Positron emission tomography in the study of human tumors

How quickly does FLASH need to be delivered? A theoretical study of radiolytic oxygen depletion kinetics in tissues

Purpose. Radiation delivered over ultra-short timescales ('FLASH' radiotherapy) leads to a reduction in normal tissue toxicities for a range of tissues in the preclinical setting. Experiments have shown this reduction occurs for total delivery times less than a 'critical' time that varies by two orders of magnitude between brain (∼0.3 s) and skin (⪆10 s), and three orders of magnitude across different bowel experiments, from ∼0.01 to ⪆(1-10) s. Understanding the factors responsible for this broad variation may be important for translation of FLASH into the clinic and understanding the mechanisms behind FLASH.Methods.Assuming radiolytic oxygen depletion (ROD) to be the primary driver of FLASH effects, oxygen diffusion, consumption, and ROD were evaluated numerically for simulated tissues with pseudorandom vasculatures for a range of radiation delivery times, capillary densities, and oxygen consumption rates (OCR's). The resulting time-dependent oxygen partial pressure distribution histograms were used to estimate cell survival in these tissues using the linear quadratic model, modified to incorporate oxygen-enhancement ratio effects.Results. Independent of the capillary density, there was a substantial increase in predicted cell survival when the total delivery time was less than the capillary oxygen tension (mmHg) divided by the OCR (expressed in units of mmHg/s), setting the critical delivery time for FLASH in simulated tissues. Using literature OCR values for different normal tissues, the predicted range of critical delivery times agreed well with experimental values for skin and brain and, modifying our model to allow for fluctuating perfusion, bowel.Conclusions. The broad three-orders-of-magnitude variation in critical irradiation delivery times observed inin vivopreclinical experiments can be accounted for by the ROD hypothesis and differences in the OCR amongst simulated normal tissues. Characterization of these may help guide future experiments and open the door to optimized tissue-specific clinical protocols.

Review of Thermal and Physiological Properties of Human Breast Tissue

Electromagnetic thermal therapies for cancer treatment, such as microwave hyperthermia, aim to heat up a targeted tumour site to temperatures within 40 and 44 °C. Computational simulations used to investigate such heating systems employ the Pennes' bioheat equation to model the heat exchange within the tissue, which accounts for several tissue properties: density, specific heat capacity, thermal conductivity, metabolic heat generation rate, and blood perfusion rate. We present a review of these thermal and physiological properties relevant for hyperthermia treatments of breast including fibroglandular breast, fatty breast, and breast tumours. The data included in this review were obtained from both experimental measurement studies and estimated properties of human breast tissues. The latter were used in computational studies of breast thermal treatments. The measurement methods, where available, are discussed together with the estimations and approximations considered for values where measurements were unavailable. The review concludes that measurement data for the thermal and physiological properties of breast and tumour tissue are limited. Fibroglandular and fatty breast tissue properties are often approximated from those of generic muscle or fat tissue. Tumour tissue properties are mostly obtained from approximating equations or assumed to be the same as those of glandular tissue. We also present a set of reliable data, which can be used for more accurate modelling and simulation studies to better treat breast cancer using thermal therapies.

Achievement in active agent structures as a power tools in tumor angiogenesis imaging

According to World Health Organization (WHO) cancer is the second most important cause of death globally. Because angiogenesis is considered as an essential process of growth, proliferation and tumor progression, within this review we decided to shade light on recent development of chemical compounds which play a significant role in its imaging and monitoring. Indeed, the review gives insight about the current achievements of active agents structures involved in imaging techniques such as: positron emission computed tomography (PET), magnetic resonance imaging (MRI) and single photon emission computed tomography (SPECT), as well as combination PET/MRI and PET/CT. The review aims to provide the journal audience with a comprehensive and in-deep understanding of chemistry policy in tumor angiogenesis imaging.

Experimental Carbonic Anhydrase Inhibitors for the Treatment of Hypoxic Tumors

Carbonic anhydrase (CA, EC 4.2.1.1) isoforms IX and XII are overexpressed in many hypoxic tumors as a consequence of the hypoxia inducible factor (HIF) activation cascade, being present in limited amounts in normal tissues. These enzymes together with many others are involved in the pH regulation and metabolism of hypoxic cancer cells, and were validated as antitumor targets recently. A multitude of targeting strategies against these enzymes have been proposed and are reviewed in this article. The small molecule inhibitors, small molecule drug conjugates (SMDCs), antibody-drug conjugates (ADACs) or cytokine-drug conjugates but not the monoclonal antibodies against CA IX/XII will be discussed. Relevant synthetic chemistry efforts, coupled with a multitude of preclinical studies, demonstrated that CA IX/XII inhibition leads to the inhibition of growth of primary tumors and metastases and depletes cancer stem cell populations, all factors highly relevant in clinical settings. One small molecule inhibitor, sulfonamide SLC-0111, is the most advanced candidate, having completed Phase I and being now in Phase Ib/II clinical trials for the treatment of advanced hypoxic solid tumors.

Polymerized human hemoglobin facilitated modulation of tumor oxygenation is dependent on tumor oxygenation status and oxygen affinity of the hemoglobin-based oxygen carrier

Administration of hemoglobin-based oxygen carriers (HBOCs) into the systemic circulation is a potential strategy to relieve solid tumor hypoxia in order to increase the effectiveness of chemotherapeutics. Previous computational analysis indicated that the oxygen (O₂) status of the tumor and HBOC O₂ affinity may play a role in increased O₂ delivery to the tumor. However, no study has experimentally investigated how low- and high-affinity HBOCs would perform in normoxic and hypoxic tumors. In this study, we examined how the HBOC, polymerized human hemoglobin (PolyhHb), in the relaxed (R) or tense (T) quaternary state modulates O₂ delivery to hypoxic (FME) and normoxic (LOX) human melanoma xenografts in a murine window chamber model. We examined microcirculatory fluid flow via video shearing optical microscopy, and O₂ distributions via phosphorescence quenching microscopy. Additionally, we examined how weekly infusion of a 20% top-load dose of PolyhHb influences growth rate, vascularization, and regional blood flow in the FME and LOX tumor xenografts. Infusion of low-affinity T-state PolyhHb led to increased tissue oxygenation, decreased blood flow, decreased tumor growth, and decreased vascularization in hypoxic tumors. However, infusion of both T-state and R-state PolyhHbs led to worse outcomes in normoxic tumors. Of particular concern was the high-affinity R-state PolyhHb, which led to no improvement in hypoxic tumors and significantly worsened outcomes in normoxic tumors. Taken together, the results of this study indicate that the tumor O₂ status is a primary determinant of the potency and outcomes of infused PolyhHb.

The glucose transporter GLUT1 is required for ErbB2-induced mammary tumorigenesis

BACKGROUND

Altered tumor cell metabolism is an emerging hallmark of cancer; however, the precise role for glucose in tumor initiation is not known. GLUT1 (SLC2A1) is expressed in breast cancer cells and is likely responsible for avid glucose uptake observed in established tumors. We have shown that GLUT1 was necessary for xenograft tumor formation from primary mammary cells transformed with the polyomavirus middle-T antigen but that it was not necessary for growth after tumors had formed in vivo, suggesting a differential requirement for glucose depending on the stage of tumorigenesis.

METHODS

To determine whether GLUT1 is required early during mammary tumorigenesis, we crossed MMTV-NIC mice, which express activated HER2/NEU/ERBB2 and Cre recombinase, to Slc2a1 ^Flox/Flox (GLUT1^Flox/Flox) mice to generate NIC-GLUT1^+/+, NIC-GLUT1^Flox/+, and NIC-GLUT1^Flox/Flox mice. In addition, we evaluated effects of glucose restriction or GLUT1 inhibition on transformation in MCF10A-ERBB2 breast epithelial cells in three-dimensional culture. Finally, we utilized global gene expression profiling data of primary human breast tumors to determine the relationship between SLC2A1 and stage of tumorigenesis.

RESULTS

All of the NIC-GLUT1^+/+ mice developed tumors in less than 200 days. In contrast, only 1 NIC-GLUT1^Flox/Flox mouse and 1 NIC-GLUT1^Flox/+ mouse developed mammary tumors, even after 18 months. Mammary gland development was not disrupted in NIC mice lacking GLUT1; however, epithelial content of mature glands was reduced compared to NIC-GLUT1^Flox/+ mice. In MCF10A-ERBB2 cells, glucose restriction or GLUT1 inhibition blocked transformation induced by activated ERBB2 through reduced cell proliferation. In human breast cancers, SLC2A1 was higher in ductal carcinoma in situ compared to the normal breast, but lower in invasive versus in situ lesions, suggesting the requirement for GLUT1 decreases as tumors progress.

CONCLUSIONS

This study demonstrates a strict requirement for GLUT1 in the early stages of mammary tumorigenesis in vitro and in vivo. While metabolic adaptation has emerged as a hallmark of cancer, our data indicate that early tumor cells rely heavily on glucose and highlight the potential for glucose restriction as a breast cancer preventive strategy.

Comparison of the Accumulation Kinetics of L-(Methyl-11C)-Methionine and D-(Methyl-11C)-Methionine in Brain Tumors Studied with Positron Emission Tomography

Five patients with glioma were examined with positron emission tomography after the administration of 11C-L-methionine and at a following day with 11C-D-methionine. The rates of accumulation of the tracers were determined in the tumor and in the normal brain tissue according to a graphical technique of Patlak et coll. (24). The accumulation rates for L-methionine were on the average 2.4 times higher than those of D-methionine in the tumors. The corresponding ratio for normal brain tissue was 2.3. It is concluded that in this group of tumors without obvious blood-tumor-barrier breakdown, a stereospecific process with similar properties as in the normal brain tissue, is responsible for the accumulation of the labelled methionine.

Computational Model for Tumor Oxygenation Applied to Clinical Data on Breast Tumor Hemoglobin Concentrations Suggests Vascular Dilatation and Compression

We present a computational model for trans-vascular oxygen transport in synthetic tumor and host tissue blood vessel networks, aiming at qualitatively explaining published data of optical mammography, which were obtained from 87 breast cancer patients. The data generally show average hemoglobin concentration to be higher in tumors versus host tissue whereas average oxy-to total hemoglobin concentration (vascular segment RBC-volume-weighted blood oxygenation) can be above or below normal. Starting from a synthetic arterio-venous initial network the tumor vasculature was generated by processes involving cooption, angiogenesis, and vessel regression. Calculations of spatially resolved blood flow, hematocrit, oxy- and total hemoglobin concentrations, blood and tissue oxygenation were carried out for ninety tumor and associated normal vessel networks starting from various assumed geometries of feeding arteries and draining veins. Spatial heterogeneity in the extra-vascular partial oxygen pressure distribution can be related to various tumor compartments characterized by varying capillary densities and blood flow characteristics. The reported higher average hemoglobin concentration of tumors is explained by growth and dilatation of tumor blood vessels. Even assuming sixfold metabolic rate of oxygen consumption in tumorous versus host tissue, the predicted oxygen hemoglobin concentrations are above normal. Such tumors are likely associated with high tumor blood flow caused by high-caliber blood vessels crossing the tumor volume and hence oxygen supply exceeding oxygen demand. Tumor oxy- to total hemoglobin concentration below normal could only be achieved by reducing tumor vessel radii during growth by a randomly selected factor, simulating compression caused by intra-tumoral solid stress due to proliferation of cells and extracellular matrix. Since compression of blood vessels will impede chemotherapy we conclude that tumors with oxy- to total hemoglobin concentration below normal are less likely to respond to chemotherapy. Such behavior was recently reported for neo-adjuvant chemotherapy of locally advanced breast tumors.

[Positron emission tomography-computed tomography in tumors of the locomotor apparatus]

Positron emission tomography/computed tomography (PET/CT) is a hybrid imaging technique that combines the anatomic information from CT with the metabolic information acquired from PET after the administration of specific radiotracers, the most commonly used of which is F18-fluorodeoxyglucose (FDG). In oncology, this technique is based on the increased uptake of FDG by malignant lesions. In the locomotor apparatus, some uptake by bones and soft tissues is physiological or benign and this uptake must be differentiated from uptake by malignancies, whether primary or secondary. The most important limitations are active inflammatory or infectious processes, which are positive on PET images, and malignant lesions that are smaller than 1cm, cystic, necrotic, or low-grade, which are negative on PET images. PET/CT in the locomotor apparatus is especially useful for the detection of metastases from the most common tumors. It is also used for staging and monitoring the response to treatment of some hematological tumors like lymphoma, where it is fundamental to determine whether the bone marrow has been infiltrated, or myeloma. Lastly, although it is not yet an established indication, PET/CT is being increasingly used to study sarcomas, because it can provide additional information that can be useful for the characterization and grading of tumors, for guiding biopsies, for staging and re-staging, and for evaluating the response to neoadjuvant therapy as well as for evaluating new drugs in clinical trials.

Differential effects of 5-fluorouracil on glucose transport and expressions of glucose transporter proteins in gastric cancer cells

Although 5-fluorouracil (5-FU) is a widely used chemotherapeutic agent in the treatment of gastric cancer, the underlying mechanism for 5-FU resistant phenotype, has yet to be elucidated. We hypothesized that the sensitivity of gastric cancer to 5-FU treatment might be related to the rate of glucose transport (GLUT), and investigated the expressions of GLUT1, 2, 3, and 4 in two different gastric cancer cells (SNU-216, moderately differentiated gastric adenocarcinoma; and SNU-668, signet ring cell gastric carcinoma). Immunohistochemistry of GLUT1 and GLUT4 and immunoblot analysis of glycogen synthase kinase 3 were also performed. Hexokinase activity was measured. We found that 5-FU suppressed glucose uptake in SNU-216, while it stimulated GLUT in SNU-668. Further analysis revealed that 5-FU decreased the expression levels of GLUT1, 2, and 4 in SNU-216 cells and increased the expression levels of GLUT1, 2, and 4 in SNU-668 cells. Consistent with GLUT expression levels, immunohistochemistry analysis showed that 5-FU increased GLUT1 and GLUT4 levels in SNU-216 and decreased GLUT1 and GLUT4 levels in SNU-668. We also observed that glycogen synthase kinase 3 activity was decreased in SNU-216 and increased in SNU-668 with 5-FU treatment. No significant difference in hexokinase activities was observed with 5-FU treatment. Taken together, these results suggest that 5-FU exerts differential effects on GLUT depending on gastric cancer cell types, which may indicate a possible explanation, at least in part, for the differing responses to 5-FU chemotherapy in gastric cancer.

Expression of GLUT1 in primary renal tumors: morphologic and biologic implications

This study aimed to assess whether glucose transporter 1 (GLUT1) is useful in prognostication or differential diagnosis of renal tumors. GLUT1 immunostain for 228 renal tumors showed a membranous or cytoplasmic pattern. The membranous pattern was seen in 86.2% of 145 clear cell renal cell carcinomas (RCCs) and 100% of 11 transitional cell carcinomas (TCCs) but in no oncocytomas, other subtypes of RCC, or sarcomatoid areas of RCCs. The cytoplasmic pattern was seen in 55.2% of 145 clear cell RCCs, 38% of papillary RCCs (11/29), 13% of chromophobe RCCs (2/16), 22% of oncocytomas (5/23), and 82% of TCCs (9/11). Western blot showed a markedly increased GLUT1 protein content in clear cell RCCs compared with a low level in papillary RCCs and normal kidney specimens. GLUT1 expression in clear cell RCC was not significantly correlated with patient survival, tumor grade, or tumor stage. GLUT1 may be a novel target for immunotherapy and a useful marker in the differential diagnosis and classification of renal tumors.

Hypoxia in breast cancer: role of blood flow, oxygen diffusion distances, and anemia in the development of oxygen depletion

Heterogeneously distributed hypoxic areas are a characteristic property of locally advanced breast cancers. Hypoxia results from an imbalance between the supply and consumption of oxygen (O2). Major pathogenetic mechanisms for the emergence of hypoxia are (i) structural and functional abnormalities in the tumor microvasculature, (ii) an adverse diffusion geometry, and (iii) tumor-related and therapy-induced anemia leading to a reduced O2 transport capacity of the blood. There is pronounced intertumor variability in the extent of hypoxia, which is independent of clinical size, stage, histology and grade. Hypoxia is intensified in anemic patients, especially in tumor (areas) with low perfusion rates. Tumor hypoxia is a therapeutic problem since it makes solid tumors resistant to sparsely ionizing radiation, some forms of chemotherapy, and photodynamic therapy. However, besides more direct mechanisms involved in the development of therapeutic resistance, there are, in addition, indirect machineries that can cause barriers to therapies. These include hypoxia-mediated alterations in gene expression, proteomic and genomic changes, and clonal selection. These in turn can drive subsequent events that are known to further increase resistance to therapy in addition to critically affecting long-term prognosis.

Molecular and cellular regulation of glucose transporter (GLUT) proteins in cancer

Malignant cells are known to have accelerated metabolism, high glucose requirements, and increased glucose uptake. Transport of glucose across the plasma membrane of mammalian cells is the first rate-limiting step for glucose metabolism and is mediated by facilitative glucose transporter (GLUT) proteins. Increased glucose transport in malignant cells has been associated with increased and deregulated expression of glucose transporter proteins, with overexpression of GLUT1 and/or GLUT3 a characteristic feature. Oncogenic transformation of cultured mammalian cells causes a rapid increase of glucose transport and GLUT1 expression via interaction with GLUT1 promoter enhancer elements. In human studies, high levels of GLUT1 expression in tumors have been associated with poor survival. Studies indicate that glucose transport in breast cancer is not fully explained by GLUT1 or GLUT3 expression, suggesting involvement of another glucose transporter. Recently, a novel glucose transporter protein, GLUT12, has been found in breast and prostate cancers. In human breast and prostate tumors and cultured cells, GLUT12 is located intracellularly and at the cell surface. Trafficking of GLUT12 to the plasma membrane could therefore contribute to glucose uptake. Several factors have been implicated in the regulation of glucose transporter expression in breast cancer. Hypoxia can increase GLUT1 levels and glucose uptake. Estradiol and epidermal growth factor, both of which can play a role in breast cancer cell growth, increase glucose consumption. Estradiol and epidermal growth factor also increase GLUT12 protein levels in cultured breast cancer cells. Targeting GLUT12 could provide novel methods for detection and treatment of breast and prostate cancer.

Comparison of Arterial Spin-Labeling Techniques and Dynamic Susceptibility-Weighted Contrast-Enhanced MRI in Perfusion Imaging of Normal Brain Tissue

OBJECTIVES

To evaluate relative cerebral blood flow (rCBF) in normal brain tissue using arterial spin-labeling (ASL) methods and first-pass dynamic susceptibility-weighted contrast-enhanced (DSC) magnetic resonance imaging (MRI).

METHODS

Sixty-two patients with brain metastases were examined on a 1.5 T-system up to 6 times during routine follow-up after stereotactic radiosurgery. Perfusion values in normal gray and white matter were measured using the ASL techniques ITS-FAIR in 38 patients, Q2TIPS in 62 patients, and the first-pass DSC echo-planar (EPI) MRI after bolus administration of gadopentetate dimeglumine in 42 patients. Precision of the ASL sequences was tested in follow-up examinations in 10 healthy volunteers.

RESULTS

Perfusion values in normal brain tissue obtained by all sequences correlated well by calculating Pearson's correlation coefficients (P < 0.0001) and remained unchanged after stereotactic radiosurgery as shown by analysis of variance (P > 0.05).

CONCLUSION

Both ASL and DSC EPI MRI yield highly comparable perfusion values in normal brain tissue.

Utilization of metabolic, transport and receptor-mediated processes to deliver agents for cancer diagnosis

The use of radiopharmaceuticals for the non-invasive diagnosis of cancer has been established in diagnostic radiology over the last few decades. In particular, with the use of sophisticated imaging modalities such as PET and SPECT and a myriad of radioisotopes, advances have been made in the detection and treatment of cancer. This article focuses on three available methods of tumor targeting with radiopharmaceuticals: the utilization of metabolic, transport and receptor-mediated processes to deliver agents for cancer diagnosis. With selected reference to both clinically approved drugs and drugs currently under development, methods of uptake are presented either in terms of flow, metabolic or receptor mediated uptakes. A section of this article is devoted to the monitoring of cancer therapy regimes using radiopharmaceuticals. This review also discusses some mechanistic approaches available in radiopharmaceutical chemistry to be able to effectively diagnose and treat sufferers of cancer in the future.

PET scanning in head and neck oncology: a review

BACKGROUND

The objective of this study was to review and describe the usage of fluorine-labeled deoxyglucose (FDG) and positron emission tomography (PET) in the diagnosis and management of head and neck cancer.

METHODS

Several prospective series,-including 159 newly diagnosed and previously untreated and 23 previously irradiated head and neck squamous cell carcinoma patients initially seen at the Wake Forest University Medical Center and evaluated by clinical examination, conventional computed tomography/ magnetic resonance imaging (CT/MRI) scans, PET scans, and histopathologic studies,-were reviewed and the findings summarized for comparison of the correct differentiation of primary and metastatic cancers and for postirradiation tumor clearance in a subsegment of those cases.

RESULTS

Positron emission tomography scanning using a fluorine-labeled deoxyglucose (FDG) radiotracer proved as reliable as conventional scanning for primary and metastatic tumor identification. Compared with clinical examination, PET was better for identification of nodal metastatic tumors but poorer for small primary tumors. For previously irradiated patients treated at least 4 months before the test, PET scanning was clearly superior to clinical examination and conventional imaging in differentiating tumor recurrence from soft-tissue irradiation effects.

CONCLUSIONS

Fluorine-labeled deoxyglucose-PET scanning is comparable to conventional imaging of head and neck cancers in detecting primary and metastatic carcinoma. Lack of anatomic detail remains its major drawback. Currently, its greatest role is in the evaluation of the postradiotherapy patient.

Radioimmunoscintigraphy in patients with breast adenocarcinoma using technetium-99m labelled monoclonal antibody 170H.82: report of a phase II study

Fifty-three women with clinical evidence of adenocarcinoma of the breast were studied with technetium-99m labelled monoclonal antibody (MAb) 170H.82 at protein doses of 1, 2 and 4 mg. An overall per lesion efficacy of 83.5% sensitivity and 97.7% positive predictive value was obtained. Efficacy appears higher in lesions restricted to the breast and local regional disease than systemic metastases. For the 2 mg dose the breast/local regional disease efficacy was 90% sensitivity and 90.2% positive predictive value. The biodistribution of this MAb was best represented by a two-compartment model with a distribution-phase half-life of 4.0+/-1.4 h, followed by an elimination-phase half-life of 39.6+/-6.6 h. In all six patients studied, the critical organ was the kidney, with a mean radiation absorbed dose of 37+/-6.9 mGy/GBq. The accuracy of this imaging technique allows the development of diagnostic strategies for the routine use of the compound in patients with breast cancer.

Positron emission tomography. A new tool for characterization of malignant disease and selection of therapy

Present therapy for cancer patients is based primarily on tumor histology and anatomy. Despite treatment advances, clinicians have often been frustrated by their inability to assess tumor biology. Metabolic imaging by positron emission tomography is a promising new technology that has opened up a whole realm of study in oncology. Glucose metabolism, hemodynamics, oxygen utilization, protein synthesis and thymidine incorporation may yield valuable data regarding tumor aggressiveness and stage, and allow assessment of tumor response early during treatment, before morphological changes are detectable. Other metabolic determinations, including tumor hypoxia and estrogen receptor density, may predict tumor response to therapy, and lead to selection of more appropriate treatment regimens, such as with neutrons or hypoxic cell sensitizers for documentably hypoxic tumors. While further clinical validation is required, positron emission tomography promises to provide vital information complementary to present anatomical imaging modalities that will aid oncologists in optimal management of their patients.

Positron emission tomography with fluorine-18-deoxyglucose in the detection and staging of breast cancer

BACKGROUND

An increasing number of patients with breast cancer is being treated with preoperative chemotherapy. Evaluation of treatment response may be facilitated by positron emission tomography (PET) with 18F-fluoro-2-deoxy-D-glucose (FDG). This noninvasive technique may allow prediction of the chemotherapy outcome in an early phase of the treatment.

METHODS

Prerequisites for treatment monitoring with PET are good FDG uptake in the tumor, high specificity, and a reliable quantification technique. These factors were studied in 20 patients with primary breast cancer, lymph node metastases, benign breast lesions, a combination of these abnormalities, or no abnormality.

RESULTS

In 10 of 11 patients with primary breast cancer, the tumor was visualized. The median tumor-to-normal-tissue-uptake ratio was 4.9. In all five patients with increased uptake in the lymph node basin, pathologic proof of metastatic cancer was found. Of the patients with benign or no disease of the breast, slightly increased uptake was seen in one patient with fibrocystic disease.

CONCLUSION

It is concluded that PET with FDG can be used for breast cancer imaging and staging.

Recurrent malignant glioma: detection with 131I labeled monoclonal antibody G-22, positron emission tomography and magnetic resonance imaging

A 45-year-old man with suspected recurrent malignant glioma was evaluated by magnetic resonance imaging (MRI), positron emission tomography (PET) and 131I labeled monoclonal antibody G-22 (G-22) scan. Following Gadolinium-DTPA, a TI-weighted spin echo image (TR 500 msec, TE 20 msec) demonstrated a large mass with an irregular margin in the left temporo-parietal area. An 18F labeled fluorodeoxyglucose PET study demonstrated marked accumulations in the left temporo-parietal area. Serial 131I-G-22 scintigraphy was obtained for a week after the injection. The uptake was most increased on the 2nd day after the injection. 131I G-22 was specific for tumor-associated antigens.

Synthesis of [18F]fluoroalanine and [18F]fluorotamoxifen for imaging breast tumors

To develop ligands for imaging breast tumors, [18F]fluoro analogue of tamoxifen and [18F]fluoroalanine were radiosynthesized. In vivo biodistribution studies were performed in mammary tumor-bearing rats. In studies on the biodistribution of an [18F]fluoro analogue of tamoxifen, tumor uptake decreased when rats were pretreated with diethylstilbestrol (DES), suggesting that tracer uptake in tumors was receptor-mediated. An estrogen receptor assay indicated that tumors have a receptor density of 7.5 fmol/mg protein. Studies of the distribution of [18F]fluoroalanine in tissue showed that the tumor-to-tissue ratio increases as a function of time. Positron emission tomography (PET) images of tumor-bearing rats demonstrated that tumors can be visualized 1 h after rats are injected with an [18F]fluoro analogue of tamoxifen. PET imaging of pigs after injection of 10 mCi of [18F]fluoro analogue of tamoxifen showed uterine uptake that could be blocked by DES (50 mg). The findings suggest that both radiotracers are useful for imaging breast tumors.

Functional imaging of the brain using single photon emission computerized tomography (SPECT)

The use of tracers is an important technique available for studying cerebral function. Changes in 'signal' are large, but as a result of its photon limited nature, the measurement of this signal is limited: spatially, temporally and in terms of accuracy. The most commonly used single photon (SPECT) system (as apposed to positron) is that with a rotating gamma camera, although multi-headed devices and special purpose rings are now also commonly available. The problems of obtaining good functional information are however identical. Firstly the devices need to be optimised in terms of resolution and sensitivity. Secondly several sources of error, notably those associated with scatter, attenuation and limited spatial resolution, need to be corrected, with the aim of obtaining quantitative estimates of radioactivity concentration. Finally such quantitative estimates need to be converted into meaningful estimates of physiological variables by use of an appropriate model. The general aim of many SPECT measurements is to estimate blood flow for example using Tc-99m labelled HMPAO as a tracer. Good results have been obtained in many clinical conditions: stroke, dementia, tumour and epilepsy, for example. Many other tracers are also available, for example to measure density of receptor sites. The use of SPECT in conjunction with other techniques after image registration is suggested as being an essential tool in extracting maximal clinical information.

[14C]deoxyglucose uptake and imaging in malignant melanoma

Since malignant tumors utilize more glucose than normal tissues, tumor uptake and autoradiographic imaging studies using the 14C-labeled glucose analog 2-deoxyglucose (DG) provide a useful preclinical system to determine if similar human tumors will image in vivo with positron emission tomography (PET) using 18F-labeled DG (FDG-PET). We studied B16 murine melanomas of increasing metastatic potential (F1, low; BL-6, intermediate; F10, high) as a feasibility study to determine the potential for human melanoma imaging using FDG-PET. Male C57BL-6 mice (50 g) were implanted sc with 1-mm3 fragments of B16 melanomas. Fourteen days later mice were injected ip with 1.25 muCi of [14C]DG. Sixty minutes later tumor (T) and gastrocnemius muscle (M) were harvested, solubilized, and counted for [14C]DG dpm/mg to estimate glucose utilization. Autoradiographic imaging was carried out similarly, using 2.0 muCi or [14C]DG with 30-day exposure of T and M tissue sections (20 microns thick) to X-ray film. The uptake of [14C]DG (expressed as dpm/mg; % injected dose/g; and tumor-to-muscle uptake ratios) was 6 to 10 times higher in tumors than in muscle tissue (P less than 0.001). All three melanoma cell lines imaged successfully with [14C]DG autoradiography. Tumor uptake of [14C]DG did not correlate with increasing metastatic potential. The experimental B16 murine melanomas F1, BL-6, and F10 extract glucose at higher rates than muscle tissue, a property necessary for successful PET imaging of cutaneous melanoma. The lack of correlation between glucose extraction and metastatic potential suggests that the demands for glucose during tumor growth and metastasis are not related. This is the first laboratory study to predict that human malignant melanoma will image with FDG-PET.

State-of-the-art of external photon beam radiation treatment planning. Photon Treatment Planning Collaborative Working Group

A virtual revolution in computer capability has occurred in the last few years, largely based on rapidly decreasing costs and increasing reliability of digital memory and mass-storage capability. These developments have now made it possible to consider the application of both computer and display technologies to a much broader range of problems in radiation therapy, including planning of treatment, dose computation, and treatment verification. Several methods of three-dimensional dose computations in heterogeneous media capable of 3% accuracy are likely to be available, but significant work still remains, particularly for high energy x-rays where electron transport, and possibly pair production, need to be considered. Innovative display and planning techniques, as well as plan evaluation schemes, are emerging and show great promise for the future. No doubt these advances will lead to substantially improved treatment planning systems in the next few years. However, it must be emphasized that for many of these applications a tremendous software and hardware development effort is required.

Quantitative measurement of monoclonal antibody distribution and blood flow using positron emission tomography and 124iodine in patients with breast cancer

The uptake and in vivo quantitation of monoclonal antibodies (MAbs) has been measured non-invasively using positron emission tomography (PET) and 124iodine in 9 patients with breast ductal carcinoma. Blood-flow measurements were also made using 15oxygen-labelled water and PET to evaluate antibody delivery; 7 patients were studied with HMFGI antibody and 2 patients with a non-specific antibody. Tumour uptake ranged from 2-7.7 x 10(-3)% of injected dose per gram of tissue. Values for normal tissues including liver, lung and bone were also obtained. In 2 out of 7 patients studied with the specific antibody, uptake was greater than that seen with the non-specific antibody. There was no correlation between antibody uptake and blood flow. This report exemplifies the potential of PET for the non-invasive and accurate quantitative assessment of targeted antibody which is a prerequisite to therapy.

Monoclonal antibodies and neuroblastoma

Several antineuroblastoma monoclonal antibodies (MoAbs) have been described and two have been used in radioimmunoimaging and radioimmunotherapy in patients. MoAb 3F8 is a murine IgG3 antibody specific for the ganglioside GD2. Radioiodine-labeled 3F8 has been shown to specifically target human neuroblastoma in patients, and radioimmunoimaging with this agent has provided consistently high uptakes with tumor-to-background ratios of greater than or equal to 10:1. Radioimmunotherapy has been attempted with both MoAb 3F8 and MoAb UJ13A, and although encouraging results have been obtained, dosimetry data and tissue dose response information for these agents is lacking, which impedes the development of such therapy. 124I, a positron emitter, can be used with 3F8 in positron emission tomography (PET) scanning to provide dosimetry information for radioimmunotherapy. The tumor radiation dose response from radiolabeled MoAb also can be followed with PET images with fluorodeoxyglucose (FDG) scanning of neuroblastoma tumors. Results to date indicate that radioimmunoimaging has clinical use in the diagnosis of neuroblastoma and the potential for radioimmunotherapy for this cancer remains high.

Monitoring the transport and phosphorylation of 2-deoxy-D-glucose in tumor cells in vivo and in vitro by 13C nuclear magnetic resonance spectroscopy

We describe the use of 2-deoxy-D-[6-13C]glucose to follow simultaneously, by 13C NMR, both transport and phosphorylation to its 6-phosphate form, in MCF-7 breast cancer cells in vitro and in vivo in subcutaneous tumors in nude mice.

Biodistribution and scintigraphy of 11C-toremifene in rats bearing DMBA-induced mammary carcinoma

A new antioestrogenic antitumour compound toremifene was labeled with 11C or 3H. The tissue distribution and tumour uptake of the compounds in DMBA induced breast tumour bearing rats was investigated. 11C-toremifene was localized by gamma camera scintigraphy and tissue counting. 3H-Toremifene was determined by liquid scintillation counting after oxidizing the tissue samples. Toremifene was distributed to several tissues due to the lipophilicity and was not taken up specifically by the tumours to any great extent. However, the radioactivity of the tumours increased as a function of time although it declined e.g. in the liver. The accumulation to the tumour was a slow process and cannot be followed up reliably by such short half-life radionuclides as 11C. The tumour uptake properties of toremifene resemble those of tamoxifen and several other oestrogen receptor binding compounds. These substances have limited use in diagnosing and imaging oestrogen receptor rich breast tumours in man.

Early and late stage positron emission tomography (PET) studies on the haemocirculation and metabolism of seemingly normal brain tissue in patients with gliomas following radiochemotherapy

Haemocirculatory and metabolic changes in seemingly normal brain tissue following radiochemotherapy including nimustine hydrochloride (ACNU) and tegafur (FT) were analyzed using oxygen-15 and fluorine-18 positron emission tomography (PET) in seven patients with gliomas. At an early stage (within one month) after radiochemotherapy, marginal increases in regional cerebral blood flow (rCBF) and cerebral blood volume (rCBV) were found contralateral to the tumour in gray matter which was apparently normal brain structure, as seen on computerized tomography (CT). The oxygen extraction fraction (rOEF) decreased significantly (p less than 0.05 by a paired-t test) from that of the pretreatment study, due to surgical decompression and radiochemotherapy. At the late stage (three to thirty-one months with a mean of thirteen months), rCBF decreased significantly from the early stage study (p less than 0.05); oxygen consumption (rCMRO2) fell in all cases significantly from the pretreatment study (p less than 0.01) and from the early stage study (p less than 0.05); consequently, rOEF remained unchanged at a level similar to the early stage study. Glucose consumption (rCMRG1) increased slightly as compared with the early stage study but failed to be restored to the level of the pretreatment study. Noteworthy was a coupling reduction of rCBF and rCMRO2--presumably, a late delayed effect of radiochemotherapy. These preliminary results indicate that with PET studies it may be possible to predict damage to normal brain tissue after radiochemotherapy.

PET in clinical oncology

Positron Emission Tomography (PET) is an imaging technique that produces cross sectional images based on tissue biochemical and physiological processes. PET complements other anatomic imaging techniques such as x-ray CT and magnetic resonance imaging (MRI). Fundamental processes such as glucose metabolism, oxygen metabolism, and blood flow can be imaged and quantified with PET, in addition to many other processes of both clinical and investigative interest. PET is now emerging as a clinical tool in oncology and is useful in noninvasively grading tumors, in determining tumor activity and recurrence, and in monitoring the effects of a variety of therapeutic interventions with tumors. While most of the applications of PET in oncology to date have been in brain tumors, the technique is now being applied in tumor evaluations outside of the central nervous system.

Fluorodeoxyglucose imaging: a method to assess the proliferative activity of human cancer in vivo. Comparison with DNA flow cytometry in head and neck tumors

Thirteen patients with malignant head and neck tumors were studied before they were treated with (18F) fluorodeoxyglucose (FDG) imaging and DNA flow cytometry (FCM). The nuclear DNA content and the percentage of proliferative cells (S + G2/M) were compared with the FDG uptake; FDG was retained in the primary tumor and/or neck metastasis in all patients. The accumulation of FDG did not correlate with histologic grade of the tumors, but there was a clear correlation (r = 0.86, P less than 0.001) between the proportion of the cells in S + G2/M phases of the cell cycle and the intensity of FDG accumulation. The uptake of FDG by the tumor also correlated with the percentage of S-phase cells (r = 0.82, P less than 0.001). The result suggests that enhanced glucose metabolism, measured by FDG uptake, is associated with the proliferative activity of the tumor. Thus, imaging with FDG may offer a new method to assess the aggressiveness of human cancer growth in vivo.

Initial experience with Tc-99m-HM-PAO in the study of brain tumors

A preliminary study of the distribution of the 99mTc complex of hexamethylpropylene amine oxime (HM-PAO) in 12 patients with brain neoplasms before, during, and after radiotherapy has been performed. Untreated brain tumors were found to exhibit a range of 99mTc-HM-PAO uptake, varying from areas of markedly increased isotope activity to photopenic areas, when compared to normal brain tissue. A ratio of 99mTc-HM-PAO tumor uptake to contralateral normal tissue uptake was calculated prior to and during radiotherapy. This ratio tended to return towards unity in lesions responding to therapy. A predictable alteration in whole brain 99mTc-HM-PAO uptake during radiotherapy was not demonstrated. Unlike the radiolabeled amines, 99mTc-HM-PAO localizes in primary tumors, probably indicating that its uptake mechanism is independent of non specific amine receptors. 99mTc-HM-PAO may be useful in the study of brain tumor physiology and response to therapy.

Positron emission tomographic evaluation of radiochemotherapeutic effect on regional cerebral hemocirculation and metabolism in patients with gliomas

Hemocirculatory and metabolic changes in tumor regions and the remote brain structure were analyzed using oxygen-15 and fluorine-18 positron emission tomography (PET) in eight patients with gliomas after radiation and chemotherapy of 1-(4-amino-2-methyl-5-pyrimidinyl)methyl-3-(2-chloroethyl)-3-nitrosourea hydrochloride (ACNU) and N-(2-tetrahydrofuryl)-5-fluorouracil (FT-207). In the tumor regions after the radiochemotherapy, regional cerebral blood flow (rCBF) and cerebral blood volume (rCBV) varied widely and there was a tendency for oxygen consumption (rCMRO2) to fall. The change in glucose consumption (rCMRG1) was especially noteworthy with regard to clinical correlations. Six patients with decreased rCMRG1 values had 16% to 29% regressions in tumor size measured by X-ray computerized tomography (CT), and showed some period of clinical relief. In contrast, one patient with an increased rCMRG1 value had some progression of tumor growth, and there were no clinical amelioration. The hemocirculation and metabolism of the contralateral gray matter seem to fluctuate by various factors as intracranial pressure and the effectiveness of the therapy. In gliomas therapy, tumor rCMRG1 values can be a good indicator of therapeutic effectiveness.

Clinical comparison of 11C-ACPC (aminocyclopentane carboxylic acid) and 13N-ammonia as tumour tracers

Positron emission tomography is a potential method for exploring the biochemical behaviour of tumours. In 28 patients with known neoplastic lesions a comparison was made between two agents which are known to be accumulated in malignant tumours, viz. 13N-ammonia and 11C-aminocyclopentane carboxylic acid (ACPC). Absolute concentration of both agents in various tumoural tissues and normal organs was calculated. As a rule a parallelism was found between the two tracers as to their accumulation in a given tumour, although the concentration was often higher for ACPC. In normal tissues the ACPC accumulation was either lower or at most equal to NH3 levels. As tumour tracer ACPC is superior to NH3 because of its higher absolute accumulation in many neoplastic lesions and its lower uptake in various non-tumorous tissues. ACPC concentration in tumours seems to be largely independent of blood flow.