The prognostic value of pimonidazole and tumour pO2 in human cervix carcinomas after radiation therapy: A prospective international multi-center study

A Population-Based Tumor-Volume Model for Head and Neck Cancer During Radiation Therapy With a Dynamic Oxygenated Compartment

PURPOSE

With the coming era of digital medicine and healthcare technology, mathematical modeling of tumors has become a key step to optimize and realize precision radiation therapy. The purpose of this study was to develop a mathematical model for simulating the change of head and neck (HN) tumor volume during radiation therapy.

METHODS AND MATERIALS

A formula was developed to describe the dynamic change of oxygenated compartment within a tumor, which was combined with the lethal lesions model to describe various cell processes during radiation therapy, including potentially lethal lesion repair and misrepair, cell proliferation/loss, and tumor reoxygenation. Parameter sensitivity analysis was performed to evaluate the impacts of lesion- and repair-related biological factors on radiation therapy outcomes.

RESULTS

We tested our model on 14 available patients with HN cancer and compared the performance with 3 other models. The mean error of our model for the 12 good fit cases was 12.2%, which is considerably smaller than that of the linear quadratic model (19.7%), the generalized linear quadratic model (19.1%), and a 4-level cell population model (16.6%). Correlation analysis results revealed that for small tumors, there was a positive correlation (correlation coefficient r=0.9416) between hypoxic fraction (hf) and tumor volume, whereas the correlation became negative and not significant (r=-0.4365) for large tumors. It is demonstrated from sensitivity analysis that the production rate of lethal lesions (ηl) has a far greater impact on tumor volume than other parameters. The hf had an insignificant impact on tumor volume but had a notable influence on the volume of surviving cells. The final volume of surviving cells athf=0.5 was almost 8 ×102 times that of hf=0.01. The potentially lethal lesion-related parameters (the production rate of potentially lethal lessions per unit dose ηpl, the rate of correct repair per unit time εpl, and the rate of binary misrepair per unit time ε2pl) had rather small impacts (<1%) on both tumor volume and the volume of surviving cells, which indicates that the repaired and misrepaired sublethal cells only take up a small portion of the total cancer cell population.

CONCLUSIONS

A population-based tumor-volume model for HN cancer during radiation therapy with a dynamic oxygenated compartment was developed in this study. Comprehensively considering the damage process of tumor cells caused by radiation therapy, the accurate prediction of the volume change of HN tumors during treatment was revealed. Meanwhile, various cell activities and their principles in the process of antitumor treatment were reflected, which has positive clinical reference significance for radiobiology.

18F-Fluoroazomycin Arabinoside (FAZA) PET/MR as a Biomarker of Hypoxia in Rectal Cancer: A Pilot Study

Tumor hypoxia is a negative prognostic factor in many tumors and is predictive of metastatic spread and poor responsiveness to both chemotherapy and radiotherapy. Purpose: To assess the feasibility of using 18F-Fluoroazomycin arabinoside (FAZA) PET/MR to image tumor hypoxia in patients with locally advanced rectal cancer (LARC) prior to and following neoadjuvant chemoradiotherapy (nCRT). The secondary objective was to compare different reference tissues and thresholds for tumor hypoxia quantification. Patients and Methods: Eight patients with histologically proven LARC were included. All patients underwent 18F-FAZA PET/MR prior to initiation of nCRT, four of whom also had a second scan following completion of nCRT and prior to surgery. Tumors were segmented using T2-weighted MR. Each voxel within the segmented tumor was defined as hypoxic or oxic using thresholds derived from various references: ×1.0 or ×1.2 SUVmean of blood pool [BP] or left ventricle [LV] and SUVmean +3SD for gluteus maximus. Correlation coefficient (CoC) between HF and tumor SUVmax/reference SUVmean TRR for the various thresholds was calculated. Hypoxic fraction (HF), defined as the % hypoxic voxels within the tumor volume was calculated for each reference/threshold. Results: For all cases, baseline and follow-up, the CoCs for gluteus maximus and for BP and LV (×1.0) were 0.241, 0.344, and 0.499, respectively, and HFs were (median; range) 16.6% (2.4-33.8), 36.8% (0.3-72.9), and 30.7% (0.8-55.5), respectively. For a threshold of ×1.2, the CoCs for BP and LV as references were 0.611 and 0.838, respectively, and HFs were (median; range) 10.4% (0-47.6), and 4.3% (0-20.1%), respectively. The change in HF following nCRT ranged from (-18.9%) to (+54%). Conclusions: Imaging of hypoxia in LARC with 18F-FAZA PET/MR is feasible. Blood pool as measured in the LV appears to be the most reliable reference for calculating the HF. There is a wide range of HF and variable change in HF before and after nCRT.

Hypoxia A Typical Target in Human Lung Cancer Therapy

Lung cancer (LC) is the leading cause of cancer-related death globally. Comprehensive knowledge of the cellular and molecular etiology of LC is perilous for the development of active treatment approaches. Hypoxia in cancer is linked with malignancy, and its phenotype is implicated in the hypoxic reaction, which is being studied as a prospective cancer treatment target. The hypervascularization of the tumor is the main feature of human LC, and hypoxia is a major stimulator of neo-angiogenesis. It was seen that low oxygen levels in human LC are a critical aspect of this lethal illness. However, as there is a considerable body of literature espousing the presumed functional relevance of hypoxia in LC, the direct measurement of oxygen concentration in Human LC is yet to be determined. This narrative review aims to show the importance and as a future target for novel research studies that can lead to the perception of LC therapy in hypoxic malignancies.

miR-210 Expression Is Strongly Hypoxia-Induced in Anaplastic Thyroid Cancer Cell Lines and Is Associated with Extracellular Vesicles and Argonaute-2

Hypoxia, or low oxygen tension, is frequently found in highly proliferative solid tumors such as anaplastic thyroid carcinoma (ATC) and is believed to promote resistance to chemotherapy and radiation. Identifying hypoxic cells for targeted therapy may thus be an effective approach to treating aggressive cancers. Here, we explore the potential of the well-known hypoxia-responsive microRNA (miRNA) miR-210-3p as a cellular and extracellular biological marker of hypoxia. We compare miRNA expression across several ATC and papillary thyroid cancer (PTC) cell lines. In the ATC cell line SW1736, miR-210-3p expression levels indicate hypoxia during exposure to low oxygen conditions (2% O2). Furthermore, when released by SW1736 cells into the extracellular space, miR-210-3p is associated with RNA carriers such as extracellular vesicles (EVs) and Argonaute-2 (AGO2), making it a potential extracellular marker for hypoxia.

A Review of Nuclear Medicine Approaches in the Diagnosis and the Treatment of Gynecological Malignancies

Nuclear medicine is defined as the diagnosis and the treatment of disease using radiolabeled compounds known as radiopharmaceuticals. Single-photon emission computed tomography/computed tomography (SPECT/CT) and positron emission tomography/computer tomography (PET/CT) based radiopharmaceuticals have proven reliable in diagnostic imaging in nuclear medicine and cancer treatment. One of the most critical cancers that also relies on an early diagnosis is gynecological cancer. Given that approximately 25% of all cancers in developing countries are a subset of gynecological cancer, investigating this cancer subtype is of significant clinical worth, particularly in light of its high rate of mortality. With accurate identification of high grade distant abdominal endometrial cancer as well as extra abdominal metastases, 18F-Fluorodeoxyglucose ([18F]FDG) PET/CT imaging is considered a valuable step forward in the investigation of gynecological cancer. Considering these factors, [18F]FDG PET/CT imaging can assist in making management of patient therapy more feasible. In this literature review, we will provide a short overview of the role of nuclear medicine in the diagnosis of obstetric and gynecological cancers.

Detection of Hypoxia in Cancer Models: Significance, Challenges, and Advances

The rapid proliferation of cancer cells combined with deficient vessels cause regions of nutrient and O2 deprivation in solid tumors. Some cancer cells can adapt to these extreme hypoxic conditions and persist to promote cancer progression. Intratumoral hypoxia has been consistently associated with a worse patient prognosis. In vitro, 3D models of spheroids or organoids can recapitulate spontaneous O2 gradients in solid tumors. Likewise, in vivo murine models of cancer reproduce the physiological levels of hypoxia that have been measured in human tumors. Given the potential clinical importance of hypoxia in cancer progression, there is an increasing need to design methods to measure O2 concentrations. O2 levels can be directly measured with needle-type probes, both optical and electrochemical. Alternatively, indirect, noninvasive approaches have been optimized, and include immunolabeling endogenous or exogenous markers. Fluorescent, phosphorescent, and luminescent reporters have also been employed experimentally to provide dynamic measurements of O2 in live cells or tumors. In medical imaging, modalities such as MRI and PET are often the method of choice. This review provides a comparative overview of the main methods utilized to detect hypoxia in cell culture and preclinical models of cancer.

Hypoxic gene expression is a prognostic factor for disease free survival in a cohort of locally advanced squamous cell cancer of the uterine cervix

INTRODUCTION

Tumour hypoxia in locally advanced squamous cervical cancer (LACC) has been shown to be of substantial prognostic importance. The aims of the present study were therefore to investigate if hypoxia could be identified by a newly validated hypoxic gene expression classifier and used as a prognostic factor for disease free survival (DFS).

MATERIAL AND METHODS

Paraffin embedded biopsies were obtained from 190 patients with LACC with squamous cell carcinoma treated 2005-2016 with chemo-radiation and image guided adaptive brachytherapy. Analysis of hypoxia was successful in 183 patients (96%). Hypoxic classification of tumours into 'more' or 'less' hypoxic was based on 15 genes using the same method as in a prospective head and neck cancer trial (NCT02661152). HPV was genotyped using INNO-LiPA. Local tumour invasion was evaluated by the T-score. Primary endpoint was DFS analysed by Kaplan-Meier and Cox regression. Events were death of any cause, persistent disease, or recurrence.

RESULTS

The FIGO₂₀₀₉ stage distribution was IB-IIA 9%, IIB 64%, and III-IVA 27%, and mean T-score was 7.2. Pathological nodes were present in 53%. Median observation time was 5.2 years. Local control rate at 5 years was 96%, and pelvic (loco-regional) control 91%. Overall, 36% of the tumours were classified as 'more' hypoxic. The frequency of 'more' hypoxic tumours increased with local tumour intrusion (30% for T-score 0-9 vs. 55% for T-score ≥10, p = 0.004). Hypoxia was associated with decreased DFS in univariate, HR 1.71 (1.04-2.82), and multivariate analysis, HR 1.75 (1.04-2.92), and the effect was particularly observed among tumours with a T-score ≥10. HPV 16/18 was not associated with improved DFS in neither in univariate nor in multivariate analysis.

CONCLUSION

Hypoxic gene expression is a prominent prognostic factor for DFS in LACC with SCC histology and should be considered for treatment stratification in clinical trials.

The importance of hypoxia in radiotherapy for the immune response, metastatic potential and FLASH-RT

PURPOSE

Hypoxia (low oxygen) is a common feature of solid tumors that has been intensely studied for more than six decades. Here we review the importance of hypoxia to radiotherapy with a particular focus on the contribution of hypoxia to immune responses, metastatic potential and FLASH radiotherapy, active areas of research by leading women in the field.

CONCLUSION

Although hypoxia-driven metastasis and immunosuppression can negatively impact clinical outcome, understanding these processes can also provide tumor-specific vulnerabilities that may be therapeutically exploited. The different oxygen tensions present in tumors and normal tissues may underpin the beneficial FLASH sparing effect seen in normal tissue and represents a perfect example of advances in the field that can leverage tumor hypoxia to improve future radiotherapy treatments.

Impact of hypoxia on cervical cancer outcomes

The annual global incidence of cervical cancer is approximately 604 000 cases/342 000 deaths, making it the fourth most common cancer in women. Cervical cancer is a major healthcare problem in low and middle income countries where 85% of new cases and deaths occur. Secondary prevention measures have reduced incidence and mortality in developed countries over the past 30 years, but cervical cancer remains a major cause of cancer deaths in women. For women who present with Fédération Internationale de Gynécologie et d'Obstétrique (FIGO 2018) stages IB3 or upwards, chemoradiation is the established treatment. Despite high rates of local control, overall survival is less than 50%, largely due to distant relapse. Reducing the health burden of cervical cancer requires greater individualization of treatment, identifying those at risk of relapse and progression for modified or intensified treatment. Hypoxia is a well known feature of solid tumors and an established therapeutic target. Low tumorous oxygenation increases the risk of local invasion, metastasis and treatment failure. While meta-analyses show benefit, many individual trials targeting hypoxia failed in part due to not selecting patients most likely to benefit. This review summarizes the available hypoxia-targeted strategies and identifies further research and new treatment paradigms needed to improve patient outcomes. The applications and limitations of hypoxia biomarkers for treatment selection and response monitoring are discussed. Finally, areas of greatest unmet clinical need are identified to measure and target hypoxia and therefore improve cervical cancer outcomes.

First-In-Human Study in Cancer Patients Establishing the Feasibility of Oxygen Measurements in Tumors Using Electron Paramagnetic Resonance With the OxyChip

OBJECTIVE

The overall objective of this clinical study was to validate an implantable oxygen sensor, called the 'OxyChip', as a clinically feasible technology that would allow individualized tumor-oxygen assessments in cancer patients prior to and during hypoxia-modification interventions such as hyperoxygen breathing.

METHODS

Patients with any solid tumor at ≤3-cm depth from the skin-surface scheduled to undergo surgical resection (with or without neoadjuvant therapy) were considered eligible for the study. The OxyChip was implanted in the tumor and subsequently removed during standard-of-care surgery. Partial pressure of oxygen (pO2) at the implant location was assessed using electron paramagnetic resonance (EPR) oximetry.

RESULTS

Twenty-three cancer patients underwent OxyChip implantation in their tumors. Six patients received neoadjuvant therapy while the OxyChip was implanted. Median implant duration was 30 days (range 4-128 days). Forty-five successful oxygen measurements were made in 15 patients. Baseline pO2 values were variable with overall median 15.7 mmHg (range 0.6-73.1 mmHg); 33% of the values were below 10 mmHg. After hyperoxygenation, the overall median pO2 was 31.8 mmHg (range 1.5-144.6 mmHg). In 83% of the measurements, there was a statistically significant (p ≤ 0.05) response to hyperoxygenation.

CONCLUSIONS

Measurement of baseline pO2 and response to hyperoxygenation using EPR oximetry with the OxyChip is clinically feasible in a variety of tumor types. Tumor oxygen at baseline differed significantly among patients. Although most tumors responded to a hyperoxygenation intervention, some were non-responders. These data demonstrated the need for individualized assessment of tumor oxygenation in the context of planned hyperoxygenation interventions to optimize clinical outcomes.

Red Blood Cell Transfusion Practices for Patients With Cervical Cancer Undergoing Radiotherapy

IMPORTANCE

Packed red blood cell (PRBC) transfusions are used to treat anemia in patients with cervical cancer undergoing radiotherapy (RT) owing to concerns of hypoxia-induced radioresistance. In the absence of high-quality evidence informing transfusion practices for patients receiving external beam RT (EBRT) and brachytherapy, various arbitrary hemoglobin target levels are used worldwide.

OBJECTIVE

To develop consensus statements to guide PRBC transfusion practices in patients with cervical cancer receiving curative-intent RT with EBRT and brachytherapy.

DESIGN, SETTING, AND PARTICIPANTS

This international Delphi consensus study was completed between November 1, 2019, and July 31, 2020. A total of 63 international clinical experts in gynecologic radiation oncology were invited; 39 (62%) accepted and consented to participate. Consensus building was achieved using a 3-round anonymous Delphi consensus method. Participants rated their agreement or disagreement with statements using a 5-point Likert scale. An a priori threshold of 75% or more was required for consensus.

MAIN OUTCOMES AND MEASURES

The preplanned primary outcome of this study was to assess hemoglobin transfusion thresholds and targets for both EBRT and brachytherapy by expert consensus.

RESULTS

Response rates of 100% (39 of 39), 92% (36 of 39), and 97% (35 of 36) were achieved for the first, second, and third rounds of surveys, respectively. Twenty-three experts (59%) practiced in Canada, 11 (28%) in the United States, 3 (8%) in South America, 1 (3%) in Europe, and 1 (3%) in Asia. Consensus was reached for 44 of 103 statements (43%), which were combined to form the final 27-statement consensus guideline. No specific hemoglobin transfusion threshold was agreed on by consensus for EBRT or brachytherapy. By consensus (89% [31 of 35]), a hemoglobin transfusion target for patients who receive a PRBC transfusion should be 9 g/dL or more and less than 12 g/dL.

CONCLUSIONS AND RELEVANCE

This study presents the first international expert consensus guideline informing PRBC transfusion practices for patients with cervical cancer undergoing EBRT and brachytherapy. A minimum hemoglobin transfusion target of 9 g/dL was endorsed to balance tumor radiosensitivity with appropriate use of a scarce resource. Randomized clinical trials are required to evaluate the optimal transfusion threshold and target that maximize clinical benefit in this patient population.

Lost in application: Measuring hypoxia for radiotherapy optimisation

The history of radiotherapy is intertwined with research on hypoxia. There is level 1a evidence that giving hypoxia-targeting treatments with radiotherapy improves locoregional control and survival without compromising late side-effects. Despite coming in and out of vogue over decades, there is now an established role for hypoxia in driving molecular alterations promoting tumour progression and metastases. While tumour genomic complexity and immune profiling offer promise, there is a stronger evidence base for personalising radiotherapy based on hypoxia status. Despite this, there is only one phase III trial targeting hypoxia modification with full transcriptomic data available. There are no biomarkers in routine use for patients undergoing radiotherapy to aid management decisions, and a roadmap is needed to ensure consistency and provide a benchmark for progression to application. Gene expression signatures address past limitations of hypoxia biomarkers and could progress biologically optimised radiotherapy. Here, we review recent developments in generating hypoxia gene expression signatures and highlight progress addressing the challenges that must be overcome to pave the way for their clinical application.

Imaging of Tumor Hypoxia for Radiotherapy: Current Status and Future Directions

Tumor regions that are transiently or chronically undersupplied with oxygen (hypoxia) and nutrients, and enriched with acidic waste products, are common due to an abnormal and inefficient tumor vasculature, and a deviant highly glycolytic energy metabolism. There is compelling evidence that tumor hypoxia is strongly linked to poor prognosis since oxygen-deprived cells are highly resistant to therapy including radio- and chemotherapy, and survival of such cells is a primary cause of disease relapse. Despite a general improvement in cancer survival rates, hypoxia remains a formidable challenge. Recent progress in radiation delivery systems with improved spatial accuracy that allows dose escalation to hypoxic tumors or even tumor subvolumes, and the development of hypoxia-selective drugs, including bioreductive prodrugs, holds great promise for overcoming this obstacle. However, apart from one notable exception, translation of promising preclinical therapies to the clinic have largely been disappointing. A major obstacle in clinical trials on hypoxia-targeting strategies has been the lack of reliable information on tumor hypoxia, which is crucial for patient stratification into groups of those that are likely to benefit from intervention and those who are not. Further, in many newer trials on hypoxia-selective drugs the choice of cancer disease and combination therapy has not always been ideal, especially not for clinical proof of principle trials. Clearly, there is a pending need for clinical applicable methodologies that may allow us to quantify, map and monitor hypoxia. Molecular imaging may provide the information required for narrowing the gap between potential and actual patient benefit of hypoxia-targeting strategies. The grand majority of preclinical and clinical work has focused on the usefulness of PET-based assessment of hypoxia-selective tracers. Since hypoxia PET has profound inherent weaknesses, the use of other methodologies, including more indirect methods that quantifies blood flow or oxygenation-dependent flux changes through ATP-generating pathways (eg, anaerobic glycolysis) is being extensively studied. In this review, we briefly discuss established and emerging hypoxia-targeting strategies, followed by a more thorough evaluation of strengths and weaknesses of clinical applicable imaging methodologies that may guide timely treatment intensification to overcome hypoxia-driven resistance. Historically, most evidence for the linkage between hypoxia and poor outcome is based on work in the field of radiotherapy. Therefore, main emphasis in this review is on targeting and imaging of hypoxia for improved radiotherapy.

Effect of TTLL6 expression on CDDP sensitivity of EC109/CDDP cells in hypoxia/acidosis microenvironment

Multidrug resistance is a major obstacle to the effective treatment of esophageal carcinoma. It occurs more readily in hypoxia and acidosis microenvironment. TTLL6 is one of Tubulin tyrosine ligase-like family members. In this study, the effect of TTLL6 on the regulation of cisplatin (CDDP) sensitivity was evaluated in CDDP-resistant esophageal carcinoma (EC) cells both in vitro and in vivo. In hypoxia/acidosis condition, overexpression of TTLL6 in EC109/CDDP cells significantly lowered the IC₅₀ of CDDP and increased the CDDP-induced apoptosis; while knockdown of TTLL6 expression in EC109/CDDP cells exhibited the opposite effects. Further study showed that, mechanistically, TTLL6 was inversely correlated with ERBB2 and TOPOIIA, and positively correlated with apoptosis-associated factor Caspase 9. Furthermore, animal model confirmed that TTLL6 negatively regulated the growth of xenograft tumor after chemotherapy. Alternated expression of TTLL6 also regulated the expression of ERBB2, TOPOIIA and Caspase 9 in EC109/CDDP cells in vivo. In conclusion, our results suggest that TTLL6 could reverse the drug resistant of EC109/CDDP cells, it might provide a potential treatment strategy for the clinical reversing the chemotherapy resistance.

High-Resolution pO2 Imaging Improves Quantification of the Hypoxic Fraction in Tumors During Radiation Therapy

PURPOSE

The extreme microscopic heterogeneity of tumors makes it difficult to characterize tumor hypoxia. We evaluated how changes in the spatial resolution of oxygen imaging could alter measures of tumor hypoxia and their correlation to radiation therapy response.

METHODS AND MATERIALS

Cherenkov-Excited Luminescence Imaging in combination with an oxygen probe, Oxyphor PtG4 was used to directly image tumor pO₂ distributions with 0.2 mm spatial resolution at the time of radiation delivery. These pO₂ images were analyzed with variations of reduced spatial resolution from 0.2 mm to 5 mm, to investigate the influence of how reduced imaging spatial resolution would affect the observed tumor hypoxia. As an in vivo validation test, mice bearing tumor xenografts were imaged for hypoxic fraction and median pO₂ to examine the predictive link with tumor response to radiation therapy, while accounting for spatial resolution.

RESULTS

In transitioning from voxel sizes of 200 μm to 3 mm, the median pO₂ values increased by a few mm Hg, and the hypoxic fraction decreased by more than 50%. When looking at radiation-responsive tumors, the median pO₂ values changed just a few mm Hg as a result of treatment, and the hypoxic fractions changed by as much as 50%. This latter change, however, could only be seen when sampling was performed with high spatial resolution. Median pO₂ or similar quantities obtained from low resolution measurements are commonly used in clinical practice, however these parameters are much less sensitive to changes in the tumor microenvironment than the tumor hypoxic fraction obtained from high-resolution oxygen images.

CONCLUSIONS

This study supports the hypothesis that for adequate measurements of the tumor response to radiation therapy, oxygen imaging with high spatial resolution is required to accurately characterize the hypoxic fraction.

In vivo Monitoring of Oxygen Levels in Human Brain Tumor Between Fractionated Radiotherapy Using Oxygen-enhanced MR Imaging

BACKGROUND

It was known that the response of tumor cells to radiation is closely related to tissue oxygen level and fractionated radiotherapy allows reoxygenation of hypoxic tumor cells. Non-invasive mapping of tissue oxygen level may hold great importance in clinic.

OBJECTIVE

The aim of this study is to evaluate the role of oxygen-enhanced MR imaging in the detection of tissue oxygen levels between fractionated radiotherapy.

METHODS

A cohort of 10 patients with brain metastasis was recruited. Quantitative oxygen enhanced MR imaging was performed prior to, 30 minutes and 22 hours after first fractionated radiotherapy.

RESULTS

The ΔR1 (the difference of longitudinal relaxivity between 100% oxygen breathing and air breathing) increased in the ipsilateral tumor site and normal tissue by 242% and 152%, respectively, 30 minutes after first fractionated radiation compared to pre-radiation levels. Significant recovery of ΔR1 in the contralateral normal tissue (p < 0.05) was observed 22 hours compared to 30 minutes after radiation levels.

CONCLUSION

R1-based oxygen-enhanced MR imaging may provide a sensitive endogenous marker for oxygen changes in the brain tissue between fractionated radiotherapy.

Tissue pO2 distributions in xenograft tumors dynamically imaged by Cherenkov-excited phosphorescence during fractionated radiation therapy

Hypoxia in solid tumors is thought to be an important factor in resistance to therapy, but the extreme microscopic heterogeneity of the partial pressures of oxygen (pO₂) between the capillaries makes it difficult to characterize the scope of this phenomenon without invasive sampling of oxygen distributions throughout the tissue. Here we develop a non-invasive method to track spatial oxygen distributions in tumors during fractionated radiotherapy, using oxygen-dependent quenching of phosphorescence, oxygen probe Oxyphor PtG4 and the radiotherapy-induced Cherenkov light to excite and image the phosphorescence lifetimes within the tissue. Mice bearing MDA-MB-231 breast cancer and FaDu head neck cancer xenografts show different pO₂ responses during each of the 5 fractions (5 Gy per fraction), delivered from a clinical linear accelerator. This study demonstrates subsurface in vivo mapping of tumor pO₂ distributions with submillimeter spatial resolution, thus providing a methodology to track response of tumors to fractionated radiotherapy.

Clinical and Statistical Considerations when Assessing Oxygen Levels in Tumors: Illustrative Results from Clinical EPR Oximetry Studies

The success of treatment for malignancies, especially those undergoing radiation therapy or chemotherapy, has long been recognized to depend on the degree of hypoxia in the tumor. In addition to the prognostic value of knowing the tumor's initial level of hypoxia, assessing the tumor oxygenation during standard therapy or oxygen-related treatments (such as breathing oxygen-enriched gas mixtures or taking drugs that can increase oxygen supply to tissues) can provide valuable data to improve the efficacy of treatments. A series of early clinical studies of tumors in humans are ongoing at Dartmouth and Emory using electron paramagnetic resonance (EPR) oximetry to assess tumor oxygenation, initially and over time during either natural disease progression or treatment. This approach has the potential for reaching the long-sought goal of enhancing the effectiveness of cancer therapy. In order to effectively reach this goal, we consider the validity of the practical and statistical assumptions when interpreting the measurements made in vivo for patients undergoing treatment for cancer.

Hypoxic Radioresistance: Can ROS Be the Key to Overcome It?

Radiotherapy is a mainstay treatment for many types of cancer and kills cancer cells via generation of reactive oxygen species (ROS). Incorporating radiation with pharmacological ROS inducers, therefore, has been widely investigated as an approach to enhance aerobic radiosensitization. However, this strategy was overlooked in hypoxic counterpart, one of the most important causes of radiotherapy failure, due to the notion that hypoxic cells are immune to ROS insults because of the shortage of ROS substrate oxygen. Paradoxically, evidence reveals that ROS are produced more in hypoxic than normoxic cells and serve as signaling molecules that render cells adaptive to hypoxia. As a result, hypoxic tumor cells heavily rely on antioxidant systems to sustain the ROS homeostasis. Thereby, they become sensitive to insults that impair the ROS detoxification network, which has been verified in diverse models with or without radiation. Of note, hypoxic radioresistance has been overviewed in different contexts. To the best of our knowledge, this review is the first to systemically summarize the interplay among radiation, hypoxia, and ROS, and to discuss whether perturbation of ROS homeostasis could provide a new avenue to tackle hypoxic radioresistance.

Computational models and tools

In this chapter, we describe two different methods, analytical (pencil beam) algorithms and Monte Carlo simulations, used to obtain the intended dose distributions in patients and evaluate their strengths and shortcomings. We discuss the difference between the prescribed physical dose and the biologically effective dose, the relative biological effectiveness (RBE) between ions and photons and the dependence of RBE on the linear energy transfer (LET). Lastly, we show how LET- or RBE-based optimization can be used to improve treatment plans and explore how the availability of multimodality ion beam facilities can be used to design a tumor-specific optimal treatment.

The hypoxic tumor microenvironment in vivo selects tumor cells with increased survival against genotoxic stresses

Tumor sensitivity to radiation therapy has been known to be dependent on O₂ concentrations. However, radiosensitivity of naturally occurring hypoxic tumor cells remains to be well fully investigated in direct comparison to that of their adjacent non-hypoxic tumor cells within the same tumor. We developed a hypoxia-sensing xenograft model using the hypoxia-response element (HRE)-driven enhanced green fluorescence protein (EGFP) as a hypoxia reporter to identify hypoxic tumor cells in situ. Here, we have found that naturally hypoxic tumor cells are moderately radioresistant compared to their neighboring non-hypoxic tumor cells in the same tumor. These naturally hypoxic tumor cells are proficient at repairing DNA damages and resist apoptosis induced by genotoxic stresses, which involves activation of the ATM/CHK1/CHK2 DNA damage-sensing pathway. Inhibition of the checkpoint kinases sensitizes the ex vivo hypoxic tumor cells to ionizing irradiation. Second, the new functional phenotypes acquired by the hypoxic tumor cells in vivo are stable even after they are maintained under non-hypoxic conditions. These new results strongly suggest that the hypoxic tumor microenvironment is capable of selecting stable tumor cell populations with increased resistance to genotoxic stresses and enhanced survival.

A Two-Component Assay for Hypoxia Incorporating Long-Term Nitroreduction and Short-Term DNA-Damage Allows Differentiation of the Three Hypoxia Sub-types

Hypoxia in tumors has many well-characterized effects that are known to prevent optimal cancer treatment. Despite the existence of a large number of assays that have supported hypoxia as an important diagnostic, there is no routine clinical assay in use, and anti-hypoxia therapies have often not included parallel hypoxia measurements. Even with a functioning hypoxia assay, it is difficult to match the oxygen dependence of treatment resistance to that of the assay, and this mismatch can vary substantially from assay to assay and even from tumor to tumor [e.g., caused by endogenous variations in non-protein sulfhydryls (NPSH)]. An underlying concern is the current inability to measure the three types of hypoxia; in particular, cycling hypoxia can affect all aspects of detection and treatment strategy. Here we present data that help validate a new two-component hypoxia assay recently suggested by our laboratory. This assay incorporates the long-term bioreduction of the 2-nitroimidazole, EF5, and the short-term production of γ-H2AX (e.g., time of ionizing radiation exposure). The former can be calibrated to provide the average tissue pO₂ over the EF5 exposure time while the latter provides the combined sum of microenvironmental radiation response modifiers (e.g., oxygen and NPSH) at the time of irradiation. Importantly, formation of γ-H2AX is not dependent on blood flow, while EF5 binding is only minimally so, due to the rapid and extensive diffusion characteristics of lipophilic compounds. While both individual assays have their limitations, which are addressed in this article, their combination can dissect the type of hypoxia present. In particular, a mismatch between the two assays can directly detect cycling hypoxia in a therapeutically relevant manner. Preliminary use of this two-component assay in small PC3 tumors showed essentially no binding of EF5. Similarly, there were no tumor regions (for uniform irradiation with 12 Gy) with the low levels of γ-H2AX expected for a condition of cycling hypoxia. Thus, both assays were consistent with an essentially aerobic, radiation-responsive tumor. In a larger PC3 tumor, all regions of high EF5 binding had low levels of γ-H2AX.

Hypoxia gene expression signatures as predictive biomarkers for personalising radiotherapy

Hypoxia is a generic micro-environmental factor of solid tumours. High levels of hypoxia lead to resistance to radiotherapy, which can be targeted by adding hypoxia-modifying therapy to improve clinical outcomes. Not all patients benefit from hypoxia-modifying therapy, and there is a need for biomarkers to enable progression to biologically personalised radiotherapy. Gene expression signatures are a relatively new category of biomarkers that can reflect tumour hypoxia. This article reviews the published hypoxia gene signatures, summarising their development and validation. The challenges of gene signature derivation and development, and advantages and disadvantages in comparison with other hypoxia biomarkers are also discussed. Current evidence supports investment in gene signatures as a promising hypoxia biomarker approach for clinical utility.

Oxygen Mapping of Melanoma Spheroids using Small Molecule Platinum Probe and Phosphorescence Lifetime Imaging Microscopy

Solid tumours display varied oxygen levels and this characteristic can be exploited to develop new diagnostic tools to determine and exploit these variations. Oxygen is an efficient quencher of emission of many phosphorescent compounds, thus oxygen concentration could in many cases be derived directly from relative emission intensity and lifetime. In this study, we extend our previous work on phosphorescent, low molecular weight platinum(II) complex as an oxygen sensing probe to study the variation in oxygen concentration in a viable multicellular 3D human tumour model. The data shows one of the first examples of non-invasive, real-time oxygen mapping across a melanoma tumour spheroid using one-photon phosphorescence lifetime imaging microscopy (PLIM) and a small molecule oxygen sensitive probe. These measurements were quantitative and enabled real time oxygen mapping with high spatial resolution. This combination presents as a valuable tool for optical detection of both physiological and pathological oxygen levels in a live tissue mass and we suggest has the potential for broader clinical application.

Progress in mass spectrometry-based proteomic research of tumor hypoxia (Review)

A hypoxic microenvironment effects various signaling pathways in the human body, including those that are critical for normal physiology and those that support tumorigenesis or cancer progression. A hypoxic tumor microenvironment, in particular, modulates cell migration, invasion and resistance to radiotherapy and chemotherapy. Development of the mass spectrometry (MS) technique has allowed for expansion of proteomic study to a wide variety of fields, with the study of tumor hypoxia being among the latest to enjoy its benefits. In such studies, changes in the proteome of tumor tissue or cells induced by the hypoxic conditions are analyzed. A multitude of hypoxic regulatory proteins have already been identified, increasing our understanding of the mechanisms underlying tumor occurrence and development and representing candidate reference markers for tumor diagnosis and therapy. The present review provides the first summary of the collective studies on tumor microenvironment hypoxia that have been completed using MS-based proteomic techniques, providing a systematic discussion of the benefits and current challenges of the various applications.

Pretreatment late-phase DCE-MRI predicts outcome in locally advanced cervix cancer

BACKGROUND

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) may provide prognostic biomarkers for cervix carcinoma. We have shown previously that the early phase of the signal intensity-versus-time curve (SITC) may have significant prognostic power. The purpose of the present investigation was to explore the prognostic value of the late phase of the SITC.

MATERIAL AND METHODS

DCE-MRI data of 80 patients (FIGO stage IB-IVA) treated with concurrent chemoradiotherapy were examined. Four parameters were calculated from the late-phase SITC: tumor volume with decreasing signal, tumor fraction with decreasing signal, tumor volume with increasing signal (TVIS), and tumor fraction with increasing signal.

RESULTS

Multivariate analysis involving clinical parameters and late-phase SITC parameters suggested that TVIS is a strong independent prognostic factor for both disease-free and overall survival. When early-phase SITC parameters were included in the multivariate analysis, the early-phase SITC, but not the late-phase SITC, was found to have independent prognostic value.

CONCLUSION

The late-phase SITC can provide prognostic factors for the outcome of cervix carcinoma, that is, a large tumor volume with increasing late-phase SITCs is associated with poor outcome. However, the prognostic power of the late-phase SITC is not as strong as that of the early-phase SITC.

Assessing Tumor Oxygenation for Predicting Outcome in Radiation Oncology: A Review of Studies Correlating Tumor Hypoxic Status and Outcome in the Preclinical and Clinical Settings

Tumor hypoxia is recognized as a limiting factor for the efficacy of radiotherapy, because it enhances tumor radioresistance. It is strongly suggested that assessing tumor oxygenation could help to predict the outcome of cancer patients undergoing radiation therapy. Strategies have also been developed to alleviate tumor hypoxia in order to radiosensitize tumors. In addition, oxygen mapping is critically needed for intensity modulated radiation therapy (IMRT), in which the most hypoxic regions require higher radiation doses and the most oxygenated regions require lower radiation doses. However, the assessment of tumor oxygenation is not yet included in day-to-day clinical practice. This is due to the lack of a method for the quantitative and non-invasive mapping of tumor oxygenation. To fully integrate tumor hypoxia parameters into effective improvements of the individually tailored radiation therapy protocols in cancer patients, methods allowing non-invasively repeated, safe, and robust mapping of changes in tissue oxygenation are required. In this review, non-invasive methods dedicated to assessing tumor oxygenation with the ultimate goal of predicting outcome in radiation oncology are presented, including positron emission tomography used with nitroimidazole tracers, magnetic resonance methods using endogenous contrasts (R₁ and R2*-based methods), and electron paramagnetic resonance oximetry; the goal is to highlight results of studies establishing correlations between tumor hypoxic status and patients’ outcome in the preclinical and clinical settings.

Decision support systems for personalized and participative radiation oncology

A paradigm shift from current population based medicine to personalized and participative medicine is underway. This transition is being supported by the development of clinical decision support systems based on prediction models of treatment outcome. In radiation oncology, these models 'learn' using advanced and innovative information technologies (ideally in a distributed fashion - please watch the animation: http://youtu.be/ZDJFOxpwqEA) from all available/appropriate medical data (clinical, treatment, imaging, biological/genetic, etc.) to achieve the highest possible accuracy with respect to prediction of tumor response and normal tissue toxicity. In this position paper, we deliver an overview of the factors that are associated with outcome in radiation oncology and discuss the methodology behind the development of accurate prediction models, which is a multi-faceted process. Subsequent to initial development/validation and clinical introduction, decision support systems should be constantly re-evaluated (through quality assurance procedures) in different patient datasets in order to refine and re-optimize the models, ensuring the continuous utility of the models. In the reasonably near future, decision support systems will be fully integrated within the clinic, with data and knowledge being shared in a standardized, dynamic, and potentially global manner enabling truly personalized and participative medicine.

Hypoxia in cervical cancer: from biology to imaging

PURPOSE

Hypoxia imaging may improve identification of cervical cancer patients at risk of treatment failure and be utilized in treatment planning and monitoring, but its clinical potential is far from fully realized. Here, we briefly describe the biology of hypoxia in cervix tumors of relevance for imaging, and evaluate positron emission tomography (PET) and magnetic resonance imaging (MRI) techniques that have shown promise for assessing hypoxia in a clinical setting. We further discuss emerging imaging approaches, and how imaging can play a role in future treatment strategies to target hypoxia.

METHODS

We performed a PubMed literature search, using keywords related to imaging and hypoxia in cervical cancer, with a particular emphasis on studies correlating imaging with other hypoxia measures and treatment outcome.

RESULTS

Only a few and rather small studies have utilized PET with tracers specific for hypoxia, and no firm conclusions regarding preferred tracer or clinical potential can be drawn so far. Most studies address indirect hypoxia imaging with dynamic contrast-enhanced techniques. Strong evidences for a role of these techniques in hypoxia imaging have been presented. Pre-treatment images have shown significant association to outcome in several studies, and images acquired during fractionated radiotherapy may further improve risk stratification. Multiparametric MRI and multimodality PET/MRI enable combined imaging of factors of relevance for tumor hypoxia and warrant further investigation.

CONCLUSIONS

Several imaging approaches have shown promise for hypoxia imaging in cervical cancer. Evaluation in large clinical trials is required to decide upon the optimal modality and approach.

Multiparametric [18F]Fluorodeoxyglucose/ [18F]Fluoromisonidazole Positron Emission Tomography/ Magnetic Resonance Imaging of Locally Advanced Cervical Cancer for the Non-Invasive Detection of Tumor Heterogeneity: A Pilot Study

Objectives

To investigate fused multiparametric positron emission tomography/magnetic resonance imaging (MP PET/MRI) at 3T in patients with locally advanced cervical cancer, using high-resolution T2-weighted, contrast-enhanced MRI (CE-MRI), diffusion-weighted imaging (DWI), and the radiotracers [¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG) and [¹⁸F]fluoromisonidazol ([¹⁸F]FMISO) for the non-invasive detection of tumor heterogeneity for an improved planning of chemo-radiation therapy (CRT).

Materials and Methods

Sixteen patients with locally advanced cervix were enrolled in this IRB approved and were examined with fused MP [¹⁸F]FDG/ [¹⁸F]FMISO PET/MRI and in eleven patients complete data sets were acquired. MP PET/MRI was assessed for tumor volume, enhancement (EH)-kinetics, diffusivity, and [¹⁸F]FDG/ [¹⁸F]FMISO-avidity. Descriptive statistics and voxel-by-voxel analysis of MRI and PET parameters were performed. Correlations were assessed using multiple correlation analysis.

Results

All tumors displayed imaging parameters concordant with cervix cancer, i.e. type II/III EH-kinetics, restricted diffusivity (median ADC 0.80x10^-3mm²/sec), [¹⁸F]FDG- (median SUV_max16.2) and [¹⁸F]FMISO-avidity (median SUV_max3.1). In all patients, [¹⁸F]FMISO PET identified the hypoxic tumor subvolume, which was independent of tumor volume. A voxel-by-voxel analysis revealed only weak correlations between the MRI and PET parameters (0.05–0.22), indicating that each individual parameter yields independent information and the presence of tumor heterogeneity.

Conclusion

MP [¹⁸F]FDG/ [¹⁸F]FMISO PET/MRI in patients with cervical cancer facilitates the acquisition of independent predictive and prognostic imaging parameters. MP [¹⁸F]FDG/ [¹⁸F]FMISO PET/MRI enables insights into tumor biology on multiple levels and provides information on tumor heterogeneity, which has the potential to improve the planning of CRT.

The contribution of women to radiobiology: Marie Curie and beyond

Marie Sklodowska-Curie, an extraordinary woman, a Polish scientist who lived and worked in France, led to the development of nuclear energy and the treatment of cancer. She was the laureate of two Nobel Prizes, the first woman in Europe who obtained the degree of Doctor of Science and opened the way for women to enter fields which had been previously reserved for men only. As a result of her determination and her love of freedom, she has become an icon for many female scientists active in radiation sciences. They are successors of Maria Curie and without the results of their work, improvement in radiation oncology will not be possible. Many of them shared some elements of Maria Curie's biography, like high ethical and moral standards, passionate dedication to work, strong family values, and scientific collaboration with their husbands. The significance of Tikvah Alper, Alma Howard, Shirley Hornsey, Juliana Denekamp, Helen Evans, Eleanor Blakely, Elizabeth L. Travis, Fiona Stewart, Andree Dutreix, Catharine West, Peggy Olive, Ingela Turesson, Penny Jeggo, Irena Szumiel, Eleonor Blakely, Sara Rockwell and Carmel Mothersill contribution to radiation oncology is presented. All the above mentioned ladies made significant contribution to the development of radiotherapy (RT) and more efficient cancer treatment. Due to their studies, new schedules of RT and new types of ionizing radiation have been applied, lowering the incidence of normal tissue toxicity. Their achievements herald a future of personalized medicine.

Safety and Efficacy of Neoadjuvant Chemotherapy Followed by Radical Surgery Versus Radical Surgery Alone in Locally Advanced Cervical Cancer Patients

OBJECTIVES

This study aimed to evaluate the safety and efficacy of neoadjuvant chemotherapy (NACT) followed by radical surgery (RS) among patients with locally advanced cervical cancer (LACC).

METHODS

Eight hundred patients with LACC received either NACT followed by RS (NACT-RS) or RS alone. The primary outcome measures assessed the efficacy and adverse effects of NACT. Secondary outcome measures compared the preoperative clinical stage to the postoperative pathologic stage in NACT-RS and RS patients, assessed intraoperative and postoperative complications, including the adverse effects of postoperative radiotherapy and radiochemotherapy, and estimated the 5-year progression-free survival and 5-year overall survival.

RESULTS

The clinical response to NACT was 89.54%. Patients in the NACT-RS group had lower preoperative hemoglobin levels (115.20 vs 122.04 g/L, P < 0.001), a longer operative time (mean, 233.66 vs 224.37 minutes, P = 0.008), more intraoperative bleeding (750.34 vs 684.41 mL, P = 0.011), a shorter duration of catheter use (mean, 29.84 vs 32.14 days, P = 0.036), and a lower incidence of postoperative complications (7.30% vs 13.62%, P = 0.002) and postoperative radiotherapeutic and radiochemotherapeutic adverse effects (3.16% vs 4.63%, P < 0.001) compared to patients in the RS group. The 5-year progression-free survival and 5-year overall survival were 80.30% and 81.10% in the NACT-RS group and 81.00% and 78.50% in the RS group (P > 0.05). Pathological poor differentiation, nonsquamous cell carcinoma, parametrial invasion, positive pelvic lymph node, and lymphovascular invasion (P < 0.05) were independent risk factors for recurrence.

CONCLUSIONS

Neoadjuvant chemotherapy may reduce RS-associated complications and postoperative radiotherapeutic and radiochemotherapeutic adverse effects in Chinese patients with LACC.

Therapeutic targeting of hypoxia and hypoxia-inducible factors in cancer

Insufficient tissue oxygenation, or hypoxia, contributes to tumor aggressiveness and has a profound impact on clinical outcomes in cancer patients. At decreased oxygen tensions, hypoxia-inducible factors (HIFs) 1 and 2 are stabilized and mediate a hypoxic response, primarily by acting as transcription factors. HIFs exert differential effects on tumor growth and affect important cancer hallmarks including cell proliferation, apoptosis, differentiation, vascularization/angiogenesis, genetic instability, tumor metabolism, tumor immune responses, and invasion and metastasis. As a consequence, HIFs mediate resistance to chemo- and radiotherapy and are associated with poor prognosis in cancer patients. Intriguingly, perivascular tumor cells can also express HIF-2α, thereby forming a "pseudohypoxic" phenotype that further contributes to tumor aggressiveness. Therefore, therapeutic targeting of HIFs in cancer has the potential to improve treatment efficacy. Different strategies to target hypoxic cancer cells and/or HIFs include hypoxia-activated prodrugs and inhibition of HIF dimerization, mRNA or protein expression, DNA binding capacity, and transcriptional activity. Here we review the functions of HIFs in the progression and treatment of malignant solid tumors. We also highlight how HIFs may be targeted to improve the management of patients with therapy-resistant and metastatic cancer.

Patient-derived xenograft models of squamous cell carcinoma of the uterine cervix

Patient-derived xenograft (PDX) models of cancer are considered to reflect the biology and treatment response of human tumors to a larger extent than xenograft models initiated from established cell lines. The characterization of a panel of four novel PDX models of cervical carcinoma of the uterine cervix is described in this communication. The outcome of treatment differed substantially among the donor patients, and the PDX models were found to mirror the histology, aggressiveness, and metastatic propensity of the donor patients' tumors. Two of the models (BK-12 and LA-19) were highly metastatic, one model (ED-15) was poorly metastatic, and one model (HL-16) was non-metastatic. The primary tumors of the two highly metastatic models showed high density of intratumoral lymphatics, whereas the other two models did not develop intratumoral lymphatics. The potential of the models to metastasize to lymph nodes was associated with high expression of both angiogenesis-related genes and cancer stem cell-related genes. The models may be highly valuable for studying mechanisms linking lymph node metastasis to lymphangiogenesis, hemangiogenesis, and the presence of cancer stem cells.

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.

Analysis of the intra- and intertumoral heterogeneity of hypoxia in pancreatic cancer patients receiving the nitroimidazole tracer pimonidazole

Background:

Hypoxia is thought to be an adverse feature of pancreatic cancer, but direct measurement in patients is technically challenging. To address this, we characterised the intra/interpatient heterogeneity of hypoxia in surgical specimens from patients who received the 2-nitroimidazole tracer pimonidazole pre-operatively.

Methods:

Pimondazole was given intravenously 16–20 h before pancreatectomy, and the extent and intratumoral heterogeneity of hypoxia determined by image analysis applied to multiple tissue blocks stained by immunohistochemistry. Intra/interpatient heterogeneity was estimated by variance component analysis.

Results:

Pimonidazole staining was analysed in 10 tumours. The extent of labelling varied amongst patients (0–26%), with a broader range of hypoxia in the epithelial (1–39%) compared with the stromal (1–13%) compartments. Variance component analysis demonstrated greater inter- than intrapatient variability of hypoxia, and that multiple (4–5) tumour sections are required to provide a consistent evaluation of its extent in individual tumours.

Conclusions:

There is significant intra- and intertumoral heterogeneity of hypoxia in pancreatic cancers, and these do not appear to be generally more hypoxic than other cancer types. This study establishes the feasibility to assess hypoxia in pancreatic cancer patients using pimonidazole, but questions the reliability of measurements made using a single tissue section.

Short-term pretreatment DCE-MRI in prediction of outcome in locally advanced cervical cancer

BACKGROUND AND PURPOSE

Several investigators have indicated that dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) has the potential to provide biomarkers for personalized treatment of cervical carcinoma. However, some clinical studies have suggested that treatment failure is associated with low tumor signal enhancement, whereas others have reported associations between high signal enhancement and poor outcome. The purpose of this investigation was to clear up these conflicting reports and to provide a method for identifying biomarkers that easily can be implemented in routine DCE-MRI diagnostics.

METHODS

The study involved 85 patients (FIGO stage IB through IVA) treated with concurrent chemoradiotherapy. Low-enhancing tumor volume (LETV) and low-enhancing tumor fraction (LETF), defined as the volume and fractional volume of low-enhancing voxels, respectively, were calculated from signal intensities recorded within 1 min after contrast administration by using two methods reported to give conflicting conclusions.

RESULTS

Multivariate analysis involving tumor volume, lymph node status, FIGO stage, and LETV or LETF revealed that LETV and LETF provided independent prognostic information on treatment outcome, independent of the method of calculation.

CONCLUSION

Low signal enhancement is associated with poor prognosis in cervical carcinoma, and biomarkers predicting poor outcome can be provided by short-term DCE-MRI without advanced image analysis.

Cellular and molecular mechanisms underlying oxygen-dependent radiosensitivity

Molecular oxygen has long been recognized as a powerful radiosensitizer that enhances the cell-killing efficiency of ionizing radiation. Radiosensitization by oxygen occurs at very low concentrations with the half-maximum radiosensitization at approximately 3 mmHg. However, robust hypoxia-induced signal transduction can be induced at <15 mmHg and can elicit a wide range of cellular responses that will affect therapy response as well as malignant progression. Great strides have been made, especially since the 1990s, toward identification and characterization of the oxygen-regulated molecular pathways that affect tumor response to ionizing radiation. In this review, we will discuss the current advances in our understanding of oxygen-dependent molecular modification and cellular signal transduction and their impact on tumor response to therapy. We will specifically address mechanistic distinctions between radiobiological hypoxia (0-3 mmHg) and pathological hypoxia (3-15 mmHg). We also propose a paradigm that hypoxia increases radioresistance by maintaining the cancer stem cell phenotype.

The clinical importance of assessing tumor hypoxia: relationship of tumor hypoxia to prognosis and therapeutic opportunities

Tumor hypoxia is a well-established biological phenomenon that affects the curability of solid tumors, regardless of treatment modality. Especially for head and neck cancer patients, tumor hypoxia is linked to poor patient outcomes. Given the biological problems associated with tumor hypoxia, the goal for clinicians has been to identify moderately to severely hypoxic tumors for differential treatment strategies. The "gold standard" for detecting and characterizing of tumor hypoxia are the invasive polarographic electrodes. Several less invasive hypoxia assessment techniques have also shown promise for hypoxia assessment. The widespread incorporation of hypoxia information in clinical tumor assessment is severely impeded by several factors, including regulatory hurdles and unclear correlation with potential treatment decisions. There is now an acute need for approved diagnostic technologies for determining the hypoxia status of cancer lesions, as it would enable clinical development of personalized, hypoxia-based therapies, which will ultimately improve outcomes. A number of different techniques for assessing tumor hypoxia have evolved to replace polarographic pO2 measurements for assessing tumor hypoxia. Several of these modalities, either individually or in combination with other imaging techniques, provide functional and physiological information of tumor hypoxia that can significantly improve the course of treatment. The assessment of tumor hypoxia will be valuable to radiation oncologists, surgeons, and biotechnology and pharmaceutical companies who are engaged in developing hypoxia-based therapies or treatment strategies.

Noninvasive tumor hypoxia measurement using magnetic resonance imaging in murine U87 glioma xenografts and in patients with glioblastoma

PURPOSE

There is a clinical need for noninvasive, nonionizing imaging biomarkers of tumor hypoxia and oxygenation. We evaluated the relationship of T1 -weighted oxygen-enhanced magnetic resonance imaging (OE-MRI) measurements to histopathology measurements of tumor hypoxia in a murine glioma xenograft and demonstrated technique translation in human glioblastoma multiforme.

METHODS

Preclinical evaluation was performed in a subcutaneous murine human glioma xenograft (U87MG). Animals underwent OE-MRI followed by dynamic contrast-enhanced MRI (DCE-MRI) and histological measurement including reduced pimonidazole adducts and CD31 staining. Area under the curve (AUC) was measured for the R1 curve for OE-MRI and the gadolinium concentration curve for DCE-MRI. Clinical evaluation in five patients used analogous imaging protocols and analyses.

RESULTS

Changes in AUC of OE-MRI (AUCOE ) signal were regionally heterogeneous across all U87MG tumors. Tumor regions with negative AUCOE typically had low DCE-MRI perfusion, had positive correlation with hypoxic area (P = 0.029), and had negative correlation with vessel density (P = 0.004). DCE-MRI measurements did not relate to either hypoxia or vessel density in U87MG tumors. Clinical data confirmed comparable signal changes in patients with glioblastoma.

CONCLUSION

These data support further investigation of T1 -weighted OE-MRI to identify regional tumor hypoxia. The quantification of AUCOE has translational potential as a clinical biomarker of hypoxia.

LET-painting increases tumour control probability in hypoxic tumours

LET-painting was suggested as a method to overcome tumour hypoxia. In vitro experiments have demonstrated a well-established relationship between the oxygen enhancement ratio (OER) and linear energy transfer (LET), where OER approaches unity for high-LET values. However, high-LET radiation also increases the risk for side effects in normal tissue. LET-painting attempts to restrict high-LET radiation to compartments that are found to be hypoxic, while applying lower LET radiation to normoxic tissues. Methods. Carbon-12 and oxygen-16 ion treatment plans with four fields and with homogeneous dose in the target volume, are applied on an oropharyngeal cancer case with an identified hypoxic entity within the tumour. The target dose is optimised to achieve a tumour control probability (TCP) of 95% when assuming a fully normoxic tissue. Using the same primary particle energy fluence needed for this plan, TCP is recalculated for three cases assuming hypoxia: first, redistributing LET to match the hypoxic structure (LET-painting). Second, plans are recalculated for varying hypoxic tumour volume in order to investigate the threshold volume where TCP can be established. Finally, a slight dose boost (5-20%) is additionally allowed in the hypoxic subvolume to assess its impact on TCP. Results. LET-painting with carbon-12 ions can only achieve tumour control for hypoxic subvolumes smaller than 0.5 cm(3). Using oxygen-16 ions, tumour control can be achieved for tumours with hypoxic subvolumes of up to 1 or 2 cm(3). Tumour control can be achieved for tumours with even larger hypoxic subvolumes, if a slight dose boost is allowed in combination with LET-painting. Conclusion. Our findings clearly indicate that a substantial increase in tumour control can be achieved when applying the LET-painting concept using oxygen-16 ions on hypoxic tumours, ideally with a slight dose boost.

Predicting outcomes in radiation oncology--multifactorial decision support systems

With the emergence of individualized medicine and the increasing amount and complexity of available medical data, a growing need exists for the development of clinical decision-support systems based on prediction models of treatment outcome. In radiation oncology, these models combine both predictive and prognostic data factors from clinical, imaging, molecular and other sources to achieve the highest accuracy to predict tumour response and follow-up event rates. In this Review, we provide an overview of the factors that are correlated with outcome-including survival, recurrence patterns and toxicity-in radiation oncology and discuss the methodology behind the development of prediction models, which is a multistage process. Even after initial development and clinical introduction, a truly useful predictive model will be continuously re-evaluated on different patient datasets from different regions to ensure its population-specific strength. In the future, validated decision-support systems will be fully integrated in the clinic, with data and knowledge being shared in a standardized, instant and global manner.