Delineation and agreement of FET PET biological volumes in glioblastoma: results of the nuclear medicine credentialing program from the prospective, multi-centre trial evaluating FET PET In Glioblastoma (FIG) study—TROG 18.06
Nathaniel Barry, Roslyn J. Francis, Martin A. Ebert, Eng‐Siew Koh, Pejman Rowshanfarzad, Ghulam Mubashar Hassan, Jake Kendrick, Hui Gan, Sze T. Lee, Eddie Lau, Bradford A. Moffat, Greg Fitt, Alisha Moore, Paul Thomas, David A. Pattison, Tim Akhurst, Ramin Alipour, E. Louise Thomas, Edward Hsiao, Geoffrey Schembri, Peter Lin, Tam Ly, June Yap, Ian Kirkwood, Wilson Vallat, Shahroz Khan, Dayanethee Krishna, Stanley Ngai, Christopher Yu, Scott Beuzeville, Tow C. Yeow, Dale L. Bailey, Olivia Cook, Angela Whitehead, Rachael Dykyj, Alana Rossi, Andrew Grose, Andrew M. Scott
Abstract
Abstract Purpose The O-(2-[ 18 F]-fluoroethyl)- l -tyrosine (FET) PET in Glioblastoma (FIG) trial is an Australian prospective, multi-centre study evaluating FET PET for glioblastoma patient management. FET PET imaging timepoints are pre-chemoradiotherapy (FET1), 1-month post-chemoradiotherapy (FET2), and at suspected progression (FET3). Before participant recruitment, site nuclear medicine physicians (NMPs) underwent credentialing of FET PET delineation and image interpretation. Methods Sites were required to complete contouring and dynamic analysis by ≥ 2 NMPs on benchmarking cases ( n = 6) assessing biological tumour volume (BTV) delineation (3 × FET1) and image interpretation (3 × FET3). Data was reviewed by experts and violations noted. BTV definition includes tumour-to-background ratio (TBR) threshold of 1.6 with crescent-shaped background contour in the contralateral normal brain. Recurrence/pseudoprogression interpretation (FET3) required assessment of maximum TBR (TBR max ), dynamic analysis (time activity curve [TAC] type, time to peak), and qualitative assessment. Intraclass correlation coefficient (ICC) assessed volume agreement, coefficient of variation (CoV) compared maximum/mean TBR (TBR max /TBR mean ) across cases, and pairwise analysis assessed spatial (Dice similarity coefficient [DSC]) and boundary agreement (Hausdorff distance [HD], mean absolute surface distance [MASD]). Results Data was accrued from 21 NMPs (10 centres, n ≥ 2 each) and 20 underwent review. The initial pass rate was 93/119 (78.2%) and 27/30 requested resubmissions were completed. Violations were found in 25/72 (34.7%; 13/12 minor/major) of FET1 and 22/74 (29.7%; 14/8 minor/major) of FET3 reports. The primary reasons for resubmission were as follows: BTV over-contour (15/30, 50.0%), background placement (8/30, 26.7%), TAC classification (9/30, 30.0%), and image interpretation (7/30, 23.3%). CoV median and range for BTV, TBR max , and TBR mean were 21.53% (12.00–30.10%), 5.89% (5.01–6.68%), and 5.01% (3.37–6.34%), respectively. BTV agreement was moderate to excellent (ICC = 0.82; 95% CI, 0.63–0.97) with good spatial (DSC = 0.84 ± 0.09) and boundary (HD = 15.78 ± 8.30 mm; MASD = 1.47 ± 1.36 mm) agreement. Conclusion The FIG study credentialing program has increased expertise across study sites. TBR max and TBR mean were robust, with considerable variability in BTV delineation and image interpretation observed.