Simultaneous LSPR and electronic sensing of potential induced ion adsorption onto gold nanowire arrays is presented. The formation of a Stern layer upon applying an electrochemical potential generated a complex optical response. Simulation of a lossy atomic layer on the nanowire array using the Multiple Multipole Program (MMP) corresponded very well to the experimentally observed peak position, intensity, and radius of curvature changes. Additionally, a significant voltage-dependent change in the resistance of the gold nanowire array was observed during the controlled formation of the electrical double layer. The results demonstrated that an applied electrochemical potential induces measurable changes in the optical and electrical properties of the gold nanowire surface. This is the first demonstration of combined plasmonic and nanowire resistance-based sensing of a surface process in the literature.

You have accessJournal of UrologyProstate Cancer: Localized (III)1 Apr 2013680 VESSEL SEALING DEVICE WITH NANO-COATING SIGNIFICANTLY REDUCES HEAT SPREAD FOR NEUROVASCULAR BUNDLE PREPARATION Robert MacKenzie, Jelena Skorucak, Ashkan Mortezavi, Janos Vörös, and Daniel Eberli Robert MacKenzieRobert MacKenzie Zürich, Switzerland More articles by this author , Jelena SkorucakJelena Skorucak Zürich, Switzerland More articles by this author , Ashkan MortezaviAshkan Mortezavi Zürich, Switzerland More articles by this author , Janos VörösJanos Vörös Zürich, Switzerland More articles by this author , and Daniel EberliDaniel Eberli Zürich, Switzerland More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2013.02.235AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Vessel Sealing Devices (VSD) offer the advantage of less hemorrhage and shorter operation times. The blood vessel sealing is achieved through application of bipolar high frequency current and simultaneous compression of the tissue. However, the use of cautery instruments in vicinity to sensitive structures may be of concern due to lateral temperature spread with potential damage to the neurovascular bundle resulting in poor continence and potency rates. To reduce this harm to surrounding tissue we developed a coating with phase change material for the VSD (Ligasure) and investigated the reduction of lateral heat spread in an in vitro model. METHODS We have developed a novel coating with a phase change material based on fat/oil droplets embedded in silicone, with the ability to absorb significant amounts of excessive heat. This new instrument was evaluated in an established in vitro model to define the precise heat spread along musculofascial tissues, which reflects the in vivo situation during nerve sparing radical prostatectomy. Bovine meat slices were cauterized with coated and uncoated VSDs up to the termination signal; the maximal thermal spread and the effects on the tissue were examined by continuous temperature measurement with a high performance infrared camera and by histology with molecular assay for lactate-dehydrogenase. 45 °C was used as the cut off value for possible neural damage. RESULTS The mean temperature (±SD) measured at the device edge was 51.3 ±7.7 °C for the uncoated and 42.6 ±8.3 °C for the coated VSD (n=12, p=0.007). The save distance with temperatures below 45 °C was 1.7 ±1 mm for the uncoated and 0.7 ±0.9 mm °C for the coated instrument (n=12, p=0.008). The histology revealed that the distance between the edge of the device and the first cells with intact enzyme function was 1.1 ±0.6 mm for uncoated and 0.7 ±0.5 mm for coated devices (p= 0.0176), respectively. CONCLUSIONS In this study we have demonstrated that our coating with a phase change material can significantly reduce lateral temperature spread during vessel sealing with a cautery device resulting in a reduced safety distance necessary to protect critical surrounding structures. In future, phase change material coatings may allow usage of cautery devices for nerve sparing procedures during radical prostatectomies. © 2013 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 189Issue 4SApril 2013Page: e279 Advertisement Copyright & Permissions© 2013 by American Urological Association Education and Research, Inc.MetricsAuthor Information Robert MacKenzie Zürich, Switzerland More articles by this author Jelena Skorucak Zürich, Switzerland More articles by this author Ashkan Mortezavi Zürich, Switzerland More articles by this author Janos Vörös Zürich, Switzerland More articles by this author Daniel Eberli Zürich, Switzerland More articles by this author Expand All Advertisement Advertisement PDF DownloadLoading ...

Purpose: To map the distribution of microscopic disease (MD) in head-and-neck cancer by analyzing digital images of whole-mounted serial sections of tongue cancer specimens.Methods and Materials: Ten T1-3 oral tongue cancer specimens were evaluated. The specimens were sliced into 3-mm blocks from which one or more 4-mu m slides were taken and digitized to create whole-mounted serial sections. Gross tumor and microscopic disease were digitally contoured on each slide. Lines perpendicular to the gross tumor volume (GTV) edge were created at 0.05-mm intervals and the distance between GTV and MD measured.Results: Of 88 slides assessed, 44 (50%) had evidence of MD. Of the 63,809 perpendicular lines drawn along the GTV edges, 2320 (3.6%) encountered microscopic disease along their path. The majority of MD abutted the GTV, and only 26.7% was noncontiguous with the GTV edge. The maximum distance from the border was 7.8 mm. Ninety-nine percent of all MD was within 4.75 mm and 95% was within 395 mm of the GTV.Conclusion: In this study we were able to assess the distribution of MD more accurately than has been possible with routine pathologic techniques. The results indicate that when the GTV is correctly identified, there is very little MD to be found outside this volume. This has implications for the volume of tissue resected at surgery and the volume included in the clinical target volume in conformal radiotherapy planning. (C) 2012 Elsevier Inc.

The controlled in situ growth of ordered gold nanoparticles and nanowire arrays has been studied by optically tracking changes in the local surface plasmon resonance (LSPR) spectrum. A spectrometer and custom-programmed analysis software track changes in the LSPR spectrum. The peak position, peak height (i.e. extinction intensity) and peak width (e.g. radius of curvature) were tracked over time to quantify the dynamic growth of gold as soon as the system was exposed to a commercial gold enhancement solution. This enables the controlled dynamic growth of nano-objects without the necessity of characterizing the growth and aggregation kinetics of the gold enhancement solution. The result was the successful enhancement of their electrically conductive and plasmonic properties, as well as the controlled growth and transformation of line-patterned nanoparticles into conductive particle-based nanowires.

Purpose: To study the experience, as it relates to quality of life (QoL) of patients living with Percutaneous Endoscopic Gastrostomy (PEG) tubes for nutrition support during treatment for head and neck cancer. OBJECTIVE: PEG tubes have become a preferred option for intermediate term nutritional support for those undergoing aggressive head and neck cancer treatment. The nutritional and medical outcome benefits of PEG tubes have become well established. The experience of receiving nutritional support via PEG tube from the patients' perspective has not been studied sufficiently. Anecdotal feedback from the outpatient population with PEG tubes has been very positive and patients have reported that PEG placement is a worthwhile treatment. Our study objective was to explore the general experience and quality of life of patients living with a PEG tube. It is proposed that a better understanding of the patient perspective contributes to the success of the intervention and overall improvement in patient care. Methods: A neutral questionnaire with closed and open-ended questions was developed, tested, and used to collect data in person, over the phone and via the internet. Quantitative data were analyzed to determine whether the patients' experiences were positive, neutral or negative. Chi square was used to test for significance. A frequency count of qualitative data was also done. Results: Of the 51 participants, 84% felt the PEG tube had a positive/neutral effect on their QoL. 90% felt that the PEG tube was “very much” or “quite a bit” worthwhile. Additionally, 96% would recommend it to another patient. Of the 12 questions reflecting domains of QoL impacted by living with a PEG tube, 11 were answered positively or neutrally by greater than 70% of participants. Comments from patients included: “it's a lifesaver”, “it's a great invention”, “the benefits outweigh the negatives”, “just do it”. Conclusion: The experience of patients in this study, who received a PEG tube during their treatment for head and neck cancer, is generally positive or neutral. This will assist with the decision-making for patients considering a PEG tube and for clinicians evaluating its impact. These results also provide support and encouragement for outpatient PEG tube placement programs.

BACKGROUNDThe optimal fractionation schedule for whole-breast irradiation after breast-conserving surgery is unknown.METHODSWe conducted a study to determine whether a hypofractionated 3-week schedule of whole-breast irradiation is as effective as a 5-week schedule. Women with invasive breast cancer who had undergone breast-conserving surgery and in whom resection margins were clear and axillary lymph nodes were negative were randomly assigned to receive whole-breast irradiation either at a standard dose of 50.0 Gy in 25 fractions over a period of 35 days (the control group) or at a dose of 42.5 Gy in 16 fractions over a period of 22 days (the hypofractionated-radiation group).RESULTSThe risk of local recurrence at 10 years was 6.7% among the 612 women assigned to standard irradiation as compared with 6.2% among the 622 women assigned to the hypofractionated regimen (absolute difference, 0.5 percentage points; 95% confidence interval [ CI], -2.5 to 3.5). At 10 years, 71.3% of women in the control group as compared with 69.8% of the women in the hypofractionated-radiation group had a good or excellent cosmetic outcome (absolute difference, 1.5 percentage points; 95% CI, -6.9 to 9.8).CONCLUSIONSTen years after treatment, accelerated, hypofractionated whole-breast irradiation was not inferior to standard radiation treatment in women who had undergone breast-conserving surgery for invasive breast cancer with clear surgical margins and negative axillary nodes. (ClinicalTrials.gov number, NCT00156052.)

The purpose of this work was to determine whether 2 different types of linear accelerators manufacturers with similar MLC leaf widths deliver equivalent IMRT distributions for head and neck radiotherapy patients. In this study, plans delivered with Siemens linacs were re-optimized with an Elekta linac and vice versa. To test for significance, paired t-tests were computed to examine differences in target and normal tissue doses and monitor units. Dose distributions, dose-volume histograms, and dose to targets and normal tissues were found to be equivalent irrespective of the linac type. However, approximately 15% more monitor units were delivered when planned on the Elekta machine (p < 0.002). Both linear accelerators provide plans of comparable dosimetric quality; however, Elekta machines deliver slightly more monitor units than Siemens machines. This increase is likely due differences in geometric properties of the machine head designs, as modeled in the treatment planning system.

This work explores the alternative use of noble metal nanowire systems in large-scale array configurations to exploit both the nanowires’ conductive nature and localized surface plasmon resonance (LSPR). The first known nanowire-based system has been constructed, with which optical signals are influenced by the simultaneous application of electrochemical potentials. Optical characterization of nanowire arrays was performed by measuring the bulk refractive index sensitivity and the limit of detection. The formation of an electrical double layer was controlled in NaCl solutions to study the effect of local refractive index changes on the spectral response. Resonance peak shifts of over 4 nm, a bulk refractive index sensitivity up to 115 nm/RIU and a limit of detection as low as 4.5 × 10−4 RIU were obtained for gold nanowire arrays. Simulations with the Multiple Multipole Program (MMP) confirm such bulk refractive index sensitivities. Initial experiments demonstrated successful optical biosensing using a novel form of particle-based nanowire arrays. In addition, the formation of an ionic layer (Stern-layer) upon applying an electrochemical potential was also monitored by the shift of the plasmon resonance.

Aims To determine the value of routine follow-up in detecting and salvaging recurrence after radical treatment of locally advanced head and neck squamous cell carcinoma and to identify clinical or pathological prognostic factors that predicted for survivalMaterials and methods A retrospective medical chart review was conducted at the Odette Cancer Centre between January 2000 and May 2006 Two hundred and twenty-three patients with advanced (stage III or IV) squamous cell carcinoma of the head and neck who were treated with curative intent were reviewed Recurrences were divided into local regional or distant recurrences The detection method for each recurrence was categorised as self or physician detected A self-detected recurrence arose from symptoms that led to investigations that confirmed a recurrence (even if initiated at the time of a routine visit) whereas a physician-detected recurrence was found during the routine follow-up examination and was asymptomaticResults There was no evidence to suggest a significant improvement in disease-free or overall survival in the physician-detected versus patient-detected groups Regional and distant recurrences were only detected by physicians in one-fifth of cases and overall patients self-detected their own recurrence in two-thirds of the cases that experienced disease progression within the sample Of the 12 clinical/pathological variables considered only the response to treatment and perineural invasion were associated with survivalConclusions Current surveillance methods do not appear to improve cancer control in the stage III/IV head and neck squamous cell carcinoma population However technological advances and biomarker development may lead to surveillance technique enhancements Also post-treatment follow-up remains important for the evaluation of treatment results emotional support and management of late complications Among the clinical and pathological factors considered only the treatment response and perineural invasion predicted survival (C) 2010 The Royal College of Radiologists Published by Elsevier Ltd All rights reserved

Purpose: A co-registered multimodality pattern analysis segmentation system (COMPASS) was developed to automatically delineate the radiation targets in head-and-neck cancer (HNC) using both F-18-fluoro-deoxy glucose-positron emission tomography (PET) and computed tomography (CT) images. The performance of the COMPASS was compared with the results of existing threshold-based methods and radiation oncologist-drawn contours.Methods and Materials: The COMPASS extracted texture features from corresponding PET and CT voxels. Using these texture features, a decision-tree-based K-nearest-neighbor classifier labeled each voxel as either "normal" or "abnormal." The COMPASS was applied to the PET/CT images of 10 HNC patients. Automated segmentation results were validated against the manual segmentations of three radiation oncologists using the volume, sensitivity, and specificity. The performance of the COMPASS was compared with three PET-based threshold methods: standard uptake value of 2.5, 50% maximal intensity, and signal/background ratio.Results: The tumor delineations of the COMPASS were both quantitatively and qualitatively more similar to those of the radiation oncologists than the delineations from the other methods. The specificity was 95% 2%, 84% +/- 9%, 98% +/- 3%, and 96% +/- 4%, and the sensitivity was 90% +/- 12%, 93% +/- 10%, 48% +/- 20%, and 68% +/- 25% for the COMPASS, for a standard uptake value of 2.5,50% maximal intensity, and signal/background ratio, respectively. The COMPASS distinguished HNC from adjacent normal tissues with high physiologic uptake and consistently defined tumors with large variability in F-18-fluoro-deoxy glucose uptake, which are often problematic with the threshold-based methods.Conclusion: Automated segmentation using texture analysis of PET/CT images has the potential to provide accurate delineation of HNC. This could lead to reduced interobserver variability, reduced uncertainty in target delineation, and improved treatment planning accuracy. (C) 2009 Elsevier Inc.

Otolaryngology–Head and Neck SurgeryVolume 141, Issue S2 p. P58-P58 Abstract Sleep Apnea Following Oropharyngeal Cancer Treatment David Houlden, David HouldenSearch for more papers by this authorDanny Enepekides, Danny EnepekidesSearch for more papers by this authorKevin Higgins, Kevin HigginsSearch for more papers by this authorIan Poon, Ian PoonSearch for more papers by this authorRobert MacKenzie, Robert MacKenzieSearch for more papers by this authorJames Haight, James HaightSearch for more papers by this author David Houlden, David HouldenSearch for more papers by this authorDanny Enepekides, Danny EnepekidesSearch for more papers by this authorKevin Higgins, Kevin HigginsSearch for more papers by this authorIan Poon, Ian PoonSearch for more papers by this authorRobert MacKenzie, Robert MacKenzieSearch for more papers by this authorJames Haight, James HaightSearch for more papers by this author First published: 01 September 2009 https://doi.org/10.1016/j.otohns.2009.06.173AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume141, IssueS2September 2009Pages P58-P58 RelatedInformation

The purpose of this work was to determine whether two different types of linear accelerators manufacturers with similar MLC leaf widths deliver equivalent IMRT dose distributions for head and neck radiotherapy patients. In the first study, a retrospective analysis of 197 head and neck IMRT patients delivered on Siemens Primus and Elekta Synergy machines was undertaken to test statistical differences in machine type, monitor units, maximum target dose, and number of target doses. Both machines have 1 cm MLC leaves but have different linac head geometries. Plan were created using the direct machine parameter optimization (DMPO) routine on Philips' Pinnacle treatment planning system (TPS) system, in step and shoot mode. A multi‐variate analysis was used to test for significance, Pearson's correlations, and coefficients of determination. In the second study, a replanning exercise was conducted where deliverable plans from a Siemens machine was re‐optimized with an Elekta machine and vice‐versa. In the first study, there was no evidence of any significant difference in the IMRT plans. Elekta machines delivered more MUs than the Siemens units but the difference was not significant (). In the second study, the presentation of the dose distributions, DVHs, and mean dose to target and normal tissue structures were equivalent. However, approximately 15% more monitor units were delivered when plans were planned or re‐planned on the Elekta machine. This work suggests that for plans of comparable quality, Elekta machines deliver more monitor units than Siemens machines, likely due to differences in the geometric properties of the machines.

Chemoradiation (CRT) regimens form the primary option for Stage III/IV head and neck cancer (HNC). CRT has improved locoregional control over radiotherapy (RT) alone, but the risk of recurrence is still substantial with additive toxicities. Also, conventional RT alone still successfully treats a proportion of patients. There are many pre-treatment clinical, radiological, genetic, and pathological factors that predict for locoregional failure but all lack the predictive values needed to guide management decisions. Early identification of CRT failures may allow for the early termination of CRT and salvage resection or alternatively, radiation dose intensification. Intra-treatment FDG PET studies for esophageal carcinoma has demonstrated a strong predictive ability despite simplistic FDG parameters. The following is a preliminary analysis of a planned 100 patient study. The purpose of the analysis is to evaluate the change in FDG uptake using common regions of interest (ROI). An FDG PET scan was performed pre-treatment, and between the 10th and 15th radiation fraction in 13 Stage III/IV, HNC patients with 35 ROIs (13 primaries, 22 lymph nodes (LN)). The ROIs were defined manually, as a 1.5 cm square centered around the max pixel placed on the slice with the greatest uptake (fixed size ROI), and automatically using a seed-based, region-growing approach. The PET parameters studied include SUV-mean, SUV-max. All 13 patients have had a complete response (CR) with no recurrences with follow-up <1 year. The parameters studied all show a fairly significant reduction between the first and second scans: manual ROI, SUV-mean (4.4±1.1,3.6±0.8); fixed-size ROI, SUV-mean (6.3±2.8,4.3±1.0); automatic ROI, SUV-mean (5.1±2.5,4.2±0.9) and finally SUV-max (8.5±3.6,5.8±1.9). This correlates to a percent reduction of 17.9%, 31.8%, 18.9% and 32%, respectively. The LNs demonstrated a less significant reduction in all FDG uptake values between pre- and intra-treatment scans: manual ROI, SUV-mean (2.6±0.9,2.3±0.6); fixed-size ROI, SUV-mean (3.3±1.5,2.7±1.1); automatic ROI, SUV-mean (3.3±1.3,2.8±1.2) and finally SUV-max (4.6±2.0,3.5±1.6). This correlates to a percent reduction of 11%, 19.6%, 15.5%, and 22%, respectively. All studied FDG PET parameters demonstrated a substantial decrease in FDG activity in the primaries and minimal FDG decreases within the LN. With all patients experiencing a CR to date, this data suggests that different approaches to image analysis may be needed for LN versus primary response. Future analysis will include analysis of dynamic parameters as well as more comprehensive whole tumor ROIs that will be correlated to 2 year patient outcome.

Purpose/Objective(s)To compare observer variability in identifying nodal disease in head and neck cancers (HNC) when using CT alone to that identified when FDG PET-CT is used.Background: Observer variability may be the greatest source of geometric uncertainty in precision radiotherapy. For IMRT of HNC, regions of suspected lymphadenopathy may be identified and optimized to a higher dose. Few reports exist to quantify the variability in identifying these nodes, yet extensive resources can be used to customize the dose to these regions.Materials/MethodsA prospective study of 28 patients with intact HNC was conducted. All patients underwent PET-CT-simulation. Prior to contouring, consensus guidelines for localization were established by 3 radiation oncologists specializing in HNC, 1 nuclear medicine physician, and 1 radiologist. Each of 3 radiation oncologists contoured the primary tumor and individual positive nodes using CT alone and then using PET-CT while blinded to the results of others. Diagnostic CT and medical reports were available while contouring. This presentation will focus only on the nodes. On CT, nodes were considered positive if they were >1.5 cm for level 2 nodes and >1.0 cm at all other levels. If the node appears necrotic, then it was also considered positive. On PET-CT, nodes were considered positive if they were FDG-avid relative to the surrounding tissues. The number and location of each node for each observer were recorded for each imaging modality.ResultsA total of 105 possible nodes were identified by any one of the observers and in either modality among the 28 cases. There was complete agreement on the number and location of nodes among all 3 observers in 4 of 28 cases (14%) and 9 of 28 cases (32%) for CT only and PET/CT, respectively. In 14, 10, and 4 cases, PET/CT improved, did not change, or reduced the total number of agreements between all observers, respectively. For each observer, the total numbers of positive nodes identified were 85, 50, and 56 for CT alone and 75, 55, and 57 for PET/CT. The use of PET/CT changed the nodal status of 19%, 7%, and 10% of the nodes identified on CT by each observer, respectively. Kappa analysis suggests that agreement between any pair of observers was improved with PET/CT compared to CT alone.ConclusionsObserver variability in identification of positive nodes in HNC is large with CT alone and in some cases, can be reduced with the use of PET-CT images. However, even with PET-CT, variability remains high. The accurate identification of nodal involvement in IMRT planning remains a challenge. Purpose/Objective(s)To compare observer variability in identifying nodal disease in head and neck cancers (HNC) when using CT alone to that identified when FDG PET-CT is used.Background: Observer variability may be the greatest source of geometric uncertainty in precision radiotherapy. For IMRT of HNC, regions of suspected lymphadenopathy may be identified and optimized to a higher dose. Few reports exist to quantify the variability in identifying these nodes, yet extensive resources can be used to customize the dose to these regions. To compare observer variability in identifying nodal disease in head and neck cancers (HNC) when using CT alone to that identified when FDG PET-CT is used. Background: Observer variability may be the greatest source of geometric uncertainty in precision radiotherapy. For IMRT of HNC, regions of suspected lymphadenopathy may be identified and optimized to a higher dose. Few reports exist to quantify the variability in identifying these nodes, yet extensive resources can be used to customize the dose to these regions. Materials/MethodsA prospective study of 28 patients with intact HNC was conducted. All patients underwent PET-CT-simulation. Prior to contouring, consensus guidelines for localization were established by 3 radiation oncologists specializing in HNC, 1 nuclear medicine physician, and 1 radiologist. Each of 3 radiation oncologists contoured the primary tumor and individual positive nodes using CT alone and then using PET-CT while blinded to the results of others. Diagnostic CT and medical reports were available while contouring. This presentation will focus only on the nodes. On CT, nodes were considered positive if they were >1.5 cm for level 2 nodes and >1.0 cm at all other levels. If the node appears necrotic, then it was also considered positive. On PET-CT, nodes were considered positive if they were FDG-avid relative to the surrounding tissues. The number and location of each node for each observer were recorded for each imaging modality. A prospective study of 28 patients with intact HNC was conducted. All patients underwent PET-CT-simulation. Prior to contouring, consensus guidelines for localization were established by 3 radiation oncologists specializing in HNC, 1 nuclear medicine physician, and 1 radiologist. Each of 3 radiation oncologists contoured the primary tumor and individual positive nodes using CT alone and then using PET-CT while blinded to the results of others. Diagnostic CT and medical reports were available while contouring. This presentation will focus only on the nodes. On CT, nodes were considered positive if they were >1.5 cm for level 2 nodes and >1.0 cm at all other levels. If the node appears necrotic, then it was also considered positive. On PET-CT, nodes were considered positive if they were FDG-avid relative to the surrounding tissues. The number and location of each node for each observer were recorded for each imaging modality. ResultsA total of 105 possible nodes were identified by any one of the observers and in either modality among the 28 cases. There was complete agreement on the number and location of nodes among all 3 observers in 4 of 28 cases (14%) and 9 of 28 cases (32%) for CT only and PET/CT, respectively. In 14, 10, and 4 cases, PET/CT improved, did not change, or reduced the total number of agreements between all observers, respectively. For each observer, the total numbers of positive nodes identified were 85, 50, and 56 for CT alone and 75, 55, and 57 for PET/CT. The use of PET/CT changed the nodal status of 19%, 7%, and 10% of the nodes identified on CT by each observer, respectively. Kappa analysis suggests that agreement between any pair of observers was improved with PET/CT compared to CT alone. A total of 105 possible nodes were identified by any one of the observers and in either modality among the 28 cases. There was complete agreement on the number and location of nodes among all 3 observers in 4 of 28 cases (14%) and 9 of 28 cases (32%) for CT only and PET/CT, respectively. In 14, 10, and 4 cases, PET/CT improved, did not change, or reduced the total number of agreements between all observers, respectively. For each observer, the total numbers of positive nodes identified were 85, 50, and 56 for CT alone and 75, 55, and 57 for PET/CT. The use of PET/CT changed the nodal status of 19%, 7%, and 10% of the nodes identified on CT by each observer, respectively. Kappa analysis suggests that agreement between any pair of observers was improved with PET/CT compared to CT alone. ConclusionsObserver variability in identification of positive nodes in HNC is large with CT alone and in some cases, can be reduced with the use of PET-CT images. However, even with PET-CT, variability remains high. The accurate identification of nodal involvement in IMRT planning remains a challenge. Observer variability in identification of positive nodes in HNC is large with CT alone and in some cases, can be reduced with the use of PET-CT images. However, even with PET-CT, variability remains high. The accurate identification of nodal involvement in IMRT planning remains a challenge.