Comparison of 4'-[methyl-(11)C]thiothymidine ((11)C-4DST) and 3'-deoxy-3'-[(18)F]fluorothymidine ((18)F-FLT) PET/CT in human brain glioma imaging

Correlation of 4'-[methyl-11C]-thiothymidine PET with Ki-67 immunohistochemistry separately in patients with newly diagnosed and recurrent gliomas

OBJECTIVE

4'-[methyl-11C]-thiothymidine (4DST) uptake on PET was correlated with proliferative activity separately in patients with newly diagnosed and recurrent gliomas.

METHODS

A total of 29 patients, 18 with newly diagnosed gliomas and 11 with recurrent gliomas who underwent 4DST PET/computed tomography (CT) were available for a retrospective analysis of prospectively collected data. The maximum standardized uptake value (SUVmax) of tumor (T) and the mean SUV of normal contralateral hemisphere (N) were calculated, and the tumor-to-normal (T/N) ratio was determined. Proliferative tumor volume (PTV) and total lesion proliferation (TLP) were also calculated. Proliferative activity as indicated by the Ki-67 index was estimated in tissue specimens. Immunohistochemical findings were correlated with 4DST PET parameters.

RESULTS

All gliomas but three newly diagnosed gliomas had 4DST uptake on PET. No significant differences in SUVmax, T/N ratio, PTV, or TLP were observed between the newly diagnosed and recurrent gliomas. In the former, correlations between SUVmax (r = 0.57, P = 0.02), T/N ratio (r = 0.51, P = 0.03), PTV (r = 0.74, P < 0.001), and TLP (r = 0.76, P < 0.001) and the Ki-67 index were found. In the latter, the results did not seem to suggest any correlations between any of the PET parameters and Ki-67 index.

CONCLUSION

Although preliminary, these results suggest that 4DST PET may be useful for the noninvasive evaluation of proliferation in patients with newly diagnosed gliomas. These data in a small recurrent patient population do not support a clear-cut correlation between 4DST uptake and proliferation.

Correlation of 4'-[methyl-11C]-thiothymidine PET with Gd-enhanced and FLAIR MRI in patients with newly diagnosed glioma

PURPOSE

To elucidate the biological association between tumor proliferation, tumor infiltration and neovascularization, we analyzed the association between volumetric information of 4'-[methyl-¹¹C]thiothymidine (4DST) positron emission tomography (PET) and fluid-attenuated inversion recovery (FLAIR) and T1-weighted gadopentetate dimeglumine (Gd)-enhanced magnetic resonance imaging (MRI), in patients with newly diagnosed glioma.

METHODS

A total of 23 patients with newly diagnosed glioma who underwent both 4DST PET/CT and Gd-enhanced MRI before therapy were available for a retrospective analysis of prospectively collected data. The maximum standardized uptake value (SUVmax) for tumor (T) and the mean SUV for normal contralateral hemisphere (N) were calculated, and the tumor-to-normal (T/N) ratio was determined. Proliferative tumor volume (PTV) from 4DST PET and the volume of Gd enhancement (GdV) and hyperintense region on FLAIR (FLAIRV) from MRI were calculated.

RESULTS

All gliomas but 3 diffuse astrocytomas and one anaplastic astrocytoma had 4DST uptake and Gd enhancement on MRI. There was no significant difference between PTV and GdV although the exact edges of the tumor differed in each modality. The FLAIRV was significantly larger than PTV (P < 0.001). Significant correlations between PTV and GdV (ρ = 0.941, P < 0.001) and FLAIRV (ρ = 0.682, P < 0.001) were found.

CONCLUSION

These preliminary results indicate that tumor proliferation assessed by 4DST PET is closely associated with tumor-induced neovascularization determined by Gd-enhanced MRI in patients with newly diagnosed glioma.

Carbon-11: Radiochemistry and Target-Based PET Molecular Imaging Applications in Oncology, Cardiology, and Neurology

The positron emission tomography (PET) molecular imaging technique has gained its universal value as a remarkable tool for medical diagnosis and biomedical research. Carbon-11 is one of the promising radiotracers that can report target-specific information related to its pharmacology and physiology to understand the disease status. Currently, many of the available carbon-11 (t_1/2 = 20.4 min) PET radiotracers are heterocyclic derivatives that have been synthesized using carbon-11 inserted different functional groups obtained from primary and secondary carbon-11 precursors. A spectrum of carbon-11 PET radiotracers has been developed against many of the upregulated and emerging targets for the diagnosis, prognosis, prediction, and therapy in the fields of oncology, cardiology, and neurology. This review focuses on the carbon-11 radiochemistry and various target-specific PET molecular imaging agents used in tumor, heart, brain, and neuroinflammatory disease imaging along with its associated pathology.

Clinical value of PET/CT with carbon-11 4DST in the evaluation of malignant and benign lung tumors

OBJECTIVES

The aim of this study was to assess the clinical value of [¹¹C]4DST uptake in patients with lung nodules, including benign and malignant tumors, and to assess the correlation between [¹¹C]4DST uptake and proliferative activity of tumors in comparison with [¹⁸F]FDG uptake.

METHODS

Twenty-six patients (22 males and 4 females, mean age of 65.5-year-old) were analyzed in this prospective study. Patients underwent [¹¹C]4DST and [¹⁸F]FDG PET/CT imaging on the same day. Diagnosis of each lung nodule was confirmed by histopathological examination of tissue specimens at surgery, or during clinical follow-up after the PET/CT studies. To assess the utility of the semi-quantitative evaluation method, the SUV_max was calculated of [¹¹C]4DST and [¹⁸F]FDG uptake by the lesion. Proliferative activities of each tumor as indicated by the immunohistochemical Ki-67 index was also estimated using surgical specimens of patients. Then the relationship between the SUV_max of both PET/CT and the Ki-67 index was examined. Furthermore, the relationship between the uptake of [¹¹C]4DST or [¹⁸F]FDG and the histopathological findings, the clinical stage, and the clinical outcome of patients were also assessed.

RESULTS

There was a positive linear relationship between the SUV_max of [¹¹C]4DST images and the Ki-67 index (Correlation coefficients = 0.68). The SUV_max of [¹¹C]4DST in the 26 lung nodules were 1.65 ± 0.40 for benign lesions, 3.09 ± 0.83 for adenocarcinomas (P < 0.001 between benign and adenocarcinoma), and 2.92 ± 0.58 for SqCCs (P < 0.001 between benign and SqCC). Whereas, the SUVmax of [¹⁸F]FDG were 2.38 ± 2.27 for benign lesions, 6.63 ± 4.24 for adenocarcinomas (n.s.), and 7.52 ± 2.84 for SqCCs (n.s.). The relationship between TNM tumor stage and the SUV_max of [¹¹C]4DST were 2.54 ± 0.37 for T1, 3.48 ± 0.57 for T2, and 4.17 ± 0.72 for T3 (P < 0.005 between T1 and T2, and P < 0.001 between T1 and T3). In comparison with the TNM pathological stage, SUVmax of [¹¹C]4DST were 2.63 ± 0.49 for stage I, 3.36 ± 0.23 for stage II, 3.40 ± 1.12 for stage III, and 4.65 for stage IV (P < 0.05 between stages I and II). In comparison of the clinical outcome, the SUV_max of [¹¹C]4DST were 2.72 ± 0.56 for the no recurrence (No Rec.) group, 3.10 ± 0.33 for the recurrence-free with adjuvant chemotherapy after the surgery (the No Rec. Adjv. CTx. group) and 4.66 ± 0.02 for the recurrence group (Rec. group) (P < 0.001 between the No Rec and Rec. groups, and P < 0.005 between the No Rec. Adjv. CTx. and Rec. groups).

CONCLUSIONS

PET/CT with [¹¹C]4DST is as feasible for imaging of lung tumors as [¹⁸F]FDG PET/CT. For diagnosing lung tumors, [¹¹C]4DST PET is useful in distinguishing benign nodules from malignancies. [¹¹C]4DST uptake in lung carcinomas is correlated with the proliferative activity of tumors, indicating a promising noninvasive PET imaging of DNA synthesis in malignant lung tumors.

Correlation of 4'-[methyl-11C]-thiothymidine uptake with human equilibrative nucleoside transporter-1 and thymidine kinase-1 expressions in patients with newly diagnosed gliomas

OBJECTIVE

We examined expressions of human equilibrative nucleoside transporter-1 (hENT1) and thymidine kinase-1 (TK1), the key enzyme in 4'-[methyl-¹¹C]-thiothymidine (4DST) phosphorylation, to elucidate the mechanism of 4DST uptake in patients with newly diagnosed gliomas.

METHODS

A total of 19 patients with newly diagnosed gliomas were examined with 4DST PET. Tumor lesions were identified as areas of focally increased uptake, exceeding that of normal brain background. For semi-quantitative analysis, tumor-to-contralateral normal brain tissue (T/N) ratio was determined by dividing the maximal standardized uptake value (SUV) for tumor by that of the mean SUV for reference tissue. The expressions of hENT1, TK1 and Ki-67 in tumor specimens were examined by immunohistochemistry and compared with 4DST T/N ratio.

RESULTS

All but two gliomas showed focally increased 4DST uptake. All gliomas showed hENT1 staining, except one grade II glioma, which was also not visualized on 4DST PET. A significant correlation was observed between T/N ratio and hENT1 score (ρ = 0.90, p < 0.001). All gliomas showed TK1 staining, except two gliomas which were also not visualized on 4DST PET. There was a significant correlation between T/N ratio and TK1 score (ρ = 0.92, p < 0.001). There was a significant correlation between T/N ratio and Ki-67 index (ρ = 0.50, p < 0.03).

CONCLUSION

Results of this preliminary study indicate that expressions of hENT1 and TK1 appear to be important determinants of 4DST uptake in newly diagnosed gliomas.

Brain Tumor Imaging

Modern imaging techniques, particularly functional imaging techniques that interrogate some specific aspect of underlying tumor biology, have enormous potential in neuro-oncology for disease detection, grading, and tumor delineation to guide biopsy and resection; monitoring treatment response; and targeting radiotherapy. This brief review considers the role of magnetic resonance imaging and spectroscopy, and positron emission tomography in these areas and discusses the factors that limit translation of new techniques to the clinic, in particular, the cost and difficulties associated with validation in multicenter clinical trials.

Repeatability of 18F-FLT PET in a Multicenter Study of Patients with High-Grade Glioma

Quantitative 3'-deoxy-3'-¹⁸F-fluorothymidine (¹⁸F-FLT) PET has potential as a noninvasive tumor biomarker for the objective assessment of response to treatment. To guide interpretation of these quantitative data, we evaluated the repeatability of ¹⁸F-FLT PET as part of a multicenter trial involving patients with high-grade glioma. Methods:¹⁸F-FLT PET was performed on 10 patients with recurrent high-grade glioma at 5 different institutions within the Adult Brain Tumor Consortium trial ABTC1101. Data were acquired according to a double baseline protocol in which PET examinations were repeated within 2 d of each other with no intervening treatment. On each of the 2 imaging days, dedicated brain PET was performed at 2 time points, 1 and 3 h after ¹⁸F-FLT administration. Tumor SUVs and related parameters were measured at a central laboratory using various volumes of interest: isocontour at 30% of the maximum pixel (SUV_{mean_30%}), gradient-based segmentation (SUV_{mean_gradient}), the maximum pixel (SUV_max), and a 1-mL sphere at the region of highest uptake (SUV_peak). Repeatability coefficients (RCs) were calculated from the relative differences between corresponding SUV measurements obtained on the 2 d. Results: RCs for tumor SUVs were 22.5% (SUV_{mean_30%}), 23.8% (SUV_{mean_gradient}), 23.2% (SUV_max), and 18.5% (SUV_peak) at 1 h after injection. Corresponding data at 3 h were 22.4%, 25.0%, 27.3%, and 23.6%. Normalizing the tumor SUV data with reference to a background region improved repeatability, and the most stable parameter was the tumor-to-background ratio derived using SUV_peak (RC, 16.5%). Conclusion: SUV quantification of ¹⁸F-FLT uptake in glioma had an RC in the range of 18%-24% when imaging began 1 h after ¹⁸F-FLT administration. The volume-of-interest methodology had a small but not negligible influence on repeatability, with the best performance obtained using SUV_peak Although changes in ¹⁸F-FLT SUV after treatment cannot be directly interpreted as a change in tumor proliferation, we have established ranges beyond which SUV differences are likely due to legitimate biologic effects.

Evaluation of DNA synthesis with carbon-11-labeled 4′-thiothymidine

In the cancer research field, the preferred method for evaluating the proliferative activity of cancer cells in vivo is to measure DNA synthesis rates. The cellular proliferation rate is one of the most important cancer characteristics, and represents the gold standard of pathological diagnosis. Positron emission tomography (PET) has been used to evaluate in vivo DNA synthetic activity through visualization of enhanced nucleoside metabolism. However, methods for the quantitative measurement of DNA synthesis rates have not been fully clarified. Several groups have been engaged in research on 4′-[methyl-¹¹C]-thiothymidine (¹¹C-4DST) in an effort to develop a PET tracer that allows quantitative measurement of in vivo DNA synthesis rates. This mini-review summarizes the results of recent studies of the in vivo measurement of cancer DNA synthesis rates using ¹¹C-4DST.

Influence of volumetric 4'-[methyl-11C]-thiothymidine PET/CT parameters for prediction of the clinical outcome of head and neck cancer patients

OBJECTIVE

This prospective study compared the value of pretreatment 4'-[methyl-¹¹C]-thiothymidine (¹¹C-4DST) volumetric parameters and those of 2-deoxy-2-[18F] fluoro-D-glucose (¹⁸F-FDG) in predicting the clinical outcome in patients with head and neck squamous cell carcinoma (HNSCC).

METHODS

Fifty patients with HNSCC underwent ¹¹C-4DST PET/CT and ¹⁸F-FDG PET/CT prior to anticancer therapy. ¹⁸F-FDG metabolic tumor volume (¹⁸F-FDG MTV) and total lesion glycolysis (TLG) were calculated from ¹⁸F-FDG PET, and ¹¹C-4DST MTV and total lesion proliferation (TLP) were calculated from ¹¹C-4DST PET. All parameters were measured for the primary lesion and metastatic lymph nodes. Associations between clinical factors and PET/CT parameters and prognostic value were analyzed.

RESULTS

Receiver-operating characteristic analysis revealed that MTV, TLG, and TLP acquired from the primary lesion and metastatic lymph nodes were good parameters for predicting disease relapse and death. The area under the curves (AUCs) ranged from 0.63 to 0.71 for ¹⁸F-FDG PET/CT parameters. The AUCs of ¹¹C-4DST PET/CT parameters were larger than those of ¹⁸F-FDG (range 0.72-0.81). Univariate analysis revealed that individuals with tumors showing a high value for any PET/CT parameter were at a significantly increased risk of relapse. Upon multivariate analysis, ¹⁸F-FDG MTV, ¹¹C-4DST MTV and ¹¹C-4DST TLP were significant independent factors for relapse-free survival (P = 0.04, P = 0.0001 and P = 0.0005, respectively).

CONCLUSION

Pretreatment ¹¹C-4DST PET/CT volume-based parameters can provide important prognostic information about patients with HNSCC.

Usefulness of positron emission tomographic studies for gliomas

Non-invasive positron emission tomography (PET) enables the measurement of metabolic and molecular processes with high sensitivity. PET plays a significant role in the diagnosis, prognosis, and treatment of brain tumors and predominantly detects brain tumors by detecting their metabolic alterations, including energy metabolism, amino acids, nucleic acids, and hypoxia. Glucose metabolic tracers are related to tumor cell energy and exhibit good sensitivity but poor specificity for malignant tumors. Amino acid metabolic tracers provide a better delineation of tumors and cellular proliferation. Nucleic acid metabolic tracers have a high sensitivity for malignant tumors and cellular proliferation. Hypoxic metabolism tracers are useful for detecting resistance to radiotherapy and chemotherapy. Therefore, PET imaging techniques are useful for detecting biopsy-targeting points, deciding on tumor resection, radiotherapy planning, monitoring therapy, and distinguishing brain tumor recurrence or progression from post-radiotherapy effects. However, it is not possible to use only one PET tracer to make all clinical decisions because each tracer has both advantages and disadvantages. This study focuses on the different kinds of PET tracers and summarizes their recent applications in patients with gliomas. Combinational uses of PET tracers are expected to contribute to differential diagnosis, prognosis, treatment targeting, and monitoring therapy.

Correlation of 4'-[methyl-(11)C]-thiothymidine uptake with Ki-67 immunohistochemistry and tumor grade in patients with newly diagnosed gliomas in comparison with (11)C-methionine uptake

OBJECTIVE

A novel radiopharmaceutical, 4'-[methyl-(11)C]thiothymidine ((11)C-4DST), has been developed as an in vivo cell proliferation marker based on the DNA incorporation method. The purpose of this study was to evaluate (11)C-4DST uptake in patients with newly diagnosed glioma and to correlate the results with proliferative activity and tumor grade, in comparison with L-[methyl-(11)C]-methionine ((11)C-MET).

METHODS

Investigations of (11)C-4DST and (11)C-MET PET/CT were performed retrospectively in 23 patients with newly diagnosed glioma. The maximum standardized uptake value (SUVmax) for tumor (T) and the mean SUV for normal contralateral hemisphere (N) were calculated, and the tumor-to-normal (T/N) ratio was determined. Metabolic tumor volume (MTV) was defined as the volume with a threshold of 40% of the SUVmax. Proliferative activity as indicated by the Ki-67 index was estimated in tissue specimens.

RESULTS

Of 23 gliomas examined, (11)C-4DST PET/CT and (11)C-MET PET/CT detected 20 and 22, respectively. Linear regression analysis between (11)C-4DST and (11)C-MET indicated a weak correlation for SUVmax (r = 0.54, P < 0.008), for T/N ratio (r = 0.56, P < 0.006), and for MTV (r = 0.60, P < 0.003). Linear regression analysis indicated a weak correlation between (11)C-4DST and Ki-67 index for SUVmax (r = 0.46, P < 0.03), for T/N ratio (r = 0.43, P < 0.05), and for MTV (r = 0.68, P < 0.001) and between (11)C-MET MTV and Ki-67 index (r = 0.43, P < 0.04). Using (11)C-4DST, there was a significant difference in SUVmax between grades II and IV (P < 0.03) and in MTV between grades II and IV (P < 0.009) and grades III and IV (P < 0.02). Using (11)C-MET, there was a significant difference in SUVmax (P < 0.009) and T/N ratio (P < 0.02) between grades II and IV and in MTV between grades II and IV (P < 0.03) and grades III and IV (P < 0.02).

CONCLUSION

(11)C-4DST PET/CT is feasible for imaging of brain gliomas, as well as (11)C-MET PET/CT. Especially, it showed the highest correlation coefficient between (11)C-4DST MTV and Ki-67 index in newly diagnosed gliomas.