Dependence of FDG uptake on tumor microenvironment

Energy sources identify metabolic phenotypes in pancreatic cancer

Metabolic reprogramming is one of the emerging hallmarks of cancers. As a highly malignant tumor, pancreatic ductal adenocarcinoma (PDA) is not only a metabolic disease but also a heterogeneous disease. Heterogeneity induces PDA dependence on distinct nutritive substrates, thereby inducing different metabolic phenotypes. We stratified PDA into four phenotypes with distinct types of energy metabolism, including a Warburg phenotype, a reverse Warburg phenotype, a glutaminolysis phenotype, and a lipid-dependent phenotype. The four phenotypes possess distinct metabolic features and reprogram their metabolic pathways to adapt to stress. The metabolic type present in PDA should prompt differential imaging and serologic metabolite detection for diagnosis and prognosis. The targeting of an individual metabolic phenotype with corresponding metabolic inhibitors is considered a promising therapeutic approach and, in combination with chemotherapy, is expected to be a novel strategy for PDA treatment.

Prognostic value of tumoral heterogeneity and volumetric parameters as measured by F18-FDG PET/CT in sinonasal cancer

The objective of this study was to investigate the value of parameters assessed with F18-FDG PET/CT in predicting recurrence-free survival (RFS) and disease-specific survival (DSS) in patients with cancer of nasal cavity and paranasal sinus. Thirty-eight patients with cancer of nasal cavity (n = 14) and paranasal sinus (n = 24) who underwent PET/CT prior to curative treatment were enrolled. A volume of interest was placed on PET/CT images covering the entire tumor volume, and the maximum SUV (SUV_max), the mean SUV (SUV_mean), and volumetric parameters of metabolic tumor volume (MTV) and total lesion glycolysis (TLG) were measured using thresholds of 40 % of SUV_max. The heterogeneity factor (HF) defined as the derivative of volume-threshold function from 40 to 80 % of SUV thresholds. RFS and DSS were defined as the time from the diagnosis to recurrence and death. Median values of SUV_max, SUV_mean, MTV, TLG, and HF were 14.81, 9.16, 25.84, 150.74, and -0.496. SUV_max was higher in patients with advanced stage and nodal metastasis. High MTV and low HF group showed shorter RFS. Cox proportional hazards regression analysis revealed low HF was the only significant predictive factor on RFS. Furthermore, high TLG was associated with shorter DSS. High TLG was potent predictor of DSS by Cox proportional hazards regression analysis. In conclusion, the tumoral heterogeneity and volumetric parameters as measured by F18-FDG PET/CT could be significant prognostic surrogate markers in patients with sinonasal cancer.

Prognostic value of preoperative intratumoral FDG uptake heterogeneity in early stage uterine cervical cancer

OBJECTIVE

We investigated the prognostic value of intratumoral [¹⁸F]fluorodeoxyglucose (FDG) uptake heterogeneity (IFH) derived from positron emission tomography/computed tomography (PET/CT) in patients with cervical cancer.

METHODS

Patients with uterine cervical cancer of the International Federation of Obstetrics and Gynecology (FIGO) stage IB to IIA were imaged with [¹⁸F]FDG PET/CT before radical surgery. PET/CT parameters such as maximum and average standardized uptake values (SUV(max) and SUV(avg)), metabolic tumor volume (MTV), total lesion glycolysis (TLG), and IFH were assessed. Regression analyses were used to identify clinicopathological and imaging variables associated with progression-free survival (PFS).

RESULTS

We retrospectively reviewed clinical data of 85 eligible patients. Median PFS was 32 months (range, 6 to 83 months), with recurrence observed in 14 patients (16.5%). IFH at an SUV of 2.0 was correlated with primary tumor size (p<0.001), SUV(tumor) (p<0.001), MTV(tumor) (p<0.001), TLG(tumor) (p<0.001), depth of cervical invasion (p<0.001), and negatively correlated with age (p=0.036). Tumor recurrence was significantly associated with TLG(tumor) (p<0.001), MTV(tumor) (p=0.001), SUV(LN) (p=0.004), IFH (p=0.005), SUV(tumor) (p=0.015), and FIGO stage (p=0.015). Multivariate analysis identified that IFH (p=0.028; hazard ratio, 756.997; 95% CI, 2.047 to 279,923.191) was the only independent risk factor for recurrence. The Kaplan-Meier survival graphs showed that PFS significantly differed in groups categorized based on IFH (p=0.013, log-rank test).

CONCLUSION

Preoperative IFH was significantly associated with cervical cancer recurrence. [¹⁸F]FDG based heterogeneity may be a useful and potential predicator of patient recurrence before treatment.

Value of 18F-FDG heterogeneity for discerning metastatic from benign lymph nodes in nasopharyngeal carcinoma patients with suspected recurrence

OBJECTIVE

This study investigated the value of fluorine-18 fludeoxyglucose (¹⁸F-FDG) heterogeneity as an indicator of metastatic lymph nodes (LNs) in patients with nasopharyngeal carcinoma (NPC). We further assessed whether addition of this parameter improves diagnostic performance beyond that provided by maximum standardized uptake value (SUV_max).

METHODS

We analyzed 74 LNs that were suspicious for metastasis. These LNs were measured for coefficient of variation (CV) of ¹⁸F-FDG uptake, which was used as a parameter for ¹⁸F-FDG heterogeneity.

RESULTS

Multivariate logistic regression analyses revealed that a high CV (hazard ratio, 20.97; 95% confidence interval, 2.26-194.62; p = 0.007) was an independent predictor of metastatic LNs. However, receiver-operating characteristic curve analysis (p = 0.278) and net reclassification (p = 0.539) were unable to show improved diagnostic performance by addition of CV to SUV_max.

CONCLUSION

High CV of ¹⁸F-FDG uptake is an independent risk factor for metastatic LNs in patients with NPC displaying suspicious LNs following treatment. Advances in knowledge: Heterogeneity of ¹⁸F-FDG uptake has a potential as a biomarker of metastatic LNs.

Texture analysis of 18F-FDG PET/CT to predict tumour response and prognosis of patients with esophageal cancer treated by chemoradiotherapy

PURPOSE

This retrospective study was done to examine whether the heterogeneity in primary tumour F-18-fluorodeoxyglucose (¹⁸F-FDG) distribution can predict tumour response and prognosis of patients with esophageal cancer treated by chemoradiotherapy (CRT).

METHODS

The enrolled 52 patients with esophageal cancer underwent ¹⁸F-FDG-PET/CT studies before CRT. SUVmax, SUVmean, metabolic tumour volume (MTV, SUV ≥ 2.5), total lesion glycolysis (TLG) and six heterogeneity parameters assessed by texture analysis were obtained. Patients were classified as responders or non-responders according to Response Evaluation Criteria in Solid Tumors. Progression-free survival (PFS) and overall survival (OS) were calculated by the Kaplan-Meier method. Prognostic significance was assessed by Cox proportional hazards analysis.

RESULTS

Thirty four non-responders showed significantly higher MTV (p = 0.006), TLG (p = 0.007), intensity variability (IV; p = 0.003) and size-zone variability (SZV; p = 0.004) than 18 responders. The positive and negative predictive values for non-responders were 77 % and 69 % in MTV, 76 % and 100 % in TLG, 78 % and 67 % in IV and 78 % and 82 % in SZV, respectively. Although PFS and OS were significantly shorter in patients with high MTV (PFS, p = 0.018; OS, p = 0.014), TLG (PFS, p = 0.009; OS, p = 0.025), IV (PFS, p = 0.013; OS, p = 0.007) and SZV (PFS, p = 0.010; OS, p = 0.007) at univariate analysis, none of them was an independent factor, while lymph node status, stage and tumour response status were independent factors at multivariate analysis.

CONCLUSION

Texture features IV and SZV, and volumetric parameters MTV and TLG can predict tumour response, but all of them have limited value in prediction of prognosis of patients with esophageal cancer treated by CRT.

A Lesion-Based Response Prediction Model Using Pretherapy PET/CT Image Features for Y90 Radioembolization to Hepatic Malignancies

We present a probabilistic approach to identify patients with primary and secondary hepatic malignancies as responders or nonresponders to yttrium-90 radioembolization therapy. Recent advances in computer-aided detection have decreased false-negative and false-positive rates of perceived abnormalities; however, there is limited research in using similar concepts to predict treatment response. Our approach is driven by the goal of precision medicine to determine pretherapy fluorine-18-2-fluoro-2-deoxy-d-glucose positron emission tomography and computed tomography imaging parameters to facilitate the identification of patients who would benefit most from yttrium-90 radioembolization therapy, while avoiding complex and costly procedures for those who would not. Our algorithm seeks to predict a patient's response by discovering common co-occurring image patterns in the lesions of baseline fluorine-18-2-fluoro-2-deoxy-d-glucose positron emission tomography and computed tomography scans by extracting invariant shape and texture features. The extracted imaging features were represented as a distribution of each subject based on the bag-of-feature paradigm. The distribution was applied in a multinomial naive Bayes classifier to predict whether a patient would be a responder or nonresponder to yttrium-90 radioembolization therapy based on the imaging features of a pretherapy fluorine-18-2-fluoro-2-deoxy-d-glucose positron emission tomography and computed tomography scan. Comprehensive published criteria were used to determine lesion-based clinical treatment response based on fluorine-18-2-fluoro-2-deoxy-d-glucose positron emission tomography and computed tomography imaging findings. Our results show that the model is able to predict a patient with liver cancer as a responder or nonresponder to yttrium-90 radioembolization therapy with a sensitivity of 0.791 using extracted invariant imaging features from the pretherapy fluorine-18-2-fluoro-2-deoxy-d-glucose positron emission tomography and computed tomography test. The sensitivity increased to 0.821 when combining extracted invariant image features with variable features of tumor volume.

Revisiting the Robustness of PET-Based Textural Features in the Context of Multi-Centric Trials

Purpose

This study aimed to investigate the variability of textural features (TF) as a function of acquisition and reconstruction parameters within the context of multi-centric trials.

Methods

The robustness of 15 selected TFs were studied as a function of the number of iterations, the post-filtering level, input data noise, the reconstruction algorithm and the matrix size. A combination of several reconstruction and acquisition settings was devised to mimic multi-centric conditions. We retrospectively studied data from 26 patients enrolled in a diagnostic study that aimed to evaluate the performance of PET/CT ⁶⁸Ga-DOTANOC in gastro-entero-pancreatic neuroendocrine tumors. Forty-one tumors were extracted and served as the database. The coefficient of variation (COV) or the absolute deviation (for the noise study) was derived and compared statistically with SUVmax and SUVmean results.

Results

The majority of investigated TFs can be used in a multi-centric context when each parameter is considered individually. The impact of voxel size and noise in the input data were predominant as only 4 TFs presented a high/intermediate robustness against SUV-based metrics (Entropy, Homogeneity, RP and ZP). When combining several reconstruction settings to mimic multi-centric conditions, most of the investigated TFs were robust enough against SUVmax except Correlation, Contrast, LGRE, LGZE and LZLGE.

Conclusion

Considering previously published results on either reproducibility or sensitivity against delineation approach and our findings, it is feasible to consider Homogeneity, Entropy, Dissimilarity, HGRE, HGZE and ZP as relevant for being used in multi-centric trials.

A Continuously Infused Microfluidic Radioassay System for the Characterization of Cellular Pharmacokinetics

Measurement of cellular tracer uptake is widely applied to learn the physiologic status of cells and their interactions with imaging agents and pharmaceuticals. In-culture measurements have the advantage of less stress to cells. However, the tracer solution still needs to be loaded, unloaded, and purged from the cell culture during the measurements. Here, we propose a continuously infused microfluidic radioassay (CIMR) system for continuous in-culture measurement of cellular uptake. The system was tested to investigate the influence of the glucose concentration in cell culture media on ¹⁸F-FDG uptake kinetics.

METHODS

The CIMR system consists of a microfluidic chip integrated with a flow-control unit and a positron camera. Medium diluted with radioactive tracer flows through a cell chamber continuously at low speed. Positrons emitted from the cells and from tracer in the medium are measured with the positron camera. The human cell lines SkBr3 and Capan-1 were incubated with media of 3 different glucose concentrations and then measured with ¹⁸F-FDG on the CIMR system. In addition, a conventional uptake experiment was performed. The relative uptake ratios between different medium conditions were compared. A cellular 2-compartment model was applied to estimate the cellular pharmacokinetics on CIMR data. The estimated pharmacokinetic parameters were compared with expressions of glucose transporter-1 (GLUT1) and hexokinase-2 measured by quantitative real-time polymerase chain reaction.

RESULTS

The relative uptake ratios obtained from CIMR measurements correlated significantly with those from the conventional uptake experiments. The relative SDs of the relative uptake ratios obtained from the CIMR uptake experiments were significantly lower than those from the conventional uptake experiments. The fit of the cellular 2-compartment model to the ¹⁸F-FDG CIMR measurements was of high quality. For SkBr3, the estimated pharmacokinetic parameters k₁ and k₃ were consistent with the messenger RNA expression of GLUT1 and hexokinase-2: culturing with low glucose concentrations led to higher GLUT1 and hexokinase-2 expression as well as higher estimated k₁ and k₃ For Capan-1, the estimated k₁ and k₃ increased as the glucose concentration in the culture medium decreased, and this finding did not match the corresponding messenger RNA expression.

CONCLUSION

The CIMR system captures dynamic uptake within the cell culture and enables estimation of the cellular pharmacokinetics.

Expression and clinical significance of glucose transporter-1 in pancreatic cancer

Increasing evidence has demonstrated that malignant cells exhibit increased glucose uptake, which facilitates survival and growth in a hypoxic environment. The glucose transporter-1 (GLUT-1) is overexpressed in a variety of malignant tumors. However, the association between GLUT-1 expression and clinicopathological factors, ¹⁸F-fluorodeoxyglucose uptake and tumor proliferation in pancreatic cancer has not been investigated to date. In the present study, the expression of GLUT-1 in 53 pancreatic cancer tissues was analyzed, which revealed that GLUT-1 was overexpressed in pancreatic tissue and correlated with poor prognosis and clinicopathological characteristics, including increased tumor size, clinical stage and lymph node metastasis, maximum standardized uptake value (SUV_max) and Ki-67 expression. The receiver operating characteristic curve analysis indicated that a cut-off SUV_max value of 4.830 was associated with optimal sensitivity (88%) and specificity (71.4%) for the detection of strong positive GLUT-1 expression. In addition, as the expression of GLUT-1 was found to correlate with Ki-67 expression, GLUT-1 may exhibit a significant effect on cell proliferation in pancreatic cancer. Overall, these findings indicate that GLUT-1 may represent a prognostic indicator, and a potential therapeutic target for pancreatic cancer.

Prognostic value of preoperative intratumoral FDG uptake heterogeneity in patients with epithelial ovarian cancer

OBJECTIVES

To investigate the prognostic value of intratumoral FDG uptake heterogeneity (IFH) derived from PET/CT in patients with epithelial ovarian cancer (EOC).

METHODS

We retrospectively reviewed patients with pathologically proven epithelial ovarian cancer who underwent preoperative ¹⁸F-FDG PET/CT scans. PET/CT parameters such as maximum and average standardized uptake values (SUV_max and SUV_avg), sum of all metabolic tumour volume (MTV), cumulative total lesion glycolysis (TLG) and IFH were assessed. Regression analyses were used to identify clinicopathological and imaging variables associated with disease-free survival (DFS).

RESULTS

Clinicopathological data were reviewed for 61 eligible patients. The median duration of DFS was 13 months (range, 6-26 months), and 18 (29.5 %) patients experienced recurrence. High IFH values were associated with tumour recurrence (P = 0.005, hazard ratio 4.504, 95 % CI 1.572-12.902). The Kaplan-Meier survival graphs showed that DFS significantly differed in groups categorized based on IFH (P = 0.002, log-rank test). Moreover, there were significant differences in DFS (P = 0.009) and IFH (P = 0.040) between patients with and without recurrence.

CONCLUSIONS

Preoperative IFH measured by ¹⁸F-FDG PET/CT was significantly associated with EOC recurrence. FDG-based heterogeneity could be a useful and potential predicator of EOC recurrence before treatment.

KEY POINTS

• Preoperative IFH was significantly associated with recurrence of EOC • Disease-free survival significantly differed in groups categorized by IFH • FDG-based heterogeneity could be a potential predicator of EOC recurrence before treatment.

Warburg Effect - a Consequence or the Cause of Carcinogenesis?

Ever since its discovery (1924) the Warburg effect (aerobic glycolysis) remains an unresolved puzzle: why the aggressive cancer cells "prefer" to use the energetically highly inefficient method of burning the glucose at the cellular level? While in the course of the last 90 years several hypotheses have been suggested, to this date there is no clear explanation of this rather unusual effect. Even though it is commonly assumed that Warburg effect is a consequence of carcinogenesis, yet another hypothesis could be brought up that the cellular switch to aerobic glycolysis may represent the very point in time when a normal cell becomes cancerous. Furthermore, this switch may happen at the point where the fate of pyruvic acid is determined, caused by the inadequate supply of enzymes that promote citric as opposed to lactic acid cycle. Currently, few clinical observations, like low cancer incidence in Type 1 diabetes mellitus and increased cancer incidence in people on high carbohydrate diets might be called upon to support such hypothesis.

Diagnostic value of metabolic heterogeneity as a reliable parameter for differentiating malignant parotid gland tumors

OBJECTIVE

Exact classifying between malignant and benign tumors in the parotid gland is important because the cancer has relatively poor prognosis. There have been several studies that F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) can differentiate between malignant and benign parotid gland tumors. However, the role of FDG PET is still controversial because many benign parotid gland tumors, such as Warthin's tumor and pleomorphic adenoma, show high FDG uptake. We hypothesized that metabolic heterogeneity would differentiate malignant parotid tumors because tumoral heterogeneity is an important characteristic in the malignancies.

METHODS

From January 2010 to April 2015, we retrospectively reviewed the 46 patients who showed FDG uptake at the parotid gland. To differentiate malignant parotid gland tumors, we obtained maximum SUV and mean SUV. Metabolic tumor volume and total lesion glycolysis were measured as metabolic volumetric parameters. We also included heterogeneity parameters of FDG PET such as heterogeneity factor (HF) and the coefficient of variation for all patients.

RESULTS

There was significant difference of HF between malignant (-0.30 ± 0.25; range -0.937 to -0.084) and benign parotid gland tumors (-0.06 ± 0.05; range -0.291 to -0.012; p < 0.0001). In receiver operating characteristic analysis, when ≤-0.084 was used as the cut-off value for HF, the sensitivity and specificity were 100 % (95 % CI 81.5-100) and 89.2 % (95 % CI 71.8-97.7), respectively. HF showed the highest area under the curve of 0.947 among the parameters. In logistic regression analysis, the HF was the most powerful factor for differentiation of the parotid gland tumors (p = 0.002).

CONCLUSIONS

Our results suggest that HF can be utilized as a reliable and non-invasive method for differentiation of malignant and benign parotid gland tumors.

Prognostic significance of hypoxic PET using (18)F-FAZA and (62)Cu-ATSM in non-small-cell lung cancer

OBJECTIVES

Tumor hypoxia is believed to have a strong correlation with the resistance to chemoradiotherapy. Noninvasive evaluation of hypoxic status in tumors using molecular imaging has the potential to characterize the tumor aggressiveness. We evaluated the clinical usefulness of newly-developed tumor hypoxic positron emission tomography (PET) tracers in localized non-small-cell lung cancer (NSCLC).

PATIENTS AND METHODS

Forty-seven patients with localized NSCLC received either or both hypoxic PETs using the tracers: (18)F-fluoroazomycin arabinoside ((18)F-FAZA) (n=45) and/or (62)Cu-diacetyl-bis (N4)-methylsemithiocarbazone ((62)Cu-ATSM) (n=22). All received (18)F-fluorodeoxyglucose ((18)F-FDG) PET tracer (n=47). We examined the correlation between uptake of three PET tracers and clinicopathological factors, and evaluated their impacts on survival after treatment retrospectively.

RESULTS

A couple of commonly-identified unfavorable factors such as presence of vascular invasion and pleural invasion was significantly correlated with higher uptake of these hypoxic agents as well as that of (18)F-FDG. Larger tumor diameter, high neutrophil-to-lymphocyte ratio and advanced pathological stage were also associated with accumulation of hypoxic PETs ((18)F-FAZA, p<0.01; (62)Cu-ATSM, p<0.04), but not with that of (18)F-FDG. The patients with a higher accumulation had significantly poorer overall survival [(18)F-FAZA, HR (hazard ratio), 9.50, p<0.01; (62)Cu-ATSM, HR, 4.06, p<0.05] and progression free survival ((18)F-FAZA, HR, 5.28, p<0.01, (62)Cu-ATSM, HR, 2.72, p<0.05).

CONCLUSION

Both (18)F-FAZA and (62)Cu-ATSM PET provide useful information regarding tumor aggressiveness and prediction of survival among NSCLC patients. We believe these hypoxic PETs could contribute to the establishment of the optimally individualized treatment of NSCLC.

The value of intratumoral heterogeneity of (18)F-FDG uptake to differentiate between primary benign and malignant musculoskeletal tumours on PET/CT

OBJECTIVE

The cumulative standardized uptake value (SUV)-volume histogram (CSH) was reported to be a novel way to characterize heterogeneity in intratumoral tracer uptake. This study investigated the value of fluorine-18 fludeoxyglucose ((18)F-FDG) intratumoral heterogeneity in comparison with SUV to discriminate between primary benign and malignant musculoskeletal (MS) tumours.

METHODS

The subjects comprised 85 pathologically proven MS tumours. The area under the curve of CSH (AUC-CSH) was used as a heterogeneity index, with lower values corresponding with increased heterogeneity. As 22 tumours were indiscernible on (18)F-FDG positron emission tomography, maximum standardized uptake value (SUVmax), mean standardized uptake value (SUVmean) and AUC-CSH were obtained in 63 positive tumours. The Mann-Whitney U test and receiver operating characteristic (ROC) analysis were used for analyses.

RESULTS

The difference between benign (n = 35) and malignant tumours (n = 28) was significant in AUC-CSH (p = 0.004), but not in SUVmax (p = 0.168) and SUVmean (p = 0.879). The sensitivity, specificity and accuracy for diagnosing malignancy were 61%, 66% and 64% for SUVmax (optical threshold value, >6.9), 54%, 60% and 57% for SUVmean (optical threshold value, >3) and 61%, 86% and 75% for AUC-CSH (optical threshold value, ≤0.42), respectively. The area under the ROC curve was significantly higher in AUC-CSH (0.71) than SUVmax (0.60) (p = 0.018) and SUVmean (0.51) (p = 0.005).

CONCLUSION

The heterogeneity index, AUC-CSH, has a higher diagnostic accuracy than SUV analysis in differentiating between primary benign and malignant MS tumours, although it is not sufficiently high enough to obviate histological analysis.

ADVANCES IN KNOWLEDGE

AUC-CSH can assess the heterogeneity of (18)F-FDG uptake in primary benign and malignant MS tumours, with significantly greater heterogeneity associated with malignant MS tumours. AUC-CSH is more diagnostically accurate than SUV analysis in differentiating between benign and malignant MS tumours.

Preclinical Kinetic Analysis of the Caspase-3/7 PET Tracer 18F-C-SNAT: Quantifying the Changes in Blood Flow and Tumor Retention After Chemotherapy

Early detection of tumor response to therapy is crucial to the timely identification of the most efficacious treatments. We recently developed a novel apoptosis imaging tracer, (18)F-C-SNAT (C-SNAT is caspase-sensitive nanoaggregation tracer), that undergoes an intramolecular cyclization reaction after cleavage by caspase-3/7, a biomarker of apoptosis. This caspase-3/7-dependent reaction leads to an enhanced accumulation and retention of (18)F activity in apoptotic tumors. This study aimed to fully examine in vivo pharmacokinetics of the tracer through PET imaging and kinetic modeling in a preclinical mouse model of tumor response to systemic anticancer chemotherapy.

METHODS

Tumor-bearing nude mice were treated 3 times with intravenous injections of doxorubicin before undergoing a 120-min dynamic (18)F-C-SNAT PET/CT scan. Time-activity curves were extracted from the tumor and selected organs. A 2-tissue-compartment model was fitted to the time-activity curves from tumor and muscle, using the left ventricle of the heart as input function, and the pharmacokinetic rate constants were calculated.

RESULTS

Both tumor uptake (percentage injected dose per gram) and the tumor-to-muscle activity ratio were significantly higher in the treated mice than untreated mice. Pharmacokinetic rate constants calculated by the 2-tissue-compartment model showed a significant increase in delivery and accumulation of the tracer after the systemic chemotherapeutic treatment. Delivery of (18)F-C-SNAT to the tumor tissue, quantified as K1, increased from 0.31 g⋅(mL⋅min)(-1) in untreated mice to 1.03 g⋅(mL⋅min)(-1) in treated mice, a measurement closely related to changes in blood flow. Accumulation of (18)F-C-SNAT, quantified as k3, increased from 0.03 to 0.12 min(-1), proving a higher retention of (18)F-C-SNAT in treated tumors independent from changes in blood flow. An increase in delivery was also found in the muscular tissue of treated mice without increasing accumulation.

CONCLUSION

(18)F-C-SNAT has significantly increased tumor uptake and significantly increased tumor-to-muscle ratio in a preclinical mouse model of tumor therapy. Furthermore, our kinetic modeling of (18)F-C-SNAT shows that chemotherapeutic treatment increased accumulation (k3) in the treated tumors, independent of increased delivery (K1).

Validation of functional imaging as a biomarker for radiation treatment response

Major advances in radiotherapy techniques, increasing knowledge of tumour biology and the ability to translate these advances into new therapeutic approaches are important goals towards more individualized cancer treatment. With the development of non-invasive functional and molecular imaging techniques such as positron emission tomography (PET)-CT scanning and MRI, there is now a need to evaluate potential new biomarkers for tumour response prediction, for treatment individualization is not only based on morphological criteria but also on biological tumour characteristics. The goal of individualization of radiotherapy is to improve treatment outcome and potentially reduce chronic treatment toxicity. This review gives an overview of the molecular and functional imaging modalities of tumour hypoxia and tumour cell metabolism, proliferation and perfusion as predictive biomarkers for radiation treatment response in head and neck tumours and in lung tumours. The current status of knowledge on integration of PET/CT/MRI into treatment management and bioimage-guided adaptive radiotherapy are discussed.

The increase in tumor oxygenation under carbogen breathing induces a decrease in the uptake of [(18)F]-fluoro-deoxy-glucose

We investigated the impact of oxygenation status (measured by EPR oximetry) on the uptake of (18)F-FDG (measured by PET) in two different tumor models during a carbogen breathing challenge. We observed a significant drop in (18)F-FDG uptake under carbogen breathing that suggests a rapid metabolic adaptation to the oxygen environment.

Intratumoral Heterogeneity of Subcutaneous Nodules in a Never-Smoker Woman of Lung Squamous Cell Carcinoma Detected on 18F-Fluorodeoxyglucose Positron Emission Tomography and Computed Tomography: A Case Report

Subcutaneous tissue is a rare site of metastasis, accounting for only 1-2% of all lung neoplasms. Positron emission tomography (PET) using ¹⁸F-fluorodeoxyglucose (FDG) has been reported to increase the diagnostic accuracy of subcutaneous metastasis. A 58-year-old woman presented with complaints of dry coughing, in which three positive subcutaneous nodules were found on ¹⁸F-FDG positron emission tomography and computed tomography (PET/CT). Pathologic examination confirmed that each of the nodules contained 1) necrotic fat, 2) small amounts of blood cells and glandular epithelium, and 3) subcutaneous metastasis of moderately differentiated lung squamous cell carcinoma, respectively. Although PET/CT is useful for the detection of subcutaneous metastasis of primary lung cancer, we noted heterogeneous accumulation of ¹⁸F-FDG in subcutaneous tumors. This case highlights the importance of obtaining histological confirmation of malignant diseases whenever possible.

The reverse Warburg effect and 18F-FDG uptake in non-small cell lung cancer A549 in mice: a pilot study

The purpose of this study was to observe the effect of fasting and feeding on (18)F-FDG uptake in a mouse model of human non-small cell lung cancer.

METHODS

In in vivo studies, (18)F-FDG small-animal PET scans were acquired in 5 mice bearing non-small cell lung cancer A549 xenografts on each flank with continuous feeding and after overnight fasting to observe the changes in intratumoral distribution of (18)F-FDG and tumor (18)F-FDG standardized uptake value (SUV). In ex vivo studies, intratumoral spatial (18)F-FDG distribution assessed by autoradiography was compared with the tumor microenvironment (including hypoxia by pimonidazole and stroma by hematoxylin and eosin stain). Five overnight-fasted mice and 5 fed mice with A549 tumors were observed.

RESULTS

Small-animal PET scans were obtained in fed animals on day 1 and in the same animals after overnight fasting; the lapse was approximately 14 h. Blood glucose concentration after overnight fasting was not different from fed mice (P = 0.42), but body weight loss was significant after overnight fasting (P = 0.001). Intratumoral distribution of (18)F-FDG was highly heterogeneous in all tumors examined, and change in spatial intratumoral distribution of (18)F-FDG between 2 sets of PET images from the same mouse was remarkably different in all mice. Tumor (18)F-FDG mean SUV and maximum SUV were not significantly different between fed and fasted animals (all P > 0.05, n = 10). Only tumor mean SUV weakly correlated with blood glucose concentration (R(2) = 0.17, P = 0.03). In ex vivo studies, in fasted mice, there was spatial colocalization between high levels of (18)F-FDG uptake and pimonidazole-binding hypoxic cancer cells; in contrast, pimonidazole-negative normoxic cancer cells and noncancerous stroma were associated with low (18)F-FDG uptake. However, high (18)F-FDG uptake was frequently observed in noncancerous stroma of tumors but rarely in viable cancer cells of the tumors in fed animals.

CONCLUSION

Host dietary status may play a key role in intratumoral distribution of (18)F-FDG. In the fed animals, (18)F-FDG accumulated predominantly in noncancerous stroma in the tumors, that is, reverse Warburg effect. In contrast, in fasted status, (18)F-FDG uptake was found in hypoxic cancer cells component (Pasteur effect). Our findings may provide a better understanding of competing cancer glucose metabolism hypotheses: the Warburg effect, reverse Warburg effect, and Pasteur effect.

Is carbonic anhydrase IX a validated target for molecular imaging of cancer and hypoxia?

The presence of hypoxia is a general feature of most solid malignancies, and hypoxia is considered as one of major factors for anticancer therapy failure. Carbonic anhydrase IX (CAIX) has been reported to be an endogenous hypoxia marker, CAIX monoclonal antibodies, their segments and inhibitors are developed for CAIX imaging. However, growing evidence indicates that CAIX expression under hypoxia condition may be cancer cell lines or cancer-type dependent. Here we review the current literature on CAIX and discuss the advantage and limitation of CAIX as a target for tumor hypoxia imaging. Accordingly, CAIX would be unreliable as a universal target for cancer and tumor hypoxia visualization.

Dose painting based on tumor uptake of Cu-ATSM and FDG: a comparative study

BACKGROUND

Hypoxia and increased glycolytic activity of tumors are associated with poor prognosis. The purpose of this study was to investigate differences in radiotherapy (RT) dose painting based on the uptake of 2-deoxy-2-[(18) F]-fluorodeoxyglucose (FDG) and the proposed hypoxia tracer, copper(II)diacetyl-bis(N(4))-methylsemithiocarbazone (Cu-ATSM) using spontaneous clinical canine tumor models.

METHODS

Positron emission tomography/computed tomography scans of five spontaneous canine sarcomas and carcinomas were obtained; FDG on day 1 and (64)Cu-ATSM on day 2 and 3 (approx. 3 and 24 hours pi.). Sub-volumes for dose escalation were defined by a threshold-based method for both tracers and five dose escalation levels were formed in each sub-volume. Volumetric modulated arc therapy plans were optimized based on the dose escalation regions for each scan for a total of three dose plans for each dog. The prescription dose for the GTV was 45 Gy (100%) and it was linearly escalated to a maximum of 150%. The correlations between dose painting plans were analyzed with construction of dose distribution density maps and quality volume histograms (QVH). Correlation between high-dose regions was investigated with Dice correlation coefficients.

RESULTS

Comparison of dose plans revealed varying degree of correlation between cases. Some cases displayed a separation of high-dose regions in the comparison of FDG vs. (64)Cu-ATSM dose plans at both time points. Among the Dice correlation coefficients, the high dose regions showed the lowest degree of agreement, indicating potential benefit of using multiple tracers for dose painting. QVH analysis revealed that FDG-based dose painting plans adequately covered approximately 50% of the hypoxic regions.

CONCLUSION

Radiotherapy plans optimized with the current approach for cut-off values and dose region definitions based on FDG, (64)Cu-ATSM 3 h and 24 h uptake in canine tumors had different localization of the regional dose escalation levels. This indicates that (64)Cu-ATSM at two different time-points and FDG provide different biological information that has to be taken into account when using the dose painting strategy in radiotherapy treatment planning.

Early response monitoring with 18F-FDG PET and cetuximab-F(ab')2-SPECT after radiotherapy of human head and neck squamous cell carcinomas in a mouse model

Only a subset of patients with head and neck squamous cell carcinomas (HNSCCs) benefit from radiotherapy and concurrent epidermal growth factor receptor (EGFR) inhibitor therapy with cetuximab, indicating the need for patient selection. The aim of this study was to visualize the change in systemically accessible EGFR with (111)In-cetuximab-F(ab')2 SPECT before and after radiotherapy, while simultaneously evaluating (18)F-FDG PET uptake.

METHODS

Mice with HNSCC xenografts, cetuximab-sensitive SCCNij202 and cetuximab-resistant SCCNij167, were imaged with SPECT/CT using (111)In-cetuximab-F(ab')2 as a tracer, directly followed by PET imaging with (18)F-FDG. Scans were acquired 7 d before radiotherapy (10 Gy) and 1, 7, and 14 d after treatment. Intratumoral localization of (111)In-cetuximab-F(ab')(2) was evaluated by autoradiography and histologic markers evaluated by immunofluorescence staining in the same tumor sections.

RESULTS

Growth of irradiated SCCNij202 and SCCNij167 tumors was significantly delayed, compared with controls (P < 0.05). No changes in uptake of (18)F-FDG were observed in either of the xenografts after radiotherapy. SPECT images of tumor-bearing mice showed a significant increase in uptake of (111)In-cetuximab-F(ab')(2) in the SCCNij202 tumors after irradiation (tumor-to-liver ratio, 4.3 ± 1.1 vs. 10.5 ± 3.3, 7 d before and 14 d after treatment, respectively, P < 0.01) but not in SCCNij167 tumors. Immunohistochemical EGFR staining showed a translocation of the EGFR from the cytoplasm to the cell membrane in irradiated SCCNij202 xenografts. Intratumoral distribution of (111)In-cetuximab-F(ab')(2) as determined by autoradiography correlated well with the distribution of EGFR as determined immunohistochemically (r = 0.85; range, 0.69-0.95).

CONCLUSION

EGFR accessibility can be visualized with (111)In-cetuximab-F(ab')(2). (111)In-cetuximab-F(ab')(2) uptake increased after irradiation only in cetuximab-sensitive SCCNij202 xenografts, implying that the tracer can be used to measure irradiation-induced changes of EGFR expression and can monitor the compensatory response of tumors to radiotherapy.

Modeling the relationship between fluorodeoxyglucose uptake and tumor radioresistance as a function of the tumor microenvironment

High fluorodeoxyglucose positron emission tomography (FDG-PET) uptake in tumors has often been correlated with increasing local failure and shorter overall survival, but the radiobiological mechanisms of this uptake are unclear. We explore the relationship between FDG-PET uptake and tumor radioresistance using a mechanistic model that considers cellular status as a function of microenvironmental conditions, including proliferating cells with access to oxygen and glucose, metabolically active cells with access to glucose but not oxygen, and severely hypoxic cells that are starving. However, it is unclear what the precise uptake levels of glucose should be for cells that receive oxygen and glucose versus cells that only receive glucose. Different potential FDG uptake profiles, as a function of the microenvironment, were simulated. Predicted tumor doses for 50% control (TD₅₀) in 2 Gy fractions were estimated for each assumed uptake profile and for various possible cell mixtures. The results support the hypothesis of an increased avidity of FDG for cells in the intermediate stress state (those receiving glucose but not oxygen) compared to well-oxygenated (and proliferating) cells.

Prognostic significance of the intratumoral heterogeneity of (18) F-FDG uptake in oral cavity cancer

BACKGROUNDS

We evaluated the prognostic value of the intratumoral heterogeneity of (18) F-FDG uptake in oral cavity cancer.

MATERIALS AND METHODS

We enrolled 45 patients who underwent pretreatment (18) F-FDG PET/CT. The intratumoral heterogeneity of (18) F-FDG uptake was represented as the heterogeneity factor (HF), defined as the derivative (dV/dT) of a volume-threshold function for a primary tumor. We measured the maximum standardized uptake value (SUVmax ) and volumetric PET parameters. The relationship between HF and clinical parameters, as well as other PET parameters, was evaluated.

RESULTS

The HF was significantly correlated with SUVmax (r = -0.353, P = 0.017), metabolic tumor volume (r = -0.708, P < 0.0001), and total lesion glycolysis (r = -0.709, P < 0.0001). A multivariate analysis revealed not only cervical lymph node metastasis (hazard ratio = 5.983; P = 0.022) but also HF (hazard ratio = 2.49 × 10(-4) ; P = 0.002) to be independent predictors of overall survival. Those patients with HF < -0.13 showed a worse prognosis than those with HF ≥ -0.13 (P = 0.005).

CONCLUSIONS

The intratumoral heterogeneity of (18) F-FDG uptake may be a significant prognostic factor for overall survival in addition to cervical lymph node metastasis in oral cavity cancer. J. Surg. Oncol. 2014 110:702-706. © 2014 Wiley Periodicals, Inc.

Application of fluorodeoxyglucose positron emission tomography in the management of head and neck cancers

The use of fluorodeoxyglucose positron emission tomography (FDG PET) scan technology in the management of head and neck cancers continues to increase. We discuss the biology of FDG uptake in malignant lesions and also discuss the physics of PET imaging. The various parameters described to quantify FDG uptake in cancers including standardized uptake value, metabolic tumor volume and total lesion glycolysis are presented. PET scans have found a significant role in the diagnosis and staging of head and neck cancers. They are also being increasingly used in radiation therapy treatment planning. Many groups have also used PET derived values to serve as prognostic indicators of outcomes including loco-regional control and overall survival. FDG PET scans are also proving very useful in assessing the efficacy of treatment and management and follow-up of head and neck cancer patients. This review article focuses on the role of FDG-PET computed tomography scans in these areas for squamous cell carcinoma of the head and neck. We present the current state of the art and speculate on the future applications of this technology including protocol development, newer imaging methods such as combined magnetic resonance and PET imaging and novel radiopharmaceuticals that can be used to further study tumor biology.

Correlation of intra-tumor 18F-FDG uptake heterogeneity indices with perfusion CT derived parameters in colorectal cancer

METHODS

Thirty patients with proven colorectal cancer prospectively underwent integrated 18F-FDG PET/DCE-CT to assess the metabolic-flow phenotype. Both CT blood flow parametric maps and PET images were analyzed. Correlations between PET heterogeneity and perfusion CT were assessed by Spearman's rank correlation analysis.

RESULTS

Blood flow visualization provided by DCE-CT images was significantly correlated with 18F-FDG PET metabolically active tumor volume as well as with uptake heterogeneity for patients with stage III/IV tumors (|ρ|:0.66 to 0.78; p-value<0.02).

CONCLUSION

The positive correlation found with tumor blood flow indicates that intra-tumor heterogeneity of 18F-FDG PET accumulation reflects to some extent tracer distribution and consequently indicates that 18F-FDG PET intra-tumor heterogeneity may be associated with physiological processes such as tumor vascularization.

Prognostic value of pretreatment 18F-FDG PET/CT parameters including visual evaluation in patients with head and neck squamous cell carcinoma

OBJECTIVE

The purpose of this study was to determine whether pretreatment quantitative and visual parameters seen on PET/CT using (18)F-FDG add prognostic information for clinical staging in patients with head and neck cancer.

MATERIALS AND METHODS

We enrolled 108 patients with histologically proven oral, oropharyngeal, hypopharyngeal, and laryngeal squamous cell carcinomas who underwent FDG PET/CT before treatment and, later, definitive therapy in our study. PET/CT parameters-maximum standardized uptake value (SUVmax), metabolic tumor volume (MTV), total lesion glycolysis (TLG), and uptake pattern (sphere-shaped or ring-shaped)-were recorded. The prognostic value of these parameters was evaluated using univariate and multivariate Cox regression analyses.

RESULTS

In the univariate analysis, all of the FDG PET/CT parameters--SUVmax (> 10 g/mL) of the primary tumor, MTV (> 20 cm(3)), TLG (> 70 g), and uptake pattern (ring-shaped)--were significantly associated with negative effects on disease-specific survival (DSS) and disease-free survival (DFS). In the multivariate analysis, the MTV and uptake pattern remained associated with DSS after corrections for the Union for International Cancer Control (UICC) stage and definitive therapy (p = 0.023 and < 0.001, respectively). Another multivariate model that included MTV as a continuous variable, uptake pattern, and UICC stage showed that the uptake pattern remained significantly associated with DSS, whereas the association between DSS and MTV was not significant (p < 0.001 and = 0.332, respectively).

CONCLUSION

Our data indicate that the pretreatment PET/CT parameters had prognostic value. In particular, a qualitative factor, uptake pattern, provided better prognostic information to the clinical staging of head and neck squamous cell carcinomas than the other PET/CT parameters.

(18)F-fluorodeoxyglucose uptake and tumor hypoxia: revisit (18)f-fluorodeoxyglucose in oncology application

This study revisited ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) uptake and its relationship to hypoxia in various tumor models. METHODS: We generated peritoneal carcinomatosis and subcutaneous xenografts of colorectal cancer HT29, breast cancer MDA-MB-231, and non–small cell lung cancer A549 cell lines in nude mice. The partial oxygen pressure (pO₂) of ascites fluid was measured. ¹⁸F-FDG accumulation detected by digital autoradiography was related to tumor hypoxia visualized by pimonidazole binding and glucose transporter-1 (GLUT-1) in frozen tumor sections. RESULTS: Ascites pO₂ was 0.90 ± 0.53 mm Hg. Single cancer cells and clusters suspended in ascites fluid as well as submillimeter serosal tumors stained positive for pimonidazole and GLUT-1 and had high ¹⁸F-FDG uptake. In contrast, ¹⁸F-FDG uptake was significantly lower in normoxic portion (little pimonidazole binding or GLUT-1 expression) of larger serosal tumors or subcutaneous xenografts, which was not statistically different from that in the liver. CONCLUSIONS: Glucose demand (¹⁸F-FDG uptake) in severely hypoxic ascites carcinomas and hypoxic portion of larger tumors is significantly higher than in normoxic cancer cells. Warburg effect originally obtained from Ehrlich ascites carcinoma may not apply to normoxic cancer cells. Our findings may benefit the better understanding of ¹⁸F-FDG PET in oncology application.

2-Deoxy-2-[18F]fluoro-D-glucose positron emission tomography demonstrates target inhibition with the potential to predict anti-tumour activity following treatment with the AKT inhibitor AZD5363

PURPOSE

The phosphatidyl inositol 3 kinase, AKT and mammalian target of rapamycin are frequently deregulated in human cancer and are among one of the most promising targets for cancer therapy. AZD5363 (AstraZeneca) is an AKT inhibitor in phase 1 clinical trials. Given its utility in assessing glucose metabolism, we investigated the role of 2-Deoxy-2-[18F]fluoro-D-glucose (18F-FDG) positron emission tomography (PET) as a biomarker to demonstrate target inhibition and its potential to predict and demonstrate the anti-tumour activity of AZD5363.

METHODS

18F-FDG PETscans were performed in nude mice in a number of xenograft models (U87-MG glioblastoma, BT474C breast carcinoma and Calu-6 lung). Mice were fasted prior to imaging, and either static or dynamic 18F-FDG PET imaging was performed.

RESULTS

We have shown that 18F-FDG uptake in tumour xenografts was reduced by 39% reduction compared to vehicle after a single dose of AZD5363, demonstrating activation of the AKT pathway after only 4 h of dosing. Multiple doses of AZD5363 showed an anti-tumour volume effect and a reduction in 18F-FDG uptake (28% reduction compared to vehicle), highlighting the potential of 18F-FDG PET as an efficacy biomarker. Furthermore, the degree of inhibition of 18F-FDG uptake corresponded with the sensitivity of the tumour model to AZD5363. The use of dynamic 18F-FDG PET and a two-compartmental analysis identified the mechanism of this change to be due to a change in cellular uptake of 18F-FDG following administration of AZD5363.

CONCLUSIONS

We conclude that 18F-FDG PET is a promising pharmacodynamic biomarker of AKT pathway inhibition, with potential to predict and demonstrate anti-tumour activity. It is a biomarker that may stop ineffective drug schedules, helping to make early stop decisions and identify responding subsets of patients, resulting in improved clinical decision making both during drug development and patient management.

An alternative approach to histopathological validation of PET imaging for radiation therapy image-guidance: a proof of concept

PURPOSE

In radiotherapy, PET images can be used to guide the delivery of selectively escalated doses to biologically relevant tumour subvolumes. Validation of PET for such applications requires demonstration of spatial coincidence between PET tracer uptake pattern and the histopathologically confirmed target. This study introduces a novel approach to histopathological validation of PET image segmentation for radiotherapy guidance.

METHODS AND MATERIALS

Sequential tissue sections from surgically excised whole-tumour specimens were used to acquire full 3D-sets of both histopathological images (microscopy) and PET tracer distribution images (autoradiography). After these datasets were accurately registered, a full 3D autoradiographic distribution of PET tracer was reconstructed and used to obtain synthetic PET images (sPET) by simulating the image deterioration induced by processes involved in PET image formation. To illustrate the method, sPET images were used in this study to investigate spatial coincidence between high FDG uptake areas and the distribution of viable tissue in two small animal tumour models.

RESULTS

The reconstructed 3D autoradiographic distribution of the PET tracer was spatially coherent, as indicated by the high average value of the normalised pixel-by-pixel correlation of intensities between successive slices (0.84 ± 0.05 and 0.94 ± 0.02). The loss of detail in the sPET images versus the 3D autoradiography was significant as indicated by Dice coefficient values corresponding to the two tumours (0 and 0.1 at 70% threshold). The maximum overlap between the FDG segmented volumes and the extent of the viable tissue as indicated by Dice coefficient values, was 0.8 for one tumour (for the image thresholded at 22% of max intensity) and 0.88 for the other (threshold of 14% of max intensity).

CONCLUSION

It was demonstrated that the use of synthetic PET images for histopathological validation allows for bypassing a technically challenging and error-prone step of registering non-invasive PET images with histopathology.

Combined Injection of (18)F-Fluorodeoxyglucose and 3'-Deoxy-3'-[(18)F]fluorothymidine PET Achieves More Complete Identification of Viable Lung Cancer Cells in Mice and Patients than Individual Radiopharmaceutical: A Proof-of-Concept Study

PURPOSE

The objective is to validate the combination of 3'-deoxy-3'-[(18)F]fluorothymidine ((18)F-FLT) and (18)F-fluorodeoxyglucose ((18)F-FDG) as a "novel" positron emission tomography (PET) tracer for better visualization of cancer cell components in solid cancers than individual radiopharmaceutical.

METHODS

Nude mice with subcutaneous xenografts of human non-small cell lung cancer A549 and HTB177 cells and patients with lung cancer were included. In ex vivo study, intratumoral radioactivity of (18)F-FDG, (18)F-FLT, and the cocktail of (18)F-FDG and (18)F-FLT detected by autoradiography was compared with hypoxia (by pimonidazole) and proliferation (by bromodeoxyuridine) in tumor section. In in vivo study, first, (18)F-FDG PET and (18)F-FLT PET were conducted in the same subjects (mice and patients) 10 to 14 hours apart. Second, PET scan was also performed 1 hour after one tracer injection; subsequently, the other was administered and followed the second PET scan in the mouse. Finally, (18)F-FDG and (18)F-FLT cocktail PET scan was also performed in the mouse.

RESULTS

When injected individually, (18)F-FDG highly accumulated in hypoxic zones and high (18)F-FLT in proliferative cancer cells. In case of cocktail injection, high radioactivity correlated with hypoxic regions and highly proliferative and normoxic regions. PET detected that intratumoral distribution of (18)F-FDG and (18)F-FLT was generally mismatched in both rodents and patients. Combination of (18)F-FLT and (18)F-FDG appeared to map more cancer tissue than single-tracer PET.

CONCLUSIONS

Combination of (18)F-FDG and (18)F-FLT PET imaging would give a more accurate representation of total viable tumor tissue than either tracer alone and would be a powerful imaging strategy for cancer management.

Dose escalation to high-risk sub-volumes based on non-invasive imaging of hypoxia and glycolytic activity in canine solid tumors: a feasibility study

INTRODUCTION

Glycolytic activity and hypoxia are associated with poor prognosis and radiation resistance. Including both the tumor uptake of 2-deoxy-2-[18 F]-fluorodeoxyglucose (FDG) and the proposed hypoxia tracer copper(II)diacetyl-bis(N4)-methylsemithio-carbazone (Cu-ATSM) in targeted therapy planning may therefore lead to improved tumor control. In this study we analyzed the overlap between sub-volumes of FDG and hypoxia assessed by the uptake of 64Cu-ATSM in canine solid tumors, and evaluated the possibilities for dose redistribution within the gross tumor volume (GTV).

MATERIALS AND METHODS

Positron emission tomography/computed tomography (PET/CT) scans of five spontaneous canine solid tumors were included. FDG-PET/CT was obtained at day 1, 64Cu-ATSM at day 2 and 3 (3 and 24 h pi.). GTV was delineated and CT images were co-registered. Sub-volumes for 3 h and 24 h 64Cu-ATSM (Cu3 and Cu24) were defined by a threshold based method. FDG sub-volumes were delineated at 40% (FDG40) and 50% (FDG50) of SUVmax. The size of sub-volumes, intersection and biological target volume (BTV) were measured in a treatment planning software. By varying the average dose prescription to the tumor from 66 to 85 Gy, the possible dose boost (DB) was calculated for the three scenarios that the optimal target for the boost was one, the union or the intersection of the FDG and 64Cu-ATSM sub-volumes.

RESULTS

The potential boost volumes represented a fairly large fraction of the total GTV: Cu3 49.8% (26.8-72.5%), Cu24 28.1% (2.4-54.3%), FDG40 45.2% (10.1-75.2%), and FDG50 32.5% (2.6-68.1%). A BTV including the union (∪) of Cu3 and FDG would involve boosting to a larger fraction of the GTV, in the case of Cu3∪FDG40 63.5% (51.8-83.8) and Cu3∪FDG50 48.1% (43.7-80.8). The union allowed only a very limited DB whereas the intersection allowed a substantial dose escalation.

CONCLUSIONS

FDG and 64Cu-ATSM sub-volumes were only partly overlapping, suggesting that the tracers offer complementing information on tumor physiology. Targeting the combined PET positive volume (BTV) for dose escalation within the GTV results in a limited DB. This suggests a more refined dose redistribution based on a weighted combination of the PET tracers in order to obtain an improved tumor control.

PET imaging of tumor hypoxia using 18F-fluoroazomycin arabinoside in stage III-IV non-small cell lung cancer patients

Tumor hypoxia hampers the efficacy of radiotherapy because of its increased resistance to ionizing radiation. The aim of the present study was to estimate the potential added clinical value of the specific hypoxia tracer (18)F-fluoroazomycin arabinoside ((18)F-FAZA) over commonly used (18)F-FDG in the treatment of advanced-stage non-small cell lung cancer (NSCLC).

METHODS

Eleven patients with stage III or stage IV NSCLC underwent (18)F-FDG and (18)F-FAZA PET before chemoradiotherapy. The maximum standardized uptake value (SUVmax) was used to depict (18)F-FDG uptake, and the tumor-to-background (T/B) ratio and tumor fractional hypoxic volume (FHV) were used to quantify hypoxia. The spatial correlation between (18)F-FDG and (18)F-FAZA uptake values was investigated using voxel-based analysis. Partial-volume correction was applied.

RESULTS

All 11 patients showed clear uptake of (18)F-FAZA in the primary tumor. However, different patterns of (18)F-FDG and (18)F-FAZA uptake distributions were observed and varied widely among different tumors. No significant correlation was observed between (18)F-FDG SUVmax and (18)F-FAZA T/B ratio (P = 0.055). The median FHV of 1.4 was 48.4% (range, 5.0-91.5). A significant positive correlation was found between the (18)F-FAZA T/B ratio and FHV of 1.4 (P < 0.001). There was no correlation between the lesion size and FHV or between the (18)F-FDG SUVmax and FHV. The pattern of tumoral (18)F-FDG uptake was rather homogeneous, whereas (18)F-FAZA uptake was more heterogeneous, suggesting that (18)F-FAZA identifies hypoxic areas within metabolically active areas of tumor. A significant correlation between (18)F-FDG SUVmax and lesion size (P = 0.002) was observed.

CONCLUSION

(18)F-FAZA PET imaging is able to detect heterogeneous distributions of hypoxic subvolumes out of homogeneous (18)F-FDG background in a clinical setting. Therefore, (18)F-FAZA might be considered a tool for guiding dose escalation to the hypoxic fraction of the tumor.

Temporal analysis of intratumoral metabolic heterogeneity characterized by textural features in cervical cancer

PURPOSE

The aim of this pilot study was to explore heterogeneity in the temporal behavior of intratumoral [(18)F]fluorodeoxyglucose (FDG) accumulation at a regional scale in patients with cervical cancer undergoing chemoradiotherapy.

METHODS

Included in the study were 20 patients with FIGO stages IB1 to IVA cervical cancer treated with combined chemoradiotherapy. Patients underwent FDG PET/CT before treatment, during weeks 2 and 4 of treatment, and 12 weeks after completion of therapy. Patients were classified based on response to therapy as showing a complete metabolic response (CMR), a partial metabolic response (PMR), or residual disease and the development of new disease (NEW). Based on the presence of residual primary tumor following therapy, patients were divided into two groups, CMR and PMR/NEW. Temporal profiles of intratumoral FDG heterogeneity as characterized by textural features at a regional scale were assessed and compared with those of the standardized uptake value (SUV) indices (SUVmax and SUVmean) within the context of differentiating response groups.

RESULTS

Textural features at a regional scale with emphasis on characterizing contiguous regions of high uptake in tumors decreased significantly with time (P < 0.001) in the CMR group, while features describing contiguous regions of low uptake along with those measuring the nonuniformity of contiguous isointense regions in tumors exhibited significant temporal changes in the PMR/NEW group (P < 0.03) but showed no persistent trends with time. Both SUV indices showed significant changes during the course of the disease in both patient groups (P < 0.001 for SUVmax and SUVmean in the CMR group; P = 0.0109 and 0.0136, respectively, for SUVmax and SUVmean in the PMR/NEW group), and also decreased at a constant rate in the CMR group and decreased up to the 4th week of treatment and then increased in the PMR/NEW group.

CONCLUSION

The temporal changes in the heterogeneity of intratumoral FDG distribution characterized at a regional scale using image-based textural features may provide an adjunctive or alternative option for understanding tumor response to chemoradiotherapy and interpreting FDG accumulation dynamics in patients with malignant cervical tumors during the course of the disease.

Preclinical molecular imaging using PET and MRI

Molecular imaging fundamentally changes the way we look at cancer. Imaging paradigms are now shifting away from classical morphological measures towards the assessment of functional, metabolic, cellular, and molecular information in vivo. Interdisciplinary driven developments of imaging methodology and probe molecules utilizing animal models of human cancers have enhanced our ability to non-invasively characterize neoplastic tissue and follow anti-cancer treatments. Preclinical molecular imaging offers a whole palette of excellent methodology to choose from. We will focus on positron emission tomography (PET) and magnetic resonance imaging (MRI) techniques, since they provide excellent and complementary molecular imaging capabilities and bear high potential for clinical translation. Prerequisites and consequences of using animal models as surrogates of human cancers in preclinical molecular imaging are outlined. We present physical principles, values and limitations of PET and MRI as molecular imaging modalities and comment on their high potential to non-invasively assess information on hypoxia, angiogenesis, apoptosis, gene expression, metabolism, and cell trafficking in preclinical cancer research.

Radioluminescence microscopy: measuring the heterogeneous uptake of radiotracers in single living cells

Radiotracers play an important role in interrogating molecular processes both in vitro and in vivo. However, current methods are limited to measuring average radiotracer uptake in large cell populations and, as a result, lack the ability to quantify cell-to-cell variations. Here we apply a new technique, termed radioluminescence microscopy, to visualize radiotracer uptake in single living cells, in a standard fluorescence microscopy environment. In this technique, live cells are cultured sparsely on a thin scintillator plate and incubated with a radiotracer. Light produced following beta decay is measured using a highly sensitive microscope. Radioluminescence microscopy revealed strong heterogeneity in the uptake of [(18)F]fluoro-deoxyglucose (FDG) in single cells, which was found consistent with fluorescence imaging of a glucose analog. We also verified that dynamic uptake of FDG in single cells followed the standard two-tissue compartmental model. Last, we transfected cells with a fusion PET/fluorescence reporter gene and found that uptake of FHBG (a PET radiotracer for transgene expression) coincided with expression of the fluorescent protein. Together, these results indicate that radioluminescence microscopy can visualize radiotracer uptake with single-cell resolution, which may find a use in the precise characterization of radiotracers.

Nasopharyngeal carcinoma: investigation of intratumoral heterogeneity with FDG PET/CT

OBJECTIVE

The purpose of this study was to quantitatively evaluate the role of intratumoral heterogeneity of (18)F-FDG uptake in characterizing nasopharyngeal carcinoma (NPC).

SUBJECTS AND METHODS

Forty consecutively registered patients with newly diagnosed NPC underwent PET/CT. The heterogeneity factor, defined as the derivative of a volume threshold function, was computed for each tumor. The relations between heterogeneity factor and maximum standardized uptake value (SUV(max)), tumor volume, and TNM category were determined by two-tailed Spearman correlation. Factors that potentially affect outcome determined by disease-free survival were studied by Kaplan-Meier analysis with a log-rank test for univariate analysis and the Cox proportional hazard model for multivariate analysis.

RESULTS

The heterogeneity factor ranged from -1.80 to -0.13 (mean, -0.40 [SD, 0.40]) and significantly correlated with SUV(max) (r = -0.372; p = 0.018), tumor volume (r = -0.983; p < 0.001), and T category (r = -0.457; p = 0.003) but not with N and M categories. There was a significant difference in heterogeneity factor between T1 and T2 tumors and T3 and T4 tumors (p = 0.012). The 2-year disease-free survival rate among the 38 patients was 67.4%. According to the results of Kaplan-Meier analysis with the log-rank test, heterogeneity factor and M category significantly affected disease-free survival. Patients with tumors that had a heterogeneity factor greater than -0.24 (less-heterogeneous group) (p = 0.0498) or M0 status (p < 0.001) had better disease-free survival rates. Multivariate analysis showed only M category to be an independent predictor of disease-free survival (p < 0.001).

CONCLUSION

The intratumoral heterogeneity of FDG uptake varies across NPC tumors, significantly correlates with tumor aggressiveness, and is predictive of patient outcome. These findings may be useful for characterizing NPC, predicting survival, and improving patient care.

Tumor microenvironment-dependent 18F-FDG, 18F-fluorothymidine, and 18F-misonidazole uptake: a pilot study in mouse models of human non-small cell lung cancer

(18)F-FDG, (18)F-fluorothymidine, and (18)F-misonidazole PET scans have emerged as important clinical tools in the management of cancer; however, none of them have demonstrated conclusive superiority. The aim of this study was to compare the intratumoral accumulation of (18)F-FDG, (18)F-fluorothymidine, and (18)F-misonidazole and relate this to specific components of the tumor microenvironment in mouse models of human non-small cell lung cancer (NSCLC).

METHODS

We used NSCLC A549 and HTB177 cells to generate subcutaneous and peritoneal xenografts in nude mice. Animals were coinjected with a PET radiotracer, pimonidazole (hypoxia marker), and bromodeoxyuridine (proliferation marker) intravenously 1 h before animal euthanasia. Tumor perfusion was assessed by Hoechst 33342 injection, given 1 min before sacrifice. The intratumoral distribution of PET radiotracers was visualized by digital autoradiography and related to microscopic visualization of proliferation, hypoxia, perfusion, stroma, and necrosis.

RESULTS

NSCLC xenografts had complex structures with intermingled regions of viable cancer cells, stroma, and necrosis. Cancer cells were either well oxygenated (staining negatively for pimonidazole) and highly proliferative (staining positively for bromodeoxyuridine) or hypoxic (pimonidazole-positive) and noncycling (little bromodeoxyuridine). Hypoxic cancer cells with a low proliferation rate had high(18)F-FDG and (18)F-misonidazole uptake but low (18)F-fluorothymidine accumulation. Well-oxygenated cancer cells with a high proliferation rate accumulated a high level of (18)F-fluorothymidine but low (18)F-FDG and(18)F-misonidazole. Tumor stroma and necrotic zones were always associated with low (18)F-FDG, (18)F-misonidazole, and (18)F-fluorothymidine activity.

CONCLUSION

In NSCLC A549 and HTB177 subcutaneously or intraperitoneally growing xenografts, (18)F-fluorothymidine accumulates in well-oxygenated and proliferative cancer cells, whereas (18)F-misonidazole and (18)F-FDG accumulate mostly in poorly proliferative and hypoxic cancer cells. (18)F-FDG and (18)F-misonidazole display similar intratumoral distribution patterns, and both mutually exclude (18)F-fluorothymidine.

Tumour microenvironment heterogeneity affects the perceived spatial concordance between the intratumoural patterns of cell proliferation and 18F-fluorothymidine uptake

BACKGROUND AND PURPOSE

PET imaging with (18)F-fluorothymidine ((18)F-FLT) can potentially be used to identify tumour subvolumes for selective dose escalation in radiation therapy. The purpose of this study is to analyse the co-localization of intratumoural patterns of cell proliferation with (18)F-FLT tracer uptake.

MATERIALS AND METHODS

Mice bearing FaDu or SQ20B xenograft tumours were injected with (18)F-FLT, and bromodeoxyuridine (proliferation marker). Ex vivo images of the spatial pattern of intratumoural (18)F-FLT uptake and that of bromodeoxyuridine DNA incorporation were obtained from thin tumour tissue sections. These images were segmented by thresholding and Relative Operating Characteristic (ROC) curves and Dice similarity indices were evaluated.

RESULTS

The thresholds at which maximum overlap occurred between FLT-segmented areas and areas of active cell proliferation were significantly different for the two xenograft tumour models, whereas the median Dice values were not. However, ROC analysis indicated that segmented FLT images were more specific at detecting the proliferation pattern in FaDu tumours than in SQ20B tumours.

CONCLUSION

Highly dispersed patterns of cell proliferation observed in certain tumours can affect the perceived spatial concordance between the spatial pattern of (18)F-FLT uptake and that of cell proliferation even when high-resolution ex vivo autoradiography imaging is used for (18)F-FLT imaging.

Individualization of cancer treatment from radiotherapy perspective

Radiotherapy is today used in about 50% of all cancer patients, often in multidisciplinary approaches. With major advance in radiotherapy techniques, increasing knowledge on tumor genetics and biology and the continuous introduction of specifically targeted drugs into combined radio-oncological treatment schedules, individualization of radiotherapy is of high priority to further improve treatment outcomes, i.e. to increase long-term tumor cure and/or to reduce chronic treatment toxicity. This review gives an overview on the importance of predictive biomarkers for the field of radiation oncology. The current status of knowledge on potential biomarkers of tumor hypoxia, tumor cell metabolism, DNA repair, cancer stem cells and biomarkers for combining radiotherapy with inhibition of the epidermal growth factor receptor using monoclonal antibodies is described.

Lactate MRSI and DCE MRI as surrogate markers of prostate tumor aggressiveness

Longitudinal studies of lactate MRSI and dynamic contrast-enhanced MRI were performed at 4.7 T in two prostate tumor models grown in rats, Dunning R3327-AT (AT) and Dunning R3327-H (H), to determine the potential of lactate and the perfusion/permeability parameter Ak(ep) as markers of tumor aggressiveness. Subcutaneous AT (n = 12) and H (n = 6) tumors were studied at different volumes between 100 and 2900 mm(3) (Groups 1-5). Lactate concentration was determined using selective multiple quantum coherence MRSI with the phantom substitution method. Tumor enhancement after the administration of gadolinium diethylenetriaminepenta-acetic acid was analyzed using the Brix-Hoffmann model and the Ak(ep) parameter was used as a measure of tumor perfusion/permeability. Lactate was not detected in the smallest AT tumors (Group 1; 100-270 mm(3) ). In larger AT tumors, the lactate concentration increased from 2.8 ± 1.0 mm (Group 2; 290-700 mm(3)) to 8.4 ± 2.9 mm (Group 3; 1000-1340 mm(3)) and 8.2 ± 2.2 mm (Group 4; 1380-1750 mm(3) ), and then decreased to 5.0 ± 1.7 mm (Group 5; 1900-2500 mm(3)), and was consistently higher in the tumor core than in the rim. Lactate was not detected in any of the H tumors. The mean tumor Ak(ep) values decreased with increasing volume in both tumor types, but were significantly higher in H tumors. In AT tumors, the Ak(ep) values were significantly higher in the rim than in the core. Histological hypoxic and necrotic fractions in AT tumors increased with volume from 0% in Group 1 to about 20% and 30%, respectively, in Group 5. Minimal amounts of hypoxia and necrosis were found in H tumors of all sizes. Thus, the presence of lactate and heterogeneous perfusion/permeability are signatures of aggressive, metabolically deprived tumors.

Characterizing tumor heterogeneity with functional imaging and quantifying high-risk tumor volume for early prediction of treatment outcome: cervical cancer as a model

PURPOSE

Treatment response in cancer has been monitored by measuring anatomic tumor volume (ATV) at various times without considering the inherent functional tumor heterogeneity known to critically influence ultimate treatment outcome: primary tumor control and survival. This study applied dynamic contrast-enhanced (DCE) functional MRI to characterize tumors' heterogeneous subregions with low DCE values, at risk for treatment failure, and to quantify the functional risk volume (FRV) for personalized early prediction of treatment outcome.

METHODS AND MATERIALS

DCE-MRI was performed in 102 stage IB(2)-IVA cervical cancer patients to assess tumor perfusion heterogeneity before and during radiation/chemotherapy. FRV represents the total volume of tumor voxels with critically low DCE signal intensity (<2.1 compared with precontrast image, determined by previous receiver operator characteristic analysis). FRVs were correlated with treatment outcome (follow-up: 0.2-9.4, mean 6.8 years) and compared with ATVs (Mann-Whitney, Kaplan-Meier, and multivariate analyses).

RESULTS

Before and during therapy at 2-2.5 and 4-5 weeks of RT, FRVs >20, >13, and >5 cm(3), respectively, significantly predicted unfavorable 6-year primary tumor control (p = 0.003, 7.3 × 10(-8), 2.0 × 10(-8)) and disease-specific survival (p = 1.9 × 10(-4), 2.1 × 10(-6), 2.5 × 10(-7), respectively). The FRVs were superior to the ATVs as early predictors of outcome, and the differentiating power of FRVs increased during treatment.

DISCUSSION

Our preliminary results suggest that functional tumor heterogeneity can be characterized by DCE-MRI to quantify FRV for predicting ultimate long-term treatment outcome. FRV is a novel functional imaging heterogeneity parameter, superior to ATV, and can be clinically translated for personalized early outcome prediction before or as early as 2-5 weeks into treatment.

Intratumoral heterogeneity of F-18 FDG uptake differentiates between gastrointestinal stromal tumors and abdominal malignant lymphomas on PET/CT

OBJECTIVE

Gastrointestinal stromal tumors (GISTs) and malignant lymphomas (MLs) in the abdomen are often observed as tumors of unknown origin on F-18 FDG PET/CT. The purpose of this study was to evaluate the intratumoral metabolic heterogeneity of F-18 FDG uptake on PET to determine if it might be helpful to discriminate between these tumors.

METHODS

The F-18 FDG PET/CT findings of 21 large abdominal tumors were retrospectively evaluated (9 GISTs and 12 MLs). Intratumoral heterogeneity was evaluated by visual scoring (visual score: 0, homogeneous; 1, slightly heterogeneous; 2, moderately heterogeneous; 3, highly heterogeneous) and by the cumulative standardized uptake value (SUV) histograms on transaxial PET images at the maximal cross-sectional tumor diameter. Percent tumor areas above a threshold from 0 to 100% of the maximum SUV were plotted and the area under curve of the cumulative SUV histograms (AUC-CSH) was used as a heterogeneity index, where lower values corresponded with increased heterogeneity. Correlation between the visual score and the AUC-CSH was investigated by the Spearman's rank test.

RESULTS

GISTs exhibited heterogeneous uptake of F-18 FDG, whereas MLs showed rather homogeneous uptake on visual analysis (visual score: 2.67 ± 0.50 and 0.58 ± 0.79, respectively; p < 0.001). The AUC-CSH was significantly lower for the GISTs than for the MLs (0.41 ± 0.14 and 0.64 ± 0.08, respectively; p < 0.001). Significant correlations were observed between the visual score and the AUC-CSH (ρ = -0.866, p < 0.001).

CONCLUSION

GISTs exhibited significantly heterogeneous intratumoral tracer uptake as compared with the MLs. Evaluation of the intratumoral heterogeneity of F-18 FDG uptake may help in the discrimination between these tumors.

Hypoxia but not inflammation augments glucose uptake in human macrophages: Implications for imaging atherosclerosis with 18fluorine-labeled 2-deoxy-D-glucose positron emission tomography

OBJECTIVES

This study investigated the regulation of glucose uptake in cells that participate in atherogenesis by stimuli relevant to this process, to gain mechanistic insight into the origin of the (18)fluorine-labeled 2-deoxy-D-glucose (FdG) uptake signals observed clinically.

BACKGROUND

Patient studies suggest that positron emission tomography (PET) using FdG can detect "active" atherosclerotic plaques, yet the mechanism giving rise to FdG signals remains unknown.

METHODS

We exposed cells to conditions thought to operate in atheroma and determined rates of glucose uptake.

RESULTS

Hypoxia, but not pro-inflammatory cytokines, potently stimulated glucose uptake in human macrophages and foam cells. Statins attenuated this process in vitro, suggesting that these agents have a direct effect on human macrophages. Immunohistochemical study of human plaques revealed abundant expression of proteins regulating glucose utilization, predominantly in macrophage-rich regions of the plaques-regions previously proved hypoxic. Smooth-muscle cells and endothelial cells markedly increased rates of glucose uptake when exposed to pro-inflammatory cytokines.

CONCLUSIONS

Glucose uptake and, probably, FdG uptake signals in atheroma may reflect hypoxia-stimulated macrophages rather than mere inflammatory burden. Cytokine-activated smooth-muscle cells also may contribute to the FdG signal.