patent”) pertains to ionizing radiation treatment. The technology is designed to deliver therapeutic radiation, such as one created by a linear accelerator or “linac,” to a target area of a patient such as brain tumors for treatment purposes.  The ‘648 patent discloses that the linac, because of its great weight, requires a suitable structure to support the device while allowing a wide range of movement to focus the radiation precisely, leading to a challenge in implementing the linac-based system for treating highly sensitive, complex areas as with neurosurgery.

Representative claim 1 of the ‘648 patent recites:

A device for treating a patient with ionising radiation comprising:
a ring-shaped support, on which is provided a mount,
a radiation source attached to the mount;
the support being rotateable about an axis coincident with the centre of the ring;
the source being attached to the mount via a rotateable union having a an axis of rotation axis which is non-parallel to the support axis;
wherein the rotation axis of the mount passes through the support axis of the support and the radiation source is collimated so as to produce a beam which passes through the co-incidence of the rotation and support axes.

In the underlying inter partes review, the final written decision concluded, among other things, that claim 1 of the ’648 patent is obvious over a combination of Grady and Ruchala.  In essence, Grady teaches an X-ray imaging device having a sophisticated rotatable support structure similar to that recited in the body of claim 1, whereas Ruchala teaches a linac-based radiation device for treating tumors, which may correspond to “treating a patient with ionising radiation” of claim 1.

On appeal, the CAFC addressed Elekta’s three main arguments regarding obviousness of claim 1: (1) “the Board’s findings on a motivation to combine are unsupported by substantial evidence”; (2) “the Board failed to make any findings, explicit or implicit, on a reasonable expectation of success”; and (3) “even had the Board made such findings, those findings are not supported by substantial evidence.”  The CAFC reviewed the Board’s legal conclusions de novo and its factual findings for substantial evidence. 

  • Substantial evidence for the motivation to combine

Elekta argued that substantial evidence was lacking with the Board’s finding of a motivation to combine the references.  In particular, Elekta asserted that no motivation would have existed for a skilled artisan to combine Grady and Ruchala, one disclosing “radiation imagery” and the other for “radiation therapy,” where incorporating Ruchala’s linac radiation into Grady’s imaging system would not improve its imagery function in any aspect, whilst the linac’s heavy weight would hamper precision and control, thereby “render[ing] the device essentially inoperable.”

The Board’s obviousness conclusion relies on, among other findings, its review of the prosecution of the ’648 patent, wherein “patents directed to imaging devices were cited, and were not distinguished based on an argument that imaging devices were not relevant art,” along with the pertinent field being framed in the IPR as one that “includes the engineering design of sturdy mechanical apparatus[es] capable of rotationally manipulating heavy devices in three dimensions oriented in a variety of approach angles with high geometrical accuracy, in the context of the radiation imaging and radiation therapy environment.”

The CAFC held that there was substantial evidence for the motivation to combine. Specifically, the CAFC noted that such evidence includes the prosecution history of the ’648 patent, in which Elekta “notably did not argue that prior art references directed to imaging devices were not relevant art.”  The CAFC concluded that such failure to distinguish imaging radiation prior art during the patent prosecution, along with the asserted references and an expert testimony pointing to benefits of combining imagery and therapeutic radiation functions, substantially support the motivation to combine.

  • Findings on the reasonable expectation of success

Elekta argued that the Board’s obviousness determination was devoid of any findings on reasonable expectation of success.

The CAFC disagreed, finding that a sufficient, implicit finding was made as to the reasonable expectation of success.  The CAFC contrasted findings of reasonable expectation of success, which “can be implicit,” with those of motivation to combine, which must be “explicit.” Although an explicit finding would be usually required to support determinations made by the Board, the CAFC points to its precedent where the Board’s rejection of a patent owner’s motivation to combine argument based on teaching away constituted an implicit finding of a reasonable expectation of success, as the latter could be “reasonably discern[ed]” in the Board’s findings on “other, intertwined arguments.”

The CAFC noted that Elekta’s own arguments on the motivation to combine and the reasonable expectation of success presented before the Board were “blended”: Elekta essentially asserted that the suggested combination, lacking precision and control due to the device’s heavy weight, would fail to serve its intended purposes so as to negate motivation to combine, and consequently, would also negate reasonable expectation of success.  As such, the CAFC held that by making express findings on the motivation to combine, the Board adequately made an implicit finding on Elekta’s argument on reasonable expectation of success.

  • Substantial evidence for the reasonable expectation of success

Elekta argued that substantial evidence was lacking in the Board’s findings, if any, on reasonable expectation of success.

The CAFC succinctly rejected the argument. The CAFC noted that the evidence establishing a motivation to combine may—but not always—establish a finding of reasonable expectation of success.  And that was the case with the present appeal, where “the arguments and evidence of reasonable expectation of success are the same for motivation to combine.”


            This case presents an interesting situation pointing to one potential ramification of prosecution history made by silence: A failure to object to the scope of pertinent art during patent prosecution undercuts the patent owner’s argument in attacking the motivation to combine, where the asserted prior art is arguably from a disparate field.  It is important to consider potential benefits and downsides of presenting or not presenting certain arguments during prosecution.

            Another takeaway is the importance of formulating non-obviousness arguments on an issue-by-issue basis even if interrelated issues are involved; doing so would help keep the analysis of reasonable expectation of success from being comingled with the issues of motivation to combine.

Lets’ B. Cereus, No Reasonable Fact Finder Could Find an Expectation of Success Based on the Teachings of a Prior Art Reference That Failed to Achieve That Which The Inventor Succeeds

| December 6, 2021

University of Strathclyde vs., Clear-Vu Lighting LLC

Circuit Judges Reyna, Clevenger and Stoll (author).


Here, the University of Strathclyde (Strathclyde herein after) appeals from a final written decision of the Patent Trail and Appeal Board holding claims 1 to 4 of U.S. Patent No. 9,839,706 unpatentable as obvious.

The patent relates to effective sterilization methods for environmental decontamination of air and surfaces of, amongst other antibiotic resistant Gram-positive bacteria, Methicillin-resistant Staphylococcus aureus (MRSA). Specifically, sterilization is performed via photoinactivation without the need for a photosensitizing agent.

Claim 1[1] is as follows:

1. A method for disinfecting air, contact surfaces or materials by inactivating one or more pathogenic Gram-positive bacteria in the air, on the contact surfaces or on the materials, said method comprising exposing the one or more pathogenic Gram-positive bacteria to visible light without using a photosensitizer, wherein the one or more pathogenic Gram-positive bacteria are selected from the group consisting of Methicillin-resistant Staphylococcus aureus (MRSA), Coagulase-Negative Staphylococcus (CONS), Streptococcus, Enterococcus, and Clostridium species, and wherein a portion of the visible light that inactivates the one or more pathogenic Gram-positive bacteria consists of wavelengths in the range 400-420 nm, and wherein the method is performed outside of the human body and the contact surfaces or the materials are non-living.

The Board determined that claim 1 above would have been obvious over Ashkenazi in view of Nitzan. Ashkenazi is an article that discusses photoeradication of a Gram-positive bacterium, stating that “In the case of P. acnes (leading cause of acne) or other bacterial cells that produce porphyrins…. Blue light may photoinactivate the intact bacterial cells.” However, as noted by the CAFC, the methods of Ashkenazi always contained a photosensitive agent. Ashkenazi taught that increasing the light doses, the number of illuminations, and the length of time the bacteria are cultured resulted in greater inactivation.

The Nitzan article studied the effects of ALA (photosensitive agent) on Gram-positive bacteria, including MRSA. In Nitzan, for all the non-ALA MRSA cultures, it was reported therein that a 1.0 survival fraction was observed, meaning there was “no decrease in viability…after illumination” with blue light.

The Board ultimately held that Ashkenazi and Nitzan taught or suggested all the limitations of claim 1, and that a person of ordinary skill in the art would have been motivated to combine these two references, and “would have had a reasonable expectation of successfully doing so.”

Although neither of the references achieved inactivation of any bacteria without using a photosensitizer, the Board nonetheless found that a skilled artisan would have reasonably expected “some” amount of inactivation because the claims “do not require any specific amount of inactivation.”

Ultimately, the CAFC disagreed with the Boards’ findings.

Initially, the CAFC emphasized that “[T]he substantial evidence standard asks ‘whether a reasonable fact finder could have arrived at the agency’s decision,’ and ‘involves examination of the record as a whole, taking into account evidence that both justifies and detracts from an agency’s decision.’” OSI Pharms., LLC v. Apotex Inc., 939 F.3d 1375, 1381–82 (Fed. Cir. 2019) (quoting In re Gartside, 203 F.3d 1305, 1312 (Fed. Cir. 2000)).

That, “An obviousness determination generally requires a finding that “all claimed limitations are disclosed in the prior art,” PAR Pharm., Inc. v. TWI Pharms., Inc., 773 F.3d 1186, 1194 (Fed. Cir. 2014); cf. Koninklijke Philips N.V. v. Google LLC, 948 F.3d 1330, 1337–38 (Fed. Cir. 2020).

“Whether the prior art discloses a claim limitation, whether a skilled artisan would have been motivated to modify or combine teachings in the prior art, and whether she would have had a reasonable expectation of success in doing so are questions of fact. Tech. Consumer Prods., Inc. v. Lighting Sci. Grp. Corp., 955 F.3d 16, 22 (Fed. Cir. 2020); OSI Pharm., 939 F.3d at 1382.

Here, “the only dispute is whether these references teach inactivating one of the claimed Gram-positive bacteria without using a photosensitizer.” The CAFC stated that the “Board’s finding that this was taught by the combination of Ashkenazi and Nitzan is not supported by substantial evidence.”

Claim 1 requires both (i) exposing the bacterial to 400 to 420 nm blue light without using a photosensitizers and (ii) that the bacteria are inactivated as a result. Here, Ashkenazi achieves inactivation after exposure to 407 to 420 nm blue light but with a photosensitizer. On the other hand, Nitzan provides an example in which MRSA is exposed to 407 to 420 nm blue light without a photosensitizer, but there is no evidence that Nitzan successfully achieved inactivation under the conditions.

The Board agreed with Clear-Vu’s argument that a skilled artisan would have prepared a MRSA culture according to the method described in Nitzan and applied Ashkenazi’s teaching that increasing the light energy, number of illuminations, and length of time the bacteria are cultured, and so arrived at the Patented claims.

However, the CAFC held that “given neither Ashkenazi nor Nitzan teaches or suggests inactivation of any bacteria without using a photosensitizer” they failed “to see why a skilled artisan would opt to entirely omit a photosensitizer when combining these references.” The CAFC stressed that Nitzan itself disclosed that a photosensitizer-free embodiment was “wholly unsuccessful in achieving inactivation.”

Again, the CAFC emphasized that claim 1 requires both (i) exposing the bacterial to 400 to 420 nm blue light without using a photosensitizers and (ii) that the bacteria are inactivated as a result, and declined Clear-Vu’s invitation to read the inactivation limitation in isolation divorced from the claim as a whole concluding that “Obviousness cannot be based on the hindsight combination of components selectively culled from the prior art to fit the parameters of the patented invention.”

Next, the CAFC analyzed the Board’s finding on reasonable expectation of success and again, declined to agree.

The Board had relied upon (i) both parties agreeing that MRSA naturally produces at least some amount of endogenous porphyrins and (ii) Ashkenazi’s teaching that “blue light may” inactivate “other bacterial cells that produce porphyrins.

Here, the CAFC focused on Nitzan, as evidence on record showing the opposite. The CAFC reaffirmed that “absolute predictability of success is not required, only a reasonable expectation.” In this case, where the prior art reference fails to “achieve that at which the inventors succeeded, no reasonable fact finder could find an expectation of success based on the teachings of that same prior art.”

Thus, the CAFC concluded that the Board’s finding was not supported by substantial evidence, and so reversed its obviousness determination.


  • The substantial evidence standard asks ‘whether a reasonable fact finder could have arrived at the agency’s decision,’ and ‘involves examination of the record as a whole, taking into account evidence that both justifies and detracts from an agency’s decision.
  • If a prior art reference fails to achieve that which the inventor succeeds, it can be argued that no reasonable fact finder could find an expectation of success based thereon.

[1] Claim 2 depends on claim 1. Claim 3 is independent, but contains the same contested features highlighted above in claim 1. Claim 4 is dependent on claim 3.

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