Oral squamous cell carcinomas represent a significant number of cancers diagnosed globally. Of these cancers, surgical resection of the primary tumor is the standard treatment. Conventional methods of assessing completeness of resection are time-consuming, laborious, and cannot be used to evaluate the entire margin of a resected tumor. As such, widefield fluorescence molecular imaging is being explored as an intraoperative technique to guide resections. The widely used single-view, wide aperture techniques have had high success in identifying positive margins (those with thickness < 1mm), but limited success in identifying close margins (1-5 mm). Here a dual aperture fluorescence ratio is presented as a means of improved detection of close margins, with evidence that this technique may be highly useful for future intraoperative fluorescence molecular imaging applications. Monte Carlo simulations are conducted to assess the technique’s ability to minimize optical property heterogeneities across regions with varying absorption and scattering characteristics.
Surgical excision is the primary treatment for solid tumors in oral squamous cell carcinomas, where achieving a healthy tissue margin of >5 mm is the goal. However, current clinical methods of assessing surgical margins cannot provide assessment of the whole margins intraoperatively (while the patient is still on the operating table) and while recent intraoperative fluorescence-guided surgery approaches have shown promise for detected “positive” inadequate margins (<1 mm), they have had limited success in the detection of “close” inadequate margins (1-5 mm), in patients injected with cetuximab-IRDye 800CW prior to surgery. Here, a dual aperture fluorescence ratio (dAFR) approach presented previously by our group is expanded upon, where herein we present a version of the analysis where the measurements are normalized by a background signal. We compare this additional approach directly against a single aperture view fluorescence (sAF) and pathology measurements of margin thickness in specimens from five patients and a total 14 margin locations (1 positive, 7 close, and 6 clear margins). The area under the curve of the receiver operating characteristic, representing the ability to detect close compared to clear margins was found to be 1.0 and 0.6 using dAFR and sAF, respectively, with the improvements in dAFR being statistically significant (p < 0.01). We demonstrate that the addition of a background normalization can account for noise and low signal in narrow aperture images.
SignificanceSurgical excision is the main treatment for solid tumors in oral squamous cell carcinomas, where wide local excision (achieving a healthy tissue margin of >5 mm around the excised tumor) is the goal as it results in reduced local recurrence rates and improved overall survival.AimNo clinical methods are available to assess the complete surgical margin intraoperatively while the patient is still on the operating table; and while recent intraoperative back-bench fluorescence-guided surgery approaches have shown promise for detecting “positive” inadequate margins (<1 mm), they have had limited success in the detection of “close” inadequate margins (1 to 5 mm). Here, a dual aperture fluorescence ratio (dAFR) approach was evaluated as a means of improving detection of close margins.ApproachThe approach was evaluated on surgical specimens from patients who were administered a tumor-specific fluorescent imaging agent (cetuximab-800CW) prior to surgery. The dAFR approach was compared directly against standard wide-field fluorescence imaging and pathology measurements of margin thickness in specimens from three patients and a total of 12 margin locations (1 positive, 5 close, and 6 clear margins).ResultsThe area under the receiver operating characteristic curve, representing the ability to detect close compared to clear margins (>5 mm) was found to be 1.0 and 0.57 for dAFR and sAF, respectively. Improvements in dAFR were found to be statistically significant (p<0.02).ConclusionsThese results provide evidence that the dAFR approach potentially improves detection of close surgical margins.
Post-operative assessment of resected tumor margins is critical to ensure the entirety of malignant tissue has been removed from a patient. Microscopic assessment of tissue post-excision is the current gold standard, however the long wait times for proper specimen evaluation limit a surgeon’s ability to be certain they obtained clear margins. To address this need, fluorescence-guided surgery approaches are under development that can yield molecular contrast between healthy and malignant tissues intraoperatively. In head and neck cancer specifically, heterogenous optical properties lead to poor identification in margins greater than 1 mm thick when viewed with single projections. Thus, we demonstrate the use of variable aperture approach to decrease the effects of local optical property variations in the imaged specimen. Here we use Monte Carlo simulations to verify the utility of the idea in a homogenous medium as well in a medium with heterogenous properties. We demonstrate that a ratio metric approach can provide near identical depth discrimination as a single projection in a homogenous medium and is further capable of reducing pixel variability due to local optical properties in a heterogenous medium than a single projection alone.
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