Measuring tumor hypoxia with ¹⁸F-FETNIM PET in esophageal squamous cell carcinoma: a pilot clinical study

Advances in the Imaging of Esophageal and Gastroesophageal Junction Malignancies

Accurate imaging is key for the diagnosis and treatment of esophageal and gastroesophageal junction cancers . Current imaging modalities, such as computed tomography (CT) and 18F-FDG (2-deoxy-2-[18F]fluoro-D-glucose) positron emission tomography (PET)/CT, have limitations in accurately staging these cancers. MRI shows promise for T staging and residual disease assessment. Novel PET tracers, like FAPI, FLT, and hypoxia markers, offer potential improvements in diagnostic accuracy. 18F-FDG PET/MRI combines metabolic and anatomic information, enhancing disease evaluation. Radiomics and artificial intelligence hold promise for early detection, treatment planning, and response assessment. Theranostic nanoparticles and personalized medicine approaches offer new avenues for cancer therapy.

Value of blood oxygenation level-dependent magnetic resonance imaging in early evaluation of the response and prognosis of esophageal squamous cell carcinoma treated with definitive chemoradiotherapy: a preliminary study

BACKGROUND

To find a useful hypoxia non-invasive biomarker for evaluating early treatment response and prognosis to definitive chemoradiotherapy (dCRT) in patients with esophageal squamous cell carcinoma (ESCC), using blood oxygenation level-dependent (BOLD) magnetic resonance imaging (MRI).

METHODS

The R2* values were obtained pre- and 2-3 weeks post-dCRT in 28 patients with ESCC using BOLD MRI. Independent samples t-test (normality) or Mann-Whitney U test (non-normality) was used to compare the differences of R2*-related parameters between the complete response (CR) and the non-CR groups. Diagnostic performance of parameters in predicting response was tested with receiver operating characteristic (ROC) curve analysis. The 3-year overall survival (OS) was evaluated using Kaplan Meier curve, log rank test, and Cox proportional hazards regression analysis.

RESULTS

The post-R2*, ∆R2*, and ∆%R2* in the CR group were significantly higher than those in the non-CR group (P = 0.002, 0.003, and 0.006, respectively). The R2*-related parameters showed good prediction of tumor response, with AUC ranging from 0.813 to 0.829. The 3-year OS rate in patients with ∆R2* >-7.54 s- 1 or CR were significantly longer than those with ∆R2* ≤ -7.54 s- 1 (72.37% vs. 0.00%; Hazard ratio, HR = 0.196; 95% confidence interval, 95% CI = 0.047-0.807; P = 0.024) or non-CR (76.47% vs. 29.27%; HR = 0.238, 95% CI = 0.059-0.963; P = 0.044).

CONCLUSIONS

The preliminary results demonstrated that the R2* value might be a useful hypoxia non-invasive biomarker for assessing response and prognosis of ESCC treated with dCRT. BOLD MRI might be used as a potential tool for evaluating tumor oxygenation metabolism, which is routinely applied in clinical practice and beneficial to clinical decision-making. A large sample size was needed for further follow-up studies to confirm the findings.

Molecular imaging of tumor hypoxia: Evolution of nitroimidazole radiopharmaceuticals and insights for future development

Though growing evidence has been collected in support of the concept of dose escalation based on the molecular level images indicating hypoxic tumor sub-volumes that could be radio-resistant, validation of the concept is still a work in progress. Molecular imaging of tumor hypoxia using radiopharmaceuticals is expected to provide the required input to plan dose escalation through Image Guided Radiation Therapy (IGRT) to kill/control the radio-resistant hypoxic tumor cells. The success of the IGRT, therefore, is heavily dependent on the quality of images obtained using the radiopharmaceutical and the extent to which the image represents the true hypoxic status of the tumor in spite of the heterogeneous nature of tumor hypoxia. Available literature on radiopharmaceuticals for imaging hypoxia is highly skewed in favor of nitroimidazole as the pharmacophore given their ability to undergo oxygen dependent reduction in hypoxic cells. In this context, present review on nitroimidazole radiopharmaceuticals would be immensely helpful to the researchers to obtain a birds-eye view on what has been achieved so far and what can be tried differently to obtain a better hypoxia imaging agent. The review also covers various methods of radiolabeling that could be utilized for developing radiotracers for hypoxia targeting applications.

Functional Imaging of Hypoxia: PET and MRI

Molecular and functional imaging have critical roles in cancer care. Existing evidence suggests that noninvasive detection of hypoxia within a particular type of cancer can provide new information regarding the relationship between hypoxia, cancer aggressiveness and altered therapeutic responses. Following the identification of hypoxia inducible factor (HIF), significant progress in understanding the regulation of hypoxia-induced genes has been made. These advances have provided the ability to therapeutically target HIF and tumor-associated hypoxia. Therefore, by utilizing the molecular basis of hypoxia, hypoxia-based theranostic strategies are in the process of being developed which will further personalize care for cancer patients. The aim of this review is to provide an overview of the significance of tumor hypoxia and its relevance in cancer management as well as to lay out the role of imaging in detecting hypoxia within the context of cancer.

Recent Advances of 68Ga-Labeled PET Radiotracers with Nitroimidazole in the Diagnosis of Hypoxia Tumors

Positron emission tomography (PET) is a noninvasive molecular imaging method extensively applied in the detection and treatment of various diseases. Hypoxia is a common phenomenon found in most solid tumors. Nitroimidazole is a group of bioreducible pharmacophores that selectively accumulate in hypoxic regions of the body. Over the past few decades, many scientists have reported the use of radiopharmaceuticals containing nitroimidazole for the detection of hypoxic tumors. Gallium-68, a positron-emitting radioisotope, has a favorable half-life time of 68 min and can be conveniently produced by ⁶⁸Ge/⁶⁸Ga generators. Recently, there has been significant progress in the preparation of novel ⁶⁸Ga-labeled complexes bearing nitroimidazole moieties for the diagnosis of hypoxia. This review provides a comprehensive overview of the current status of developing ⁶⁸Ga-labeled radiopharmaceuticals with nitroimidazole moieties, their pharmacokinetics, and in vitro and in vivo studies, as well as PET imaging studies for hypoxic tumors.

Advances in PET and MRI imaging of tumor hypoxia

Tumor hypoxia is a complex and evolving phenomenon both in time and space. Molecular imaging allows to approach these variations, but the tracers used have their own limitations. PET imaging has the disadvantage of low resolution and must take into account molecular biodistribution, but has the advantage of high targeting accuracy. The relationship between the signal in MRI imaging and oxygen is complex but hopefully it would lead to the detection of truly oxygen-depleted tissue. Different ways of imaging hypoxia are discussed in this review, with nuclear medicine tracers such as [¹⁸F]-FMISO, [¹⁸F]-FAZA, or [⁶⁴Cu]-ATSM but also with MRI techniques such as perfusion imaging, diffusion MRI or oxygen-enhanced MRI. Hypoxia is a pejorative factor regarding aggressiveness, tumor dissemination and resistance to treatments. Therefore, having accurate tools is particularly important.

Oleanolic acid combined with olaparib enhances radiosensitization in triple negative breast cancer and hypoxia imaging with 18F-FETNIM micro PET/CT

The heterogeneity of triple negative breast cancer (TNBC) results in the worst prognosis among breast cancer types, making its treatment strategy very challenging. A recent study showed that oleanolic acid (OA) has a radiosensitizing effect on tumor cells, but it does not show a good clinical effect when used alone in radiotherapy. The cytotoxicity of radiotherapy can be enhanced by modulating DNA repair, so new treatment options are being investigated to inhibit DNA repair pathways and sensitize tumors to radiation. Radiation induces DNA double-strand breaks (DSBs), and inhibition of Poly (ADP-Ribose) polymerase (PARP) can prevent the repair of these lesions. Hence, we evaluated the radiosensitization and the underlying mechanism of combination treatment with OA and olaparib in TNBC. Meanwhile, tumor hypoxia was monitored with ¹⁸F-Fluoroerythronitroimidazole (FETNIM) positron emission tomography/computed tomography (PET/CT) during radiosensitization therapy. Here, we found that OA and olaparib in combination with radiotherapy significantly inhibited cell proliferation compared with other groups. The results were observed using colony formation assays [sensitization enhancement ratios (SER) 1.16-1.65]. In vivo, tumor growth was significantly delayed in transplanted tumors receiving irradiation (IR) with OA and olaparib. ¹⁸F-FETNIM PET/CT can be utilized for tumor hypoxia monitoring and radiosensitization response evaluation. In conclusion, these results suggest that the combination of OA and olaparib with IR enhances the inhibition of MDA-MB-231 in cell culture and in mice, providing a potentially novel combination for the effective treatment of TNBC patients.

Imaging of Tumor Hypoxia With Radionuclide-Labeled Tracers for PET

The hypoxic state in a solid tumor refers to the internal hypoxic environment that appears as the tumor volume increases (the maximum radius exceeds 180-200 microns). This state can promote angiogenesis, destroy the balance of the cell’s internal environment, and lead to resistance to radiotherapy and chemotherapy, as well as poor prognostic factors such as metastasis and recurrence. Therefore, accurate quantification, mapping, and monitoring of hypoxia, targeted therapy, and improvement of tumor hypoxia are of great significance for tumor treatment and improving patient survival. Despite many years of development, PET-based hypoxia imaging is still the most widely used evaluation method. This article provides a comprehensive overview of tumor hypoxia imaging using radionuclide-labeled PET tracers. We introduced the mechanism of tumor hypoxia and the reasons leading to the poor prognosis, and more comprehensively included the past, recent and ongoing studies of PET radiotracers for tumor hypoxia imaging. At the same time, the advantages and disadvantages of mainstream methods for detecting tumor hypoxia are summarized.

Hypoxia and its impact on the tumour microenvironment of gastroesophageal cancers

The malfeasant role of the hypoxic tumour microenvironment (TME) in cancer progression was recognized decades ago but the exact mechanisms that augment the hallmarks of cancer and promote treatment resistance continue to be elucidated. Gastroesophageal cancers (GOCs) represent a major burden of worldwide disease, responsible for the deaths of over 1 million people annually. Disentangling the impact of hypoxia in GOCs enables a better overall understanding of the disease pathogenesis while shining a light on novel therapeutic strategies and facilitating precision treatment approaches with the ultimate goal of improving outcomes for patients with these diseases. This review discusses the underlying principles and processes of the hypoxic response and the effect of hypoxia in promoting the hallmarks of cancer in the context of GOCs. We focus on its bidirectional influence on inflammation and how it drives angiogenesis, innate and adaptive immune evasion, metastasis, and the reprogramming of cellular bioenergetics. The contribution of the hypoxic GOC TME to treatment resistance is examined and a brief overview of the pharmacodynamics of hypoxia-targeted therapeutics is given. The principal methods that are used in measuring hypoxia and how they may enhance prognostication or provide rationale for individually tailored management in the case of tumours with significant hypoxic regions are also discussed.

Hypoxia and the phenomenon of immune exclusion

Over the last few years, cancer immunotherapy experienced tremendous developments and it is nowadays considered a promising strategy against many types of cancer. However, the exclusion of lymphocytes from the tumor nest is a common phenomenon that limits the efficiency of immunotherapy in solid tumors. Despite several mechanisms proposed during the years to explain the immune excluded phenotype, at present, there is no integrated understanding about the role played by different models of immune exclusion in human cancers. Hypoxia is a hallmark of most solid tumors and, being a multifaceted and complex condition, shapes in a unique way the tumor microenvironment, affecting gene transcription and chromatin remodeling. In this review, we speculate about an upstream role for hypoxia as a common biological determinant of immune exclusion in solid tumors. We also discuss the current state of ex vivo and in vivo imaging of hypoxic determinants in relation to T cell distribution that could mechanisms of immune exclusion and discover functional-morphological tumor features that could support clinical monitoring.

Hypoxia PET Imaging with [18F]-HX4-A Promising Next-Generation Tracer

Hypoxia—a common feature of the majority of solid tumors—is a negative prognostic factor, as it is associated with invasion, metastasis and therapy resistance. To date, a variety of methods are available for the assessment of tumor hypoxia, including the use of positron emission tomography (PET). A plethora of hypoxia PET tracers, each with its own strengths and limitations, has been developed and successfully validated, thereby providing useful prognostic or predictive information. The current review focusses on [18F]-HX4, a promising next-generation hypoxia PET tracer. After a brief history of its development, we discuss and compare its characteristics with other hypoxia PET tracers and provide an update on its progression into the clinic. Lastly, we address the potential applications of assessing tumor hypoxia using [18F]-HX4, with a focus on improving patient-tailored therapies.

Correlation of hypoxia as measured by fluorine-18 fluoroerythronitroimidazole (18F-FETNIM) PET/CT and overall survival in glioma patients

PURPOSE

Hypoxia is important in the biology of glioma in humans. Positron emission tomography/computed tomography (PET/CT) with a hypoxia tracer offers a noninvasive method to differentiate individual tumor biology and potentially modify treatment for patients with malignancies. The purpose of this study was to determine whether hypoxia, as measured by fluorine-18 fluoroerythronitroimidazole (¹⁸F-FETNIM) PET/CT, was associated with tumor grade, overall survival (OS), and immunohistochemical features related to hypoxia, proliferation, angiogenesis, and the invasion of gliomas.

PROCEDURES

Twenty-five patients with gliomas in whom gross maximal resection could be safely attempted were analyzed. All patients underwent ¹⁸F-FETNIM PET/CT studies before surgery. The maximum standardized uptake value (SUVmax) was obtained from the PET images of tumor tissues. Tumor specimens were stereotactically obtained for the immunohistochemical staining of hypoxia-inducible factor-1 alpha (HIF-1α), Ki-67, vascular endothelial growth factor (VEGF), and matrix metalloproteinase 9 (MMP-9).

RESULTS

A correlation between the SUVmax and glioma grade was found (r = 0.881, P < 0.001). The SUVmax was significantly correlated with the expression of HIF-1α, Ki-67, VEGF, and MMP-9 (r = 0.820, 0.747, 0.606, and 0.727; all P < 0.001). Patients with a high SUVmax had significantly worse 3-year OS than those with a low SUVmax (24.4% vs. 82.1%, P = 0.003).

CONCLUSIONS

¹⁸F-FETNIM PET/CT provides an excellent noninvasive assessment of hypoxia in glioma. It can be used to understand the mechanisms by which hypoxia affects the OS of glioma patients.

Hypoxia with 18F-fluoroerythronitroimidazole integrated positron emission tomography and computed tomography (18F-FETNIM PET/CT) in locoregionally advanced head and neck cancer: Hypoxia changes during chemoradiotherapy and impact on clinical outcome

Hypoxia is a well-recognized biological characteristic to therapy resistance and negative prognostic factor in patients with head and neck squamous cell carcinoma (HNSCC). This study aims to investigate the changes of hypoxia measured by F-fluoroerythronitroimidazole (FETNIM) uptake on integrated positron emission tomography and computed tomography (PET/CT) during chemoradiotherapy and its prognostic value of clinical outcome in locoregionally advanced HNSCC.Thirty-two patients with locoregionally advanced HNSCC who received definitive treatment with concurrent chemoradiotherapy underwent FETNIM PET/CT scans before and after 5 weeks of treatment. The intensity of hypoxia using the maximum standardized uptake value (SUVmax) was evaluated both on primary lesion and metastatic lymph node (MLN). The pre-SUVmax and mid-SUVmax were defined as SUVmax on pre- and mid-FETNIM PET/CT. The local control (LC), regional control (RC), distant metastatic-free survival (DMFS), and overall survival (OS) were collected in patient follow-ups.Mid-SUVmax decreased significantly both in the primary tumor (t = 8.083, P < .001) and MLN (t = 6.808, P < .001) compared to pre-SUVmax. With a median follow-up of 54 months, the 5-year LC, RC, DMFS, and OS rates were 55%, 66.7%, 64.7%, and 55%, respectively, for all of the patients. On univariate analysis, patients with high pre-SUVmax in primary tumor had significantly worse LC (56.3% vs 87.5%, P = .046) and OS (43.8% vs 87.5%, P = .023) than other patients. Patients with high mid-SUVmax had significantly worse DMFS (50% vs 84.6%, P = .049) and OS (33.3% vs 73.1%, P = .028) than other patients. The tumor grade and mid-SUVmax were the significant predictors of OS on multivariate analysis.In this study, hypoxia in tumor significantly decreased during chemoradiotherapy. The persistent hypoxia predicted poor OS. The data provided evidence that FETNIM PET/CT could be used dynamically for selecting appropriate patients and optimal timing of hypoxia-adapted therapeutic regimens.

PET/CT in radiation oncology

The progressive integration of positron emission tomography/computed tomography (PET/CT) imaging in radiation therapy has its rationale in the biological intertumoral and intratumoral heterogeneity of malignant lesions that require the individual adjustment of radiation dose to obtain an effective local tumor control in cancer patients. PET/CT provides information on the biological features of tumor lesions such as metabolism, hypoxia, and proliferation that can identify radioresistant regions and be exploited to optimize treatment plans. Here, we provide an overview of the basic principles of PET-based target volume selection and definition using ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) and then we focus on the emerging strategies of dose painting and adaptive radiotherapy using different tracers. Previous studies provided consistent evidence that integration of ¹⁸F-FDG PET/CT in radiotherapy planning improves delineation of target volumes and reduces the uncertainties and variabilities of anatomical delineation of tumor sites. PET-based dose painting and adaptive radiotherapy are feasible strategies although their clinical implementation is highly demanding and requires strong technical, computational, and logistic efforts. Further prospective clinical trials evaluating local tumor control, survival, and toxicity of these emerging strategies will promote the full integration of PET/CT in radiation oncology.

Hypoxia imaging in upper gastrointestinal tumors and application to radiation therapy

Survival for upper gastrointestinal tumors remains poor, likely in part due to treatment resistance associated with intratumoral hypoxia. In this review, we highlight advances in nuclear medicine imaging that allow for characterization of in vivo tumor hypoxia in esophageal, pancreatic, and liver cancers. Strategies for adaptive radiotherapy in upper gastrointestinal tumors are proposed that would apply information gained through hypoxia imaging to the creation of personalized radiotherapy treatment plans able to overcome hypoxia-induced treatment resistance, minimize treatment-related toxicities, and improve patient outcomes.

Clinical imaging of hypoxia: Current status and future directions

Tissue hypoxia is a key feature of many important causes of morbidity and mortality. In pathologies such as stroke, peripheral vascular disease and ischaemic heart disease, hypoxia is largely a consequence of low blood flow induced ischaemia, hence perfusion imaging is often used as a surrogate for hypoxia to guide clinical diagnosis and treatment. Importantly, ischaemia and hypoxia are not synonymous conditions as it is not universally true that well perfused tissues are normoxic or that poorly perfused tissues are hypoxic. In pathologies such as cancer, for instance, perfusion imaging and oxygen concentration are less well correlated, and oxygen concentration is independently correlated to radiotherapy response and overall treatment outcomes. In addition, the progression of many diseases is intricately related to maladaptive responses to the hypoxia itself. Thus there is potentially great clinical and scientific utility in direct measurements of tissue oxygenation. Despite this, imaging assessment of hypoxia in patients is rarely performed in clinical settings. This review summarises some of the current methods used to clinically evaluate hypoxia, the barriers to the routine use of these methods and the newer agents and techniques being explored for the assessment of hypoxia in pathological processes.

Longitudinal PET imaging of tumor hypoxia during the course of radiotherapy

Hypoxia results from an imbalance between oxygen supply and consumption. It is a common phenomenon in solid malignant tumors such as head and neck cancer. As hypoxic cells are more resistant to therapy, tumor hypoxia is an indicator for poor prognosis. Several techniques have been developed to measure tissue oxygenation. These are the Eppendorf O2 polarographic needle electrode, immunohistochemical analysis of endogenous (e.g., hypoxia-inducible factor-1α (HIF-1a)) and exogenous markers (e.g., pimonidazole) as well as imaging methods such as functional magnetic resonance imaging (e.g., blood oxygen level dependent (BOLD) imaging, T1-weighted imaging) and hypoxia positron emission tomography (PET). Among the imaging modalities, only PET is sufficiently validated to detect hypoxia for clinical use. Hypoxia PET tracers include 18F-fluoromisonidazole (FMISO), the most commonly used hypoxic marker, 18F-flouroazomycin arabinoside (FAZA), 18Ffluoroerythronitroimidazole (FETNIM), 18F-2-nitroimidazolpentafluoropropylacetamide (EF5) and 18F-flortanidazole (HX4). As technical development provides the opportunity to increase the radiation dose to subregions of the tumor, such as hypoxic areas, it has to be ensured that these regions are stable not only from imaging to treatment but also through the course of radiotherapy. The aim of this review is therefore to characterize the behavior of tumor hypoxia during radiotherapy for the whole tumor and for subregions by using hypoxia PET tracers, with focus on head and neck cancer patients.

Imaging of Tumor Characteristics and Molecular Pathways With PET: Developments Over the Last Decade Toward Personalized Cancer Therapy

PURPOSE

Improvements in personalized therapy are made possible by the advances in molecular biology that led to developments in molecular imaging, allowing highly specific in vivo imaging of biological processes. Positron emission tomography (PET) is the most specific and sensitive imaging technique for in vivo molecular targets and pathways, offering quantification and evaluation of functional properties of the targeted anatomy.

MATERIALS AND METHODS

This work is an integrative research review that summarizes and evaluates the accumulated current status of knowledge of recent advances in PET imaging for cancer diagnosis and treatment, concentrating on novel radiotracers and evaluating their advantages and disadvantages in cancer characterization. Medline search was conducted, limited to English publications from 2007 onward. Identified manuscripts were evaluated for most recent developments in PET imaging of cancer hypoxia, angiogenesis, proliferation, and clonogenic cancer stem cells (CSC).

RESULTS

There is an expansion observed from purely metabolic-based PET imaging toward antibody-based PET to achieve more information on cancer characteristics to identify hypoxia, proangiogenic factors, CSC, and others. ⁶⁴Cu-ATSM, for example, can be used both as a hypoxia and a CSC marker.

CONCLUSIONS

Progress in the field of functional imaging will possibly lead to more specific tumor targeting and personalized treatment, increasing tumor control and improving quality of life.

Hypoxia imaging with 18F-FAZA PET/CT predicts radiotherapy response in esophageal adenocarcinoma xenografts

Background

Esophageal cancer is an aggressive disease with poor survival rates. A more patient-tailored approach based on predictive biomarkers could improve outcome. We aimed to predict radiotherapy (RT) response by imaging tumor hypoxia with ¹⁸F-FAZA PET/CT in an esophageal adenocarcinoma (EAC) mouse model. Additionally, we investigated the radiosensitizing effect of the hypoxia modifier nimorazole in vitro and in vivo.

Methods

In vitro MTS cell proliferation assays (OACM5 1.C SC1, human EAC cell line) were performed under normoxic and hypoxic (< 1%) conditions: control (100 μL PBS), nimorazole, irradiation (5, 10 or 20 Gy) with or without nimorazole. In vivo, subcutaneous xenografts were induced in nude mice (OACM5 1.C SC1). Treatment was given daily for 5 consecutive days: (A) control (600 μl NaCl 0.9% intraperitoneally (IP)) (N = 5, n = 7), (B) RT (5 Gy/d) (N = 11, n = 20), (C) combination (nimorazole (200 mg/kg/d IP) 30 min before RT) (N = 13, n = 21). N = number of mice, n = number of tumors. ¹⁸F-FAZA PET/CT was performed before treatment and tumor to background (T/B) ratios were calculated. Relative tumor growth was calculated and tumor sections were examined histologically (hypoxia, proliferation).

Results

A T/B ≥ 3.59 on pre-treatment ¹⁸F-FAZA PET/CT was predictive for worse RT response (sensitivity 92.3%, specificity 71.4%). Radiation was less effective in hypoxic tumors (T/B ≥ 3.59) compared to normoxic tumors (T/B < 3.59) (P = 0.0025). In vitro, pre-treatment with nimorazole significantly decreased hypoxic radioresistance (P < 0.01) while in vivo, nimorazole enhanced the efficacy of RT to suppress cancer cell proliferation in hypoxic tumor areas (Ki67, P = 0.064), but did not affect macroscopic tumor growth.

Conclusions

Tumor tissue hypoxia as measured with ¹⁸F-FAZA PET/CT is predictive for RT response in an EAC xenograft model. The radiosensitizing effect of nimorazole was questionable and requires further investigation.

Electronic supplementary material

The online version of this article (10.1186/s13014-018-0984-3) contains supplementary material, which is available to authorized users.

Repeatability of tumour hypoxia imaging using [18F]EF5 PET/CT in head and neck cancer

Purpose

Hypoxia contributes to radiotherapy resistance and more aggressive behaviour of several types of cancer. This study was designed to evaluate the repeatability of intratumour uptake of the hypoxia tracer [¹⁸F]EF5 in paired PET/CT scans.

Methods

Ten patients with newly diagnosed head and neck cancer (HNC) received three static PET/CT scans before chemoradiotherapy: two with [¹⁸F]EF5 a median of 7 days apart and one with [¹⁸F]FDG. Metabolically active primary tumour volumes were defined in [¹⁸F]FDG images and transferred to co-registered [¹⁸F]EF5 images for repeatability analysis. A tumour-to-muscle uptake ratio (TMR) of 1.5 at 3 h from injection of [¹⁸F]EF5 was used as a threshold representing hypoxic tissue.

Results

In 10 paired [¹⁸F]EF5 PET/CT image sets, SUVmean, SUVmax, and TMR showed a good correlation with the intraclass correlation coefficients of 0.81, 0.85, and 0.87, respectively. The relative coefficients of repeatability for these parameters were 15%, 17%, and 10%, respectively. Fractional hypoxic volumes of the tumours in the repeated scans had a high correlation using the Spearman rank correlation test (r = 0.94). In a voxel-by-voxel TMR analysis between the repeated scans, the mean of Pearson correlation coefficients of individual patients was 0.65. The mean (± SD) difference of TMR in the pooled data set was 0.03 ± 0.20.

Conclusion

Pretreatment [¹⁸F]EF5 PET/CT within one week shows high repeatability and is feasible for the guiding of hypoxia-targeted treatment interventions in HNC.

Hypoxia and hypoxia response-associated molecular markers in esophageal cancer: A systematic review

PURPOSE

In this systematic review, the existing evidence of available hypoxia-associated molecular response biomarkers in esophageal cancer (EC) patients is summarized and set into the context of the role of hypoxia in the prediction of esophageal cancer, treatment response and treatment outcome.

METHODS

A systematic literature search was performed in Web of Science, MEDLINE, and PubMed databases using the keywords: hypoxia, esophagus, cancer, treatment outcome and treatment response. Eligible publications were independently evaluated by two reviewers. In total, 22 out of 419 records were included for systematic review. The described search strategy was applied weekly, with the last update being performed on April 3rd, 2017.

RESULTS

In esophageal cancer, several (non-)invasive biomarkers for hypoxia could be identified. Independent prognostic factors for treatment response include HIF-1α, CA IX, GLUT-1 overexpression and elevated uptake of the PET-tracer ¹⁸F-fluoroerythronitroimidazole (¹⁸F-FETNIM). Hypoxia-associated molecular responses represents a clinically relevant phenomenon in esophageal cancer and detection of elevated levels of hypoxia-associated biomarkers and tends to be associated with poor treatment outcome (i.e., overall survival, disease-free survival, complete response and local control).

CONCLUSION

Evaluation of tumor micro-environmental conditions, such as intratumoral hypoxia, is important to predict treatment outcome and efficacy. Promising non-invasive imaging-techniques have been suggested to assess tumor hypoxia and hypoxia-associated molecular responses. However, extensive validation in EC is lacking. Hypoxia-associated markers that are independent prognostic factors could potentially provide targets for novel treatment strategies to improve treatment outcome. For personalized hypoxia-guided treatment, safe and reliable makers for tumor hypoxia are needed to select suitable patients.

Molecular mechanisms of hypoxia in cancer

PURPOSE

Hypoxia is a condition of insufficient oxygen to support metabolism which occurs when the vascular supply is interrupted, or when a tumour outgrows its vascular supply. It is a negative prognostic factor due to its association with an aggressive tumour phenotype and therapeutic resistance. This review provides an overview of hypoxia imaging with Positron emission tomography (PET), with an emphasis on the biological relevance, mechanism of action, highlighting advantages, and limitations of the currently available hypoxia radiotracers.

METHODS

A comprehensive PubMed literature search was performed, identifying articles relating to biological significance and measurement of hypoxia, MRI methods, and PET imaging of hypoxia in preclinical and clinical settings, up to December 2016.

RESULTS

A variety of approaches have been explored over the years for detecting and monitoring changes in tumour hypoxia, including regional measurements with oxygen electrodes placed under CT guidance, MRI methods that measure either oxygenation or lactate production consequent to hypoxia, different nuclear medicine approaches that utilise imaging agents the accumulation of which is inversely related to oxygen tension, and optical methods. The advantages and disadvantages of these approaches are reviewed, along with individual strategies for validating different imaging methods. PET is the preferred method for imaging tumour hypoxia due to its high specificity and sensitivity to probe physiological processes in vivo, as well as the ability to provide information about intracellular oxygenation levels.

CONCLUSION

Even though hypoxia could have significant prognostic and predictive value in the clinic, the best method for hypoxia assessment has in our opinion not been realised.

Imaging the Tumor Microenvironment

The tumor microenvironment consists of tumor, stromal, and immune cells, as well as extracellular milieu. Changes in numbers of these cell types and their environments have an impact on cancer growth and metastasis. Non-invasive imaging of aspects of the tumor microenvironment can provide important information on the aggressiveness of the cancer, whether or not it is metastatic, and can also help to determine early response to treatment. This chapter provides an overview on non-invasive in vivo imaging in humans and mouse models of various cell types and physiological parameters that are unique to the tumor microenvironment. Current clinical imaging and research investigation are in the areas of nuclear imaging (positron emission tomography (PET) and single photon emission computed tomography (SPECT)), magnetic resonance imaging (MRI) and optical (near infrared (NIR) fluorescence) imaging. Aspects of the tumor microenvironment that have been imaged by PET, MRI and/or optical imaging are tumor associated inflammation (primarily macrophages and T cells), hypoxia, pH changes, as well as enzymes and integrins that are highly prevalent in tumors, stroma and immune cells. Many imaging agents and strategies are currently available for cancer patients; however, the investigation of novel avenues for targeting aspects of the tumor microenvironment in pre-clinical models of cancer provides the cancer researcher with a means to monitor changes and evaluate novel treatments that can be translated into the clinic.

Predicting Response to Neoadjuvant Chemoradiotherapy in Esophageal Cancer with Textural Features Derived from Pretreatment 18F-FDG PET/CT Imaging

Adequate prediction of tumor response to neoadjuvant chemoradiotherapy (nCRT) in esophageal cancer (EC) patients is important in a more personalized treatment. The current best clinical method to predict pathologic complete response is SUV_max in ¹⁸F-FDG PET/CT imaging. To improve the prediction of response, we constructed a model to predict complete response to nCRT in EC based on pretreatment clinical parameters and ¹⁸F-FDG PET/CT-derived textural features. Methods: From a prospectively maintained single-institution database, we reviewed 97 consecutive patients with locally advanced EC and a pretreatment ¹⁸F-FDG PET/CT scan between 2009 and 2015. All patients were treated with nCRT (carboplatin/paclitaxel/41.4 Gy) followed by esophagectomy. We analyzed clinical, geometric, and pretreatment textural features extracted from both ¹⁸F-FDG PET and CT. The current most accurate prediction model with SUV_max as a predictor variable was compared with 6 different response prediction models constructed using least absolute shrinkage and selection operator regularized logistic regression. Internal validation was performed to estimate the model's performances. Pathologic response was defined as complete versus incomplete response (Mandard tumor regression grade system 1 vs. 2-5). Results: Pathologic examination revealed 19 (19.6%) complete and 78 (80.4%) incomplete responders. Least absolute shrinkage and selection operator regularization selected the clinical parameters: histologic type and clinical T stage, the ¹⁸F-FDG PET-derived textural feature long run low gray level emphasis, and the CT-derived textural feature run percentage. Introducing these variables to a logistic regression analysis showed areas under the receiver-operating-characteristic curve (AUCs) of 0.78 compared with 0.58 in the SUV_max model. The discrimination slopes were 0.17 compared with 0.01, respectively. After internal validation, the AUCs decreased to 0.74 and 0.54, respectively. Conclusion: The predictive values of the constructed models were superior to the standard method (SUV_max). These results can be considered as an initial step in predicting tumor response to nCRT in locally advanced EC. Further research in refining the predictive value of these models is needed to justify omission of surgery.

Impact of PET/CT on radiation treatment in patients with esophageal cancer: A systematic review

PURPOSE

With the advances in radiotracers, positron emission tomography/computed tomography (PET/CT) is recognized as a useful adjunct to anatomic imaging with CT, MRI and endoscopic ultrasonography (EUS). The objective of this review was to comprehensively analyze the roles of PET/CT for the radiotherapy of esophageal cancer.

METHODS

In this review, we focused on issues concerning the application of PET/CT in TNM staging, target volume delineation and response to therapy, both for the primary tumor and regional lymph nodes. Furthermore, the following questions were addressed: how does PET/CT guide appropriate treatment protocols, how does it allow accurate tumor delineation and how does it guide prognosis and future treatment decisions.

RESULTS AND CONCLUSION

For the staging of esophageal cancer, PET/CT played a crucial role in exploring distant malignant lymph nodes and metastasis with high sensitivity, specificity and accuracy. PET/CT using different radiotracer provided a serial of thresholding methods based on standardized uptake value (SUV) to assist in auto-contouring the gross tumor volume (GTV). The change in SUV may offer a potential paradigm of personalized treatment to definitive chemoradiotherapy (CRT). In total, PET/CT has sought to further optimize radiotherapy treatment planning for patients with esophageal cancer.

A Comparative Study of Noninvasive Hypoxia Imaging with 18F-Fluoroerythronitroimidazole and 18F-Fluoromisonidazole PET/CT in Patients with Lung Cancer

PURPOSE

This is a clinical study to compare noninvasive hypoxia imaging using 18F-fluoroerythronitroimidazole (18F-FETNIM) and 18F-fluoromisonidazole (18F-FMISO) positron emission tomography/computed tomography (PET/CT) in patients with inoperable stages III-IV lung cancer.

METHODS

A total of forty-two patients with inoperable stages III-IV lung cancer underwent 18F-FETNIM PET/CT (n = 18) and 18F-FMISO PET/CT (n = 24) before chemo/radiation therapy. The standard uptake values (SUVs) of malignant and normal tissues depict 18F-FETNIM PET/CT and 18F-FMISO PET/CT uptake. Tumor-to-blood ratios (T/B) were used to quantify hypoxia.

RESULTS

All patients with lung cancer underwent 18F-FETNIM PET/CT and 18F-FMISO PET/CT successfully. Compared to 18F-FMISO, 18F-FETNIM showed similar uptake in muscle, thyroid, spleen, pancreas, heart, lung and different uptake in blood, liver, and kidney. Significantly higher SUV and T/B ratio with 18F-FMISO (2.56±0.77, 1.98±0.54), as compared to 18F-FETNIM (2.12±0.56, 1.42±0.33) were seen in tumor, P = 0.022, <0.001. For the patients with different histopathological subtypes, no significant difference of SUV (or T/B ratio) was observed both in 18F-FMISO and 18F-FETNIM in tumor. A significantly different SUV (or T/B ratio) was detected between < = 2cm, 2~5cm, and >5cm groups in 18F-FMISO PET/CT, P = 0.015 (or P = 0.029), whereas no difference was detected in 18F-FMISO PET/CT, P = 0.446 (or P = 0.707). Both 18F-FETNIM and 18F-FMISO showed significantly higher SUVs (or T/B ratios) in stage IV than stage III, P = 0.021, 0.013 (or P = 0.032, 0.02).

CONCLUSION

18F-FMISO showed significantly higher uptake than 18F-FETNIM in tumor/non-tumor ratio and might be a better hypoxia tracer in lung cancer.

Synthesis and radiolabeling of (64)Cu-labeled 2-nitroimidazole derivative (64)Cu-BMS2P2 for hypoxia imaging

The objective of this study was to develop a positron emission tomography (PET) probe with hypoxia targeting specificity and a relatively long half-life. The synthesis, (64)Cu-labeling in vitro and in vivo study of the novel 2-nitroimidazole complex (64)Cu-BMS2P2 is presented in this study. The hypoxia targeting capacity of (64)Cu-BMS2P2 in vitro was evaluated and compared with the (64)Cu-BMS181321, and confirmed by PET imaging in vivo and immunohistochemistry for carbonic anhydrase 9 (CA9) in a tumor mouse model. These results suggest that (64)Cu-BMS2P2 is a promising candidate for PET hypoxia imaging and worthy of further investigations in dynamic hypoxia imaging.

Hypoxia as a Biomarker and for Personalized Radiation Oncology

Tumor hypoxia is a clinically relevant cause of radiation resistance. Direct measurements of tumor oxygenation have been performed predominantly with the Eppendorf histograph and these have defined the reduced prognosis after radiotherapy in poorly oxygenated tumors, especially head-and-neck cancer, cervix cancer and sarcoma. Exogenous markers have been used for immunohistochemical detection of hypoxic tumor areas (pimonidazole) or for positron-emission tomography (PET) imaging (misonidazole). Overexpression of hypoxia-related proteins such as hypoxia-inducible factor-1α (HIF-1α) has also been linked to poor prognosis after radiotherapy and such proteins are considered as potential endogenous hypoxia markers.

Optimizing hypoxia detection and treatment strategies

Clinical studies using Eppendorf needle sensors have invariably documented the resistance of hypoxic human tumors to therapy. These studies first documented the need for individual patient measurement of hypoxia, as hypoxia varied from tumor to tumor. Furthermore, hypoxia in sarcomas and cervical cancer leads to distant metastasis or local or regional spread, respectively. For various reasons, the field has moved away from direct needle sensor oxygen measurements to indirect assays (hypoxia-inducible factor-related changes and bioreductive metabolism) and the latter can be imaged noninvasively. Many of hypoxia's detrimental therapeutic effects are reversible in mice but little treatment improvement in hypoxic human tumors has been seen. The question is why? What factors cause human tumors to be refractory to antihypoxia strategies? We suggest the primary cause to be the complexity of hypoxia formation and its characteristics. Three basic types of hypoxia exist, encompassing various diffusional (distance from perfused vessel), temporal (on or off cycling), and perfusional (blood flow efficiency) limitations. Surprisingly, there is no current information on their relative prevalence in human tumors and even animal models. This is important because different hypoxia subtypes are predicted to require different diagnostic and therapeutic approaches, but the implications of this remain unknown. Even more challenging, no agreement exists for the best way to measure hypoxia. Some results even suggest that hypoxia is unlikely to be targetable therapeutically. In this review, the authors revisit various critical aspects of this field that are sometimes forgotten or misrepresented in the recent literature. As most current noninvasive imaging studies involve PET-isotope-labeled 2-nitroimidazoles, we emphasize key findings made in our studies using 2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)acetamide (EF5) and F-18-labeled EF5. These show the importance of differentiating hypoxia subtypes, optimizing drug pharmacology, ensuring drug and isotope stability, identifying key biochemical and physiological variables in tumors, and suggesting therapeutic strategies that are most likely to succeed.

Feasibility and repeatability of PET with the hypoxia tracer [(18)F]HX4 in oesophageal and pancreatic cancer

BACKGROUND AND PURPOSE

To investigate the feasibility and to determine the repeatability of recurrent [(18)F]HX4 PET scans in patients with oesophageal (EC) and pancreatic (PC) cancer.

MATERIALS AND METHODS

32 patients were scanned in total; seven patients (4 EC/3 PC) were scanned 2, 3 and 4h post injection (PI) of [(18)F]HX4 and 25 patients (15 EC/10 PC) were scanned twice 3.5h PI, on two separate days (median 4, range 1-9days). Maximum tumour to background ratio (TBRmax) and the tumour hypoxic volume (HV) (TBR>1.0) were calculated. Repeatability was assessed using Bland-Altman analysis. Agreement in localization was calculated as the distance between the centres of mass in the HVs.

RESULTS

For EC, the TBRmax in the tumour (mean±SD) was 1.87±0.46 with a coefficient of repeatability (CoR) of 0.53 (28% of mean). The HV ranged from 3.4 to 98.8ml with a CoR of 5.1ml. For PC, the TBRmax was 1.72±0.23 with a CoR of 0.27 (16% of mean). The HV ranged from 4.6 to 104.0ml with a CoR of 7.8ml. The distance between the centres of mass in the HV was 2.2±1.3mm for EC and 2.1±1.5mm for PC.

CONCLUSIONS

PET scanning with [(18)F]HX4 was feasible in both EC and PC patients. Amount and location of elevated [(18)F]HX4 uptake showed good repeatability, suggesting [(18)F]HX4 PET could be a promising tool for radiation therapy planning and treatment response monitoring in EC and PC patients.

Imaging tumour hypoxia with positron emission tomography

Hypoxia, a hallmark of most solid tumours, is a negative prognostic factor due to its association with an aggressive tumour phenotype and therapeutic resistance. Given its prominent role in oncology, accurate detection of hypoxia is important, as it impacts on prognosis and could influence treatment planning. A variety of approaches have been explored over the years for detecting and monitoring changes in hypoxia in tumours, including biological markers and noninvasive imaging techniques. Positron emission tomography (PET) is the preferred method for imaging tumour hypoxia due to its high specificity and sensitivity to probe physiological processes in vivo, as well as the ability to provide information about intracellular oxygenation levels. This review provides an overview of imaging hypoxia with PET, with an emphasis on the advantages and limitations of the currently available hypoxia radiotracers.

Positron emission tomography to assess hypoxia and perfusion in lung cancer

In lung cancer, tumor hypoxia is a characteristic feature, which is associated with a poor prognosis and resistance to both radiation therapy and chemotherapy. As the development of tumor hypoxia is associated with decreased perfusion, perfusion measurements provide more insight into the relation between hypoxia and perfusion in malignant tumors. Positron emission tomography (PET) is a highly sensitive nuclear imaging technique that is suited for non-invasive in vivo monitoring of dynamic processes including hypoxia and its associated parameter perfusion. The PET technique enables quantitative assessment of hypoxia and perfusion in tumors. To this end, consecutive PET scans can be performed in one scan session. Using different hypoxia tracers, PET imaging may provide insight into the prognostic significance of hypoxia and perfusion in lung cancer. In addition, PET studies may play an important role in various stages of personalized medicine, as these may help to select patients for specific treatments including radiation therapy, hypoxia modifying therapies, and antiangiogenic strategies. In addition, specific PET tracers can be applied for monitoring therapy. The present review provides an overview of the clinical applications of PET to measure hypoxia and perfusion in lung cancer. Available PET tracers and their characteristics as well as the applications of combined hypoxia and perfusion PET imaging are discussed.

The application of functional imaging techniques to personalise chemoradiotherapy in upper gastrointestinal malignancies

Functional imaging gives information about physiological heterogeneity in tumours. The utility of functional imaging tests in providing predictive and prognostic information after chemoradiotherapy for both oesophageal cancer and pancreatic cancer will be reviewed. The benefit of incorporating functional imaging into radiotherapy planning is also evaluated. In cancers of the upper gastrointestinal tract, the vast majority of functional imaging studies have used (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET). Few studies in locally advanced pancreatic cancer have investigated the utility of functional imaging in risk-stratifying patients or aiding target volume definition. Certain themes from the oesophageal data emerge, including the need for a multiparametric assessment of functional images and the added value of response assessment rather than relying on single time point measures. The sensitivity and specificity of FDG-PET to predict treatment response and survival are not currently high enough to inform treatment decisions. This suggests that a multimodal, multiparametric approach may be required. FDG-PET improves target volume definition in oesophageal cancer by improving the accuracy of tumour length definition and by improving the nodal staging of patients. The ideal functional imaging test would accurately identify patients who are unlikely to achieve a pathological complete response after chemoradiotherapy and would aid the delineation of a biological target volume that could be used for treatment intensification. The current limitations of published studies prevent integrating imaging-derived parameters into decision making on an individual patient basis. These limitations should inform future trial design in oesophageal and pancreatic cancers.

Usefulness of 64Cu-ATSM in head and neck cancer: a preliminary prospective study

AIMS

Cu-diacetyl-bis(N4-methylthiosemicarbazone) (Cu-ATSM) is a hypoxia-avid, positron emitter radiotracer. The primary aim of this study is to assess the efficacy of pretherapy Cu-ATSM PET/CT as a prognostic factor of response to therapy. The secondary aims are to investigate if there is a difference between early and late PET/CT scans and if there is a difference between the biologic tumor volume (BTV) in radiotherapy treatment planning calculated between Cu-ATSM and F-FDG, and to assess if Cu-ATSM is a prognostic marker of disease progression.

METHODS

Eleven patients with head and neck cancer treated with chemoradiotherapy were enrolled prospectively; both Cu-ATSM and F-FDG PET/CT scans before and after treatment were obtained. The Cu-ATSM scans were performed after 1 hour (early) and 16 hours (late).

RESULTS

All patients had stage III or IV squamous cell head and neck cancer; 7 of 11 patients had nodal metastasis, and 22 cancer foci were detected with Cu-ATSM. SUVmax was 16.2 ± 7.9, and there was no significant SUVmax difference between early and late imaging. F-FDG SUVmax before therapy was 15.6 ± 9.4, whereas F-FDG SUVmax after therapy was 1.5 ± 1.2. Sensitivity and specificity values of Cu-ATSM calculated with receiver operating characteristic curves were 100% and 50% considering the SUVmax and 100% and 33% considering the volume, respectively. No difference has been found between the BTV contoured with Cu-ATSM and F-FDG.

CONCLUSIONS

The Cu-ATSM scans showed high sensitivity but low specificity in predicting neoadjuvant chemoradiotherapy response. No difference was noted between early and late scans. F-FDG and Cu-ATSM provided similar results about delineation of BTV.

Hypoxia imaging with 18F-fluoroerythronitroimidazole integrated PET/CT and immunohistochemical studies in non-small cell lung cancer

PURPOSE

(18)F-fluoroerythronitroimidazole ((18)F-FETNIM) PET/CT allows a noninvasive assessment of tumor hypoxia. The purpose of this study was to evaluate a noninvasive and simplicity parameter for quantization of (18)F-FETNIM uptake with expectations to predict survival in non-small cell lung cancer surgical patients and investigate the relationship between (18)F-FETNIM uptake and molecular markers related to hypoxia, glucose metabolism, and angiogenesis.

PATIENTS AND METHODS

Thirty-two patients with biopsy-proven non-small cell lung cancer for surgical treatment were enrolled from March 2007 to February 2011. All patients had PET/CT studies with (18)F-FETNIM and subsequently underwent surgery. Twenty-five patients had stage II disease of surgical staging only for statistical analysis. The tumor-to-mediastinum (T/Me) ratio was calculated and correlated with survival and immunohistochemical staining of hypoxia inducible factor 1α (HIF-1α), glucose transporter 1 (GLUT-1), and vascular endothelial growth factor (VEGF).

RESULTS

The actuarial survival was worse for patients showing a high T/Me ratio, the best discriminative cutoff value being 1.9. A statistically significant worse survival was noted in patients having a tumor with a T/Me ratio of 1.9 or greater, compared with patients showing a tumor with a T/Me ratio of less than 1.9, a 3-year survival of 43.8% and 88.9%, respectively (P = 0.034). There was a positive correlation between T/Me ratio and HIF-1α (P = 0.023), GLUT-1 (P = 0.035), and VEGF (P = 0.042).

CONCLUSIONS

T/Me ratio provides a noninvasive parameter for quantization of (18)F-FETNIM uptake on PET/CT. T/Me ratio is correlated with a worse outcome and with the expression of HIF-1α, GLUT-1, and VEGF, all up-regulated under hypoxic conditions.

Pilot study of PET imaging of 124I-iodoazomycin galactopyranoside (IAZGP), a putative hypoxia imaging agent, in patients with colorectal cancer and head and neck cancer

BACKGROUND

Hypoxia within solid tumors confers radiation resistance and a poorer prognosis. 124I-iodoazomycin galactopyranoside (124I-IAZGP) has shown promise as a hypoxia radiotracer in animal models. We performed a clinical study to evaluate the safety, biodistribution, and imaging characteristics of 124I-IAZGP in patients with advanced colorectal cancer and head and neck cancer using serial positron emission tomography (PET) imaging.

METHODS

Ten patients underwent serial whole-torso (head/neck to pelvis) PET imaging together with multiple whole-body counts and blood sampling. These data were used to generate absorbed dose estimates to normal tissues for 124I-IAZGP. Tumors were scored as either positive or negative for 124I-IAZGP uptake.

RESULTS

There were no clinical toxicities or adverse effects associated with 124I-IAZGP administration. Clearance from the whole body and blood was rapid, primarily via the urinary tract, with no focal uptake in any parenchymal organ. The tissues receiving the highest absorbed doses were the mucosal walls of the urinary bladder and the intestinal tract, in particular the lower large intestine. All 124I-IAZGP PET scans were interpreted as negative for tumor uptake.

CONCLUSIONS

It is safe to administer 124I-IAZGP to human subjects. However, there was insufficient tumor uptake to support a clinical role for 124I-IAZGP PET in colorectal cancer and head and neck cancer patients.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00588276.

PET of hypoxia: current and future perspectives

In the past 25 y, a large amount of clinical experience with hypoxia PET tracers has accumulated. This article discusses recent improvements in image acquisition protocols and tracer pharmacology that have resulted in improved understanding of the underlying physiologic processes. The widespread clinical adoption of hypoxia PET tracers will depend largely on their utility in treatment prescription and in outcome monitoring. The establishment and validation of hypoxia-directed treatment protocols are still under development, and it is envisaged that the design and use of future hypoxia PET tracers will develop as part of this process.

Innovation in cancer imaging

Cancer is rapidly becoming the worldwide leading cause of premature death. Iconographic techniques have traditionally provided information on tumor anatomy. The recent introduction of functional and molecular imaging techniques allows probing tumor physiology and biology in addition to mere anatomical description. In addition to the research implications, these novel imaging techniques offer early response assessment and target visualization which, in the era of personalized medicine, may offer significant advances in cancer therapy. Here, we provide an overview of the most important developments in cancer imaging, with a focus on the clinical applications.