Limitations of Fluorine 18 Fluoromisonidazole in Assessing Treatment-induced Tissue Hypoxia after Transcatheter Arterial Embolization of Hepatocellular Carcinoma: A Prospective Pilot Study

Assessment of Hypoxia Before Radioembolization Treatment With 18F-FMISO PET: ARTE-MISO Trial

BACKGROUND

Transarterial radioembolization (TARE) is a therapeutic option for patients with liver tumors. However, factors responsible for treatment resistance in TARE remain largely unknown. In this study, we aimed to investigate the role of hypoxia in the treatment response of liver tumors using 18F-FMISO PET imaging before TARE.

PATIENTS AND METHODS

This single-center prospective study included 25 patients with primary or metastatic liver tumors imaged with 18F-FMISO PET/CT before TARE and treated with 90Y resin microspheres. Posttreatment response was assessed with 18F-FDG PET imaging. Hypoxia status was evaluated by calculating the tumor-to-muscle (T/M) and tumor-to-blood pool (T/BP) ratios. Absorbed dose metrics were derived from 90Y PET/MRI imaging post-procedure. Lesions were categorized by response as complete responders (CR), partial responders (PR), stable disease (SD), and progressive disease (PD). Statistical analyses included ROC curve analysis, χ2 tests, and regression models to determine predictors of treatment response.

RESULTS

Among 25 patients (mean age: 60.4 ± 12 y, 56% males), 54 18F-FDG-avid lesions were evaluated. The median absorbed dose (Dmean) was 114.8 Gy for CR, 98.9 Gy for PR, 56.7 Gy for SD, and 78.3 Gy for PD. Significant differences in Dmean (P = 0.013) and T/BP ratios (P = 0.011) were observed between responder and nonresponder groups. High Dmean lesions (>89 Gy) had a response rate of 86%, compared with 56% in low Dmean lesions. Hypoxic lesions (T/BP >1.29) showed a 57% response rate, while non-hypoxic lesions (T/BP <1.29) showed a 91% response rate. In combined analyses, while non-hypoxic/high Dmean lesions had the highest response rates (93%), hypoxic/low-dose had the lowest response rate (39%).

CONCLUSIONS

In this study, we have observed that both mean absorbed radiation dose and hypoxia status are significant predictors of response to treatment after radioembolization of liver tumors. While larger studies are needed to confirm these findings, this pilot study may pave the way for further personalized treatments to achieve better results for radioembolization.

PET Imaging and Key Radiotracers for Evaluating Response to Locoregional Therapy in Hepatocellular Carcinoma

Locoregional therapies (LRTs) play a considerable role in the management of hepatocellular carcinoma (HCC), especially for patients who are not suitable for radical resection or transplantation. In clinical practice, assessment of LRTs is mainly based on computed tomography and MR imaging, but functional and metabolic information is less accessible. This article reviews the use of various the standardized uptake value parameters based on PET and multiple radiotracers for managing HCC after treatment with different LRTs, as well as parts of preclinical research. It discusses the current use of PET in more detail, as well as its advantages, disadvantages, and prospects.

Impact of Hypoxia on Radiation-Based Therapies for Liver Cancer

Background: Hypoxia, a state of low oxygen level within a tissue, is often present in primary and secondary liver tumors. At the molecular level, the tumor cells' response to hypoxic stress induces proteomic and genomic changes which are largely regulated by proteins called hypoxia-induced factors (HIF). These proteins have been found to drive tumor progression and cause resistance to drug- and radiation-based therapies, ultimately contributing to a tumor's poor prognosis. Several imaging modalities have been developed to visualize tissue hypoxia, providing insight into a tumor's microbiology. Methods: A systematic literature search was conducted in PubMed, EMBASE, Cochrane, and Google Scholar for all reports related to hypoxia on liver tumors. All relevant studies were summarized. Results: This review will focus on the impact of hypoxia on liver tumors and review PET-, MRI-, and SPECT-based imaging modalities that have been developed to predict and assess a tumor's response to radiation therapy, with a focus on liver cancers. Conclusion: While there are numerous studies that have evaluated the impact of hypoxia on tumor outcomes, there remains a relative paucity of data evaluating and quantifying hypoxia within the liver. Novel and developing non-invasive imaging techniques able to provide functional and physiological information on tumor hypoxia within the liver may be able to assist in the treatment planning of primary and metastatic liver lesions.

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.

Update on PET Radiopharmaceuticals for Imaging Hepatocellular Carcinoma

Numerous positron emission tomography (PET) targets for detection and staging of hepatocellular cancer have been developed in recent years. Hepatocellular carcinomas (HCCs) are clinically and pathologically heterogeneous tumours with a high tendency to be aggressive and unresponsive to chemotherapy. Early detection is essential, and the need for an adequate imaging biomarker, which can overcome some of the limitations of conventional radiological imaging, is persistent. Flourine-18 (18F) flourodeoxyglucose (FDG), the most widely used PET radiopharmaceutical, has proven disappointing as a possible staple in the evaluation of HCC. This disappointment had led to experimentation with carious radiotracers, such as the choline derivatives, acetate, and prostate-specific membrane antigen, which appear to complement and/or enhance the role of FDG. In this study, we look at the various PET radiopharmaceuticals that have been used for imaging HCC and the particular pathways that they target in HCC and liver cancers.

PET Oncological Radiopharmaceuticals: Current Status and Perspectives

Molecular imaging is the visual representation of biological processes that take place at the cellular or molecular level in living organisms. To date, molecular imaging plays an important role in the transition from conventional medical practice to precision medicine. Among all imaging modalities, positron emission tomography (PET) has great advantages in sensitivity and the ability to obtain absolute imaging quantification after corrections for photon attenuation and scattering. Due to the ability to label a host of unique molecules of biological interest, including endogenous, naturally occurring substrates and drug-like compounds, the role of PET has been well established in the field of molecular imaging. In this article, we provide an overview of the recent advances in the development of PET radiopharmaceuticals and their clinical applications in oncology.