From tumor biology to clinical Pet: a review of positron emission tomography (PET) in oncology

Detection of local residual tumor after laryngeal cancer treatment using FDG-PET

OBJECTIVE

Fluorine-18-fluorodeoxyglucose positron emission tomography (FDG-PET) is sometimes used as a means of follow-up after diagnosis and treatment of cancers of the head and neck region. The present study was undertaken to evaluate the ability of FDG-PET to detect local residual tumor after treatment of laryngeal cancer.

METHODS

Thirty-six patients with laryngeal cancer underwent FDG-PET before and after initial treatment. Of these patients, 20 received FDG-PET before treatment and 28 received it after treatment. The relationship between standardized uptake values (SUV) and the presence or absence of local residual tumor was investigated by setting the cut-off value of the SUV using the receiver operating characteristics (ROC) curve.

RESULTS

When the pre-treatment SUV threshold for laryngeal cancer was set at 7.20, the detection of local residual tumor after treatment using FDG-PET had a sensitivity of 77.78%, specificity of 81.82%, false positive rate of 18.18%, false negative rate of 22.22%, accuracy of 80% and a p value of 0.02. When the post-treatment SUV threshold for the larynx was set at 3.35, the test had a sensitivity of 93.75%, specificity of 91.67%, false positive rate of 8.33%, false negative rate of 6.25%, accuracy of 92.86% and a p value of 0.0001.

CONCLUSIONS

FDG-PET was found to be useful for determining the presence of local residual tumor after treatment of laryngeal cancer.

Role of positron emission tomography in decisions on treatment strategies for pancreatic cancer

BACKGROUND/PURPOSE

The purpose of this study was to estimate the usefulness of positron emission tomography (PET) in deciding on strategies for the treatment of pancreatic cancer. The following two parameters were evaluated: the ability of PET to provide an estimation of the progression of pancreatic cancer, and the ability of PET to predict survival and the effect of chemoradiotherapy.

METHODS

Forty-two patients underwent PET as part of the procedure for making a diagnosis of pancreatic tumors. The maximum standardized uptake value (SUVmax) levels were compared with clinicopathological factors and analyzed.

RESULTS

PET provided a sensitivity of 87%, a specificity of 67%, and an overall accuracy of 85% for the diagnosis of pancreatic malignancy. Tumors with distant metastases showed significantly higher SUV levels than tumors without metastasis. In the patients who received chemoradiotherapy, the overall survival of the group in which SUVmax was less than 7.0 was better than that of the group in which SUVmax was more than 7.0.

CONCLUSIONS

We conclude that PET is a useful tool for determining pathological status and distant metastasis in pancreatic cancer, and for predicting the prognosis of patients receiving chemoradiotherapy.

Diffuse optical imaging and spectroscopy for cancer

Visible light and near infrared light interact with biological tissue by absorption and scattering. Diffuse optical imaging and spectroscopy reconstructs tissue physiologic parameters based on noninvasive measurement of tissue optical properties. This technology can be used to differentiate physiologic and molecular signatures of both malignant and benign tissues, as they relate to the area of cancer research. Major advantages are the use of non-ionizing radiation, real-time continuous data acquisition, low cost, and portability. Limitations include low spatial resolution and limited reproducibility. This paper reviews the currently available state-of-the-art technologies for diffuse optical imaging and spectroscopy and their applications in cancer research.

Diagnostic accuracy of FDG PET in the follow-up of platinum-sensitive epithelial ovarian carcinoma

PURPOSE

This study was designed to retrospectively evaluate the diagnostic yield of FDG PET for the diagnosis of recurrent ovarian cancer.

METHODS

Eighty FDG PET scans were performed on 55 patients owing to suspicion of relapse, and 45 FDG PET scans were performed on 31 patients who were clinically disease free. PET results were compared with the results of conventional radiological imaging (CIM) and serum CA 125 levels, and related to pathological findings in 54 cases or clinical follow-up in 71 cases.

RESULTS

CIM correctly identified 49 cases with recurrence [sensitivity (SE) 53.3%] ,and there were 27 true negatives [specificity (SP) 81.8%] However, 43 cases were false negative and six were false positive. The positive predictive value (PPV), negative predictive value (NPV) and accuracy (ACC) of CIM were 89%, 38.6% and 60.8%, respectively. FDG PET correctly detected recurrent disease in 80/92 cases (SE 86.9%, p<0.05) and ruled out relapse in 26/33 cases (SP=78.8%). The PPV, NPV and ACC of PET were 91.9%, 68.4% and 84.8%, respectively. Standardised uptake values did not provide additional diagnostic accuracy compared with visual analysis. The CA 125 results showed an SE of 57.6%, an SP of 93.9% and an ACC of 67.2%. In 23 patients with positive serum CA 125 levels, but negative CIM, FDG PET was positive and relapse was confirmed. Furthermore, FDG PET was positive and relapse was confirmed in 11 patients with negative serum CA 125 levels and CIM.

CONCLUSION

FDG PET may detect recurrent ovarian cancer earlier than CIM, with higher sensitivity and even higher diagnostic accuracy.

Methods and goals for the use of in vitro and in vivo chemosensitivity testing

Sensitive, specific, and accurate methods to assay chemosensitivity are needed to (1) screen new therapeutic agents, (2) identify patterns of chemosensitivity for different tumor types, (3) establish patterns of cross-resistance and sensitivity in treatment of naïve and relapsing tumors, (4) identify genomic and proteomic profiles associated with sensitivity, (5) correlate in vitro response with preclinical in vivo effects and clinical outcomes for a particular therapeutic agent, and (6) tailor chemotherapy regimens to individual patients. Various methods are available to achieve these end points, including several in vitro clonogenic and proliferation assays, cell metabolic activity assays, molecular assays to monitor expression of markers for responsiveness, drug resistance, and for induction of apoptosis, in vivo tumor growth and survival assays in metastatic and orthotopic models, and in vivo imaging assays. The advantages and disadvantages of the specific assays are discussed. A summary of research questions related to chemosensitivity testing is also included.

Longitudinally quantitative 2-deoxy-2-[18F]fluoro-D-glucose micro positron emission tomography imaging for efficacy of new anticancer drugs: a case study with bortezomib in prostate cancer murine model

PURPOSE

The aim of this study was to validate quantitative metabolic response of tumors to a treatment measured by longitudinal 2-deoxy-2-[(18)F]fluoro-D-glucose (FDG) micro positron emission tomography (microPET) as a robust tool for preclinical evaluation of new anticancer agents.

PROCEDURES

Severe combined immunodeficiency mice with CWR22 xenografts were intravenously treated with bortezomib (Velcade) at 0.8 mg/kg on days 0, 3, 7, 10, and 14 and imaged with FDG microPET before, during and after treatment. Quantitative indices of tumor FDG uptake were developed.

RESULTS

FDG microPET images successfully revealed the gradual reduction of tumor FDG uptake on day 4 onward despite no absolute tumor shrinkage. The standardized uptake values of FDG in tumors was reduced to 43% of the baseline values. Using the total tumor FDG uptake as the viable tumor burden, we found 86% tumor inhibition, compared to a 55% tumor growth inhibition in tumor volume measurement.

CONCLUSION

FDG microPET imaging can provide an additional dimension of the efficacy of anticancer therapies that may otherwise be underestimated by tumor volume measurement.

Present role and future prospects of positron emission tomography in clinical oncology

Positron emission tomography (PET) has emerged as a significant molecular imaging technique in clinical oncology and cancer research. PET with (18)F-fluorodeoxyglucose ((18)F-FDG) demonstrates elevated glucose consumption by tumor cells, and is used clinically for the accurate staging and restaging of cancer, planning of radiotherapy, and predicting response or lack of response in the early stages of treatment. Combined PET and computed tomography (PET-CT) provides both functional and morphological information of the disease to allow accurate diagnosis of cancer. PET with new radiotracers such as protein synthesis markers and proliferation markers, as well as hypoxia and receptor-binding agents, will offer patient-specific images in order to yield tailored diagnostic and prognostic information.

Tumor viability evaluation by positron emission tomography with [18F]FDG in the liver metastasis rat model

We prepared a liver metastatic tumor model by injection of rat colon adenocarcinoma cells to Fischer F344 rats through portal vein, and applied positron emission tomography (PET) using 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) ([18F]FDG-PET) to this model. At an early stage of the model, multiple small tumor nodules appeared in the inferior lobes of the livers, and extended later into the superior lobes. To evaluate the tumor growth and tumor viability at the early stage, we proposed a new concept, tumor viability index (TVI), instead of the standardized uptake value (SUV) of the [18F]FDG uptake. The TVI was defined by subtracting the signal based on the normal liver from the total signal in the whole liver including tumor nodules: (whole liver SUV-normal liver SUV) x ml of whole liver region of interest (ROI). For the signal of the whole liver, ROIs were placed on six slices covering the whole liver, and the ROI of normal liver region was located in the superior lobe of the liver. The average TVI values increased with tumor growth and significantly correlated with the numbers of tumor nodules. The new concept may be useful for evaluating the tumor viability non-invasively and quantitatively by [18F]FDG-PET.

A case of hepatic inflammatory pseudotumor identified by FDG-PET

A 53-year-old man with a history of nausea and elevated liver functions presented to our clinic. A CT scan showed a small tumor in the right lobe of the liver. Fluorine-18-fluorodeoxyglucose (18F-FDG) positron emission tomography confirm abnormal metabolic activity with a high standardized uptake value of 7.3 in the lesion. These findings could indicate a malignancy such as well-differentiated hepatocellular carcinoma or cholangiocarcinoma, or a benign lesion such as hepatic abscess. He was diagnosed by histopathological examination as having an epithelioid granuloma with many inflammatory cells. This is the rare report of hepatic inflammatory pseudotumor featuring markedly increased 18F-FDG uptake.

Pulmonary suture abscess with false-positive 18F-fluorodeoxyglucose positron emission scan mimicking lung cancer recurrence

We present the case of a 57-year-old woman with pulmonary suture abscess. She had undergone right S3 segmentectomy for early lung adenocarcinoma 7 years before and right breast-conserving surgery for invasive ductal carcinoma 5 months previously, followed by irradiation plus endocrine therapy. Chest radiography and computed tomography revealed an irregular mass (3.5 cm in diameter) between the residual S1 segment and the middle lobe, neighboring the staple line of the segmentectomy. 18F-fluorodeoxyglucose uptake into the mass increased, seen by positron emission scans. Therefore, we could not rule out the possibility of local recurrence of lung cancer and resected it. Pathologically and microbiologically, the mass was a suture abscess arising around the nylon suture of the previous segmentectomy. This lesion was the result of a foreign-body reaction, as confirmed by polarized microscopy. Moreover, titanium staples at the segmentectomy and breast-conserving surgery may also have contributed to this condition.

Accumulation of glucose in keloids with FDG-PET

OBJECTIVE

Glucose metabolism has not been investigated in human (in vivo) keloids. In the present study, we performed positron emission tomography (PET) with fluorine-18-fluorodeoxyglucose (FDG) to examine glucose metabolism in keloids.

MATERIALS AND METHODS

Five patients (2 men and 3 women) with typical keloids having a thickness of more than 5 mm were studied. HEADTOME-IV SET-1400W-10 (Shimadzu, Tokyo, Japan) was employed for PET studies. Transmission scanning was performed on each patient. After fasting for more than 4 hours, the patients were injected intravenously with FDG 185-370 (MBq) following each transmission scan. Emission scans were performed 40-55 min after injection. For quantitative evaluation, the regions of interest (Circles ROIs: 6 mm in diameter) were placed on all the keloid lesions and surrounding tissues, and then their standardized uptake value (SUV = the tissue concentration/the activity injected per body weight) was calculated.

RESULTS

FDG was defined as showing the accumulation in keloids when its uptake was relatively higher in the keloid than that in the surrounding tissue. The SUV of the keloids ranged from 1.0 to 2.74, with a mean of 1.79.

CONCLUSION

FDG-PET was performed in 5 patients with keloids and low-grade accumulation of FDG was observed in all lesions. This indicated that glucose metabolism was accelerated in keloids.

Usefulness of FDG-microPET for early evaluation of therapeutic effects on VX2 rabbit carcinoma

PURPOSE

The aim of this study was to determine the potential use of high-resolution FDG-microPET for predicting the primary effects of radiotherapy and/or hyperthermia on tumor-bearing rabbits.

METHODS

Twenty-eight VX2 xenografts in the thighs of rabbits were divided into the following 5 treatment groups: radiotherapy at a single dose of 10, 20 or 30 Gy, hyperthermia (43 degrees Celsius, 1 hour), and the combination of radiotherapy and hyperthermia (10 Gy + 43 degrees Celsius, 1 hour). FDG-microPET images were obtained by using a microPET P4 system at pretreatment and at 24 hours and 7 days after treatment. For the evaluation by FDG-microPET, tumor/muscle (T/M) ratios, retention index [RI = (T/M ratio at 120 min - T/M ratio at 60 min) / T/M ratio at 60 min], and time activity curve (TAC) were acquired.

RESULTS

We divided the xenografts into a responder group (partial response + stable disease, n=14) and a non-responder group (progressive disease, n = 14). The T/M ratio at 24 hours after the treatment in the responder group was decreased remarkably with that at pre-treatment (p < 0.05), while in the non-responder group it showed no significant change between the time points. The RI and TAC patterns were comparable to T/M ratios in each treatment group. T/M ratios, RI, and TAC indicated marked changes at the time point of 24 hours in the responder group, although the tumors did not show any significant hange in volume at that time. Photomicrographs of sections showed that the number of viable tumor cells in the responder group decreased at 24 hours after treatment and that inflammatory cell infiltration was marked and almost all viable tumor cells had disappeared by day 7 after treatment.

CONCLUSION

These results suggest that early evaluation by FDG-microPET, especially 24 hours after treatment, is useful to predict the primary effects of the treatment. Histological analysis showed that inflammatory cell infiltration at 7 days after treatment was considered to be a cause of accumulation of FDG in the tumors that showed a significant decrease in tumor cell number. This false-positive should be noted when predicting tumor response by FDG accumulation.

Positron emission tomography application for gynecologic tumors

Positron emission tomography (PET) using fluorine-18-fluoro-2-deoxy-d-glucose (FDG), which originated as a research tool to evaluate glucose metabolism in cancer tissues, has now become an essential imaging modality for determining the appropriate therapeutic management of various cancer patients. The clinical role of FDG-PET for gynecologic tumors has not been established yet, but FDG-PET has come to be considered one of the important imaging modalities for evaluating patients with gynecological cancers. The objective was to review the literature regarding the utility of FDG-PET in the clinical setting of gynecological malignancies. Many articles reported that FDG-PET could be used for staging and restaging in patients with uterine cervical cancer. Although there is limited data about the feasibility of FDG-PET for endometrial cancer, preliminary results for detecting recurrence were promising. Furthermore, FDG-PET has been reported as a useful imaging modality, especially for restaging, in ovarian cancer, although the prognostic value needs to be fully investigated. Currently, a combined PET/computed tomography scanner is available, and its clinical application has begun. It is expected that this modality will contribute to the management of gynecological cancers, as has been reported recently for other malignancies.

Pneumoconiosis associated with an esophageal ulcer and uptake revealed in FDGPET

A 76-year-old man with a past history of pneumoconiosis visited the Department of Gastroenterology in our hospital suffering from dysphagia. Gastroscopy revealed an esophageal ulcer on the top of a torus lesion. Chest computed tomography (CT) revealed it was caused by a swollen lymph node in the mediastinum. Squamous cell carcinoma related antigen (SCC) was elevated to 1.8 ng/ml. To rule out malignancy, we performed fluorine-18 deoxyglucose positron emission tomography (FDGPET) which revealed a significantly increased uptake in a nodular lesion in the right upper lobe and mediastinal lymph nodes. Biopsy and cytology of the nodular lesion revealed only pneumoconiosis. We must be careful when we interpret the findings of FDGPET in pneumoconiosis patients.

Usefulness of L-[methyl-11C] methionine-positron emission tomography as a biological monitoring tool in the treatment of glioma

OBJECT

The authors retrospectively analyzed the data obtained in patients who had undergone L-[methyl-11C] methionine (MET)-positron emission tomography (PET) studies to clarify the relationship between MET uptake and tumor biological features and to discuss the clinical usefulness of MET-PET studies.

METHODS

One hundred ninety-four patients with cerebral glioma or suspected glioma underwent PET scanning 20 minutes after injection of MET, whose uptake into the tumor was expressed as a ratio to contralateral healthy brain tissue (T/N ratio). Analyses were performed to determine how MET uptake correlated with tumor pathological features and prognosis. The T/N ratios before and after various treatments were also examined. There were significant differences in the T/N ratio among the nonneoplastic lesions, low-grade gliomas, and malignant gliomas. Furthermore, there were significant correlations between patient survival and pretreatment T/N ratios. Among patients with malignant gliomas, a significant difference in survival was observed between cases with and without postoperative tumor remnant based on elevated MET uptake. The MET uptake was heterogeneous even among the homogeneous tumor areas demonstrated on MR imaging. Malignant pathological features were detected in the areas with the highest MET uptake. The effectiveness of radiotherapy or chemotherapy was expressed as a significantly decreased T/N ratio in some of the tumor types.

CONCLUSIONS

The ability of MET-PET to reflect the biological nature of gliomas makes it an excellent method for monitoring active tumor tissue, and treatments based on its findings should provide a powerful clinical protocol in the course of glioma therapy.

Technology Insight: PET and PET/CT in head and neck tumor staging and radiation therapy planning

The evolving utilization of functional imaging, mainly 2-[18F]fluoro-2-deoxyglucose (18FDG) imaging, with positron emission tomography (PET) and PET/CT, is profoundly altering head and neck tumor staging approaches, radiation treatment planning, and follow-up management. Tumor-node-metastasis staging with PET/CT has improved the characterization of patient disease versus CT, MRI, or PET alone, thereby affecting patient disease management. Therefore, the utilization of PET/CT is appropriate for head and neck cancer staging in the initial presentation and in the recurrent setting. In the setting of radiation therapy treatment planning, PET-directed tumor volume contouring is not ready for clinical practice without further technological improvements in imaging specificity/sensitivity and resolution. Patient or organ motion might interfere with the accuracy of anatomical co-alignment, and variability in defining the threshold of imaging signals on PET images can affect the contour of the biological tumor volume. The use of PET/CT for staging and detecting both primary and recurrent head and neck cancer is valuable; however, its application in radiation treatment planning should be viewed as investigational.

Cold tuberculous abscess identified by FDG PET

We report FDG PET of two cases of cold abscess due to Mycobacterium tuberculosis. Case 1 had colon cancer; FDG PET showed high FDG uptake in the colon lesion and low uptake in the inguinal lesion. The latter was a tuberculous cold abscess confirmed by CT/MRI and biopsy. Case 2 received radiotherapy for lung cancer and presented with suspected vertebral metastasis. Further studies revealed tuberculosis of the vertebra and a tuberculous cold abscess in the iliopsoas muscle. FDG PET showed moderate uptake in the third lumbar spine and low uptake in the abscess center of iliopsoas lesion. Both tuberculous cold abscesses showed moderate FDG uptake in the capsule and low uptake in the center. These features are unique compared with non-tuberculous abscess and typical tuberculosis lesions, which are characterized by high FDG uptake. Pathologically, tuberculous cold abscess is not accompanied by active inflammatory reaction. Our findings suggested that the FDG uptake by tuberculous lesion varies according to the grade of inflammatory activity. The new diagnostic features of tuberculous cold abscess may be useful in the evaluation of such lesions by FDG PET.

2-(18F)-fluoro-2-deoxy-D-glucose positron emission tomography detects clinical relevant adenomas of the colon: a prospective study

PURPOSE

2-(18F)-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) is a noninvasive imaging technique used clinically to detect malignant tumors. FDG-PET has been established as a tool for diagnosis of recurrent or metastatic colorectal carcinoma. Several case series suggest that FDG-PET also detects larger adenomas. The goal of this study was to investigate whether FDG-PET is able to detect colonic adenomas.

PATIENTS AND METHODS

FDG-PET was performed in 100 consecutive patients in whom colonic adenomas were suspected on barium enema (n = 47) or sigmoidoscopy (n = 53). A positive scan was defined as focal large bowel FDG accumulation. FDG-PET was followed in all cases by colonoscopy, and removed adenomas were examined histopathologically.

RESULTS

Colonoscopy confirmed the presence of adenomas in 68 of 100 patients. In 35 patients, there was focal FDG accumulation at site of the adenoma. The sensitivity of FDG-PET increased with adenoma size (21%, adenomas 1 to 5 mm; 47%, 6 to 10 mm; and 72%, > 11 mm). The sensitivity of FDG-PET also increased with the grade of dysplasia (33%, low grade; 76%, high grade; and 89%, carcinomas). The overall specificity was 84%.

CONCLUSION

FDG-PET detects colonic adenomas and the diagnostic test characteristics improve with size and grade of dysplasia of the adenoma.

Clotrimazole decreases human breast cancer cells viability through alterations in cytoskeleton-associated glycolytic enzymes

Cancer cells are characterized by a high rate of glycolysis, which is their primary energy source. Glycolysis is known to be controlled by allosteric regulators, as well as by reversible binding of glycolytic enzymes to cytoskeleton. Clotrimazole is an anti-fungal azole derivative recently recognized as a calmodulin antagonist with promising anti-cancer effect. Here, we show that clotrimazole induced morphological and functional alterations on human breast cancer derived cell line, MCF-7. The drug decreased cell viability in a dose- and time-dependent manner, exhibiting an IC50 of 88.6+/-5.3 microM and a t0.5 of 89.7+/-7.2 min, with 50 microM clotrimazole. Morphological changes were evident as observed by scanning electron microscopy, which revealed the completely loss of protrusion responsible for cell adhesion after a 180 min of treatment with 50 microM clotrimazole. Giemsa stained cells observed by optical microscopy show morphological alterations and a marked nuclear condensation. These changes occurred in parallel to the detachment of the glycolytic enzymes, 6-phosphofructo-1-kinase and aldolase, from cytoskeleton. After a 45 min treatment with 50 microM clotrimazole, the remaining activities in a cytoskeleton enriched fraction was 16.4+/-3.6% and 41.0+/-15.6% of control for 6-phosphofructo-1-kinase and aldolase, respectively. Immunocytochemistry experiments revealed a decrease in the co-localization of 6-phosphofructo-1-kinase and F-actin after clotrimazole treatment, suggesting the site of detachment of the enzymes. Altogether, our results support evidence for apoptotic events that might be started by clotrimazole involving inhibition of glycolytic flux in MCF-7 cells and makes this drug a promising agent in the fight against human breast cancer.

Preclinical and clinical evaluation of O-[11C]methyl-l-tyrosine for tumor imaging by positron emission tomography

We performed preclinical and clinical studies of O-[11C]methyl-L-tyrosine, a potential tracer for imaging amino acid transport of tumors by positron emission tomography (PET). Examinations of the radiation-absorbed dose by O-[11C]methyl-L-tyrosine and the acute toxicity and mutagenicity of O-methyl-L-tyrosine showed suitability of the tracer for clinical use. The whole-body imaging of monkeys and healthy humans by PET showed low uptake of O-[11C]methyl-L-tyrosine in all normal organs except for the urinary track and bladder, suggesting that the O-[11C]methyl-L-tyrosine PET has the potential for tumor imaging in the whole-body. Finally, the brain tumor imaging was preliminarily demonstrated.

Impact of tumor repopulation on radiotherapy planning

PURPOSE

Biologic/functional imaging (e.g., fluorodeoxyglucose/3'-deoxy-3'-fluorothymidine-positron emission tomography) is promising to provide information on tumor cell repopulation. Such information is important in the design of biologically conformal radiotherapy for cancer. The questions remaining unclear are whether it is necessary to escalate the dose to the regions with rapid cell repopulation in the tumor target and, if so, by how much. The purpose of this work was to address these questions using radiobiologic modeling.

METHODS AND MATERIALS

The generalized linear-quadratic model, extended to account for the effect of clonogenic cell repopulation, was used to calculate the cell-killing efficiency of radiotherapy. The standard Poisson tumor control probability (TCP) model was used to bridge cell killing to treatment outcome. Prostate cancer was chosen as the example for this study. In situ measurements of prostate cancer patients have shown that the potential doubling time of tumor cells has a large variation, ranging from 15 to 170 days. On the basis of the linear-quadratic and TCP parameters (alpha = 0.14 Gy(-1), alpha/beta = 3.1 Gy, and the number of clonogens K = 10(6)-10(7) cells) determined in earlier studies, we evaluated the influence of tumor cell repopulation during protracted treatment courses on treatment outcome. The dose escalations, which can be used to combat aggressive cell repopulation in regions with different doubling times (15-170 days) and sizes (5, 10, 15, and 40 cm(3) of a 40-cm(3) tumor), were calculated for commonly practiced radiotherapy modalities. The influence of linear-quadratic parameters on this calculation was also considered.

RESULTS

The impact of tumor cell repopulation on TCP and the corresponding dose escalation required to account for this impact were investigated for both external beam radiotherapy and permanent implantation. The results indicated that for regions with aggressive tumor cell growth, dose escalation is necessary to compensate for the repopulation effect. For example, for tumors with an effective doubling time changing from 42 days to 15 days, the prescription dose of external beam radiotherapy needs to be increased from 75.6 to 81 Gy to maintain a target TCP of 80% for intermediate-risk prostate cancer. For (125)I implants, dose escalation from 152 to 160 Gy is required for the same target TCP. These data were calculated on the basis of an alpha/beta ratio of 3.1 Gy. Greater dose escalations are required if the alpha/beta ratio is 1.5 Gy (e.g., 88 Gy for external beam radiotherapy or 180 Gy for (125)I implantation for the same treatment outcome). Our study results showed that it is important to cover the entire tumor volume, including all aggressive spots, with the desired prescription dose, especially for low-dose-rate brachytherapy.

CONCLUSION

Dose escalation is necessary to offset the accelerated tumor cell repopulation during prolonged treatment courses. This study provides a preliminary estimate of the dose escalation for prostate cancer based on the in situ measurements of potential doubling time and radiobiologic models. The proposed dose prescriptions are technically feasible for clinical trials.

18F-FDG and11C-methionine PET for evaluation of treatment response of lung cancer after stereotactic radiotherapy

This study was performed to investigate the feasibility of FDG- and L-[methyl-11C]methionine (Met)-PET for the follow up of lung cancer after stereotactic radiotherapy (SRT). Nine patients (pt) with solitary lung cancer underwent SRT. Met- and FDG-PET studies were performed one week before SRT and from one week to 8 months after SRT. Responses to SRT were complete in 2 pt and partial in 7 pt. Met- and FDG-PET scan showed high tracer uptake in all tumors before SRT. After SRT, standardized uptake values (SUV) of FDG and Met changed concordantly. Both decreased with time in 5 pt but did not decrease steadily in 4 pt, where 2 pt showed an increase at 1 to 2 weeks after SRT and 2 pt showed an increase at more than 3 months after SRT. The former appears to reflect the acute reaction to SRT and the latter radiation-induced pneumonitis. Although the addition of Met-PET did not provide additional information over FDG-PET, FDG- and Met-PET could be used to evaluate the treatment effect of SRT.

Comparison of [18F]fluorodeoxyglucose uptake with glucose transporter-1 expression and proliferation rate in human glioma and non-small-cell lung cancer

To clarify the biological significance of [18F]fluorodeoxyglucose (18F-FDG) accumulation in patients with cancer, we assessed the relationships between 18F-FDG uptake and glucose transporter-1 (GLUT-1) expression and proliferation rate in human glioma and lung cancer. We obtained FDG PET images and measured standardized uptake values (SUVs) of primary tumours in 13 patients with brain glioma and 25 patients with non-small-cell lung cancer. After surgery, portions of respected tumours were obtained, and the proliferation rate was measured as proliferation index (per cent of (S+G2+M)/(G0+G1+S+G2+M)) using DNA flow cytometry. The expression of GLUT-1 in a tumour was evaluated by using immunostaining. We classified GLUT-1 expression as grade 0 (no positive cell), grade 1 (< 10% cells positive), grade 2 (11-50% cells positive) and grade 3 (51-100% cells positive). Based on the expression of GLUT-1, cases with grades 0, 1, 2 and 3 showed SUVs of 6.1 +/- 2.8, 5.0 +/- 3.2, 8.3 +/- 3.3 and 10.4 +/- 6.6, respectively (P < 0.05). Non-small-cell lung cancer showed higher FDG uptake (SUV, 8.5 +/- 5.1) and higher GLUT-1 expression (grade, 2.0 +/- 1.0) than did brain glioma (SUV, 4.7 +/- 2.5; grade, 0.8 +/- 0.8). Based on the total number of cases, SUVs did not relate to proliferation index (r = 0.19). In non-small-cell lung cancer, SUVs did not correlate with proliferation index, whereas in glioma, SUVs were strongly related to proliferation index (r = 0.79, P < 0.01). In conclusion, FDG uptake generally correlated with GLUT-1 expression in non-small-cell lung cancer and glioma. In the case of glioma, FDG uptake also indicated increased cellular proliferation, which was not demonstrated in non-small-cell lung cancer.

11C-methionine PET as a prognostic marker in patients with glioma: comparison with 18F-FDG PET

PURPOSE

The purpose of this study was to compare the prognostic value of 11C-methionine (MET) and 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) in glioma patients.

METHODS

The study population comprised 47 patients with gliomas (19 glioblastoma, 28 others). Pretreatment magnetic resonance imaging, MET PET and FDG PET were performed within a time interval of 2 weeks in all patients. The uptake ratio and standard uptake values were calculated. Univariate and multivariate analyses were done to determine significant prognostic factors. Ki-67 index was measured by immunohistochemical staining, and compared with FDG and MET uptake in glioma.

RESULTS

Among the several clinicopathological prognostic factors, tumour pathology (glioblastoma or not), age (> or =60 or <60 years), Karnofsky performance status (KPS) (> or =70 or <70) and MET PET (higher uptake or not compared with normal cortex) were found to be significant predictors by univariate analysis. In multivariate analysis, tumour pathology, KPS and MET PET were identified as significant independent predictors. The Ki-67 proliferation index was significantly correlated with MET uptake (r=0.64), but not with FDG uptake.

CONCLUSION

Compared with FDG PET in glioma, MET PET was an independent significant prognostic factor and MET uptake was correlated with cellular proliferation. MET PET may be a useful biological prognostic marker in glioma patients.

Whole-body positron emission tomography and positron emission tomography/computed tomography in gynecologic oncology

The advent of positron emission tomography (PET) and PET/computed tomography (CT) now enables us to detect metabolically active gynecologic cancers with greater accuracy than was possible with anatomic imagings. Fluorine-18 fluorodeoxyglucose PET has been useful in differentiation of malignant from benign lymph nodes, and residual or recurrent cancers from post-treatment changes. PET/CT produces additional information for the diagnosis and tissue biopsy as well as radiotherapy planning. This paper reviews the principle and clinical utility of PET and PET/CT in the diagnosis, staging, recurrence, therapeutic response as well as prognosis of gynecologic cancers.

PET scanning in lung cancer: current status and future directions

Positron emission tomography (PET) represents a dramatic advance in the imaging of lung cancer. It is valuable for the diagnosis, staging, prognosis, and restaging of disease, and is most useful in patients considered for potentially curative therapy for non-small-cell lung cancer (NSCLC). In this work the current status and potential future applications of PET scanning in lung cancer are discussed. The relevant literature is also discussed, with an emphasis on studies with clinical applicability. Most of these studies involved the use of 18F-fluorodeoxyglucose (FDG). Numerous studies of the use of PET to assess undiagnosed pulmonary nodules have reported significant improvements in accurate diagnosis or exclusion of malignancy compared to conventional structural imaging alone. All of these studies, including metaanalysis, have shown that PET is more accurate than CT-based structural imaging in staging the mediastinum in surgical candidates. PET may have value in radiotherapy planning, and PET-based staging more accurately predicts survival in radiotherapy-treated patients than conventional staging. The rate of unsuspected distant metastasis detection in stage III disease exceeds 20%. PET also facilitates an accurate assessment of response in patients treated with radical chemoradiation or neoadjuvant therapy prior to surgery. PET has rapidly become an indispensable part of the evaluation of patients with potentially curable lung cancer; however, more work is required to define its role.

[11C]choline uptake in regenerating liver after partial hepatectomy or CCl4-administration

To characterize [methyl-(11)C]choline ([(11)C]choline) as an oncologic PET radiopharmaceutical, [(11)C]choline uptake in regenerating livers after partial hepatectomy as a model of typical proliferating tissue and after CCl(4) insult as that of proliferating tissue with inflammation, was studied in rats. [(11)C]Choline, [(18)F]2-fluoro-2-deoxy-D-glucose ([(18)F]FDG) and [2-(14)C]thymidine ([(14)C]TdR) uptake was studied in regenerating rat liver after 70% partial hepatectomy or CCl(4)-administration. [(11)C]Choline uptake in regenerating liver after partial hepatectomy was significantly increased with [(14)C]TdR uptake as a marker of DNA synthesis at 18 hours after surgery. On the other hand, the uptake was not accelerated by CCl(4)-administration, though it significantly increased [(14)C]TdR uptake. There were no differences of [(11)C]choline uptake acceleration following partial hepatectomy among the three parts of the regenerating liver. [(18)F]FDG uptake was accelerated in the regenerating liver on either partial hepatectomy or CCl(4)-administration. The magnitude of the increase in [(18)F]FDG uptake in the regenerating liver induced by partial hepatectomy was greater than that for [(11)C]choline. [(11)C]Choline uptake in the liver was accelerated by partial hepatectomy, but not by CCl(4)-administration. This might be expected given that the differentiation between proliferating tissues such as tumor and inflammatory tissue was possible by [(11)C]choline-PET.

FDG-PET scanning after radiation can predict tumor regrowth three months later

PURPOSE

Positron emission tomography (PET) with 2-[(18)F]fluoro-2-deoxy-D-glucose (FDG) is well known for providing excellent clinical information regarding malignant tumors. We investigated whether dual-time FDG-PET performed immediately post radiation could predict early regrowth of malignant tumors.

MATERIALS AND METHODS

Twenty patients with malignant tumors were included in this study. All patients received radiation, and each underwent FDG-PET before the initiation of therapy and within 10 days of completing their course of irradiation. PET images after irradiation were obtained at 60 min and 180 min post FDG injection. For 26 lesions in 20 patients, standardized uptake value (SUV) before and after treatment was calculated and then correlated with postradiation tumor response and outcome at 3 months status post irradiation.

RESULTS

Retention index [RI = (SUV on delayed image - SUV on early image)/SUV on early image] after irradiation showed a significant difference between patients with residual tumor and those without residual tumor at 3 months status post irradiation (p < 0.0025). All 9 lesions in 6 patients with residual tumors showed more than 0.1 of RI, whereas none of the lesions with less than 0.1 of RI revealed residual tumors.

CONCLUSIONS

Dual-time FDG-PET imaging just after irradiation is potentially useful for predicting early regrowth of malignant tumors.

Evaluation of Lung Injury after Three-dimensional Conformal Stereotactic Radiation Therapy for Solitary Lung Tumors: CT Appearance

PURPOSE

To evaluate the computed tomographic (CT) appearance of tumors and lung injury in patients who have undergone stereotactic radiation therapy (SRT) for solitary lung tumors.

MATERIALS AND METHODS

Twenty-seven patients with primary lung cancer and four with metastatic lung cancer who underwent SRT for solitary lung tumors were enrolled for evaluation. SRT was delivered by using a three-dimensional conformal technique with a stereotactic body frame. A total dose of 48 Gy was administered in four fractions during a period of 2 weeks. After SRT, follow-up CT images were obtained every 2-3 months. Radiation-induced pulmonary injuries were classified into four patterns on CT images. The minimal lung dose to areas demonstrating pulmonary injury at CT was evaluated, and the correlation between the dose and the percentage volume of the whole lung irradiated by more than 20 Gy in total (V20) was assessed by using Spearman rank correlation.

RESULTS

Tumor shrinkage continued for 2-15 months after SRT. Asymptomatic changes in the irradiated lung were noted at CT in all patients within 2-6 months (median, 4 months) after SRT. As the pattern at pulmonary CT changed, patchy consolidation was more predominantly seen as an acute change than were slight homogeneous increase in opacity, discrete consolidation, or solid consolidation; solid consolidation was the more predominantly seen late change. The minimal lung dose to the area demonstrating pulmonary injury in each patient ranged between 16 and 36 Gy (median, 24 Gy). The dose was significantly (P <.001) inversely correlated with the V20 in each patient.

CONCLUSION

The reaction to SRT of the lungs seems similar to the reaction to conventional radiation therapy.

F-18 fluorodeoxyglucose positron emission tomography in the evaluation of distant metastases from renal cell carcinoma

PURPOSE

We conducted a study to evaluate the role of F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) in the detection of distant metastases from renal cell carcinoma (RCC).

MATERIALS AND METHODS

Twenty-four patients with histologically proven clear-cell RCC undergoing surgical evaluation for possible resection of recurrent disease were investigated. All patients had suspected distant metastases based on conventional anatomic imaging techniques (computed tomography and magnetic resonance imaging). A total of 36 distant metastatic sites were identified. Pathology for all sites was obtained by biopsy or after surgical resection.

RESULTS

Histologically documented distant metastases from RCC were present in 33 sites (21 patients). Overall sensitivity, specificity, and positive predictive value of FDG-PET for the detection of distant metastases from RCC was 63.6% (21 of 33), 100% (three of three), and 100% (21 of 21), respectively. The mean size of distant metastases in patients with true-positive FDG-PET was 2.2 cm (95% CI, 1.7 to 2.6 cm) compared with 1.0 cm in patients with false-negative FDG-PET (95% CI, 0.7 to 1.4 cm; P =.001).

CONCLUSION

FDG-PET is not a sensitive imaging modality for the evaluation of metastatic RCC and may not adequately characterize small metastatic lesions. However, positive FDG-PET is predictive for the presence of RCC in lesions imaged, may complement anatomic radiologic imaging modalities, and may alleviate the need for a biopsy in selected situations. A negative FDG-PET, however does not rule out active malignancy.

Cellular distribution of phosphofructokinase activity and implications to metabolic regulation in human breast cancer

Neoplastic cells generally present profound changes in glucose metabolism. The mechanisms underlying such process are numerous and all may involve altered cellular hormonal responses. Here we report the first evidence that cellular location of phosphofructokinase activity in human breast cancer tissues is different from the one observed in control tissues and that this phenomenon may be involved in the increased glycolytic flux observed in those cells. Through co-sedimentation techniques, we observed that 60% of phosphofructokinase activity in neoplastic tissues is located in an actin-enriched fraction, against 36% in control tissues. Additionally, metastatic tumor tissues presented a two fold increase in this particulate activity when compared to non-metastatic tumor samples. We propose that the alteration in cellular distribution of phosphofructokinase activity in human breast cancer tissues is a mechanism associated to the process of cell transformation and may be a consequence of the altered hormonal milieu observed in several types of cancer.

Potential impact of [18F]3'-deoxy-3'-fluorothymidine versus [18F]fluoro-2-deoxy-D-glucose in positron emission tomography for colorectal cancer

Fluorine-18 labelled fluoro-2-deoxy- d-glucose ((18)FDG) positron emission tomography (PET) imaging demonstrates the increased glucose consumption of malignant cells, but problems with specificity have led to the development of new PET tracers. [(18)F]3'-deoxy-3'-fluorothymidine ((18)FLT) is a new tracer which images cellular proliferation by entering the salvage pathway of DNA synthesis. In this study we compared the cellular uptake of (18)FLT and (18)FDG in patients with colorectal cancer (CRC). Seventeen patients with 50 primary or metastatic CRC lesions were prospectively recruited. Lesions were initially identified using computed tomography. Patients underwent both (18)FDG and (18)FLT scanning. Semi-quantitative analysis of tracer uptake was carried out using standardised uptake values. All the primary tumours ( n=6) were visualised by both tracers, with (18)FDG showing on average twice the uptake of (18)FLT. Similar uptake of both tracers was seen in lung and peritoneal lesions, with (18)FLT imaging five of the six lung lesions and all of the peritoneal lesions. Of the 32 colorectal liver metastases, 11 (34%) were seen as avid for (18)FLT, compared with 31 (97%) for (18)FDG. No correlation was seen between the uptake of the two tracers ( R(2)=0.03). (18)FLT shows a high sensitivity in the detection of extrahepatic disease but poor sensitivity for the imaging of colorectal liver metastases, making it unlikely to have a role as a diagnostic tracer in CRC. We have demonstrated that (18)FDG and (18)FLT image two distinct processes. The prognostic implications of the uptake of (18)FLT need to be assessed in terms of response to chemoradiotherapy and survival.

Diagnosis of pancreatic cancer using fluorine-18 fluorodeoxyglucose positron emission tomography (FDG PET) --usefulness and limitations in "clinical reality"

The present review will provide an overview of the literature concerning the FDG PET diagnosis of pancreatic cancer and a summary from our experience of 231 cases of pancreatic lesions. FDG PET can effectively differentiate pancreatic cancer from benign lesion with high accuracy. Newly-developed PET scanners can detect small pancreatic cancers, up to 7 mm in diameter, by their high resolution, which could make a great contribution to the early detection of resectable and potentially curable pancreatic cancers. FDG PET is useful and cost-beneficial in the pre-operative staging of pancreatic cancer because an unexpected distant metastasis can be detected by whole-body PET in about 40% of the cases, which results in avoidance of unnecessary surgical procedures. FDG PET is also useful in evaluation of the treatment effect, monitoring after the operation and detection of recurrent pancreatic cancers. However, there are some drawbacks in PET diagnosis. A relatively wide overlap has been reported between semiquantitative uptake values obtained in cancers and those in inflammatory lesions. As for false-positive cases, active and chronic pancreatitis and autoimmune pancreatitis sometimes show high FDG accumulation and mimic pancreatic cancer with a shape of focal uptake. There were 8 false negative cases in the detection of pancreatic cancer by FDG PET, up to 33 mm in diameter, mainly because of their poor cellularity in cancer tissues. In addition, there are 19% of cancer cases with a decline in FDG uptake from 1 hr to 2 hr scan. FDG PET was recently applied to and was shown to be feasible in the differential diagnosis of cystic pancreatic lesions, such as intraductal papillary mucinous tumor of the pancreas. Further investigations are required to clarify the clinical value of FDG PET in predicting prognosis of the pancreatic patients.

Value of whole-body FDG PET in management of lung cancer

18F-fluorodeoxyglucose (FDG) PET imaging provides physiologic and metabolic information that characterizes lesions that are indeterminate by CT. FDG PET imaging is sensitive to the detection of lung cancer in patients who have indeterminate lesions on CT, whereas low grade malignancy such as bronchioloalveolar carcinoma and carcinoid may be negative on FDG PET. The specificity of PET imaging is less than its sensitivity because some inflammatory processes, such as active granulomatous infections, avidly accumulate FDG. This possibility should be kept in mind in the analysis of PET studies of glucose metabolism aimed at differentiating malignant from benign solitary pulmonary nodules. FDG uptake is considered to be a good marker of cell differentiation, proliferative potential, aggressiveness, and the grade of malignancy in patients with lung cancer. FDG PET accurately stages the distribution of lung cancer. Several studies have documented the increased accuracy of PET compared with CT in the evaluation of the hilar and mediastinal lymphnode status in patients with lung cancer. Whole-body PET studies detect metastatic disease that is unsuspected by conventional imaging. Management changes have been reported in up to 41% of patients on the basis of the results of whole-body studies. Whole-body FDG PET is also useful for the detection of recurrence. Several studies have indicated that the degree of FDG uptake in primary lung cancer can be used as an independent prognostic factor. Thus, whole-body FDG PET is clinically very useful in the management of lung cancer.

Tumor detection using 18F-labeled matrix metalloproteinase-2 inhibitor

Matrix metalloproteinase-2 (MMP-2) is a key enzyme involved in tumor invasiveness. (2R)-2- [4-(6-[(18)F]Fluorohex-1-ynyl)-benzenesulfonylamino]-3-methylbutyric acid ([(18)F]SAV03), a new fluorine-18 labeled MMP-2 inhibitor developed for tumor imaging with PET, was biologically evaluated using in vivo tumor model. Enzymatic MMP-2 assay of SAV03 yielded an IC(50) value of 1.9 microM. Biodistribution study of [(18)F]SAV03 using Ehrlich tumor bearing mice showed that the uptake in tumor was higher than in other organs, except for the liver, small intestine, and bone. When [(18)F]SAV03M, a methyl ester of [(18)F]SAV03, was used as a prodrug, the uptake in liver at 30 min after injection decreased by half and that in tumor increased by 2.4 times, compared with [(18)F]SAV03. Radio-thin-layer chromatographic analysis of [(18)F]SAV03M metabolites revealed that administered [(18)F]SAV03M was easily converted to the parent drug in vivo and accumulated in tumor tissue. Thus, [(18)F]SAV03M is suitable as the prodrug of [(18)F]SAV03 with potent efficacy. Whole body autoradiography using [(18)F]SAV03M also indicated tumor-specific accumulation of radioactivity, while higher accumulations in bone and intestinal contents were observed. Our results suggest that [(18)F]SAV03M could be potentially suitable for tumor imaging with PET.