No abstract

The aim of this study was to evaluate the clinical significance of combined fluorine-18 fluorodeoxyglucose positron emission tomography and computed tomography (FDG-PET/CT) in patients with lymphoma, and to compare the FDG-PET/CT staging results with those of FDG-PET and CT alone. Twenty-seven patients were studied. Each patient had clinical follow-up for >12 months and entered complete follow-up evaluation. Patient-based evaluation showed a sensitivity of 78% for CT alone, 86% for FDG-PET alone, 93% for CT and FDG-PET read side by side, and 93% for combined FDG-PET/CT imaging. Region-based evaluation showed a sensitivity for regional lymph node involvement of 61%, 78%, 91% and 96% respectively. FDG-PET/CT imaging is superior to CT alone ( P=0.02) and has additional benefit over FDG-PET alone due to exact anatomical localisation. We conclude that FDG-PET/CT imaging is accurate in re-staging lymphoma and offers advantages over separate FDG-PET and CT imaging.

Objective and design: Cross-sectional studies have reported an increased prevalence of circulating thyroglobulin autoantibodies (TgAbs) in patients with differentiated thyroid carcinoma (DTC). With the advent of more sensitive assays, a longitudinal study monitoring the development of TgAb levels after ablative therapy was warranted. Methods: One hundred and twelve consecutive patients with follicular cell-derived thyroid cancer were followed for 3 years. All patients had been thyroidectomized and received, on average, two radioiodine therapies. Residual tissue was quantified scintigraphically by 131 I 24-h uptake. TgAb and thyroglobulin (Tg) serum levels were determined with a sensitive direct radioligand assay and an IRMA respectively. Results: The prevalence of TgAbs at the initial examination was 29% (median 130 U/ml). During follow-up, TgAb levels rose transiently in one-tenth of the patients, but the prevalence of demonstrable TgAbs decreased to , 10% after 3 years. The median serum half-life of TgAbs in treated DTC patients was 10 weeks. At initial examination (when all patients still had residual thyroid tissue and 17 had metastases), rising TgAb levels were correlated with the inability to detect Tg in 4, 30 and 73% of the patients, when initial TgAbs were , 6, 6 -50 or .50 U/ml respectively. While the Tg recovery test was valid for all patients, an in vitro dilution assay with TgAb serum reduced Tg values by up to 32%. Conclusions: The development and course of TgAbs in DTC patients cannot be predicted by initial or residual tumour volume, TgAb or Tg levels. The presence of TgAbs, even in low concentrations, may cause Tg underestimation despite valid recovery tests in DTC patients.European Journal of Endocrinology 153 49-55

Iodine kinetics and lesion dose per administered 131 I activity (LDpA) of differentiated thyroid cancer metastases were determined using 124 I PET. These data were analyzed to derive an optimized dosimetry protocol. Methods: We evaluated the timeactivity-concentration curves of 37 lesions in 17 patients who had undergone thyroidectomies. LDpA determination involved 124 I PET images acquired at 4, 24, 48, 72, and 96 h after intake of a capsule containing 20-40 MBq of 124 I. A combination of a linear and a monoexponential or a monoexponential function only parameterized the time-activity-concentration curves. The LDpAs, calculated using data from all 5 PET time points, served as reference. The lesions were classified into 3 groups, according to potential for cure with 131 I therapy: low (#5 Gy GBq 21 ; n 5 14), medium (between 5 and 10 Gy GBq 21 ; n 5 9), or high LDpAs (.10 Gy GBq 21 ; n 5 14). Using the reference approach, the differences in the empiric kinetic parameters within the LDpA groups were evaluated. The reference LDpAs were compared with those derived from only 2, 3, or 4 PET data points and from 1 adapted 2-point approach. Lin's concordance correlation coefficient (r c ) and the mean absolute percentage deviation in LDpAs were used to assess agreement between simplified and reference approaches. Results: The effective 124 I half-life, linear activity-concentration rate (a), and 24-h activity concentration (CpA) (the latter 2 per administered 124 I activity) differed significantly among the LDpA groups (P , 0.05). LDpAs correlated with 24-h CpAs (r 5 0.94, P , 0.001). Using the 4-, 24-, and 96-h measurements, a r c value of greater than or equal to 0.90 was found, and the mean absolute percentage deviation was less than or equal to 16%. Similar statistical values were obtained for the adapted approach, which was based on 24-and 96-h PET data points only. Conclusion: Lesion classification into LDpA groups was feasible using a single PET scan at ;24 h. Because of the highly variable kinetics, 1 additional measurement at ;96 h was needed to obtain a sufficiently reliable LDpA estimate. The adapted 24-96-h approach appears to be the optimal 124 I protocol and is a reliable simplification of the 5-point protocol.Key Words: PET; radionuclide therapy; dosimetry; iodine-124; differentiated thyroid cancer Several groups (1-5) have successfully used 124 I PET alone and with CT to guide postsurgical treatment and, in particular, radioiodine therapy in patients with differentiated thyroid carcinoma (DTC). Preradiotherapeutic 124 I PET is valuable in restaging disease; dosimetric analysis of the imaging data can identify the patients most likely to benefit from radioiodine therapy and can determine safe and effective individualized therapeutic activities of radioiodine.Our original ;20, and ;44 h after 124 I administration; sometimes a fourth scan was acquired at 96-144 h. However, to our knowledge, no group has yet published the results of any systematic investigation to determine the number and timing of PET sca...

The authors qualitatively and quantitatively assessed a solution containing 0.2% locust bean gum (LBG) and 2.5% mannitol (mannitol-LBG) dissolved in water to provide a negative oral contrast material in dual-modality positron emission tomography (PET)/computed tomography (CT) scanning. PET/CT was performed in 60 patients with cancer after oral administration of barium, water, or mannitol-LBG. Qualitative and quantitative analyses were conducted to determine bowel distention and a potential influence of the contrast agents on the PET data. Intestinal distention with mannitol-LBG proved superior to that with water or barium. Findings at both quantitative and qualitative analysis revealed apparently increased tracer uptake in the small bowel with barium in comparison to that with mannitol-LBG or water. Mannitol-LBG may, therefore, be used as a negative oral contrast agent at PET/CT scanning because it provides excellent bowel distention while avoiding contrast material-induced PET artifacts.

No abstract

Recovery correction is mandatory for (124)I PET quantification, even for large structures. To ensure accurate dosimetry, thorough absolute recovery measurements must be individually established for the particular PET scanner and radionuclide to be used.

In normal human tissues (68)Ga-DOTATOC imaging has been related to the expression of sst2 at the level of mRNA. The novel normative database may improve diagnostics, monitoring and therapy of sst-expressing tumours or inflammation on a molecular basis.