Carlo Cavedon DPhil, Presenter: Nothing to Disclose

Emanuele Zivelonghi, Abstract Co-Author: Nothing to Disclose

Stefania Guariglia, Abstract Co-Author: Nothing to Disclose

Maria Grazia Giri, Abstract Co-Author: Nothing to Disclose

Daniela Grigolato, Abstract Co-Author: Nothing to Disclose

Michele Zuffante, Abstract Co-Author: Nothing to Disclose

Marina Cucca, Abstract Co-Author: Nothing to Disclose

Marco Ferdeghini MD, Abstract Co-Author: Nothing to Disclose

To find the optimal number of phase bins in respiratory-gated PET-CT (4D PET-CT) in order to improve SUV quantification in lung tumors while preserving signal-to-noise ratio.

28 patients with lung tumors were studied with 18F-FDG 4D PET-CT. Only patients that showed respiratory-induced tumor motion greater than 5 mm were enrolled. 4D PET-CT was performed by means of a Philips Gemini BigBore TOF scanner and the Varian RPM respiratory gating system. 3.0 MBq/kg, 2 min/bed and retrospective-mode for both PET and CT modalities were used. Images were reconstructed using 1 (no sorting) up to 10 phase bins. SUVmax values within the lesion were studied as a function of the number of phase-bins. The lower number of phase bins that allowed SUV quantification no smaller than 90% compared to the gold standard (10 phases) was considered as optimal. Lesion volumes were estimated by three different segmentation methods: fixed SUV=2.2 threshold, 40% of SUVmax isocontour and gradient-based method. These volumes were also studied as a function of the number of phase bins.

SUVmax measured at max exp was on average 63.2% higher in the gated acquisition (10 phases) compared to the non-gated case (range 11.5%-328.3%). The underestimation of SUV in non-gated PET-CT was strongly dependent on lesion volume and location, small lesions in the lower lung region being the most affected. When comparing 4D PET-CT in 4 and 10 phases, the underestimation reduced to 12.3% (range 2.0%-37.7%). The corresponding value for 6 and 10 phase bins was 6.9% (range 0.0%-23.3%). Volumes estimated by the fixed-threshold method increased with the number of phase bins, SUVmax percentage-based volumes decreased and gradient-based volumes did not show a unique trend.

4D PET-CT offers an advantage in 18F-FDG SUV quantification for tumors that move with respiration. The balance between acquisition/reconstruction time, SNR and accuracy of SUV estimation seems to be achievable using 4 to 6 phase bins, depending on lesion volume and location. SUV-based volume quantification obtained by multiple segmentation methods is less prone to inconsistent results when respiratory gating is used.

4D PET-CT can improve SUV quantification in tumors that move with respiration. This might be especially useful when metabolic data are used to help delineate reference volumes in Radiation Oncology.

Cavedon, C, Zivelonghi, E, Guariglia, S, Giri, M, Grigolato, D, Zuffante, M, Cucca, M, Ferdeghini, M, Impact of 4D PET-CT on SUV Quantification in Lung Tumors: How Many Phase-bins?.  Radiological Society of North America 2013 Scientific Assembly and Annual Meeting, December 1 - December 6, 2013 ,Chicago IL. http://archive.rsna.org/2013/13027226.html