RT Journal Article SR Electronic T1 Evaluation of gradient PET segmentation for total glycolysis compared to thresholds and manual contouring JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 2077 OP 2077 VO 52 IS supplement 1 A1 Aaron Nelson A1 Maria Werner-Wasik A1 Walter Choi A1 Arai Yoshio A1 Peter Faulhaber A1 Nitin Ohri A1 Patrick Kang A1 Fabio Almeida A1 Sara Pirozzi A1 Dennis Nelson YR 2011 UL http://jnm.snmjournals.org/content/52/supplement_1/2077.abstract AB 2077 Objectives Assessing response to therapy or prognosis using SUVmax has a number of limitations including sensitivity to noise. Total lesion glycolysis (TLG) is less sensitive to noise and incorporates both size and activity (SUVmean x volume) into one measure. Accuracy of PET segmentation is important for TLG since it utilizes volume. Previously we demonstrated the superior volumetric accuracy of a gradient PET segmentation method (GRAD) compared to thresholds (THRESH) and manual contouring (MC) in realistic Monte Carlo simulated PET scans of the thorax. In this study we evaluated the effect of segmentation accuracy on TLG. Methods Thirty-one lung tumors of varying size, shape, and location were segmented by 7 clinicians on 25 realistic digital PET scans of the thorax. GRAD, THRESH and MC methods were used. GRAD identifies tumor edges based on a change in count levels at the tumor border. THRESH was performed using 25-50% of maximum counts at 5% increments. Accuracy and bias were measured by calculating the mean absolute % error and mean % errors respectively (abs%error and %error) for TLG using all methods. Results GRAD was the most accurate technique with abs%error of 6.1 (10.3 SD). Both 25% THRESH, the most accurate threshold, and MC were significantly less accurate with abs%error of 10.2 (19.1) and 14.5 (17.2) respectively (p < 0.0013). 25% THRESH had the smallest bias with %error of -1.1 (21.6) followed by GRAD with -3.8 (11.4), however, the difference was not significant (p = 0.13). Conclusions GRAD resulted in significantly more accurate TLG calculations than the other contouring methods. GRAD has the potential to play an important role in both determining prognosis and assessing response to therap