Are the simplified methods to estimate Ki in 18F-FDG PET studies feasible in clinical routine? Comparison between three simplified methods.

BACKGROUND: The aim of this study was to verify the feasibility, in clinical practice, of three simplified methods (Hunter, Sadato and another one proposed by our group) to calculate Ki and MRglu of 18F-FDG, comparing the results with those derived by the linear regression (LR) method (considered the golden standard), and also with SUV. METHODS: Forty-five patients (32males, mean age 69±9years) with non-small-cell-lung cancer prospectively enrolled, underwent dynamic 18F-FDG PET-CT over the thorax. Ki was estimated as follows: from a static acquisition and performing one venous blood sampling using the Hunter method; multiplying the SUV for the average plasma clearance rate (kP(T)) and for the initial distribution volume (V0bw) without performing any blood sampling using the Sadato method; multiplying the SUV for a factor F (which encompasses the mean value of haematocrit and plasma volume, both according to patient's sex) without performing any blood sample using ours method. Wilcoxon signed rank and coefficient of determination (R2) were used for statistical analysis. RESULTS: No significant difference was observed between the Ki and MRglu estimated by all three simplified methods and the Ki and MRglu estimated by LR. The highest P values and the lower values of mean differences were observed with our method compared with LR: Ki=0.0392±0.0178 min-1 vs. Ki=0.0392±0.0202 min-1 (P=0.897, MD=0.0001 min-1), respectively; MRglu= 4.47±2.23 ml/min/100g vs. MRglu= 4.43±2.38 ml/min/100g (P=0.839, MD= -0.0373 mL/min/100g), respectively. The highest correlation was observed between the Ki estimated by both Hunter and our methods and the Ki estimated by LR: R2=0.87, R2=0.86, respectively. A good correlation (R2=0.83) was observed between SUV and Ki estimated by LR. CONCLUSIONS: These three simplified methods represent a valid alternative to the more invasive and complex full kinetic analysis. Their "pros" are: the non-invasiveness, the feasibility, the good correlation with the golden standard; their "cons" is that full kinetic analysis provides highest accuracy in Ki determination. Therefore, in clinical oncology routine, the nuclear physicians can choose among different simplified methods especially for monitoring the response to treatment, for tumour grading, and for prognostic stratification, letting the full kinetic analysis to specific centre/studies.

Dynamic O-(2-[18F]fluoroethyl)-L-tyrosine (F-18 FET) PET for glioma grading: assessment of individual probability of malignancy.

PURPOSE: (1) To investigate the diagnostic value of some O-(2-[F]fluoroethyl)-L-tyrosine (F-18 FET) indices derived from the dynamic acquisition to differentiate low-grade gliomas from high-grade; (2) to analyze the course of tumor time-activity curves (TACs); and (3) to calculate the individual probability of a high-grade glioma using the logistic regression. METHODS: Seventeen low-grade (WHO I-II) and 15 high-grade (WHO III-IV) gliomas were studied with dynamic F-18 FET PET. Regions of interests were drawn over the tumor and contralateral brain, and TACs were analyzed. We considered early standardized uptake value (SUV), middle SUV, late SUV, early-to-middle SUV tumor ratio, early-to-late SUV tumor ratio; time to peak (Tpeak), in minutes, from the beginning of the dynamic acquisition up to the maximum SUV of the tumor; and SoD (sum of the frame-to-frame differences). To assess the individual probability of high-grade, logistic regression was also used. RESULTS: High-grade gliomas showed significantly (P < 0.0001) higher values when compared with low-grade gliomas in early SUV, early-to-middle ratio, early-to-late ratio, Tpeak, and SoD. For the grading of gliomas, the best indices were early-to-middle ratio and Tpeak providing a diagnostic accuracy of 94%. TACs analysis provided an 87% diagnostic accuracy. For individual high-grade diagnosis, the logistic regression provided 93% sensitivity, 100% specificity, and 97% accuracy. CONCLUSION: Early-to-middle SUV tumor ratio and Tpeak were the best indices for assessing the grading of gliomas. Since early-to-middle ratio derives from the first 35 minutes of the dynamic acquisition, the PET study could last half an hour instead of 1 hour. By logistic regression, it is possible to assess the individual probability of high-grade, useful for prognosis and treatment.

Comparison of 123I-MIBG SPECT-CT and 18F-DOPA PET-CT in the evaluation of patients with known or suspected recurrent paraganglioma.

OBJECTIVES: Detection of recurrent disease is essential for treatment planning in patients with paraganglioma. The aim of this study was to compare 123I-metaiodobenzylguanidine (123I-MIBG) scintigraphy [whole-body and single-photon emission computed tomography (SPECT) computed tomography (CT) scanning] and fluorine-18-L-dihydroxyphenylalanine positron emission tomography CT (18F-DOPA PET-CT) in the re-staging of patients with known or suspected recurrent paraganglioma. METHODS: Twelve patients with known or suspected recurrent paraganglioma after initial surgery were included in the study. 18F-DOPA PET-CT and 123I-MIBG scintigraphy (whole-body and SPECT-CT scanning) were performed in all patients; the results were compared on a per patient and a per lesion basis. Cytohistology (when available) and a combination of laboratory and imaging studies and follow-up were used as reference standard; any modification in treatment planning was recorded. In all cases recurrent disease (local or distant) was confirmed by cytohistology (four cases) or at subsequent follow-up (eight cases). RESULTS: All patients had positive 18F-DOPA studies (100% sensitivity) whereas nine had positive 123I-MIBG studies (75% sensitivity; P=not significant). 18F-DOPA detected 98% of lesions, whereas 38% were detected with 123I-MIBG (P=0.04). 18F-DOPA showed more lesions than 123I-MIBG in eight patients; both techniques showed the same number of lesions in two cases whereas in two patients 123I-MIBG showed a greater number of lesions. A change in treatment planning was suggested by 18F-DOPA in one patient. CONCLUSION: These data support the superiority of 18F-DOPA PET-CT over 123I-MIBG scintigraphy to assess disease extension in patients with recurrent paraganglioma; however, in cases with inoperable disease, 123I-MIBG maintains a unique role in allowing the selection of patients suitable for 123I-MIBG therapy.

Thyroid carcinomas with a variable insular component: prognostic significance of histopathologic patterns.

BACKGROUND: An insular growth pattern may be observed focally both in papillary and follicular thyroid carcinoma. The aim of the current study was to determine whether a greater extension of the insular component (IC) influences different clinical and histologic features at diagnosis, and a different tumor aggressiveness in terms of frequency in the occurrence of metastases as well as survival. METHODS: Thirty-three patients with histopathologic findings consistent with IC were included in the study. IC was focal (<50% of the tumor area) in 16 patients and predominant (>50% of the tumor area) in 17 patients. These 2 groups were compared with a control group of 66 patients with differentiated thyroid carcinoma. RESULTS: At diagnosis, carcinomas with predominant IC differed from those with focal IC with regard to greater tumor size and a higher frequency of extrathyroidal extension and distant metastases. Patient follow-up ranged from 5 to 188 months. The cumulative rate of distant metastases was significantly higher in patients with predominant IC. At the time of last follow-up, carcinomas with predominant IC demonstrated a lesser frequency of disease-free outcome (P = .002) and a higher number of tumor-related deaths (P = .002), either when distant metastases were present (P = .03) or absent (P = .05) at the time of diagnosis. CONCLUSIONS: The presence of predominant IC is associated with a poor prognosis in terms of ongoing disease or death. Predominant IC should be considered a separate entity from not only the classical papillary or follicular carcinomas but also the focal IC tumor.