Correlations between [68Ga]Ga-DOTA-TOC Uptake and Absorbed Dose from [177Lu]Lu-DOTA-TATE

Fri, 10 Feb 2023 00:00:00 +0000

The aim of this paper was to investigate correlations between pre- therapeutic [⁶⁸Ga]Ga-DOTA-TOC uptake and absorbed dose to tumours from therapy with [¹⁷⁷Lu]Lu-DOTA-TATE. This retrospective study included 301 tumours from 54 GEP-NET patients. The tumours were segmented on pre-therapeutic [⁶⁸Ga]Ga-DOTA-TOC PET/CT, and post-therapy [¹⁷⁷Lu]Lu-DOTA-TATE SPECT/CT images, using a fixed 40% threshold. The SPECT/CT images were used for absorbed dose calculations by assuming a linear build-up from time zero to day one, and mono-exponential wash-out after that. Both SUV_mean and SUV_max were measured from the PET images. A linear absorbed-dose prediction model was formed with SUV_mean as the independent variable, and the accuracy was tested with a split 70-30 training-test set. Mean SUV_mean and SUV_max from [⁶⁸Ga]Ga-DOTA-TOC PET was 24.0 (3.6-84.4) and 41.0 (6.7-146.5), and the mean absorbed dose from [¹⁷⁷Lu]Lu-DOTA-TATE was 26.9 Gy (2.4-101.9). A linear relationship between SUV_mean and [¹⁷⁷Lu]Lu-DOTA-TATE activity concentration at 24 h post injection was found (R² = 0.44, p < 0.05). In the prediction model, a root mean squared error and a mean absolute error of 1.77 and 1.33 Gy/GBq, respectively, were found for the test set. There was a high inter- and intra-patient variability in tumour measurements, both for [⁶⁸Ga]Ga-DOTA-TOC SUVs and absorbed doses from [¹⁷⁷Lu]Lu-DOTA-TATE. Depending on the required accuracy, [⁶⁸Ga]Ga-DOTA-TOC PET imaging may estimate the [¹⁷⁷Lu]Lu-DOTA-TATE uptake. However, there could be a high variance between predicted and actual absorbed doses.

Comparison of [18F]fluciclovine and [18F]FDG PET/CT in Newly Diagnosed Multiple Myeloma Patients

Sat, 01 Oct 2022 00:00:00 +0000

[¹⁸F]FDG PET/CT in multiple myeloma (MM) is currently the best technology to demonstrate patchy and extramedullary disease. However, [¹⁸F]FDG PET has some limitations, and imaging with alternative tracers should be explored. In this study, we aimed to evaluate the performance of [¹⁸F]fluciclovine PET compared to [¹⁸F]FDG PET in newly diagnosed MM patients. Thirteen newly diagnosed transplant eligible MM patients were imaged both with [¹⁸F]FDG PET/CT and [¹⁸F]fluciclovine PET/CT within 1 week in a prospective study. The subjects were visually assessed positive or negative for disease. The number of lesions and the SUV_max of selected lesions were measured for both tracers. Furthermore, tracer uptake ratios were obtained by dividing lesion SUV_max by blood or bone marrow SUV_max. Between-group differences and correlations were assessed with paired t-tests and Pearson tests. Bone marrow SUVs were compared to bone marrow plasma cell percentage in biopsy samples. Nine subjects were assessed positively by [¹⁸F]FDG PET (69%) and 12 positives by [¹⁸F]fluciclovine PET (92%). All positive subjects had [¹⁸F]fluciclovine scans that were qualitatively scored as easier to interpret visually than the [¹⁸F]FDG scans. The number of lesions was also higher; seven of nine subjects with distinct hot spots on [¹⁸F]fluciclovine PET had fewer or no visible lesions on [¹⁸F]FDG PET. The mean lesion SUV_max values were 8.2 and 3.8 for [¹⁸F]fluciclovine and [¹⁸F]FDG, respectively. The mean tumour to blood values were 6.4 and 2.0 for [¹⁸F]fluciclovine and [¹⁸F]FDG, and the mean ratios between tumour and bone marrow were 2.1 and 1.5 for [¹⁸F]fluciclovine and [¹⁸F]FDG. The lesion SUV_max and ratios were significantly higher for [¹⁸F]fluciclovine (all p < 0.01). Local [¹⁸F]fluciclovine SUV_max or SUV_mean values in os ilium and the percentage of plasma cells in bone marrow biopsies were linearly correlated (p = 0.048). There were no significant correlations between [¹⁸F]FDG SUVs and plasma cells (p = 0.82). Based on this pilot study, [¹⁸F]fluciclovine is a promising tracer for MM. The visual and semi-quantitative evaluations indicate that [¹⁸F]fluciclovine PET/CT can out-perform [¹⁸F]FDG PET/CT at diagnosis.

James Connelly | Theragnostic Imaging

Correlations between [68Ga]Ga-DOTA-TOC Uptake and Absorbed Dose from [177Lu]Lu-DOTA-TATE

Comparison of [18F]fluciclovine and [18F]FDG PET/CT in Newly Diagnosed Multiple Myeloma Patients