Dose reduction in ¹⁸F-FDG high-resolution dedicated breast PET

Objectives: A new high-resolution dedicated breast positron emission tomography (dbPET), equipped with ring-shaped detectors, has been developed for the detection of early-stage breast cancers. Since ring-shaped dbPETs have highly sensitive detectors and do not use X-ray computed tomography to perform attenuation correction, they are expected to greatly reduce the radiation dose to patients. We previously evaluated the dose reduction related to the use of dbPET based on phantom tests and clinical cases: by employing 25% of the standard ¹⁸F-2-fluorodeoxy-D-glucose (¹⁸F-FDG) dose, it is possible to obtain a clinically acceptable image quality, while 12.5% of the standard dose results in an image quality that is still sufficient for the detection of lesions [1]. Compared to other conventional imaging techniques, PET offers excellent reproducibility and quantification. Quantitative dbPET parameters are important for predicting prognosis and evaluating therapeutic effects in breast cancer patients. The purpose of this study was to perform a detailed evaluation of dbPET physical parameters variations in dose-reduced images.

Methods: A breast phantom containing four spheres of various diameters (5, 7.5, 10, and 16 mm), a background ¹⁸F-FDG radioactivity of 2.28 kBq/mL, and a sphere-to-background radioactivity ratio of 8:1 was used in this study. True dose-reduced images were obtained using data acquired for 20 min in list mode at multiple time points over 7 h of radioactive decay. Moreover, simulated dose-reduced images were reconstructed by using part of the list-mode acquired data. Subsequently, the true and simulated dose-reduced phantom images were compared visually and quantitatively for the following PET parameters: the maximum and mean standardized uptake value, the % of background variability (N_5mm), and the % of contrast (Q_H,5mm).

Results: In this study, the minimal required radiation doses were of 12.5% for the detection of 5-mm spheres and of 25% for the precise semi-quantification of FDG in the spheres (SUV_max [Figure 1-A], SUV_mean [Figure 1-B], % background variability [Figure 2-A], and % contrast [Figure 2-B]). No qualitative differences were identified between the true and simulated dose-reduced phantom images [Figure 3]. When applied to clinical cases, the image quality and lesion conspicuity were clinically acceptable for 25% of the dose images. Lesion detectability was maintained in 12.5% of the dose images, despite a degradation of the image quality [Figure 4]. However, small lesions near the chest wall resulted sometimes unclear at low doses.

Conclusions: By applying 25% of the standard ¹⁸F-FDG dose for dbPET, we obtained images which were qualitatively and quantitatively acceptable. Meanwhile, by applying 12.5% of the standard dose we obtained images which were qualitatively clinically acceptable, but which presented a poor quantitative reproducibility. Finally, the quantification of lesions near the chest wall (located around the edge of the detector) was particularly challenging. References: Satoh Y, Sekine T, Omiya Y, Onishi H, Motosugi U. Reduction of the fluoline-18-labeled fluorodeoxyglucose dose for clinically dedicated breast positron emission tomography. EJNMMI Phys. 2019 Nov 29; 6(1): 21.

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