Purpose: A Positron Emission Tomography/Computed Tomography quality assurance program is necessary to ensure that patients receive optimal imaging and care. We summarize the AAPM Task Group (TG) 126 report on acceptance and quality assurance (QA) testing of PET/CT systems. Methods: TG 126 was charged with developing PET/CT acceptance testing and QA procedures. The TG aimed to develop procedures that would allow for standardized evaluation of existing short-axis cylindrical-bore PET/CT systems in the spirit of NEMA NU 2 standards without requiring specialized phantoms or proprietary software tools. Results: We outline eight performance evaluations using common phantoms and freely available software whereby the clinical physicist monitors each PET/CT system by comparing periodic Follow-Up Measurements to Baseline Measurements acquired during acceptance testing. For each of the eight evaluations, we also summarize the expected testing time and materials necessary and the recommended pass/fail criteria. Conclusion: Our report provides a guideline for periodic evaluations of most clinical PET/CT systems that simplifies procedures and requirements outlined by other agencies and will facilitate performance comparisons across vendors, models, and institutions.

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Purpose: To develop and test the design of a new phantom, which is capable of producing experimental models of realistic activity distributions as observed in PET patients, for the evaluation of PET quantification accuracy and image segmentation algorithms. Methods: A phantom is constructed from thin plastic foils, less than 0.1 mm thick, which are cut along computer generated contours derived from the activity distribution of a large tumor in a patient PET scan. These sheets are used to displace activity inside a rectangular non‐uniform activity (NonU) cell (11.6 × 11.4 × 10.1 cm3), filled with a single activity solution of 18F‐ fluorodeoxyglucose (FDG), thus producing a non‐uniform activity distribution with variable activity gradients within a single PET slice or across multiple slices. The NonU cell is centered in a larger cylinder containing background activity. Corrections for omitted or deformed plastic sheets and for trapped air bubbles are applied to recover the known reference activity distribution. The phantom is tested in three different PET/CT scanners and the obtained images are compared to the known reference activity for different slices. Results: The resulting images retain the features of the selected region of interest of the original PET images of a patient tumor and agree well with the known activity distribution in the phantom. Differences between the known reference activity and the PET scan were found to be strongly dependent on registration and are less than 30% for more than 65% of the voxels for most of the tested slices. Conclusions: Using the NonU phantom to produce images of known activity distributions derived from clinically realistic activity configurations will aid in more accurate testing of PET quantification accuracy and in the development of image reconstruction, artifact correction and image segmentation algorithms. Improvements of the phantom design based on the test results are suggested.

Rationale: 68 Ga-labelled somatostatin analog PET/CT (SSA PET/CT) is now standard of care component in management of neuroendocrine tumors (NETs). However, treatment response for NETs is still performed with morphologic size measurements from other modalities, which can result in inaccurate disease burden. Functional tumor volume (FTV) acquired from SSA PET/CT has been suggested as a possible metric, but no validated measurement tool to measure FTV exists. We tested the precision of multiple FTV computational approaches compared to morphologic volume measurements to identify a candidate for incorporation into future FTV studies to assess tumor burden more completely and accurately. Methods: The clinical and imaging data of 327 NET patients was collected at MSKCC between December 2016 and April 2018. Patients were required to have SSA PET/CT and dedicated CT scans within 6 weeks. and were excluded if they had intervention between scans. When paired studies were evaluated, 150 correlating lesions demonstrated somatostatin analog. Lesions were excluded if they contained necrotic components or demonstrated a lobulated shape. This resulted in 94 lesions in twenty patients. The FTV for each lesion was evaluated with a hand-drawn assessment and three automated techniques -a 50% threshold from SUVmax, 42% threshold from SUVmax, and background-subtracted lesion histogram-based (BSL) method. These measurements were compared to volume calculated from morphologic volume measurements. Results:The FTV calculation methods demonstrated varying amount of correlation to morphologic volume measurements. FTV using threshold of 42% of SUVmax with 0.706 correlation, hand-drawn volume from PET imaging with 0.657 correlation, FTV using threshold of 50% of SUVmax with 0.645 correlation, and BSL method with 0.596 correlation. The Bland-Altman plots indicates that all FTV methods have positive mean difference compared to morphological volume, with FTV from threshold of 50% relative to SUVmax demonstrating the smallest mean difference. Conclusion: FTV determined with thresholding of SUVmax demonstrated the strongest correlation with traditional morphologic lesion volume assessment and the least bias. This method outperformed FTV calculated from hand drawn volume assessments with regards to accuracy. Automated FTV assessment based on a threshold shows promise to better determine extent of disease and make better prognostic assessments for patients with NETs.

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