ObjectivesTo establish a new three-dimensional quantitative evaluation method for bone metastasis, we applied bone single photon emission tomography with computed tomography (SPECT/CT). The total bone uptake (TBU), which measures active bone metastatic burden, was calculated as the sum of [mean uptake obtained as standardized uptake value (SUV) above a cut-off level] × (the volume of the lesion) in the trunk using bone SPECT/CT. We studied the threshold value and utility of TBU in prostate cancer patients treated with radium-223 (Ra-223) therapy.MethodsTo establish the threshold value of TBU, we compared bone metastatic and non-metastatic regions in 61 prostate cancer patients with bone metastasis and 69 without. Five fixed sites in each patient were selected as evaluation points and divided into bone metastatic and non-metastatic sites. Sensitivity and specificity analysis was applied to establish the threshold level. Using the obtained threshold value, we then calculated the TBU in nine prostate cancer patients who received Ra-223 therapy, and compared the results with the bone scan index (BSI) by BONENAVI® and visual evaluation of bone scintigraphy.ResultsUptake was significantly lower in non-metastatic sites in patients with bone metastasis than in patients without metastasis. Sensitivity and specificity analysis revealed SUV = 7.0 as the threshold level. There was a discrepancy between TBU and BSI change in two of the nine patients, in whom TBU change correlated with visual judgement, but BSI change did not. In two patients, BSI was nearly 0 throughout the course, but the TBU was positive and changed, although the change was not large. These results suggest that TBU may be more accurate and sensitive than BSI for quantitative evaluation of active bone metastatic burden.ConclusionWe established a threshold value (SUV > 7.0) for three-dimensional TBU for evaluating active bone metastatic burden in prostate cancer patients using bone SPECT/CT. Despite the small number of patients, we expect the change in TBU could be more accurate and sensitive than the change in BSI among patients who received Ra-223.

Several cross-calibration schemes have been proposed to produce quantitative values in bone SPECT imaging. Differences in the radionuclide sources and geometric conditions can decrease the accuracy of crosscalibration factor (CCF). The present study aimed to validate the effects of calibration schemes using different sources under various geometric conditions. Methods: Temporal variations as well as variations in acquisition counts and the shapes of 57 Co standard and 99m Tc point sources and a 99m Tc disk source were determined. The effects of the geometric conditions of the source-to-camera distance (SCD) and lateral distance on the CCF were investigated by moving the camera or source away from the origin. The system planar sensitivity of NEMA incorporated into a Symbia Intevo SPECT/CT device (Siemens®) was defined as reference values. Results: The temporal variation in CCF using the 57 Co source was relatively stable within the range of 0.7% to 2.3%, whereas the 99m Tc source ranged from 2.7% to 7.3%. In terms of source shape, the 57 Co standard point source was the most stable. Both SCD and lateral distance decreased as a function of distance from the origin. Errors in the geometric condition were higher for the 57 Co standard point source than the 99m Tc disk source. Conclusions: Different calibration schemes influenced the reliability of quantitative values. The 57 Co standard point source was stable over a long period, and this helped to maintain the quality of quantitative SPECT/CT imaging data. The CCF accuracy of the 99m Tc source decreased depending on the preparative method. The method of calibration for quantitative SPECT should be immediately standardized to eliminate uncertainty.

Objective: Texture analysis is one of the lung cancer countermeasures in the field of radiomics. Even though image quality affects texture features, the reproducibility of principal component analysis (PCA)-based data-driven respiratory gating (DDG) on texture features remains poorly understood. Hence, this study aimed to clarify the reproducibility of PCA-based DDG on texture features in non-small cell lung cancer (NSCLC) patients with 18 F-Fluorodeoxyglucose ( 18 F-FDG) Positron emission tomography/computed tomography (PET/CT). Methods: Twenty patients with NSCLC who underwent 18 F-FDG PET/CT in routine clinical practice were retrospectively analyzed. Each patient's PET data were reconstructed in two PET groups of no gating (NG-PET) and PCAbased DDG gating (DDG-PET). Forty-six image features were analyzed using LIFEx software. Reproducibility was evaluated using Lin's concordance correlation coefficient (𝜌 c ) and percentage difference (%Diff). Non-reproducibility was defined as having unacceptable strength (𝜌 c < 0.8) and a %Diff of >10%. NG-PET and DDG-PET were compared using the Wilcoxon signed-rank test. Results: A total of 3/46 (6.5%) image features had unacceptable strength, and 9/46 (19.6%) image features had a %Diff of >10%. Significant differences between the NG-PET and DDG-PET groups were confirmed in only 4/46 (8.7%) of the high %Diff image features. Conclusion:Although the DDG application affected several texture features, most image features had adequate reproducibility. PCA-based DDG-PET can be routinely used as interchangeable images for texture feature extraction from NSCLC patients. K E Y W O R D S18F-FDG, data-driven respiratory gating, image feature, non-small cell lung cancer, PET/CT, texture analysis, texture featureThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.