Robert K. Doot

Tumor Metabolism and Blood Flow Changes by Positron Emission Tomography: Relation to Survival in Patients Treated With Neoadjuvant Chemotherapy for Locally Advanced Breast Cancer

PURPOSE Patients with locally advanced breast carcinoma (LABC) receive preoperative chemotherapy to provide early systemic treatment and assess in vivo tumor response. Serial positron emission tomography (PET) has been shown to predict pathologic response in this setting. We evaluated serial quantitative PET tumor blood flow (BF) and metabolism as in vivo measurements to predict patient outcome. PATIENTS AND METHODS Fifty-three women with primary LABC underwent dynamic [(18)F]fluorodeoxyglucose (FDG) and [(15)O]water PET scans before and at midpoint of neoadjuvant chemotherapy. The FDG metabolic rate (MRFDG) and transport (FDG K(1)) parameters were calculated; BF was estimated from the [(15)O]water study. Associations between BF, MRFDG, FDG K(1), and standardized uptake value and disease-free survival (DFS) and overall survival (OS) were evaluated using the Cox proportional hazards model. RESULTS Patients with persistent or elevated BF and FDG K(1) from baseline to midtherapy had higher recurrence and mortality risks than patients with reductions. In multivariable analyses, BF and FDG K(1) changes remained independent prognosticators of DFS and OS. For example, in the association between BF and mortality, a patient with a 5% increase in tumor BF had a 67% higher mortality risk compared with a patient with a 5% decrease in tumor BF (hazard ratio = 1.67; 95% CI, 1.24 to 2.24; P < .001). CONCLUSION LABC patients with limited or no decline in BF and FDG K(1) experienced higher recurrence and mortality risks that were greater than the effects of clinical tumor characteristics. Tumor perfusion changes over the course of neoadjuvant chemotherapy measured directly by [(15)O]water or indirectly by dynamic FDG predict DFS and OS.

Motor-protein “roundabouts”: Microtubules moving on kinesin-coated tracks through engineered networks

Nanotechnology promises to enhance the functionality and sensitivity of miniaturized analytical systems. For example, nanoscale transport systems, which are driven by molecular motors, permit the controlled movement of select cargo along predetermined paths. Such shuttle systems may enhance the detection efficiency of an analytical system or facilitate the controlled assembly of sophisticated nanostructures if transport can be coordinated through complex track networks. This study determines the feasibility of complex track networks using kinesin motor proteins to actively transport microtubule shuttles along micropatterned surfaces. In particular, we describe the performance of three basic structural motifs: (1) crossing junctions, (2) directional sorters, and (3) concentrators. We also designed track networks that successfully sort and collect microtubule shuttles, pointing the way towards lab-on-a-chip devices powered by active transport instead of pressure-driven or electroosmotic flow.

Kinetic analysis of 18F-fluoride PET images of breast cancer bone metastases

The most common site of metastasis for breast cancer is bone. Quantitative 18F-fluoride PET can estimate the kinetics of fluoride incorporation into bone as a measure of fluoride transport, bone formation, and turnover. The purpose of this analysis was to evaluate the accuracy and precision of 18F-fluoride model parameter estimates for characterizing regional kinetics in metastases and normal bone in breast cancer patients. Methods: Twenty metastatic breast cancer patients underwent dynamic 18F-fluoride PET. Mean activity concentrations were measured from serial blood samples and regions of interest placed over bone metastases, normal vertebrae, and cardiac blood pools. This study examined parameter identifiability, model sensitivity, error, and accuracy using parametric values from the patient cohort. Results: Representative time–activity curves and model parameter ranges were obtained from the patient cohort. Model behavior analyses of these data indicated 18F-fluoride transport and flux (K1 and Ki, respectively) into metastatic and normal osseous tissue could be independently estimated with a reasonable bias of 9% or less and reasonable precision (coefficients of variation ≤ 16%). Average 18F-fluoride transport and flux into metastases from 20 patients (K1 = 0.17 ± 0.08 mL·cm−3·min−1 and Ki = 0.10 ± 0.05 mL·cm−3·min−1) were both significantly higher than for normal bone (K1 = 0.09 ± 0.03 mL·cm−3·min−1 and Ki = 0.05 ± 0.02 mL·cm−3·min−1, P < 0.001). Conclusion: Fluoride transport and flux can be accurately and independently estimated for bone metastases and normal vertebrae. Reasonable bias and precision for estimates of K1 and Ki from simulations and significant differences in values from patient modeling results in metastases and normal bone suggest that 18F-fluoride PET images may be useful for assessing changes in bone turnover in response to therapy. Future studies will examine the correlation of parameters to biologic features of bone metastases and to response to therapy.

PET Tumor Metabolism in Locally Advanced Breast Cancer Patients Undergoing Neoadjuvant Chemotherapy: Value of Static versus Kinetic Measures of Fluorodeoxyglucose Uptake

Purpose: Changes in tumor metabolism from positron emission tomography (PET) in locally advanced breast cancer (LABC) patients treated with neoadjuvant chemotherapy (NC) are predictive of pathologic response. Serial dynamic [18F]-FDG (fluorodeoxyglucose) PET scans were used to compare kinetic parameters with the standardized uptake value (SUV) as predictors of pathologic response, disease-free survival (DFS), and overall survival (OS). Experimental Design: Seventy-five LABC patients underwent FDG PET prior to and at midpoint of NC. FDG delivery (K1), FDG flux (Ki), and SUV measures were calculated and compared by clinical and pathologic tumor characteristics using regression methods and area under the receiver operating characteristic curve (AUC). Associations between K1, Ki, and SUV and DFS and OS were evaluated using the Cox proportional hazards model. Results: Tumors that were hormone receptor negative, high grade, highly proliferative, or of ductal histology had higher FDG Ki and SUV values; on an average, FDG K1 did not differ systematically by tumor features. Predicting pathologic response in conjunction with estrogen receptor (ER) and axillary lymph node positivity, kinetic measures (AUC = 0.97) were more robust predictors than SUV (AUC = 0.84, P = 0.005). Changes in K1 and Ki predicted both DFS and OS, whereas changes in SUV predicted OS only. In multivariate modeling, only changes in K1 remained an independent prognosticator of DFS and OS. Conclusion: Kinetic measures of FDG PET for LABC patients treated with NC accurately measured treatment response and predicted outcome compared with static SUV measures, suggesting that kinetic analysis may hold advantage of static uptake measures for response assessment. Clin Cancer Res; 17(8); 2400–9. ©2011 AACR.

Tumor Metabolism and Blood Flow as Assessed by Positron Emission Tomography Varies by Tumor Subtype in Locally Advanced Breast Cancer

Purpose: Dynamic positron emission tomography (PET) imaging can identify patterns of breast cancer metabolism and perfusion in patients receiving neoadjuvant chemotherapy (NC) that are predictive of response. This analysis examines tumor metabolism and perfusion by tumor subtype. Experimental Design: Tumor subtype was defined by immunohistochemistry in 71 patients with locally advanced breast cancer undergoing NC. Subtype was defined as luminal [estrogen receptor (ER)/progesterone receptor (PR) positive], triple negative [TN; ER/PR negative, human epidermal growth factor receptor 2 (HER2) negative], and HER2 (ER/PR negative, HER2 overexpressing). Metabolic rate (MRFDG) and blood flow (BF) were calculated from PET imaging before NC. Pathologic complete response (pCR) to NC was classified as pCR versus other. Results: Twenty-five (35%) of 71 patients had TN tumors; 6 (8%) were HER2 and 40 (56%) were luminal. MRFDG for TN tumors was on average 67% greater than for luminal tumors (95% confidence interval, 9-156%) and average MRFDG/BF ratio was 53% greater in TN compared with luminal tumors (95% confidence interval, 9-114%; P < 0.05 for both). Average BF levels did not differ by subtype (P = 0.73). Most luminal tumors showed relatively low MRFDG and BF (and did not achieve pCR); high MRFDG was generally matched with high BF in luminal tumors and predicted pCR. This was not true in TN tumors. Conclusion: The relationship between breast tumor metabolism and perfusion differed by subtype. The high MRFDG/BF ratio that predicts poor response to NC was more common in TN tumors. Metabolism and perfusion measures may identify subsets of tumors susceptible and resistant to NC and may help direct targeted therapy. Clin Cancer Res; 16(10); 2803–10. ©2010 AACR.

Dynamic and Static Approaches to Quantifying 18F-FDG Uptake for Measuring Cancer Response to Therapy, Including the Effect of Granulocyte CSF

The response of cancer to chemotherapy can be quantified using 18F-FDG to indicate changes in tumor metabolism. Quantification using the standardized uptake value (SUV) is more feasible for clinical practice than is the metabolic rate of 18F-FDG (MRFDG), which requires longer, dynamic scanning. The relationship between MRFDG and SUV depends in part on how each accounts for blood clearance of tracer. We tested whether chemotherapy and treatment with granulocyte colony-stimulating factor (CSF) changed the blood clearance curves and therefore affected the relationship between MRFDG and SUV. Methods: Thirty-nine patients with locally advanced breast cancer underwent 18F-FDG PET before and after chemotherapy, including granulocyte CSF. The area under the curve (AUC) for blood clearance was determined before and after therapy. MRFDGs were determined by graphical analyses, whereas SUVs were calculated using the standard formula normalized by body weight. MRFDG and SUVs were compared with each other and with tumor response. Paired percentage changes in MRFDG and SUV were also divided into tertiles based on pretherapy SUV to investigate differences in the relative sensitivity of SUV changes to MRFDG changes due to baseline tumor uptake. Results: Despite a small but statistically significant 6% decrease in blood AUCs after therapy (P = 0.02), SUV and MRFDG did not differ significantly in slope (P = 0.53) or in correlation before and after therapy (r = 0.95 for both). Percentage changes in MRFDG and SUV between serial scans correlated with each other (r = 0.84) and with patient response (P ≤ 0.06). The maximum detectable percentage change in SUV and the slope of percentage changes in MRFDG versus SUV for the patient tertile with the lowest baseline SUVs (65% ± 5% [±SE], slope (m) = 0.40 ± 0.12, n = 13) were significantly lower than for the other patients (86% ± 3%, m = 0.85 ± 0.10, n = 26, P = 0.01 for both). Conclusion: Chemotherapy and granulocyte CSF treatment resulted in a lower 18F-FDG blood AUC. The maximum detectable percentage change in 18F-FDG uptake is less when quantifying via static SUV than via dynamic MRFDG. This effect is small in most patients but may have clinical significance for measuring the response of patients with a low pretherapy 18F-FDG uptake.

Instrumentation factors affecting variance and bias of quantifying tracer uptake with PET∕CT

PURPOSE The variances and biases inherent in quantifying PET tracer uptake from instrumentation factors are needed to ascertain the significance of any measured differences such as in quantifying response to therapy. The authors studied the repeatability and reproducibility of serial PET measures of activity as a function of object size, acquisition, reconstruction, and analysis method on one scanner and at three PET centers using a single protocol with long half-life phantoms. METHODS The authors assessed standard deviations (SDs) and mean biases of consecutive measures of PET activity concentrations in a uniform phantom and a NEMA NU-2 image quality (IQ) phantom filled with 9 months half-life 68Ge in an epoxy matrix. Activity measurements were normalized by dividing by a common decay corrected true value and reported as recovery coefficients (RCs). Each experimental set consisted of 20 consecutive PET scans of either a stationary phantom to evaluate repeatability or a repositioned phantom to assess reproducibility. One site conducted a comprehensive series of repeatability and reproducibility experiments, while two other sites repeated the reproducibility experiments using the same IQ phantom. An equation was derived to estimate the SD of a new PET measure from a known SD based on the ratios of available coincident counts between the two PET measures. RESULTS For stationary uniform phantom scans, the SDs of maximum RCs were three to five times less than predicted for uncorrelated pixels within circular regions of interest (ROIs) with diameters ranging from 1 to 15 cm. For stationary IQ phantom scans from 1 cm diameter ROIs, the average SDs of mean and maximum RCs ranged from 1.4% to 8.0%, depending on the methods of acquisition and reconstruction (coefficients of variation range 2.5% to 9.8%). Similar SDs were observed for both analytic and iterative reconstruction methods (p > or = 0.08). SDs of RCs for 2D acquisitions were significantly higher than for 3D acquisitions (p < or =s 0.008) for same acquisition and processing parameters. SDs of maximum RCs were larger than corresponding mean values for stationary IQ phantom scans ( < or = 0.02), although the magnitude of difference is reduced due to noise correlations in the image. Increased smoothing decreased SDs ( < or =s 0.045) and decreased maximum and mean RCs (p < or = 0.02). Reproducibility of GE DSTE, Philips Gemini TF, and Siemens Biograph Hi-REZ PET/CT scans of the same IQ phantom, with similar acquisition, reconstruction, and repositioning among 20 scans, were, in general, similar (mean and maximum RC SD range 2.5% to 4.8%). CONCLUSIONS Short-term scanner variability is low compared to other sources of error. There are tradeoffs in noise and bias depending on acquisition, processing, and analysis methods. The SD of a new PET measure can be estimated from a known SD if the ratios of available coincident counts between the two PET scanner acquisitions are known and both employ the same ROI definition. Results suggest it is feasible to use PET/CTs from different vendors and sites in clinical trials if they are properly cross-calibrated.

Quantifying and Reducing the Effect of Calibration Error on Variability of PET/CT Standardized Uptake Value Measurements

The purpose of this study was to measure the errors introduced by regular calibration of PET/CT scanners and to minimize the effect of calibration error on standardized uptake value measurements. Methods: Global calibration factors from 2 PET/CT scanners were recorded for 3.5 and 1.8 y, comparing manufacturer-recommended protocols with modified protocols to evaluate error contributions due to operator-influenced procedures. Dose calibrator measurements were evaluated using National Institute of Standards and Technology–traceable sources. Results: Dose calibrator variability was less than 1%, although there was a consistent bias. Global scaling variability was reduced from 6% to 4% for scanner 1 and from 11% to 4% for scanner 2 when quality assurance and quality control procedures were applied to the calibration protocol. When calibrations were done using a 68Ge/68Ga phantom, the variability for both scanners was reduced to approximately 3%. Conclusion: Applying quality assurance and quality control procedures to scanner calibration reduces variability, but there is a still a residual longitudinal scanner variability of 3%–4%. The procedures proposed here reduce the impact of operator error on scanner calibration and thereby minimize longitudinal variability in standarized uptake value measurements.

Engineered networks of oriented microtubule filaments for directed cargo transport

Nature uses networks of oriented filaments to guide intracellular movement of cargo. We describe the first method for designing and constructing interconnected networks of oriented microtubules to create a two-dimensional in vitro transport system. Microfabricated open channels with surface-bound kinesin motor proteins are used to orient short microtubule seeds relative to each other. Guided by the channel geometry, the oriented microtubule seeds are then grown into oriented networks of microtubules, which support motility of kinesin-coated nanospheres with a directional preference determined by the microtubule orientation. In contrast to in vitro gliding motility assays where microtubules glide on kinesin-coated surfaces, engineered stationary microtubule networks could simultaneously utilize different motors, e.g. motors walking in opposite directions. Different motors, via their specific scaffolding proteins, could be utilized to selectively transport specific cargos. The presented method is the first step towards building oriented and interconnected microtubule networks with a user-designed geometry at the micron and submicron scale. The resulting platform enables multiple applications, from cargo sorting to adaptive camouflage.

Quantitative assessment of dynamic PET imaging data in cancer imaging.

Clinical imaging in positron emission tomography (PET) is often performed using single-time-point estimates of tracer uptake or static imaging that provides a spatial map of regional tracer concentration. However, dynamic tracer imaging can provide considerably more information about in vivo biology by delineating both the temporal and spatial pattern of tracer uptake. In addition, several potential sources of error that occur in static imaging can be mitigated. This review focuses on the application of dynamic PET imaging to measuring regional cancer biologic features and especially in using dynamic PET imaging for quantitative therapeutic response monitoring for cancer clinical trials. Dynamic PET imaging output parameters, particularly transport (flow) and overall metabolic rate, have provided imaging end points for clinical trials at single-center institutions for years. However, dynamic imaging poses many challenges for multicenter clinical trial implementations from cross-center calibration to the inadequacy of a common informatics infrastructure. Underlying principles and methodology of PET dynamic imaging are first reviewed, followed by an examination of current approaches to dynamic PET image analysis with a specific case example of dynamic fluorothymidine imaging to illustrate the approach.