Metabolic imaging by positron emission tomography in oncology

Central nervous system toxicity from cancer treatment

Neurologic complications of cancer therapy are an increasingly important concern in patient management. Improvements in systemic therapies and increasing use of local treatments to target such specific tumor sites as brain or leptomeningeal metastases have resulted in increased incidence of treatment toxicity in the central nervous system (CNS). Recognition of specific treatment-related toxicities, and more importantly, differentiation of treatment toxicity from reversible causes of neurologic dysfunction, are critical. This article reviews the evaluation and treatment of major CNS toxicities related to cancer treatment and conditions that present with similar signs and symptoms. The three most common of these, alterations in cognition and consciousness, seizures, and cerebellar dysfunction, are discussed. Prompt recognition of these problems and their causes will have an impact on patient care in all areas of oncology.

Hypoxia imaging in brain tumors

Assessment of the oxygenation status of brain tumors has been studied increasingly with imaging techniques in light of recent advances in oncology. Tumor oxygen tension is a critical factor influencing the effectiveness of radiation and chemotherapy and malignant progression. Hypoxic tumors are resistant to treatment, and prognostic value of tumor oxygen status is shown in head and neck tumors. Strategies increasing the tumor oxygenation are being investigated to overcome the compromising [figure: see text] effect of hypoxia on tumor treatment. Administration of nicotinamide and inhalation of various high oxygen concentrations have been implemented. Existing methods for assessment of tissue oxygen level are either invasive or insufficient. Accurate and noninvasive means to measure tumor oxygenation are needed for treatment planning, identification of patients who might benefit from oxygenation strategies, and assessing the efficacy of interventions aimed to increase the radiosensitivity of tumors. Of the various imaging techniques used to assess tissue oxygenation, MR spectroscopy and MR imaging are widely available, noninvasive, and clinically applicable techniques. Tumor hypoxia is related closely to insufficient blood flow through chaotic and partially nonfunctional tumor vasculature and the distance between the capillaries and the tumor cells. Information on characteristics of tumor vasculature such as blood volume, perfusion, and increased capillary permeability can be provided with MR imaging. MR imaging techniques can provide a measure of capillary permeability based on contrast enhancement and relative cerebral blood volume estimates using dynamic susceptibility MR imaging. Blood oxygen level dependent contrast MR imaging using gradient echo sequence is intrinsically sensitive to changes in blood oxygen level. Animal models using blood oxygen level-dependent contrast imaging reveal the different responses of normal and tumor vasculature under hyperoxia. Normobaric hyperoxia is used in MR studies as a method to produce MR contrast in tissues. Increased T2* signal intensity of brain tissue has been observed using blood oxygen level-dependent contrast MR imaging. Dynamic blood oxygen level-dependent contrast MR imaging during hyperoxia is suggested to image tumor oxygenation. Quantification of cerebral oxygen saturation using blood oxygen level-dependent MR imaging also has been reported. Quantification of cerebral blood oxygen saturation using MR imaging has promising clinical applications; however, technical difficulties have to be resolved. Blood oxygen level dependent MR imaging is an emerging technique to evaluate the cerebral blood oxygen saturation, and it has the potential and versatility to assess oxygenation status of brain tumors. Upon improvement and validation of current MR techniques, better diagnostic, prognostic, and treatment monitoring capabilities can be provided for patients with brain tumors.

Is enteral administration of fluorine-18-fluorodeoxyglucose (F-18 FDG) a palatable alternative to IV injection? Pre-clinical evaluation in normal rodents

To establish effective methods of enteral 2-[18F]-fluoro-2-deoxy-D-glucose (FDG) administration, the efficiency of FDG absorption in the gastrointestinal tracts following enteral administrations was evaluated using the FDG biodistribution in normal rodents, in combination with various fasting conditions and FDG diluents. The blood FDG curve using hypotonic solution showed a rapid increase, while that in iso- and hypertonic groups showed slow rises. Brain FDG uptake had a close positive correlation with blood AUC (area under curve) and an inverse relationship with the stomach contents.

Effects of substituting a OH group by a F atom in D-glucose. Ab initio and DFT analysis

High-level ab initio and DFT methods up to MP2/6-311++G//B3LYP/6-31G and B3LYP/6-311++G//B3LYP/6-31G levels have been used to assess the relative energies of 17 different structures of D-glucose and 13 different structures of 4-deoxy-4-fluoro-D-glucose. The structures were confirmed to correspond to minima on the potential energy surface at the RHF/6-31G level. Solvation Model 5.4/AM1 was used to calculate the effects of aqueous solution. The substitution of a OH group by a F atom does not much change the shape and electrostatic potential around corresponding conformers, but in the gas phase it destabilizes the cooperative network of intramolecular hydrogen bonds. This destabilization mostly affects structures with a chain of intramolecular hydrogen bonds oriented counterclockwise, as fluorine is unable to donate a hydrogen bond and therefore causes a gap in the chain. In contrast, for clockwise-oriented networks of hydrogen bonds, the fluorine can act as an acceptor at the end of a chain of cooperative hydrogen bonds. A slightly higher energy of anomeric and exo-anomeric stabilization is another effect of substituting the fourth hydroxyl group by a fluorine atom in D-glucose, observed both in the gas phase and in aqueous solution. For this reason, the alpha anomers contribute more to the equilibrium population of structures of 4-deoxy-4-fluoro-D-glucose than D-glucose. In aqueous solution, both D-glucose and its 4-deoxy-4-fluoro analogue are present as a mixture of mainly three corresponding structures. This indicates that 4-deoxy-4-fluoro-D-glucose is a good substitute for D-glucose in terms of its biochemical and biological activity. Moreover, this suggests that, for molecules with limited conformational freedom, the substitution of a OH group by a F atom is very likely to lead to a potential new drug. In contrast, it had already been shown that, for conformationally labile aliphatic compounds, replacement of a hydroxyl by a fluorine increases conformational diversity, so the fluorine-containing aliphatic molecules were not likely to be an example of a successful drug design. On the other hand, this work shows that, among molecules with limited conformational freedom, such as cyclic compounds, one is very likely to find targets for a successful rational drug design.

2[F]-fluoro-2-deoxy-D-glucose positron emission tomography is a sensitive tool for the detection of occult primary cancer (carcinoma of unknown primary syndrome) with head and neck lymph node manifestation

BACKGROUND

The neck lymph nodes are a common site of metastases from carcinoma of unknown primary (CUP syndrome). 2[(18) F]-fluoro-2-deoxy-D-glucose positron emission tomography (18-FDG-PET) has been shown to be a sensitive tool for detecting primary malignant lesions as well as metastatic spread. We have prospectively investigated the sensitivity of 18-FDG-PET in detecting occult primary carcinomas with manifestation in the head and neck lymph nodes.

METHODS

From May 1994 to July 1998, in 723 patients a cancer of the head and neck was diagnosed at the University of Cologne ENT outpatient clinic. The routinely performed staging procedures were chest radiography; full blood count; cervical and liver ultrasound; endoscopy of the nasopharynx, oropharynx, hypopharynx, larynx, and esophagus; and laboratory analyses. After the staging workup, in 27 of 723 patients (3.7%) CUP syndrome had to be presumed because the primary cancer could not be detected. In these patients 18-FDG-PET was performed, and images were reconstructed with a transmission-emission fusion technique.

RESULTS

In 7 of 27 patients (26%) 18-FDG-PET revealed an unknown primary: in 2 a bronchial carcinoma, in 2 a nasopharyngeal carcinoma, in 1 a squamous cell carcinoma of the parotid gland, in 1 a squamous cell carcinoma of the hypopharynx, and in 1 a carcinoma of the tonsil. In 4 of 7 patients the occult primary tumor was removed surgically. In 8 of 27 patients therapeutic strategy was changed as a result of the 18-FDG-PET findings.

CONCLUSION

18-FDG-PET should be performed in all patients with CUP syndrome after conventional diagnostic workup fails to identify the primary.